Scope Case Study

STRATEGIC MARKETING Mid-Semester test Spring, 2009 Name Erika Woodhouse 1. Evaluate the changes that have occurred in the Canadian mouthwash grocery in the past three years and their force of place setting. Be specific. (20) In 1987 the growth rate for the mouthwash market experienced a 26 per centum increase due to the introduction of new flavors. Brands were adding unique customization to clear consumers to their brand, and as a result the market as a unanimous grew. Since then the growth rate has dec delimitated to a level of 5 percent. 2. direction believes that the stead quo is the best strategy.The team has been asked to make the case for and against this position, including in their sermon an evaluation of the positions of all or almost all members of the team. (20) a. _ Status quo_ b. _ Against status quo_ Scope should take action anddo something to compete with Plax and Listerines new claims. proctor & Gamble states in their statement of purpose and strategy, We wil l continuously dwell ahead of competition while aggressively defending our established moneymaking business against major competitive challenges despite short term receipts consequences. Therefore doing nothing is simple not an option. The market had an increase of 5 percent last year, while Scope suffered from a . 7 percent loss. Plax as a new competitor to the marked was able to carry through a 10 percent market consider in over only three years, and will continue to grow and could take from our share if nothing is buste. If we created a bring out tasking pre-brush rinse we can also correspond this to Scope when entered the market.Scope had all the same attributes of Listerine but offered a better taste, and was able to penetrate the market and be successful with a 12 percent market share in one year. 3. Management has wondered what impact the line extension strategy (using the Scope name) would have on boilersuit profits of the Division if the price were held constant an d if the price were increased 10 percent, assuming veritable volume. Accounting has provided the following information to assist in your analysis Current variable cost 20. 2/unit varying cost likely increase with the line extension 13% follow fixed cost $2. 5 million + advertising, promotion, and general office costs. Scope should not introduce a line extension to compete. A line extension with the scope name would be likely to confuse its current customers. Also if the growth fails it could reflect poorly on Scope. They also dont have the ability to make a superior product therefore they could hurt the brand image of providing quality and value.

Purple Short Crabs

Purple beach direct, Hemigrapsus nudus, are vitiated crabs that are similar in structure to true crabs. They bring on carapaces that are normally form to be 4-5. 6 cm. A distinguishing feature of the Purple Shore crab is their lack of setae. They are usually found to be dark purple, olive green or red with blank or cream marks, on their carapace. Their legs match the color of their carapace only when have white tipped claws. Though Purple Shore Crabs are capable of living out of water for several hours, they entreat moisture to survive.These crabs respire with a gill system in which they take in oxygen-rich water orally, obtaining oxygen by diffusion thus expelling the excess water and carbon dioxide through their gills. They are commonly found under rocks anywhere from low-tide to mid-tide zones as well as reefs as far down as 10 metres. Purple Shore Crabs prefer an environment in which the put downs are medium-energy to high-energy. When their shelters are disturbed, th ey tend to range towards shelters such as other rocks, ledges, holes and crevices.Purple Shore Crabs are scavangers with dietetic preferences that include worms, dead organisms, molluscs, small gastropods, small crabs, algae, carrion and seaweed. The purpose of our investigation is to get back whether there is a relationship between the relative infinite to the shore and the population density of Purple Shore Crabs. To understand this, 3 transects were laid perpendicular to the shoreline of Eagle Bay, Bamfield.A random number generator was used to determine 5 completely unbiased numbers. These numbers were used to establish the distance of which the quadrats were placed. For each number, 1 quadrat was placed by the top left boxwood of each of the 3 transects. To calculate the population density of Purple Shore Crabs, the number of Purple Shore Crabs within each quadrat was counted and recorded. To cancel re-counting of an individual crab, crabs were counted after being colle cted in a bucket.

Analysis of The Lottery Essay

The draftsmanship is a film based on the short story of the akin name by Shirley Jackson. The story takes place in a refined village, where the people held an anniversary activity of lottery. One person in the township is randomly chosen, and the person who got the lottery would be hit to death by stones for the sake of harvest of the following year. In my opinion, The draft is a bewilderment and horror story. The film begins under a friendly cash dispenser. The people in the village are close and familiar with each other. Before the lottery, everyone seems in a peace mind and friendly to each other.For instance, Mrs. Hutchinson arrives late, just with an confession of forgetting what day it was. They talk to each other as usual ordain me a false impression that the lottery is an event similar as the square dance that is welcomed and festive. I expect that the winner of the lottery forget receive a prize, money or some issue. Mr. Warner who was the eldest person in the tow n says with pride, Seventy-seventh year I have been in the Lottery. I everlastingly conjecture the lottery is a pleasant event until the very signification Tessie screams when she sees her husband pick the black dot.The conclusion surprises me that the winners parcel is death by friends and family. With this conclusion, the film becomes a horror story. The film centers on the actions of each town people from an objective perspective to reflect the unreasoning obedience, less of rationality and cruel coldness of humans nature of the consentaneous town people. In this mundane town, everyone knows each other. However, when Tessie receives the black spot, Mrs. Delacroix tells her, Be a good sport Tessie. Peoples reflection to the cruel thing is quite cold-blooded.This film presents a weakness in human individuals. Lottery as such a terrible activity for so many an(prenominal) years, with no objections or questions asked. Even someone doubts the lottery has been answered with T here has evermore been a lottery. Even people may not be merely comfortable with the event, but everyone still goes along with it. No one openly expresses fear or disgust toward the lottery. Even Tessie is friendly and pretending to be pleased to be present before she receives the black spot. I think if Tessie is not the target, she will also own the stones to the winner.The film shows hypocrisy and human weakness in the small town. It is horrible when people always relying on the traditions, especially some brutal sacrificial ceremonies like the lottery. The holiday atmosphere and surprised conclusion of the lottery intensify the horror of the story. The horror of the lottery is not only the cruel behavior of the people, but also casual reflection to the victim. They feel not guilt to the victim, and even excited when they throw the stones. The lurking evil of human kind is the most horror thing that reflected by the film.

Dangers of Childhood Immunizations Essay

Evidence Supporting ThesisIn order to extrapolate the safety of vaccinums, you have to know salwaysal things, including how a babys immune system schools from birth onwards, and what vaccines do biochemically in the body. That work has never been done. Found in the book Just a Little Prick by Hilary ButlerNo one medical treatment impart work the same way on all person it is used on, so why would we expect for generalized vaccines to work the same way in e actually babe? It is merely unacceptable to know how your squirts immune system will do to vaccines, but there are consequences set in place for parents deal myself who do non guess in giving annual vaccines. For instance if your minors vaccines are not up to date, then your child is not allowed to go to school, be involved in team sports, and a host of other activities.Main PointsStudies have not been done to luff how each individual vaccine affects the body in both demonstrable and negative ways. Alternative measur es should be on tap(predicate) for those parents who are against vaccinating their children. more(prenominal) studies quest to be conducted to see what role, if any, vaccinations play in the behavioral tantrum of a childs development. Studies have not been done to plant how each individual vaccine affects the body in both tyrannical and negative ways. What are the affirmative effects that vaccines have on a childs body? Vaccines can do to prevent many of the serious complications that occur as a result of serious sicknesss.Vaccines help to ensure that if a child comes in contact with a disease, they will only develop a mild case of the disease versus a child never having the vaccine who develops a natural immunity to the disease which will in turn cause the non-vaccinated child to have very severe complications. Varicella transmittal points to Pneumonia if no vaccine has been given. Polio Infection leads to permanent paralysis if no vaccine has been given. Mumps Infectio n could lead to deafness and infertility in young boys if no vaccine has been given. Hib transmitting can lead to permanent brain dam duration if no vaccine has been given. Vaccinations help to build immunity to diseases that may be foreign strains of radiation pattern diseases. ** What are the negative effects that vaccines have on a childs body?Because there have not been any studies on the exact biochemical effect that vaccines have on a childs body, there is not much supporting evidence to why vaccines are negative. However, there are some studies that suggest that vaccines may be closely tied to various behavior problems such as adhd, add, and the ever controversial autism. It has been proven that vaccines cause mild side effects such as swelling, fever, flu-like symptoms, and in more severe cases seizures.Alternative measures should be available to parents who are opposed to vaccinating their children. The bottom line School age children are required to have up-to-date vacc inations before being allowed to appear school. There arent any alternative options for parents who do not believe in vaccinating their children Children are not allowed to attend school.Children are not allowed to participate in group activities such as team sports, and clubs. be we really harming our children by vaccinating them? Studies have not been done to sight how each individual vaccine affects the body in both positive and negative ways. Alternative measures should be available for those parents who are against vaccinating their children. * 3.More studies need to be conducted to see what role, if any, vaccinations play in the behavioral aspect of a childs development.

Pet Sematary by Stephen King Essay

Setting The allegory, caress Sematary by Stephen queen mole rat is pose mostly in Ludlow, Maine. Aside from the detail that Stephen King often sets his novels in Maine, where he was born and grew up, the quiet and laid back atmosphere of this egress which has a very small population ( tho 402 in 2000) has roundthing to do with the novel. As catalyst for the novel, a particular old-fashioned Indian entombment dry land is located within walking distance of the Creed family tin in this locality. The value of this setting in this novel is its link with hi theme.Ludlow is known to nourish a 1% American Indian Ancestry and this small argument is enough to validate the presence of the Micmac sepulchre dry land in the area. With a small population in the locality, it is most likely that most of the citizenry in the place know about the burial ground which in embodiments why a certain Timmy in the novel is referred to as having being interred in the burial ground as well. Th is sets precedence in the story and explains hoe Jud is quite well-versed with the lore of this particular burial ground.The setting in like manner helps to conceal whatever supernatural events that occur in the place and so making it more than thinkable that the great unwashed from other places did not attend about the strange occurrences in the place. So, while it is a given that King al centerings sets his novels in townspeoples and counties in Maine, the choice of Ludlow for this novel is obviously well-read and is done to achieve certain effects and objectives these basically, to make it more believable and to validate the link between the townsfolk and their apparent, inherent knowledge of the faultfinding element of the novel which is the Micmac burial ground.Other than just these technical intentions of the author, it has to be understood that the tone of the novel is also often set by the setting. In this particular novel which starts out in a sleepy, more or less passive town, the effect of having something strange and supernatural occurring serves to upset the status quo of the town. Of course, in that location is reference to a similar occurrence happening in the past, only when this works to deepen the secret of the town and so consequently explain the hush-hush attitude of the people.Drop in a metropolitan family absorbed with the more tangible representations of life, and a burial ground that is able to come up the idle, and the novel has the perfect setting for the materialization of the tangible desires of the alien family and the chaotic interplay between these values and the values of the townsfolk. Major acknowledgments Louis Creed is the main character of the story and it is his family, starting with the family cat, and then his son, and finally his wife that fall dupe to the demonic powers of the Micmac Burial ground.Creed is initially introduced to be indifferent and academic, hardly sympathetic and close to his family m embers. This is vital to his decisions later in the novel. His entrance into Ludlow, Maine sets in feat a series of events that serve to clearly emphasize the differences his family has with the people in the town not only this, it also serves to create a contrast between the ideals of the people of the town as well as his own ideals.Creed is used in the novel to foreshadow the events that would make out with their moving to Ludlow because it is his dream of a certain university student that leads him to the burial ground in the metaphysical sense. However, more than just the reality that the novel revolves more or less this main character, Jud, another character in the story, a friend of Louis plays a very important role in setting in motion the chain of events that lead to the demonic corruption of the Creed family.Jud and Louis are at the different ends of the supernatural spectrum in Pet Sematary Jud is at the initiating end and Louis at the receiving end of the initiation. Jud is a local of Ludlow and has witnessed certain events in the past machine-accessible to the powers of the Micmac burial ground so as a favor to Louis who was instrumental in saving his wife from a fatal heart attack, he takes the family cat of the Creeds which was run over by a truck to the antediluvian patriarch burial ground after which the cat returns to life.This is the first incident that involves the Creeds and the burial ground, so in effect, Jud is the instrument of paradox because it is through him that the novel begins to drop towards its gruesome and quite horrific climax. Horror Fiction Formula Of course, Pet Sematary, being set in Ludlow, Maine apparently begins with the concept of the Apollonian community.However, a unmistakable characteristic of this particular novel is the incident that the community is not at all Apollonian in the truest sense of the concept because as the novel unfolds, it reveals that in fact, the Micmac burial ground and its demons has had its victims in the past, this being Timmy, who was killed along with his father when their house was burned down. In effect, the Creeds arrive into the community at a layover when it is seemingly Apollonian, solely in reality, is solely in a transmutation period from its dark past to another, darker future.This is important in the novel because the Dionysian force comes through an instrument, Jud, who has experienced the irruption in the past in the person of Timmy. So, it is Jud who becomes the harbinger of the Dionysian force, which in this novel, is the evil that resides in the Micmac burial ground. The strange thing about this novel is the fact that even with Juds knowledge of the degree of evil of the Dionysian force he save risks this by entering the Creeds family cat into the grounds of the ancient burial site, even with the knowledge of what the consequences could be.The resurrection of the cat in the novel is the irruption in the novel because it is the manifestatio n of the Dionysian force, albeit subdued quite genteel, it actually escalates as Louis Creed decides to inter his son into the ancient burial site. The only time that the novel deviates from the horror formula is when the novel moves towards its ending, where instead of move the Dionysian force to put a stop to it or to conquer it, Louis Creed is devoured by the temptation of bringing back his wife, perhaps also blinded by his loneliness and depression.The novel ends with implications of the wife actually move from the dead. So, although, there is no pursuit of the Dionysian force, the novel still ends the way it should according to the formula with implications that the Dionysian force was not in fact defeated or destroyed. Levels of horror Perhaps the reason why this novel is so successful and so enjoyed by many horror fans is the fact that it operates on the three levels of horror in an escalating manner. In the beginning, the Apollonian community is except gripped by its d ark past and the burial ground is nothing but a folkloric piece of land behind a pet cemetery.In this part of the novel, it operates on terror because while many people from the town know of the legend of the burial ground and were witnesses to its demonic powers, the knowledge is still on the level of intangibility, like a rumor going or so town. Later, when the Dionysian force manifests itself in the form of the cat, a mild form of horror begins to emerge which is the resurrected cat more aggressive, more hostile, and possessing the qualities of a dead animal.So, in this sense, the Dionysian force acquires a face or some form of tangibility. The horror becomes more pronounced with the resurrection of Louis son, Gage. This time, the Dionysian force becomes more vivid as Gage is more demonic and more evil. This fresh resurrected creature then kills Jud which then transforms the horror into mutual exclusiveness because along with Jud, the teras kills Rachel. King implies in the s tory that Gage partially eats the stiff of Rachel. This adds to the revulsion.The end of the novel adds more to this third level of horror by turning the evil inside out. In effect, instead of the horror merely manifesting itself in the resurrected corpses, it begins to eat through the sanity of the last remaining protagonist, Louis. So, the revulsion takes a final twist, when because of the insanity of Louis, he also buries his wife in the burial site and his wife returns. In effect, the monstrosity has transcended from being express mail only to the dead coming back to the living finally hold with its evil.

Scenario

Decision Form Period 5 Company____ 3 reduplicate I Price (per unit) Advertising sales Corporate personal identity Market research report Market 1 3090 EUR 6 mEUR MEUR Yes ? x 2 Market 2 4420 FCU mEUR 3 Market 1 no. of ppl. Market 2 no. of ppl. Yes ? Yes ? Value Analysis 1 2 Sales Staff 120 90 Bid price for fond 2699 EUR/unit Relaunch (I old) Introduction (I sweet) Ecology 2. 6 4. 8 Technology COPY I old COPY I new COPY II new 35 50 o. of ppl. no. of ppl. no. of ppl. COPY I R&D mEUR mEUR mEUR mEUR mEUR mEUR Purchasing Input Materials/Parts 30,000 units COPY I Production Volume Production Lines Investment Disinvestment Maintenance Rationalization 50,000 units grammatical case B no. of new grooves no. of line(s) mEUR /line mEUR /line 1 3 Type A no. of new lines no. of line(s) mEUR /line 1 mEUR /line 1. 6 Type C no. of new lines no. of line(s) mEUR /line mEUR /line ProductionProcess Optimization Investment in environmental Technology Production Staff hire (+) / dismiss (-) Training Non-salary cost Short Term Loans Long Term Loans Purchase of securities Dividends . 3 . 20 mEUR mEUR ppl. mEUR % mEUR mEUR mEUR % of net income Financing 5 30 COPY I be after figures Sales Revenue* Return on equity Cash-Flow Market 1 100 mEUR % 15 10 mEUR Market 2 50 mEUR * Sales Revenue without Bulk Buyer and Request for Bids TOPSIM General Management chance variable 13. 0 Decision Form 8 Periods Standard Scenario www. topsim. com

A Street Car Named Desire

A Streetcar Named Desire Final judging 1 . The title A Streetcar Named Desire holds both(prenominal) factual and figurative meaning. Blanche DuBois takes an actual streetcar named Desire to transport her to the home of her sister. Blanche is liter onlyy brought to the home of the Kowalskis by Desire, precisely she is overly brought at that place by her in truth receive desire. Blanches sexual intimacies held with galore(postnominal) men has ruined her reputation and compulsive her out of her home town. Blanche is longing and wishing to pose her emotional state over in the town ofElysian Fields with her sister Stella. She feels that every one in this town entrust accept her because they are unaware of her secrets and terrible reputation. Blanche is confident in retentiveness her past a secret and portraying herself to be such a prizeed and lady-like woman. 2. Blanche DuBois in this novel could be best described as a tragic hero. She is very capable of great deeds but i s destined to fail due to such circumstances beyond her own control and fatal flaws.Blanche by means ofout the play is very fragile and piano after the tragic death of her husband leaving her with the biggest flaw of desire. Blanche after the tragic death of her husband is in great search for a man who will fulfill her desire however, she seems to never get enough. Blanche held m either intimacies ruining her reputation and before long left her home town to go live with her sister Stella in Elysian Fields. Blanche trying to portray herself as a respectable lady slowly reveals her secrets without any intentions.Blanche during her stay in New Orleans is in search of respect, love, and care returning to the conventional wants and needs of a woman during her youth time period. Blanche is not employ to the way of life in the world during present time. Vanity soon falls into a fantasy that settles in her mind as delusion. Her egotism gets in the way of her love life, leads her to te ll lies and believe them, and ultimately leads to her foray carried out by Stanley and resulting in her biggest fall yet.A Street railcar Named DesireBlanche arrives in the New Jersey apartment that is owned by the Kowalskis in particular, her sister Stella and his br early(a) in law, Stanley. Armed with her striking features, stimulate and seeming forceful characters, Blanche scum bag immediately relay what her character is all about power, feminism, liberalism, and absurdity.In general, she serves as the epitome of a new-age woman who has led her life badly. Her arrival immediately relegates the persona of her pregnant career-less sister, Stella, as a submissive, dependent, and handed-down woman. With regards to original impressions, while Blanche hindquarters be viewed with envy, antagonism, or admiration, one can only offer sympathy and frustration to Stella.As for Stanley, he is pretty much the male counterpart of Blanche. He is the embodiment of brutality, roast, re sponsibility, sensuality, and excessive power which lots exists in many patriarchal societies. Like me, any person who has respect for women would surely hate what he does to Stella. Being ignorant of the truth female genitalia the real life of Blanche, Mitch, like Stella, is another pitiful character.b. Discuss the presence of reality & illusion in the play. How is it represented?The sense of reality is presented as a consider of conflict and question not only in the storys plot but also through its characters. To start with, Blanche lived her life masked by the illusion she creates in order to large-minded herself from the dreadful results of her wrong doings. Stella also lived in an illusion where she regarded domestic abuse as a typical fraction of Stanleys love for her.Mitch also fell into a whirlwind of illusions that Blanche created. Basically, Stanley is probably the only character who is in continue with reality. The play started with an illusion that Blanche created and the quest for reality is the plot. In the end however, the launching of Blanche to illusion or madness became her reality.c. Do you think Blanche is crazy? Explain.Blanche was already at the brink of insanity prior to her brutal encounter with Stanley. end-to-end the story, we can observe that Blanche has carefully crafted her own fantasy world through the characters that she tried to portray as a distressed damsel, southern belle or the good school teacher. The way in which she tries to conceal her secrets and the lack of vicious intent to genuinely manipulate other people just exhibit her inability to interact with others in a sane manner.d. Blanches first husband was homosexual (as was Tennessee Williams). Discuss the depiction of homosexuality in the play.Although straightaway men like Stanley were unfairly portrayed as brutal, one can say that homosexuals were not depicted reasonably in the play as well. Homosexuality was portrayed through Allen Grey, the poet late h usband Blanche.His disgust to himself and his delinquency which prompted him to commit suicide proved that homosexuality was demonstrated as something that is devastating, disturbing, and self-destructing. For both Blanche and Allen, the effect was extensively disastrous as one died while the other resulted to rebellious madness.e. Is there any villain in the play? If there is, who is it? Explain.To a certain extent, both Blanche and Stanley can be treated as villains. Blanche struggled to ruin the seemingly harmonious life of Stella and Stanley. On the other hand, Stanley abuses her wife and also succeeds in crushing Blanches fantasies.f. Do you think Stanley actually harmed Blanche? Do you think she deserved it?The play implies that Stanley has raped Blanche. Regardless of any circumstance, there is no righteous justification for raping a woman. No matter how hideous ones character may be, no one deserves to be raped.

Meaning of Ceteris Paribus Essay

In economics and finance,the term is used as tachygraphy for indicating the effect of one economic variable on another, holding ceaseless all other variables that may affect the second variable unity of the disciplines in which ceteris paribus clauses be most widely used is economics, in which they are employed to simplify the formulation and description of economic end points.When using ceteris paribus in economics, assume all other variables except those under immediate amity are held constant, . In effect all extra variables remain unchanged and there are no outside influences on the variables being looked at. The moreover variables being considered are wrong and supplicate. It does not take into account whatever other things, such as inflation, product improvements, etc. This allows for the explanation, examination and judgment of basic economic rules.This operational description intentionally ignores some(prenominal) cognise and unknown factors that may also influ ence the relationship between price and quantity demanded, and thus to assume ceteris paribus is to assume away any hobble with the given example. Such factors that would be intentionally ignored include the congress change in price of substitute goods, (e. g. , the price of beef vs pork or lamb) the level of risk aversion among buyers (e. g. , fear of mad overawe disease) and the level of overall demand for a good regardless of its legitimate price level (e. g. a societal shift toward vegetarianism) In this example, the clause is used to operationally describe everything surrounding the relationship between both the price and the quantity demanded of an ordinary good. whendiscussing the laws of contribute and demand, one could say thatif demand for a given product outweighs supply, ceteris paribus, prices will rise. Here, the use of ceteris paribus is simply saying that as long as all other factors that could affect the outcome (such asthe existence of a substitute product) r emain constant, prices will outgrowth in this situation.For example as the price of Pepsi poop rises, the quantity demanded of Pepsi cola falls, ceteris paribus. If the price raise of Pepsi-cola and vigor else changes, in other words, peoples preferences stay the same, the recipe for Pepsi-cola stays the same, and so on, then in chemical reaction to the higher price of Pepsi-cola, people will buy less Pepsi-cola. In a nutshell the term ceteris paribus is used to define the law of demand and supply and it literally means all other things remain constant and nothing else changes.

Promotional mix Essay

Element of the promotional liquefy for cleared smoothies may acknowledge this such as Advertising is employ to communicate with the public approximately their products and services, this can be expensive and telephone circuites must ensure that they spend their advertisement bud define carefully methods include moving image, print, ambient such as advertising on b use of goods and servicess, digital and audio. Sales promotion is used to make headway customers to purchase your products or for distri exactlyion channels to stock your goods . methods are harm promotion (discounts), coupons, competitions, money refunds, loyalty incentives.Personal removeing is when a exemplar of the confederacy interacts directly with a potential customer using skills c whollyed pass completion a sale. Methods are face to face, telephone, email, and video or web conferencing. mankind relations are activities a business carries out to place discipline in the media without paying for it dire ctly activities might include exhibitions, sponsorship and press relations Direct marketing is when a business communicates directly with a customer, establishing an singular relationship between the business and the customer, methods are direct mail, mail enjoin catalogue, magazines and telemarketing.Advertising is used by innocent around effectively than early(a) methods of the promotional unify, methods of advertising they use is they chip in links with popular childrens websites such as union penguin , indigent in addition put adverts on the TV. Another method of advertising acquitted use is that they deal magnets on with their smoothies this is effective as it appeals to their heading audition.Innocent use advertising most effectively out of the promotional mix as they appeal to their tar demoralise hearing. Innocent use advertising as they are a forward-looking company who need recognition so their TV adverts are unforgettable and funny and they show their pri vateity this links to matching their target audience well with how they advertise.Innocent use sales promotion effectively as they hold in used promotions such as the free magnets ad order penguin deals, as if they are linked with things such as club penguin citizenry who use club penguin bequeath be more likely to corrupt their pouts as I benefits them and linking with a big business like Disney which runs club penguin means that it boosters appeal to more of their target audience, while giving them a better image and giving them a funnier personality.The innocent website ad Facebook summon work effectively with their sales promotion as it uses fun ad games to promote their products while appealing to their audience at the same time. Innocent also use other methods of the promotional mix such as public relations. Innocent use this to get more sales for illustration inviting the press to a release of a new product so that they report about it and notify the public this will then help increase their audience ad gain more customers.The press an rival the sales a business makes as if they give a crappy review and the company gets bad press they will lose customers quite of gaining them. This is effective because customers can get an unbiased opinion of the products, however it is a risky element of the promotional mix as the product/ company might get a bad review and loose customers but if the public like the product then it will gain sales. Elements of the promotional mix that innocent do not useThings such as direct marketing and personal selling are not used as effectively by innocent because they sell straight to the install such as Tesco or a wholesaler because it keeps their products staying alerter, they will sell more as they will become more reliable as they are always in the shops unlike Avon which you have to wait weeks until you get your product and chose your products and thy well have a wider customer base, this is why they use adverti sing so effectively as It continues to get their items bought from the wholesaler.An example of personal selling is a car salesperson persuading you to buy a car, innocent do not use this as it would not be value it, as they would have to pay for a person to sell the products and they would have to sell a lot before they make a queen-sized profit. A person would also have to walk around all day with the produce in the heat which can affect the produce. Innocent dont use direct marketing as they sell their goods to big supermarkets and they dont have to sell to the customers so its up to the supermarket to tell the customer about the products and deals and so forthThe promotional mix is used well by innocent as their adverts help get them customers and raise awareness of their shuffling, and appeal to their target audience. Innocent dont use direct marketing or persona selling as they dont sell to the customers personally they sell it to supermarkets instead or the wholesaler.Once they have sold their products to the wholesaler orsupermarkets they no protracted will have to sell their produce however they do have to still advertise as they need the customers to want to buy their products from the supermarkets etc. so then the supermarket will continue to stock their brand. They use the scattering channels the way they do to make sure their products stay fresh for the customer and they are kept in good condition and by selling to supermarkets before the customer it will help show their brand to a wider audience and help increase awareness of their brand.The promotional mix used by innocent is appropriate because it has worked and their business is expanding and getting larger, they also have a reliable customer base in England which will help them if they decide to sell in America. This is because they have advertised their business a lot and because of their uses of advertising this means they have a wider audience which ranges from children to adults and any gender.

Discuss the social context that influences Othello’s labelling of Desdemona as that “cunning whore of Venice”

In Othello many issues ar undertaken. According to the meter that the play was written, men hold all the power and women are considered to be of low intellect. Throughout the play Desdemona is a symbol of innocence and helplessness. At first she appears to be mature and quite perceptive of events around her. Iago frequently tells Othello that she is unfaithful. It seems that she refuses to accept what is happening and her views are impartial.She has a tendency to be appealing towards other peoples situations, like Cassio. This is what triggers Othellos jealousy when Iago pointed out they were speaking in privacy. She oftentimes pays attention to other peoples thoughts yet remains cynical if they differ to her own. She has a loyalty to her husband in all aspects of life, whether it is mental or physical.Othello shows us how a womans character, reputation and power can be keep in lined and distorted by men. The relationship between Desdemona and Othello is very peculiar, and woul d construct been considered even more so at the time at which Shakespeare was writing, it therefore stands out in the play, non least because it is a mixed-race marriage but also because at the drop dead of the play they appear to be on an equal standing, they have a mutual respect for one a nonher.We are presented with a very hefty image of women at the start of the play Desdemona has disobeyed her father and taken her chosen husband, although Desdemona does acknowledge that Othello is her Lord and that it is her duty to obey him. However, in that state, Desdemona does act as a dramatic device, bringing Othello into a domestic situation where he is inexperienced. This causes his obsession with Desdemona to grow because she has become his whole world Iago finds it easy to manipulate this situation because Othello is unfamiliar to life only in the domestic side.Although Desdemona was wise in trusting, her trust was often misplaced, for example Iago. As well as this regardless o f her intellect of what goes on around her in some cases, this was not enough to rise up in society, as women had no perspicacity in the time of the play. Although Shakespeare undertook many modern day ideas, he did not do this for a modern day society, as it would not have allowed so many events to occur, and it would not have been considered realistic by the public.When Othello dialog of wooing Desdemona he is portrayed as an eloquent storyteller and lover She gave me for my pain a world of sighs. It is through her relationship with Othello that his failure is shown not only by her spoilt opinion of him, he was previously an idol to her, but by the end of the play she has realised that men are not gods, but also by Othellos swift dismissal of her as a fair devil and a lewd minx after his view of her where he would deny her nothing has been destroyed by Iago.The dilapidation of Othello is marked by the destruction of their once close and trusting relationship, which Iago has convinced Othello that it is a foul disproportion. Desdemonas physical and vocal absence from the opening scenes speaks around womens place in the Venetian society. It is through Desdemonas absence that we are able to conjure up our own mental image of her based on what we have heard.

The Colonial Experience in West Africa

The Twentieth Century brought with it vast changes for the peoples of westerly Africa. The orthodontic braces of colonialism bound them together into a in the raw political, economic, and social order. It was as if hundreds of long time of history had suddenly ended, and begun again a mod. In the wake of the Berlin West Africa Conference, in 1885, the great powers of Europe Britain, France, Germany, and heretofore out Portugal and Belgium had carved up West Africa among themselves. European overlords either completely re nursing homed, or else adopted a supervisory gear up over the primaeval African authorities.Proud kingdoms, like those of the Asante, Benin, and Da officey, found themselves compel to admit or disappear, as West Africans struggled to institute sense of a world that had been turned completely upside stack and internal out. For inside out, could easily describe the reversal of economic roles that came on with European conquest. Formerly, European traders had stayed close to the coast, all(a)owing the African rulers and merchants to supply Europe and her New World colonies with slaves and early(a) merchandise.The British had finally succeeded in ending the slave trade several(prenominal) years before, and many of the coastal kingdoms of West Africa had languished as a result. some had been almost wholly dependent upon the trade in human beings straight off there would have to be new sources of r even soue. For the most part, these new sources of income would be developed by Europeans who would exploit West Africas people and resources for the benefit of their home countries. However, the Africans would in any case learn from their new masters. Some of them would obtain a occidental educational activity, or work to introduce the ideas of the modern industrial world to Africa.European science, technology, education, political, economic, cultural, and religious ideas would all have a profound impact on West Africa. The pre-colo nial relationship between Europeans and West Africans was one and only(a) of mutual trade. In the first half of the Nineteenth Century, Europeans vastly increased their purchases of palm oil, and also continued to buy tropical hardwoods, while Africans received the products of Europes industrial vicissitude cotton and woolen textiles and iron. 1 It was only as direct European influence began to increase that economic conditions were gradually modified.The introduction of cocoa by European delegationaries in the 1860s, led to its becoming a major bullion crop and primary ex port wine by the earliest period of European colonial domination, around 1900. golden and coca were the mainstays of the economy in the Gold Coast (now Ghana). To keep up with their seemingly insatiable demands for these and otherwise products, the British, french, and other others, introduced more modern techniques of production. In particular, they employed industrial methods of mining, and built railroads and port facilities to enable a vastly increased flow of goods.Yet it would be wrong to think that was no African response to changed economic conditions. Already, in the late 1800s, African merchant families, such as the Sarbahs, began to encourage natural condom production In contrast to the palm oil trade, the rubber trade, because of a greater monetary return per unit of labour input and weight, force into its orbit thousands of producers from the sibylline interior, including Sefwi, Kwahu, Asante and the distant states of Brong-Ahafo, all more than 100 miles from the coast.The rubber trade also gave rise to a new group of in-between-men or broken from the Fanti states, Asin, Denkyera, and Akim, who carried the trade to the further limits of the forest zone and in so doing accelerated the extension of the cash economy. Rubber became a major exporting with shipments totalling well over one million pounds volume in 1886 and by 1893, the Gold Coast ranked first among the ru bber exporting countries of the British Empire and third in the world. 3Africans were, therefore, effectivey able to adapt themselves to European conditions in order to increase the size and extent of their markets, even if this necessitated adopting new techniques, and even entirely new crops, like rubber. On the down side, an economy based on growing and harvesting rubber latex caused significant social upheavals. The influence of the coastal mercantile families and kingdoms waned in opt of inland economic interests. 4 Families like the Sarbahs expanded their trading networks deep into the Interior, opening up branch story, cajoling purchasers, and further turning economic way toward the one paramount crop.They also became increasingly dependent on fluctuations in the European market. 5 Furthermore, the infringe between European sponsored economic development, and interfering European control can be seen in the 1920s Gold Coast, where British Governor Guggisberg pursued a pol icy that was in many slipway detrimental to the future of the African peoples under his control Anti-modernisation, anti-urban, and anti-development. Regulations and barriers against innovation proliferated. functionary policy did nonhing to encourage the emergence of a commercial middle class.Its effect instead was to establish a highly formidable machinery of bureaucratic control. The most damaging effect of colonial policy on the ground was the way in which it hindered the emergence of a native modernizing cadre, one result of which was to divert into long and bitter anti-colonial struggles much brilliant endowment fund which could have been used creatively in development sectors. 6 The hyponymy of African interests to European profits condemned West Africans to economic backwards through lack of skills and genuine opportunities.The lack of skill and opportunity open to native West Africans leads naturally to a discussion of European education and the new horizons it presen ted. Prior to the era of colonial domination, West Africas peoples had had little contact with western sandwich ideas, except for he occasional interactions with Christian missionaries. The states, large and small, of West Africa had been universally pre-industrial, and had possessed nothing in the way of modern communications, transportation, or even the kind of complex educational and political institutions that existed in the Christian and Muslim worlds.Missionaries were the first to introduce Western educational methods into West Africa For them education took place in schools, where obedient pupils listened to teachers, took examinations, and received diplomas certifying knowledge. Discipline was important, not only to make the children study, but also to mold desirable habits and (that was usually considered to be even more important than learning itself). 7 On the whole, Western education extended only to teaching compositors cases that Europeans thought would be useful to t heir charges.vocational training was sufficient for people who would never have to govern themselves. 8 Nevertheless, an ikon to the Western academic tradition inspired many African families to push for a higher level of education for their children. Few pupils cute to undergo the cost and the hardship of study, only to be prepared for a rural life and a low living standard. 9 In the 1930s, in French West Africa, Colonial Government officials began to formulate a new approach that appeared to look forward to a synthesis of the European and inhering traditions.Frances redefined mission civilisatrice civilizing mission was to be fulfilled by teaching the subject populations how to live according to authentic African traditions, This vision of Frances role oversea as the protector of indigenous subtletys in the colonies challenged earlier presentations of the colonial mission that had presented France as the bearer of European civilization and French culture destine to bring Afri ca out of the darkness in which many late-nineteenth-century colonizers claimed its people lived. 10The French administrators went so far as to strongly encourage African arts and crafts, sponsor African festivals even to teach Africans how to be African( ). In order to avoid contamination by native teachers already trained in the earlier European methods, the French actually brought in teachers from France to lead the Africans in the study of their native West African culture these teachers being observed leading inseparables in local folk dances, etcetera 11 Such plans represented an interesting attempt to keep Native elites loyal to France, while at the same time, well-rooted in their Native lands and cultures.Ostensibly, such practices would avoid the stateless quality of Africans educated under the earlier trunk. Nonetheless, exposure to European educational and economic ideas even when those ideas were fused with African traditions could not forestall an African liking for greater freedom and opportunity along European lines. Colonial rulers often imposed a dual system of judge a European one for major offenses, and a Native one for those offenses deemed minor by the Colonial Authorities.The French, early on, abolished the Native courts and judicial system, except in rare cases, while even under the British, it was quite a clear that Native justice was distinctly secondary to the real justice of the Europeans. 12 Dichotomies such as these further entrenched notions of West African inferiority. The French instituted a policy of not interfering in African customs and culture, as long as those customs did not conflict with the French aim of achieving some sort of evolution among Africans. 13 It was taken utterly for granted that African culture was inherently inferior to French civilization.By contrast, the British authorities endeavored to maintain equilibrium by feature traditional African smallholder society with the demands of the British Cocoa Board. Rural West African society was to be maintained at all be to prevent a breakdown of the social order, such as occurred when jobs were but and peasants left for the cities in the hope of finding work. There, oddly enough, the British actually encouraged the growth of an urban petit bourgeoisie in the dream of preventing rebellion.With the get wise of world markets during the Great Depression, urban and peasant unrest increased with the perceptible difference that now a radicalized bourgeoisie was available to lead that unrest. 14 In short, the European colonial administrations of West Africa both helped and exploited Africans. With their thirst for profits, and a belief in the superiority of their own institutions, technology, and culture, they dreamed of locomote the native population while at the same time retention that population economically productive, and under firm European control.Yet in so doing, they introduced many attributes of the modern world to th e peoples of West Africa. European notions of development, education, and justice split traditional African life into separate public and head-to-head spheres especially for those who embraced European learning and techniques. 15 The divide that grew up between Europeanized Africans, and those who have remained closer to their traditional ways of life remains a problem even today.One of the lasting legacies of European Colonization in West Africa was this impartial transformation this creation of a society be in two worlds, trained properly for neither. Once opened to the full force of the industrial (and later post-industrial) economy, the traditional African economy could not compete. At the same time, not enough West Africans were educated, in the European sense, to provide the skills and leadership to easily lead their people into a new era. European rule has left West Africa with many choices, not all of them good.

Reciprocating Engine

224 C H A P T E R 6 RECIPROCATING INTERNAL COMBUSTION ENGINES 6. 1 access Perhaps the lift out-k nown locomotive railway locomotive in the world is the reciprocating internal blaze (IC) locomotive locomotive. Virtu anyy every person who has driven an automobile or pushed a agent lawnmower has intent unrivall(a)ed. By far the close to widely use IC railway locomotive is the electric arc- get out flatulencyoline locomotive railway locomotive, which takes us to school and calculate and on pleasure jaunts. Although an some other(a)(prenominal)s had do signifi spatet contri neverthelessions, Niklaus Otto is generally credited with the invention of the railway locomotive and with the res publicament of its theoretical stave.A nonher important engine is the reciprocating engine that made the bring off of Rudolf diesel engine famous. The diesel engine engine, the cultivatehorse of the heavy truck industry, is widely apply in industrial magnate and marine s creenings. It re baff direct the reciprocating steam engine in railway line locomotives about fifty old age ago and remains do hourant in that role today. The diver, plunger sleeping room, methampheta mine, and connecting rod provide the geometric basis of the reciprocating engine. While 2- thump- troll engines be in use and of continuing interest, the discussion here allow stress the to a greater extent widely applied four-stroke- beat engine.In this engine the piston undergoes cardinal windup(prenominal) rhythm methods for for each one thermodynamical motorbike. The pulmonary tuberculosis and coalescency just nowt againstes occur in the origin two strokes, and the military group and fire per systema skeletaleancees in the last two. These processes argon made possible by the move- skidder tool, discussed next. 6. 2 The Crank-Slider Mechanism Common to most reciprocating engines is a linkage known as a crank-slider instrument. Diagramed in code 6. 1, thi s mechanism is wizard of some(prenominal) capable of producing the straight-line, endureward-and-forward achievement known as reciprocating.Fundamentally, the crank-slider converts rotational motion into linear motion, or vice-versa. With a piston as the slider moving inside a fixed piston sleeping accommodation, the mechanism provides the vital nip of a bungle engine the force to compress and expand a tout. Before delving into this aspect of the engine, however, let us examine the crank-slider mechanism to a greater extent closely. 225 It is evident from augur 6. 2 that, while the crank arm rotates by blottos of 180, the piston moves from the position known as filch- nucleus (TC) to the other extreme, called bottom-center (BC).During this finish the piston travels a distance, S, called the stroke, that is twice the length of the crank. For an angular focal dimension of the crank, , the crank descent A has a tangential swiftness component S/2. It is evident that, at TC and at BC, the crank pin focal ratio component in the piston pedagogy, and and thence the piston velocity, is zero. At these auspicates, agree to crank angle = 0 and 180, the piston reverses direction. therefrom as varies from 0 to 180, the piston velocity accele ranks from 0 to a utmost and thus returns to 0.A similar behavior exists amongst 180 and 360. The connecting rod is a two-force member hence it is evident that there ar both(prenominal) axial and aft(prenominal)al forces on the piston at crank angles other than 0 and 180. These lateral forces ar, of course, opposed by the piston chamber walls. The resulting lateral force component commonplace to the cylinder wall gives rise to clangoringal forces between the piston rings and cylinder. It is evident that the normal force, and thus the skirmishal force, alternates from one side of the piston to the other during each motor hertz. so the piston motion establishs a challenging lubrication problem fo r the control and reepithelial duction of both wear and might loss. The position of the piston with respect to the crank centerline is granted by x = (S/2)cos + Lcos ft m (6. 1) where yA = (S/2)sin = Lsin privy be employ to bear out to obtain x/L = (S/2L)cos + 1? (S/2L)2 sin2 ? dl (6. 2) frankincense, while the axial component of the motion of the crank pin is sincere harmonic, xA = (S/2)cos, the motion of the piston and piston pin is to a greater extent(prenominal) complex. It may be 226 arrestn from Equation (6. ), however, that as S/L becomes small, the piston motion approaches simple harmonic. This becomes physically evident when it is recognized that, in this limit, the connecting rod angle, , approaches 0 and the piston motion approaches the axial motion of the crank pin. Equations (6. 1) and (6. 2) may be used to predict component velocities, accele dimensionns, and forces in the engine. The volume swept by the piston as it passes from TC to BC is called the pi ston dis key outment, disp. locomotive fault, DISP, is then the increase of the piston switching and the number of cylinders, DISP = (n)(disp).The piston shifting is the merchandise of the piston cross-sectional argona and the stroke. The cylinder inside diameter (and, approximately, a uniform the piston diameter) is called its bore. Cylinder bore, stroke, and number of cylinders ar usually quoted in engine specializedations along with or instead of engine rendering. It will be seen later that the power outfit of a reciprocating engine is proportional to its displacement. An engine of historic interest that in growth used the crank-slider mechanism is discussed in the next section. 6. 3 The Lenoir CycleAn early form of the reciprocating internal electrocution engine is credited to Etienne Lenoir. His engine, introduced in 1860, used a crank-slider-piston-cylinder arrangement 227 in which a combustible categorization confined between the piston and cylinder is ignited after TC. The resulting blaze ball up pressure forces acting on the piston deliver fake by way of the connecting rod to the rotating crank. When the piston is at BC, burning at the stake liquides atomic number 18 al first baseed to escape. The rotational momentum of the crank system drives the piston toward TC, expelling surplus gasolinees as it goes.A fresh combustible categorisation is again admitted to the burning at the stake sleeping room (cylinder) and the cycle is repeated. The theoretical Lenoir cycle, shown in put down 6. 3 on a pressure-volume draw, consists of the inhalation of the acidifying fluid (a combustible garland) from give in 0 to begin 1, a change slight-volume temperature and pressure rise from convey 1 to pass on 2, approximating the burning process, an isentropic expansion of the burning gases to kingdom 3, and a eternal-pressure expulsion of counterpoise gases blanket to state 0.Note that a portion of the piston displacement, from state 0 to state 1, is used to take in the combustible premix and does non circumstancesicipate in the power stroke from state 2 to state 3. The engine has been called an explosion engine because the power delivered is due solely to the make itingly rapid burning at the stake pressure rise or explosion of the mix in the confined space of the cylinder. Hundreds of Lenoir engines were used in the ni last(a)eenth century, and the engine is quite inefficient by todays receiveds. In 1862, Beau de Rochas pointed out that the 228 fficiency of internal combustion could be markedly improved in reciprocating engines by calculus of the oxygenate- s determination away variety show prior to combustion. In 1876 Niklaus Otto (who is thought to realize been insensible of Rochas? suggestion) demonst footstepd an engine that incorporated this important feature, as described next. 6. 4 The Otto Cycle The Otto cycle is the theoretical cycle commonly used to wager the processes in th e trip up kindling (SI) internal combustion engine. It is assumed that a fixed smokestack of cultivateing fluid is confined in the cylinder by a piston that moves from BC to TC and back, as shown in Figure 6. . The cycle consists of isentropic coalescency of an standard pressure- give notice mixture from state 1 to state 2, aeonian-volume combustion to state 3, isentropic expansion of the combustion gases to state 4, and a constant-volume arouse rejection back to state 1. The constant-volume ignite rejection is a simple advantageous to close the cycle. It obviates the need to re put in the complex expansion and bombardment of 229 combustion gases from the cylinder at the end of the cycle. Note that the Otto cycle is not c erstwhilerned with the induction of the radiate- arouse mixture or with the expulsion of residual combustion gases.Thus only two mechanic strokes of the crank-slider are needed in the Otto cycle, counter counterweight when it is used to represent an paragon four-stroke-cycle Otto engine. In this case the remaining strokes are used to execute the necessary inhalant and work through functions. Because it involves only two strokes, the Otto cycle may besides represent a two-stroke-cycle engine. The two-stroke-cycle engine is in principle capable of as such(prenominal) work in one rotation of the crank as the four-stroke engine is in two. However, it is difficult to execute because of the necessity of making the usance and overreach functions a part of those wo strokes. It is accordingly not as elevatedly developed or widely used as the four-stroke-cycle engine. We will focus on the fourstroke- cycle here. The simplest analysis of the Otto cycle assumes calorically perfect blood as the working fluid in what is called the subscriber line model cycle analysis. Fol minoring the notation of Figure 6. 4, the muscular contraction process sack up be represented by the isentropic relation for a calorically perfect gas, Equat ion (1. 21), as p2/p1 = (V1/V2)k dl (6. 3) where the coalition symmetry, CR = V1/V2, is a constitutional statement of all reciprocating engines.The diagram shows that the expansion ratio for the engine, V4 /V3, has the same apprise, V1/V2. The principalway volume, V2, is the volume enclosed between the cylinder head and the piston at TC. Thus the compression ratio may be expressed as the ratio of the sum of the clearance and displacement volumes to the clearance volume CR = V2 + (V1 ? V2)/V2 Thus, for a inclined up displacement, the compression ratio may be change magnitude by reducing the clearance volume. The strength of the cycle can be most easily compulsive by considering constantvolume- process incite transfers and the premier(prenominal) Law cyclic inherent relation, Equation (1. ). The heat transferred in the processes 23 and 41 are q23 = cv (T3 ? T2) Btu/lbm kj/kg (6. 4) and q41 = cv (T1 ? T4) Btu/lbm kJ/kg (6. 5) Both the expansion process, 34, and the com pression process, 12, are assumed to be isentropic. Thus, by exposition, they are both adiabatic. From the cyclic integral, the take in work per whole muss is then w = q23 + q41 = cv (T3 ? T2 + T1 ? T4) Btu/lbm kJ/kg (6. 6) 230 As before, the cycle thermal faculty is the ratio of the gelt work to the foreign heat supplied Otto = w/q23 = cv (T3 ? T2 + T1 ?T4) / cv (T3 ? T2) = 1 + (T1 ? T4) / (T3 ? T2) = 1 ? T1/T2 = 1 ? 1 / CR k-1 dl (6. 7) where Equation (1. 20) has been used to eliminate the temperatures. Equation (6. 7) shows that increasing compression ratio increases the cycle thermal cleverness. This is neat for real engines as well as for the idealized Otto engine. The ways in which real spark excitement engine cycles deviate from the theoretical Otto cycle are discussed later. EXAMPLE 6. 1 An Otto engine takes in an air- render mixture at 80F and standard atmosphere presssure. It has a compression ratio of 8.Using melody Standard cycle analysis, a heating esteem of 20,425 Btu/lbm, and A/F = 15, determine (a) The temperature and pressure at the end of compression, after combustion, and at the end of the power stroke. (b) The net work per pound of working fluid. (c) The thermal efficiency. ascendant We use the notation of Figure 6. 4 (a) p2 = p1(V1/V2)k = 1(8)1. 4 = 18. 38 atm T2 = T1(V1/V2)k ? 1 = (540)(8)0. 4 = 1240. 6R T3 = T2 + qa /cv = T2 + (F/A)(HV)k/cp = 1240. 6 + 1. 420,425/150. 24 = 9184R p3 = p2T3 /T2 = 18. 38(9184/1240. 6) = 136. 1 atm T4 = T3 /CRk? 1 = 9184/ 80. 4 = 3997. R p4 = p3 /CRk = 136. 1/81. 4 = 7. 4 atm (b) The constant-volume heat addition is governed by the discharge-air ratio and the supply heating value qa = HV(F/A) = 20,425/15 = 1361. 7 Btu/lbm of air 231 qr = cv (T1 ? T4) = (0. 24/1. 4)( 540 ? 3997. 4) = ? 592. 7 Btu/lbm w = qa + qr = 1361. 7 + ( ? 592. 7) = 769 Btu/lbm (c) The cycle termal efficiency may then be determined from the definition of the heat engine thermal efficiency or Equation (6. 7) th = w/qa = 7 69/1361. 7 = 0. 565 th = 1 ? 1/80. 4 = 0. 565 _____________________________________________________________________ In sentiment f the discussion of gas tight-lacedties and dissociation in Chapter 3, the value of T3 and T4 in Example 6. 1 are unrealistically mettlesome. Much of the nix run downd by the elicit would go into vibration and dissociation of the gas molecules sort of than into the translational and rotational degrees of freedom represented by the temperature. As a result, fitingly lower temperatures would be obtained. Thus, while the analysis is formally correct, the use of constant-low-temperature heat capacities in the contrast Standard cycle makes it a deplorable model for predicting temperature extremes when high naught releases occur.Some improvement is achieved by use constant-hightemperature heat capacities, but the best(p) results would be achieved by the use of real gas properties, as discussed in several of the references. 6. 5 Combustion in a Reci procating railway locomotive The constant-volume heat transfer process at TC in the Otto cycle is an artifice to avoid the difficulties of modeling the complex processes that take place in the combustion bed chamber of the SI engine. These processes, in reality, take place over a crank angle span of 30 or more just about TC.Let us consider aspects of these processes and their implementation in more detail. Normally, the mixture in the combustion chamber must(prenominal)iness have an air- open fire ratio in the neighborhood of the stoichiometric value for fit combustion. A more or little homogeneous mixture may be produced outback(a) the cylinder in a carburetor, by dig into the intake manifold, or by throttle-body pellet into a header serving several intake manifolds. In the case of the carburetor, send away is pinched into the engine from the carburetor by the low pressure created in a venturi by means of which the combustion air menstruums.As a result, increased air fuse causes lower venturi pressure and hence increased enkindle flow. The fuel system thus serves to provide an air-fuel mixture that remains close to the stoichiometric ratio for a range of air flow rates. Various whatsiss intentional into the carburetor hike adjust the fuel flow for the special direct conditions encountered, such as idling and rapid acceleration. Maximum fuel thrift is usually attained with excess air to ensure that all of the fuel is burned. A mixture with excess air is called a lean mixture.The carburetor 232 usually produces this condition in automobiles during normal constant-speed driving. On the other hand, supreme power is achieved with excess fuel to picture that all of the oxygen in the air in the combustion chamber is reacted. It is a matter of exploiting the full power-producing capability of the displacement volume. A mixture with excess fuel is called a rich mixture. The automotive carburetor produces a rich mixture during acceleration by sup plying extra fuel to the air entering the intake manifold.The equivalence ratio is some cartridge clips used to characterize the mixture ratio, whether rich or lean. The equivalence ratio, , is delimitate as the ratio of the actual fuel-air ratio to the stoichiometric fuel-air ratio. Thus 1 represents a rich mixture and 1 represents a lean mixture. In damage of air-fuel ratio, = (A/F)stoich /(A/F). Homogeneous air-fuel mixtures close to stoichiometric may ignite spontaneously (that is, without a spark or other local zip source) if the mixture temperature blow overs a temperature called the auto excitation temperature.If the mixture is brought to and held at a temperature high than the autoignition temperature, there is a limit of delay before spontaneous ignition or autoignition This time separation is called the ignition delay, or ignition lag. The ignition delay de compileds on the characteristics of the fuel and the equivalence ratio and usually decreases with increasi ng temperature. In spark-ignition engines, compression ratios and thus the temperatures at the end of compression are low enough that the air-fuel mixture is ignited by the spark plug before spontaneous ignition can occur.SI engines are designed so that a flame wait will propagate swimmingly from the spark plug into the unburned mixture until all of the mixture has been ignitied. However, as the flame foregoing progresses, the temperature and pressure of the combustion gases merchant ship it rise due to the release of the chemical energy of the fuel. As the bearing propagates, it compresses and heats the unburned mixture, some propagation termed the end-gas. Combustion is completed as planned when the front smoothly passes completely through and through the end-gas without autoignition. However, if the end-gas autoignites, a pinging or downhearted sound called concussion is heard.The avoidance of encounter due to autoignition of the end-gas is a major constraint on the desi gn compression ratio of an SI engine. If heatable spots or thermally induced compression of the end-gas ignite it before the flame front does, there is a more rapid release of chemical energy from the end-gas than during normal combustion. boot is sometimes thought of as an explosion of the end gas that creates an abrupt pulse and pressure waves that race back and forrad crosswise the cylinder at high speed, producing the familiar pinging or low-pitched sound associated with bash.Knock not only constricts engine performance but produces rapid wear and objectionable noise in the engine. Thus it is important for a SI engine fuel to have a high autoignition temperature. It is accordingly important for SI engine fuel to have a high autoignition temperature. Thus the encounter characteristics of commercially available fuels limit the upper limit deductible design compression ratio for SI engines and hence limit their best efficiency. The octane number is a measure of a gasolines ability to avoid knock. Additives such as tetraethyl lead have been used in the past to suppress engine knock.However, the accumulation of lead in the surroundings and its penetration into the food cycle has 233 resulted in the phaseout of lead additives. Instead refineries now use appropriate blends of hydrocarbons as a substitute for lead additives in unleaded fuels. The octane number of a fuel is measurable in a special variable-compression-ratio engine called a CFR (Cooperative Fuels Research) engine. The octane rating of a fuel is determined by comparison of its knocking characteristics with those of varied mixtures of isooctane, C8H18, and n-heptane, C7H16.One hundred percent isooctane is defined as having an octane number of 100 because it had the highest balkance to knock at the time the rating system was devised. On the other hand, n-heptane is assigned a value of 0 on the octane number scale because of its very poor knock bulwark. If a gasoline tested in the CFR engin e has the same knock threshold as a blend of 90% isooctane and 10% n-heptane, the fuel is assigned an octane rating of 90. In combustion chamber design, the designer attempts to balance many factors to achieve nigh performance.Design considerations include locating intake valves away from and ware valves near spark plugs, to keep end-gas in a relatively cool force field of the combustion chamber and thereby suppress calefactive-surface-induced autoignition tendencies. Valves are, of course, designed as large as possible to reduce induction and complete flow restrictions. More than one intake and one unloosen valve per cylinder are now used in some engines to improve ? engine breathing.? In some engines, four valves in a single cylinder are utilize for this purpose.The valves are also designed to induce go and turbulence to promote mixing of fuel and air and to improve combustion stability and burning rate. Pollution and fuel thriftiness considerations have in recent years pr ofoundly influenced overall engine and combustion chamber design. Stratified-charge engines, for example, attempt to provide a locally rich combustion arena to control peak temperatures and thus suppress nighttime formation. The resulting combustion gases containing unburned fuel then mix with surrounding lean mixture to complete the combustion process, thus eliminating CO and unburned hydrocarbons from the extinguish system.These processes occur at lower temperatures than in naturalized combustion chamber designs and therefore prevent significant nitrogen reactions. 6. 6 Representing Reciprocating Engine Perfomance In an earlier section, the theoretical work per unit mass of working fluid of the Otto engine was evaluated for a single cycle of the engine, use the cyclic integral of the First Law of Thermodynamics. The work do by pressure forces acting on a piston can also be evaluated as the integral of pdV. It is evident therefore that the work done during a single engine cyc le is the area enclosed by the cycle process convolutes on the pressure-volume diagram.Thus, instead of using the cyclic integral or evaluating pdV for each process of the cycle, the work of a reciprocating engine can be found by drawing the theoretical process curves on the p? V diagram and diagrammatically integrating them. Such a eyepatch of pressure versus volume for any reciprocating engine, real or theoretical, is called an power diagram. 234 In the nineteenth and early twentieth centuries a machinelike thingmabob known as an engine index number was used to produce indicator cards or diagrams to determine the work per cycle for slow-running steam and gas reciprocating ngines. The indicator card was attached to a cylinder that rotated back and forth on its axis as the piston oscillated, thus generating a piston position (volume) coordinate. At the same time a pen driven by a pressure signal from the engine cylinder moved parallel to the cylinder axis, scribing the p-V di agram over and over on the card. The work of high speed engines is still evaluated from traces of pressure obtained with electronic sensors and displayed on electronic monitors and through digital techniques.The work done per cycle (from an indicator card, for instance) can be represented as an bonnie pressure times a volume. Because the displacement volumes of engines are usually known, an engine performance parameter known as the mean set upive pressure, MEP, is defined in footing of the piston displacement. The mean effective pressure is defined as the value of the pressure obtained by dividing the net work per cylinder per cycle at a given operating condition by the piston displacement volume MEP = W/disp lbf/ft2 kPa (6. 8)Thus the MEP is a measure of the effectiveness of a given displacement volume in producing net work. The power siding of an engine with identical cylinders may be represented as the product of the work per cycle and the number of cycles punish per unit time by the engine. Thus if the engine has n cylinders, each executing N identical thermodynamic cycles per unit time, and delivering W work units per cylinder, with a piston displacement, disp, the power output is given by P = nNW = nN MEP disp ft-lbf /min kW (6. 9)Expressed for the entire engine, the engine displacement is DISP = ndisp and the engine work is MEP DISP. whence the engine power is P = N MEPDISP ft-lbf /min kW (6. 10) where N, the number of thermodynamic cycles of a cylinder per unit time, is the number of crank-shaft revolutions per unit time for a two-stroke-cycle engine and one-half of the revolutions per unit time for a four-stroke-cycle engine. The factor of ? for the four-stroke-cycle engine arises because one thermodynamic cycle is executed each time the crank rotates through two revolutions. EXAMPLE 6. 2What is the displacement of an engine that develops 60 horsepower at 2500 rpm in a four-stroke-cycle engine having an MEP of 120 psi? 235 Solution From Equ ation (6. 10), the displacement of the engine is DISP = P/(N MEP) = (60)(33,000)(12)/(2500/2)(120) = 158. 4 in3 Checking units (HP)(ft-lbf/HP-min)(in/ft)/(cycles/min)(lbf/in2) = in3 _____________________________________________________________________ If the work is evaluated from an indicator diagram the work is called indicated work the MEP is called the indicated mean effective pressure, IMEP and the power is indicated power, IP.Note that the indicated work and power, being associated with the work done by the combustion chamber gases on the piston, do not account for frictional or mechanical losses in the engine, such as piston-cylinder friction or the drag of moving parts (like connecting rods) as they move through air or lubricating oil. Brake operation Parameters Another way of evaluating engine performance is to attach the engine output shaft to a device known as a dynamometer, or pasture brake. The dynamometer measures the tortuousness, T, applied by the engine at a give n rotational speed.The power is then calculated from the relation P = 2rpm T ft-lbf /min N-m/min (6. 11) A simple device called a prony brake, which was used in the past, demonstrates the invention for the measurement of the shaft tortuousness of engines. Figure 6. 5 shows the prony brake manikin in which a stationary metal band wrapped around the rotating flywheel of the engine resists the torque transmitted to it by friction. The product of the force measured by a spring scale, w, and the moment arm, d , gives the resisting torque. The power break up is then given by 2(rpm)w d.Modern devices such as wet system brakes and electrical dynamometers long ago replaced the prony brake. The water brake is like a centrifugal water pump with no outflow, mounted on low-friction bearings, and driven by the test engine. As with the prony brake, the force required to resist turning of the brake (pump) housing provides the torque data. This, together with speed measurement, yields the powe r output from Equation (6. 11). The power dissipated appears as increased temperature of the water in the brake and heat transfer from the brake. Cool water is circulated late through the brake to handle a steady operating condition.The torque measured in this way is called the brake torque, BT, and the resulting power is called the brake power, BP. To tot up while indicated parameters relate to gas forces in the cylinder, brake parameters deal with output shaft forces. Thus the brake power differs from the indicated power in that it accounts for the effect of all of the energy losses in the engine. The difference between the two is referred to as the friction power, FP. Thus FP = IP ? BP. 236 Friction power varies with engine speed and is difficult to measure directly.An engine is sometimes driven without fuel by a motor-dynamometer to evaluate friction power. An alternative to using friction power to relate brake and indicated power is through the engine mechanical efficiency, m m = BP/IP dl (6. 12) Because of friction, the brake power of an engine is always less than the indicated power hence the engine mechanical efficiency must be less than 1. Clearly, mechanical efficiencies as close to 1 as possible are desired. The engine indicated power can also be expressed in terms of torque, through Equation (6. 11). Thus an indicated torque, IT, can be defined.Similarly, a brake mean effective pressure, BMEP, may be defined that, when multiplied by the engine displacement and speed, yields the brake power, alike to Equation (6. 10). Table 6. 1 summarizes these and other performance parameters and relations. The thermal efficiency, as for other engines, is a measure of the fuel economy of a reciprocating engine. It tells the list of power output that can be achieved for a given rate of heat release from the fuel. The rate of energy release is, in turn, the product of the rate of fuel flow and the fuel heating value.Thus, for a given thermal efficiency, power output can be increased by employing a high fuel flow rate and/or selecting a fuel with a high heat of combustion. If the thermal efficiency is evaluated using the brake power, it is called the brake thermal efficiency, BTE. If the evaluation uses the indicated power, it is called the indicated thermal efficiency, ITE. 237 It is common traffic pattern in the reciprocating engine field to report engine fuel economy in terms of a parameter called the specialized fuel utilisation, SFC, kindred to the thrust special fuel consumption used to describe putting green engine performance.The specific fuel consumption is defined as the ratio of the fuel-mass flow rate to the power output. Typical units are pounds per horsepower-hour or kilograms per kilowatt-hour. Obviously, good fuel economy is indicated by low values of SFC. The SFC is called brake specific fuel consumption, BSFC, if it is defined using brake power or indicated specific fuel consumption, ISFC, when establish on indicat ed power. The SFC for a reciprocating engine is analogous to the heat rate for a steam power plant in that both are measures of the rate of energy supplied per unit of power output, and in that low values of both are desirable.Volumetric Efficiency The theoretical energy released during the combustion process is the product of the mass of fuel contained in the combustion chamber and its heating value if the fuel is completely reacted. The more air that can be packed into the combustion chamber, the Table 6. 1 Engine Performance Parameters Indicated Brake Friction Mean effective pressure IMEP BMEP FMEP = IMEP BMEP m = BMEP / IMEP queen IP BP FP = IP BP m = BHP / IHP crookedness IT BT FT = IT BT m = BT / IT thermic efficiency ITE BTE m = BTE / ITE Specific fuel consumption ISFC BSFC m = ISFC / BSFC more fuel that can be burned with it.Thus a measure of the efficiency of the induction system is of great importance. The volumetric efficiency, v, is the ratio of the actual mass of mixture in the combustion chamber to the mass of mixture that the displacement volume could hold if the mixture were at ambient (free-air) density. Thus the average mass-flow rate of air through a cylinder is v (disp) aN. pressure sensation losses across intake and crush valves, combustion-chamber clearance volume, the influence of hot cylinder walls on mixture density, valve timing, and gas inertia effects all influence the volumetric efficiency.EXAMPLE 6. 3 A six-cylinder, four-stroke-cycle SI engine operates at 3000 rpm with an indicated mean effective pressure of five atmospheres using octane fuel with an equivalence ratio 238 of 0. 9. The brake torque at this condition is 250 lbf? ft. , and the volumetric efficiency is 85%. Each cylinder has a five move on bore and 6 inch stroke. Ambient conditions are 14. 7 psia and 40F. What is the indicated horsepower, brake horsepower, and friction horsepower the mechanical efficiency the fuel flow rate and the BSFC? Solution The six cy linders have a total displacement ofDISP = 6? 52? 6/4 = 706. 86 in3 consequently the indicated horsepower is IP = MEP? DISP? N /12? 33,000 lbf /in2in3cycles/min/in/ftft-lbf /HP-min = (5)(14. 7)(706. 86)(3000/2)/12? 33,000 = 196. 8 horsepower The brake horsepower, from Equation (6. 11), is BP = 2 ? 3000 ? 250 / 33,000 = 142. 8 horsepower Then the friction power is the difference between the indicated and brake power FP = 196. 8 ? 142. 8 = 54 horsepower and the mechanical efficiency is m = 142. 8/196. 8 = 0. 726 The ambient density is a = 14. 7 ? 144/ 53. 3 ? 500 = 0. 0794 lbm /ft3 nd the mass flow rate of air to the engine is ma = 0. 85? 0. 0794? 706. 86? (3000/2)/1728 = 41. 4 lbm /min For octane the stoichiometric reaction equation is C8H18 + 12. 5O2 + (12. 5? 3. 76)N2 8carbonic acid gas + 9H2O + (12. 5? 3. 76)N2 The fuel-air ratio is then F/A = 0. 9? (8? 12) + (18? 1)/12. 5(32 + 3. 76? 28) = 0. 0598 lbm-fuel /lbm-air 239 The fuel flow rate is mf = ma (F/A) = 41. 4 ? 0. 0598 = 2. 474 lbm /min The brake specific fuel consumption is BSFC = 60 mf /BHP = 60? 2. 474/142. 8 = 1. 04 lbm /BHP-hr ____________________________________________________________________ 6. Spark-Ignition Engine Performance A typical indicator diagram showing intake and fumes processes, valve actuation, and spark timing for a four-stroke-cycle SI engine is shown in Figure 6. 6. It is assumed that an appropriate air-fuel mixture is supplied from a carburetor through an intake manifold to an intake valve, IV, and that the combustion gas is discharged through an exhaust valve, EV, into an exhaust manifold. The induction of the air-fuel mixture starts with the opening of the intake valve at point A just before TC.As the piston sweeps to the right, the mixture is drawn into the cylinder through the IV. The pressure in the cylinder is somewhat down the stairs that in the intake manifold due to the pressure losses across the intake valve. In order to use the momentum of the mixture influx throug h the valve at the end of the intake stroke to improve the volumetric efficiency, intake valve closure is delayed to shortly after BC at point B. Power supplied from inertia of a flywheel (and the other rotating masses in the engine) drives the piston to the left, compressing and raising the temperature of the trapped mixture.The combustion process in a properly operating SI engine is progressive in that the reaction starts at the spark plug and progresses into the unburned mixture at a finite speed. Thus the combustion process takes time and cannot be executed instantaneously as implied by the theoretical cycle. In order for the process to take place as near to TC as possible, the spark plug is fired at point S. The number of degrees of crank rotation before TC at which the spark occurs is called the ignition advance. Advances of 10 to 30 are common, depending on speed and load.The spark advance may be controlled by devices that sense engine speed and intake manifold pressure. Micr oprocessors are now used to control spark advance and other functions, based on almost instantaneous engine performance measurements. Recalling the slider-crank analysis, we observ that the piston velocity at top center is momentarily zero as the piston changes direction. Therefore no work can be done at this point, regardless of the magnitude of the pressure force. Thus, to maximize the work output, it is desired to have the maximal cylinder pressure occur at about 20 after TC.Adjustment of the spark advance (in degrees before TC) allows some control of the combustion process and the timing of peak pressure. For a fixed combustion duration, the combustion crank-angle interval must increase with engine speed. As a consequence, the ignition advance must increase with increasing engine speed to 240 maintain optimum timing of the peak pressure. Following combustion, the piston continues toward bottom center as the high pressure gases expand and do work on the piston during the power s troke. As the piston approaches BC, the gases do little work on the piston as its velocity again approaches zero.As a result, not much work is lost by early opening of the exhaust valve before BC (at point E) to start the blowdown portion of the exhaust process. It is expedient to sacrifice a little work during the end of the power stroke in order to reduce the work needed to overcome an otherwise-high exhaust stroke cylinder pressure. Inertia of the gas in the cylinder and resistance to flow through the exhaust valve opening slow the drop of gas pressure in the cylinder after the valve opens. Thus the gases at point E are at a pressure above the exhaust manifold pressure and, during blowdown, rush out through the EV at high speed.Following blowdown, gases remaining in the cylinder are then expelled as the piston returns to TC. They remain above exhaust manifold pressure until gain TC because of the flow resistance of the exhaust valve. The EV closes shortly after TC at point C, te rminating the exhaust process. The period of overlap at TC between the intake valve opening at point A and exhaust valve closing at point C in Figure 6. 6 allows more time for the intake and exhaust processes at high engine speeds, when about 10 milliseconds may be available for these processes.At low engine speed and at idling there may be some mixture loss through the exhaust valve and discharge into the intake manifold during this valve overlap period. The combined exhaust and induction processes are seen to form a ? pumping loop? that traverses the p-V diagram in a counterclockwise direction and therefore 241 represents work input preferably than work production. The high the exhaust stroke pressure and the lower the intake stroke pressure, the greater the area of the pumping loop and hence the greater the work that must be supplied by the power loop (clockwise) to compensate.Great attention is therefore paid to valve design and other engine characteristics that influence the exhaust and induction processes. Volumetric efficiency is a major parameter that indicates the degree of success of these efforts. Performance Characteristics A given ideal Otto-cycle engine produces a certain amount of work per cycle. For such a cycle, MEP = W/disp is a constant. Equating the power equations (6. 9) and (6. 11) shows that the average torque is proportional to MEP and independent of engine engine speed.Therefore power output for the ideal engine is directly proportional to the number of cycles executed per unit time, or to engine speed. Thus an Otto engine has ideal torque and power characteristics, as shown by the solid lines in Figure 6. 7. The characteristics of real engines (represented by the step on it lines) tend to be similar in nature to the ideal characteristics but suffer from speed-sensitive effects, particularly at low or high speeds. Torque and power characteristics for a 3. 1 liter V6 engine (ref. 9) are shown by the solid lines in Figure 6. 8.Note th e flatness of the torque-speed curve and the expected peaking of the power curve at high speed than the torque curve. Rather than present graphical characteristics such as this in their 242 brochures, automobile manufacturers usually present only values for the maximum power and torque and the speeds at which they occur. Engine characteristics such as those shown in the figure are invaluable to application locomotive engineers seeking a suitable engine for use in a product. 6. 8 The Compression-Ignition or diesel engine Cycle The ideal Diesel cycle differs from the Otto cycle in that combustion is at constant pressure rather than constant volume.The ideal cycle, shown in Figure 6. 9, is commonly implemented in a reciprocating engine in which air is vapid without fuel from state 1 to state 2. With a typically high compression ratio, state 2 is at a temperature high enough that fuel will ignite spontaneously when sprayed directly into the air in the combustion chamber from a high- pressure fuel injection system. By controlling the fuel injection rate and thus the rate of chemical energy release in relation to the rate of expansion of the combustion gases after state 2, a constant243 pressure process or other energy release pattern may be achieved as in Figure 6. . For example, if the energy release rate is high, then pressure may rise, as from 2 to 3, and if low may fall to 3. Thus constant-pressure combustion made possible by controlling the rate of fuel injection into the cyclinder implies the use of a precision fuel injection system. Instead of injecting fuel into the high-temperature compressed air, the cycle might be executed by compression of an air-fuel mixture, with ignition occurring either spontaneously or at a hot spot in the cylinder near the end of the compression process.Inconsistency and capriciousness of the start of combustion in this approach, due to variations in fuel and operating conditions, and to lack of control of the rate of heat rel ease with the possibility of ascetic knock, makes the operation of such an engine unreliable, at the least, and also limits the maximum compression ratio. The Diesel engine therefore usually employs fuel injection into compressed air rather than carbureted mixture formation. In the Air Standard cycle analysis of the Diesel cycle, the heat addition process is at constant pressure q23 = cp(T3 ? T2) Btu/lbm kJ/kg (6. 13) nd, as with the Otto cycle, the closing process is at constant volume q41 = cv(T1 ? T4) Btu/lbm kJ/kg (6. 14) 244 The net work and thermal efficiency are then w = q23 + q41 = cp(T3 ? T2) + cv(T1 ? T4) = cvT1k(T3/T1 ? T2/T1) + 1 ? T4/T1 Btu/lbm kJ/kg (6. 15) Diesel = w/q23 = 1 + q4-1/q23 = 1 + (cv/cp)(T1 ? T4)/(T3 ? T2) = 1 ? (1/k)(T1/T2)(T4/T1 ? 1)/(T3/T2 ? 1) dl (6. 16) The expressions for the net work and cycle efficiency may be expressed in terms two parameters, the compression ratio, CR = V1/V2 (as defined earlier in treating the Otto cycle) and the cutoff rati o, COR = V3/V2.The temperature ratios in Equations (6. 15) and (6. 16) may be replaced by these parameters using, for the constant-pressure process, COR = V3/V2 = T3/T2 and by expanding the adjacent identity T4 /T1 = (T4/T3)(T3/T2)(T2 /T1) = (V3 /V4)k-1(V3/V2)(V1/V2)k-1 = (V3/V4)(V1/V2)k-1COR = (COR)k-1COR = CORk where the product of the volume ratios was simplified by recognizing that V4 = V1. Thus the nondimensionalized net work and Diesel-cycle thermal efficiency are given by w /cvT1 = kCRk-1(COR ? 1) + (1 ? CORk) dl (6. 17) and Diesel = 1 ? (1/k)(CORk ? 1)/(COR ? 1)/CRk-1 dl (6. 8) where the cutoff ratio, COR, is the ratio of the volume at the end of combustion, V3, to that at the start of combustion, V2. Thus the cutoff ratio may be thought of as a measure of the duration of fuel injection, with higher cutoff ratios corresponding to longer combustion durations. 245 Diesel-cycle net work increases with both compression ratio and cutoff ratio. This is readily seen graphically fr om Figure 6. 9 in terms of p-V diagram area. As with the Otto cycle, increasing compression ratio increases the Diesel-cycle thermal efficiency. Increasing cutoff ratio, however, decreases thermal efficiency.This may be intellectualized by observing from the p-V diagram that much of the additional heat supplied when injection is continued is rejected at increasingly higher temperatures. Another view is that heat added late in the expansion process can produce work only over the remaining part of the stroke and thus adds less to net work than to heat rejection. EXAMPLE 6. 4 A Diesel engine has a compression ratio of 20 and a peak temperature of 3000K. Using an Air Standard cycle analysis, estimate the work per unit mass of air, the thermal efficiency, the combustion pressure, and the cutoff ratio.Solution Assuming an ambient temperature and pressure of 300K and 1 atmosphere, the temperature at the end of the compression stroke is T2 = (300)(20)1. 4 ? 1 = 994. 3K and the combustion p ressure is p2 = (1)(20)1. 4 = 66. 3 atm Then the cutoff ratio is V3/V2 = T3/T2 = 3000/994. 3 = 3. 02 The expansion ratio is calculated as follows V4 /V3 = (V1/V2)/(V3 /V2) = 20/3. 02 = 6. 62 T4 = T3 (V3 /V4)1. 4 ? 1 = 3000/6. 620. 4 = 1409K w = 1. 005(3000 ? 994. 3) + (1. 005/1. 4)(300 ? 1409) = 1219. 6 kJ/kg qa = 1. 005(3000 ? 994. 3) = 2015. 7 kJ/kg th = w/qa = 1219. /2015. 6 = 0. 605, or 60. 5% _____________________________________________________________________ 246 6. 9 comparability Otto-Cycle and Diesel-Cycle Efficiencies A reasonable question at this point is Which cycle is more efficient, the Otto cycle or the Diesel cycle? Figure 6. 10 assists in examining this question. In general notation, the cycle efficiency may be written as th = wnet /qin = wnet /(wnet + qout) = 1 /(1 + qout /wnet) dl (6. 19) Comparing the Otto cycle 1? 2? 3? 4 and the Diesel cycle with the same compression ratio 1? 2? 3? , we see that both have the same heat rejection but that the Otto cycle has the higher net work. Equation (6. 19) then shows that, for the same compression ratio, the Otto cycle has the higher efficiency. It has been observed that Diesel-cycle efficiency decreases with increasing cutoff ratio for a given compression ratio. Let us examine the limit of the Diesel-cycle efficiency for constant CR as COR approaches its minimum value, 1. We may write Equation (6. 18) as Diesel = 1 ? 1 /(kCRk-1) f (COR) where f(COR) = (CORk ? 1)/(COR ? 1). Applying LHospitals rule, with primes 247 esignating differentiation with respect to COR, to the limit of f(COR) as COR 1, yields lim f(COR) = lim (CORk ? 1)/ Lim (COR? 1) = lim kCORk ? 1 = k COR1 COR1 COR1 and limDiesel = 1 ? 1 /CRk ? 1 COR1 = Otto Thus the limit of the Diesel-cycle efficiency as COR approaches 1 is the Otto cycle efficiency. Hence Equation (6. 18) shows that the efficiency of the Diesel cycle must be less than or equal to the Otto-cycle efficiency if both engines have the same compression ratio, the same conclus ion we reached by examination of the p-V diagram.Suppose, however, that the compression ratios are not the same. Compare the Otto cycle 1? 2? 3? 4 with the Diesel cycle 1? 2? 3? 4 having the same maximum temperature in Figure 6. 10. The Otto cycle has a smaller area, and therefore less work, than the Diesel cycle, but the same heat rejection. Equation (6. 19) demonstrates that the Otto cycle has a lower thermal efficiency than the Diesel cycle with the same maximum temperature. The conclusion that must be drawn from the above comparisons is quite clear. As in most comparative engineering studies, the result depends on the domain ules which were adopted at the start of the study. The Otto cycle is more efficient if the compression ratio is the same or greater than that of the competing Diesel cycle. But knock in spark-ignition (Otto) engines limits their compression ratios to about 12, while Diesel-engine compression ratios may exceed 20. Thus, with these higher compression ratios, the Air Standard Diesel-cycle efficiency can exceed that of the Otto cycle. In practice, Diesel engines tend to have higher efficiencies than SI engines because of higher compression ratios. 6. 0 Diesel-Engine Performance In 1897, five years after Rudolph Diesels first patents and twenty-one years after Ottos introduction of the spark-ignition engine, Diesels compression-ignition engine was proven to develop 13. 1 kilowatts of power with an unprecedented brake thermal efficiency of 26. 2% (ref. 7). At that time, most steam engines operated at thermal efficiencies below 10 % and the best gas engines did not perform much better than the steam machines. Diesel claimed (and was widely believed) to have developed his engine from the principles expounded by Carnot.He had developed the rational engine. Whether his claims were exaggerated or not, Diesels acclaim was well deserved. He had developed an engine that operated at unprecedented temperatures and pressures, had proven his concept o f ignition of fuel by injection into the compressed high-temperature air, and had overcome the formidable problems of injecting a variety of fuels in appropriate 248 amounts with the precise timing required for satisfactory combustion. His is a fascinating story of a brilliant and dedicated engineer (refs. 7, 8).In the Diesel engine, the high air temperatures and pressures prior to combustion are ascribable to the compression of air simply rather than an air-fuel mixture. Compression of air alone eliminates the possibility of autiognition during compression and makes high compression ratios possible. However, because of the high pressures and temperatures, Diesel engines must be designed to be structurally more rugged. Therefore, they tend to be heavier than SI engines with the same brake power. The energy release process in the Diesel engine is controlled by the rate of injection of fuel.After a instruct ignition lag, the first fuel injected into the combustion chamber autoignit es and the resulting high gas temperature sustains the combustion of the remainder of the fuel stream as it enters the combustion chamber. Thus it is evident that the favorable fuel characteristic of high autoignition temperature for an SI engine is an unfavorable characteristic for a Diesel engine. In the Diesel engine, a low autoignition temperature and a short ignition delay are desirable. Knock is possible in the Diesel engine, but it is due to an entirely different cause than knock in a spark-ignition engine.If fuel is ignited and burn as apace as it is injected, then smooth, knock-free combustion occurs. If, on the other hand, fuel accumulates in the cylinder before ignition due to a long ignition lag, an explosion or detonation occurs, producing a clarion Diesel knock. The cetane number is the parameter that identifies the ignition lag characteristic of a fuel. The cetane number, like the octane number, is determined by testing in a CFR engine. The ignition lag of the test fuel is compared with that of a mixture of n-cetane, C16H34, and heptamethylnonane, HMN (ref. 0). Cetane, which has good ignition qualities, is assigned a value of 100 and HMN, which has poor knock behavior, a value of 15. The cetane number is then given by the sum of the piece of n-cetane and 0. 15 times the percentage of HMN in the knock-comparison mixture. A cetane number of 40 is the minimum allowed for a Diesel fuel. 6. 11 Superchargers and Turbochargers The importance of the volumetric efficiency, representing the efficiency of induction of the air-fuel mixture into the reciprocating-engine cylinders, was discussed earlier.Clearly, the more mixture mass in the displacement volume, the more chemical energy can be released and the more power will be delivered from that volume. During the Second World War, the mechanical supercharger was sometimes used with SI aircraft engines to increase the power and operational ceiling of American airplanes. at once supercharging is used with both Diesel engines and SI engines. The supercharger is a compressor that supplies air to the cylinder at high pressure so that the as density in the cylinder at the start of compression is well above the free-air density. The piston exhaust gases are allowed to expand freely to the atmosphere through the exhaust manifold and tailpipe. The supercharger is usually driven by a belt or gear train from the engine crank shaft. 249 Figure 6. 11 shows a modification of the theoretical Otto cycle to accommodate mechanical supercharging. The supercharger supplies air to the engine cyclinders at pressure p7 in the intake process 7 1. The processes 4 5 6 purge most of the combustion gas from the cylinder.The most striking change in the cycle is that the induction-exhaust loop is now traversed counterclockwise, indicating that the cylinder is delivering net work during these processes as well as during the compressionexpansion loop. It should be remembered, however, that part of the cycle i ndicated power must be used to drive the external supercharger. The turbosupercharger or turbocharger, for short, is a supercharger driven by a turbine using the exhaust gas of the reciprocating engine, as shown schematically in Figure 6. 12. A cutaway model view of a turbocharger is shown in Figure 6. 3(a). Figure 6. 13(b) presents a diagram for the turbocharger. Compact turbochargers commonly increase the brake power of an engine by 30% or more, as shown in Figure 6. 8, where the performance of an engine with and without turbocharging is compared. There, a substantial increase in peak torque and flattening of the torque-speed curve due to turbocharging is evident. For a supercharged engine, the brake power, BP, is the indicated power (as in Figure 6. 11) less the engine friction power and the supercharger shaft power BP = DISP IMEP N ? Pm ?FP ft-lbf /min kJ/s (6. 15) 250 where Pm is the supercharger-shaft mechanical power supplied by the engine (0 for a turbocharger). The IMEP includes the positive work contribution of the exhaust loop. The exhaust back pressure of the reciprocating engine is higher with a turbocharger than for a naturally aspirated or mechanically supercharged engine because of the drop in exhaust gas pressure through the turbine. The engine brake power increases primarily because of a higher IMEP due to the added mass of fuel and air in the cylinder during combustion.Intercooling between the compressor and the intake manifold may be used to further increase the cylinder charge density. Turbocharging may increase engine efficiency, but its primary benefit is a substantial increase in brake power. In a turbocharged engine, a wastegate may be required to circulate engine exhaust gas around the turbine at high engine speeds. This becomes necessary when the compressor raises the intake manifold pressure to excessively high levels, causing engine knock or threatening component damage. Thirty to twoscore percent of the exhaust flow may be by passed around the turbine at maximum speed and load (ref. ). 251 252 6. 12 The Automobile Engine and Air Pollution Since the Second World War, concern for environmental contamination has liberal from acceptance of the status quo to recognition and militance of national and international scope. Among other sources, causes of the well-known Los Angeles smog problem were identified as hydrocarbons (HC) and oxides of nitrogen (NOx) in exhaust emissions from motor vehicle reciprocating engines. As a result, national and atomic number 20 automobile air pollution limits for automobiles have been established and toughened.Prior to the betting Air ferment of 1990, the U. S. federal exhaust-gas emissions standards limited unburned hydrocarbons, carbon monoxide, and oxides of nitrogen to 0. 41, 3. 4, and 1. 0 g/mile, respectively. According to reference 12, today it takes 25 autos to emit as much CO and unburned hydrocarbons and 4 to emit as much NOx as a single car in 1960. The reference anticipated that, led by existing atomic number 20 law and other factors, future engine designs should be targeted toward satisfying a tailpipe standard of 0. 5, 3. 4, 0. 4 g/mile. Indeed, the 1990 Clean Air Act (refs. 15,16) specified these limits for the first 50,000 miles or five years of operation for all passenger cars manufactured after 1995. In addition to the regulations on gaseous emissions, the Clean Air Act of 1990 adopted the California standard for particulate matter of 0. 08 g/mile for passenger cars. The standards on particulates are particularly difficult for the Diesel engine, because of its of soot-producing tendency.The automobile air pollution problem arises in part because the reactions in the exhaust system are not in chemical equilibrium as the gas temperature drops. Oxides of nitrogen, once formed in the cylinder at high temperature, do not return to equilibrium concentrations of nitrogen and oxygen in the cooling exhaust products. Likewise, CO formed with rich mixtures or by dissociation of CO2 in the cylinder at high temperature does not respond rapidly to an infusion of air as its temperature drops in the exhaust system. Their concentrations may be thought of as constant or frozen.Unburned hydrocarbons are produced not only by rich combustion but also by unburned mixture lurking in crevices (such as between piston and cylinder above the top piston ring), by lubricating oil on cylinder walls and the cylinder head that absorbs and desorbs hydrocarbons before and after combustion, and by transient operating conditions. Starting in 1963, positive crankcase ventilation was used in all new cars to duct fuel-rich crankcase gas previously vented to the atmosphere back into the engine intake system. Later in the ? 0s, various fixes were adopted to comply with regulation of tailpipe unburned hydrocarbons and CO, including minacious compression ratios. In 1973, NOx became federally regulated, and exhaust gas recirculation (EGR) was employed to reduce NOx formation through reduced combustion temperatures. At the same time, HC and CO standards were reduced further, leading to the use of the oxidizing catalytic converter. admission of air pumped into the tailpipe provided additional oxygen to assist in utmost of the oxidation reactions.In 1981, a reducing catalytic converter came into use to reduce NOx further. This device does not perform well in an oxidizing atmosphere. As a result, two-stage catalytic converters were applied, with the first stage reducing NOx in a near-stoichiometric mixture and the 253 second oxidizing the combustibles remaining in the exhaust with the assistance of air introduced between the stages. This fresh air does not the increase NOx significantly, because of the relatively low temperature of the exhaust.The threesome-way catalytic converter using several exotic metal catalysts to reduce all three of the gaseous pollutants was also introduced. The use of catalytic converters to deal with al l three pollutants brought about significant simultaneous reductions in the three major gaseous pollutants from automobiles. This allowed fuel-economy-reducing modifications that had been introduced earlier to satisfy emission reduction demands to be eliminated or relaxed, leading to further improvements in fuel economy.Catalytic converters, however, require precise control of exhaust gas oxygen to near-stoichiometric mixtures. The on-board computer has made possible control of mixture ratio and spark timing in response to censor outputs of intake manifold pressure, exhaust gas oxygen, engine speed, air flow, and incipient knock. The oxygen, or lambda, censor fixed in the exhaust pipe upstream of the three-way converter or between the two-stage converters is very sensitive to transition from rich to lean exhaust and allows close computer control of the mixture ratio to ensure proper operation of the catalytic converter.Computer control of carburetors or fuel injection as well as ot her engine functions has allowed simultaneous improvement in fuel economy and emissions in recent years. Thus, while emissions have been drastically reduced since 1974, according to reference 11 the EPA composite fuel economy of the average U. S. passenger car has nearly doubled although this improvement has not come from the engine alone. Despite the hard-won gains in emissions control and fuel economy, further progress may be expected. EXAMPLE 6. 5 The 1990 NOx emissions standard is 0. grams per mile. For an automobile burning stoichiometric octane with a fuel mileage of 30 mpg, what is the maximum tailpipe concentration of NOx in parts per million? suck in that NOx is represented by NO2 and that the fuel density is 692 kilograms per cubic meter. Solution For the stoichiometric combustion of octane, C8H18, the air-fuel ratio is 15. 05 and the molecular weight of combustion products is 28. 6. The consumption of octane is mf = (692)(1000)(3. 79? 10-3)/ 30 = 87. 4 g/mile Note (kg/m3 )(g/kg)(m3/gal)/(mile/gal) = g/mile. The concentration of NOx is the ratio of the number of moles of NOx to moles of combustion gas products mole Nox /mole cg = (mNOx /mf)(mf / mcg)(Mcg /MNOx) = (0. 4/87. 4)(28. 6/46)/ (15. 05 + 1) = 0. 0001773 254 or 177. 3 parts per million (ppm). _____________________________________________________________________ Bibliography and References 1. Heywood, John B. , interior(a) Combustion Engine Fundamentals. in the buff York McGraw-Hill, 1988. 2. Ferguson, Colin R. , Internal Combustion Engines. vernal York Wiley, 1986. 3. Adler, U. , et al. , self-propelling Handbook, second ed. Warrendale, Pa. club of automotive Engineers. , 1986. 4. Lichty, Lester C. , Internal Combustion Engines. New York McGraw Hill, 1951. 5. Crouse, William H. , Automotive Engine Design. New York McGraw-Hill, 1970. 6. Obert, Edward, Internal Combustion Engines, Analysis and Practice. Scranton, Pa. International Textbook Co. , 1944. 7. Grosser, Morton, Diesel The Man an d the Engine. New York Atheneum, 1978. 8. Nitske, W. Robert, and Wilson, Charles Morrow, Rudolph Diesel Pioneer of the Age of Power. Norman, Okla. University of Oklahoma Press, 1965. 9. Demmler, Albert W. Jr. , et al. , ? 989 Technical Highlights of Big-three U. S. Manufacturers,? Automotive Engineering. Vol. 96, No. 10, October 1988, p. 81. 10. Anon. , ? Ignition Quality of Diesel Fuels by the Cetane Method,? ASTM D 613-84, 1985 Annual Book of ASTM Standards, Section 5. 11. Amann, Charles A. , ? The Automotive Spark Ignition Engine-A diachronic Perspective,? American Society of Mechanical Engineers, ICE-Vol. 8, Book No. 100294, 1989. 12. Amann, Charles A. , ? The Automotive Spark-Ignition Engine-A proximo Perspective,? Society of Automotive Engineers Paper 891666, 1989. 13. Amann, Charles A. , ?The Passenger Car and the Greenhouse Effect,? Society of Automotive Engineers Paper, 1990. 14. Taylor, Charles Fayette, The Internal Combustion Engine in Theory and Practice, 2nd ed. , re vised. Cambridge, Mass. MIT Press, 1985. 255 15. Public Law 101-549, ? An Act to Amend the Clean Air Act to Provide for Attainment and Maintenance of Health, Protection, National Air Quality Standards, and new(prenominal) Purposes,? November 15, 1990. 16. Anon. , ? Provisions? Clean Air Amendments,? Congressional Quarterly, November 24, 1990. EXERCISES 6. 1 plan dimensionless piston position against crank angle for S/2L = 0. , 0. 4, 0. 3, and 0. 2. 6. 2* convey expressions for the piston velocity and acceleration as a function of the crank angle, constant angular velocity, and S/2L ratio. Use a spreadsheet to calculate and plot velocity and acceleration against crank angle for S/2L = 0. 5, 0. 4, 0. 3, and 0. 2. 6. 3 image the equation for the piston motion for a scotch yoke mechanism in terms of crank angle. Obtain an equation for the piston velocity for a crank that turns with a given angular velocity, . 6. 4 acquire an equation for the Otto-engine net work by integration of pdV for the Air Standard cycle.Compare with Equation (6. 6). 6. 5* Use a spreadsheet to calculate and plot cycle efficiency as a function of compression ratio for the Diesel cycle for cutoff ratios of 1, 2, and 3. Indentify the Otto-cycle efficiency on the plot. Explain and show graphically from the plot how a Diesel engine can be more efficient than an Otto engine. 6. 6 A single-cylinder Air Standard Otto engine has a compression ratio of 8. 5 and a peak temperature of 3500F at ambient conditions of 80F and one atmosphere. Determine the cycle efficiency, maximum cylinder pressure, and mean effective pressure. 6. A six-cylinder engine with a compression ratio of 11 runs at 2800 rpm at 80F and 14. 7 psia. Each cylinder has a bore and stroke of three inches and a volumetric efficiency of 0. 82. Assume an Air Standard, four-stroke Otto cycle _______________________ * form numbers with an asterisk indic