Monday, January 27, 2020

Types of Gasoline Engines

Types of Gasoline Engines ABSTRACT Apetrol engine (a.k.a. gasoline engine in  North America) is an  internal combustion engine  with  spark-ignition, designed to run on petrol and similar volatile fuels. It was invented in 1876 in Germany by German inventor  Nicolaus August Otto. Till date most vehicles run on petrol much more than any other fuel i.e. the consumption of petrol is highest among the fuels. We know that the fossil fuels are getting scarce and with the increasing rates of the fuel, there are high concerns regarding the efficiency of the engines that we use. â€Å"The Obama administration has required automakers to nearly double the average fuel economy of new cars and light trucks to 54.5 miles per gallon by 2025 under rules that took effect in 2012. The attention to fuel efficiency, Obama said, has resulted in lower costs, improved air quality and created jobs in the auto industry.†(source:The Guardian) The paper deals with getting a brief idea of the types of gasoline engines (namely 2 stroke and 4 stroke), their working and most importantly will include a study of the factors that affect the fuel efficiency. INTRODUCTION A petrol engine (a.k.a. gasoline engine in  North America) is an  internal combustion engine  with  spark-ignition, designed to run on petrol and similar volatile fuels. Internal combustion engine The combustion of fuel takes place inside the engine cylinder and heat is generated within the cylinder. This heat is added to the air inside the cylinder and thus the pressure of the air is increased tremendously which moves the piston , rotates the crank shaft and thus mechanical work is done Spark ignition engine – a mixture of air and fuel is drawn into the engine cylinder. The spark plug produces a spark and ignites the air- fuel mixture. Such combustion is called constant volume combustion (C.V.C.). Based on its working cycle, it can be divided into :- 1. Four stroke cycle engine When the cycle is completed in two revolutions of the crankshaft, it’s called four stroke cycle engine. 2. Two stroke cycle engine. When the cycle is completed in one revolution of crankshaft, it’s called two stroke cycle engine. WORKING PRINCIPLE OF I.C. ENGINE/ FOUR STROKE CYCLE ENGINE / TWO STROKE CYCLE ENGINE A mixture of fuel with correct amount of air is exploded in an engine cylinder which is closed at one end. As a result of this explosion, heat is released which causes the pressure of the burning gases to increase This pressure forces a tightfitted piston to move down the cylinder which in turn rotates the crankshaft . Power is utilized from the rotating crank shaft to do mechanical work. To obtaincontinuous rotation of the crankshaft ,the used gases are expelled from the cylinder, before the next ignition takes place .Fresh charge of fuel and air are admitted in to the cylinder and the piston moved back to its starting position. The sequences of events taking place in an engine constitute the working cycle of an engine. The sequence of events taking place inside the engine are as follows- 1. Admission of air or air-fuel mixture inside the engine cylinder ( suction ) 2. Compression of the air or air fuel mixture inside the engine (compression) 3. Injection of fuel in compressed air for ignition of the fuel or ignition of air- fuel mixture by an electric spark using a spark plug to produce thermal power inside the cylinder (power ) 4. Removal of all the burnt gases from the cylinder to receive fresh charge (exhaust) Note: Charge means admitting fresh air in to the cylinder or admitting a mixture of air and fuel in to the cylinder in the case of spark ignition engines. FOUR STROKE CYCLE ENGINE In four stroke cycle engines the four events suction, compression, power and exhaust take place inside the engine cylinder. They are completed in four strokes of the piston ( i.e 2 revolutions of the crank shaft). The engine has separate valves for controlling the inlet of charge and outlet of exhaust gases. The opening and closing of the valve is controlled by cams, fitted on camshaft. The camshaft is driven by crankshaft with help of suitable gears or chains. The camshaft runs at half the speed of the crankshaft. The events that take place are 1. Suction stroke 2. Compression stroke 3. Power stroke 4. Exhaust stroke Suction stroke In suction stroke ,the inlet valves open and the piston moves downwards. The exaust valve remains closed and air or mixture of air and fuel is sucked in. Compression stroke In this stroke, both the valves are closed and the piston moves upwards. The charge taken inis compressed by the upward stroke. The mixture is ignited by a spark plug. Power stroke After ignition of fuel, high amount of heat is produced which pushes the piston down. The downward movement of the piston at this point is called power stroke. The connecting rod or pin transmits the power from the piston to the crank shaft and the crank shaft rotates. Both valves remain closed during the power stroke. Exhaust stroke In this stroke the exhaust valve opens and the piston moves upwards, expelling the burnt gases out. The inlet valve remains closed. remains closed . Thus it is found that out of four strokes, there is only one power stroke and three idle strokes in four stroke cycle engine. The power stroke supplies necessary momentum for useful work. TWO STROKE CYCLE ENGINE (PETROL ENGINE) In two stroke cycle engines, all the events i.e., suction, compression, power and exhaust are completed in two strokes of the piston (i.e., one revolution of the crankshaft). There is no valve in this type of engine. The gas movement takes place through holes called ports in the cylinder. The crankcase of the engine is air tight in which the crankshaft rotates. Two stroke cycle Upward stroke of the piston (Suction Compression) When the piston moves upward it covers two of the ports which are the exhaust port and the transfer port, which are normally almost opposite to each other. As a result it traps the charge of air- fuel mixture drawn already into the cylinder. The further upward movement of the piston compresses the charge and uncovers the intake port. Following it fresh mixture is drawn through this port into the crankcase. Just before the end of this stroke, the mixture in the cylinder is ignited by a spark plug and thus, during this stroke both suction and compression events are completed. Downward stroke (Power + Exhaust) The burning of gases increases the pressure and forces down the piston. When the piston moves down, it closes the suction  port, which traps the fresh charge drawn into the crankcase during the previous upward stroke. The further downward movement of the piston uncovers the exhaust port first and then the transfer port. Now fresh charge in the crankcase moves into the cylinder through the transfer port. The burnt out gases are driven out through the exhaust port. Special  shaped piston crown deflect the incoming mixture up around the cylinder so that it can help in driving out the exhaust gases . During the downward stroke of the piston, power and exhaust events are completed. THE COMPARISION (2 STROKE VS 4 STROKE) The 2-stroke engine fires once every revolution, giving it twice the power of a four stroke, which only fires once every other revolution. The 2 stroke has a higher weight to power ratio because it is much lighter than the 4 stroke. It is less expensive because of its simpler design. These qualities make two stroke engines very popular for a variety of uses from dirt bikes, jet skis, mopeds and small outboard motors, to lawn and garden equipment such as mowers, leaf blowers,edgers, hedge trimmers and chain saws. Many 2 strokes are simple engines and lack valves. Thus the timing of the intake and exhaust cannot be made optimal on 2 strokes. While on the other hand ,the timing of intake and exhaust can be controlled using timing gear in 4-stroke engines. As a result they burn less cleaner than the 4 stroke. The 2-stroke engines have faster wear and shorter engine life than a four stroke due to the lack of a dedicated lubricating system .Another thing to consider is that 2 stroke engines have lubricating oil mixed with the fuel because of which it leads to incomplete combustion of the fuel. Which in turn also affect the efficiency and often cause more pollution. The 2 stroke engines also produce higher decibels of noise. Hence it is banned in some places. Thus in a sense 4 stroke engines are more fuel efficient than 2 stroke engines. FACTORS AFFECTING EFFICIENCY Of the total heat energy released by the  gasoline  consumed, about 70-75% is rejected as heat without being turned into useful work ie to the crankshaft.Approx half of this rejected heat is carried away by the exhaust gases, and half passes through the cylinder walls or cylinder head into the engine cooling system, and is passed to the atmosphere via the cooling system radiator. Some of the work generated is also lost as friction, noise, air turbulence, and work used to turn engine equipment and appliances such as  water and oil pumps  and the electrical  generator, leaving only about 25-30% of the energy released by the fuel consumed available to move the vehicle.Thus the available energy needs to be used effectively in order to gain the most out of it. Weight One of the best ways to increase the fuel efficiency of the vehicles is to reduce down the weight. Which means replacing the heavier parts with the lighter ones .This needs to be done without compromising with the safety,performance and consumer preference of the vehicle. The lightest material for the car bodies is carbon fibre.though it comes with a hefty price. It is currently reserved for the very expensive cars and the high end sports car industry. Ten years ago, carbon fibre cost $150 for a pound.Now it costs around $10 a pound. On the other hand steel costs less than a dollar. Replacing the steel components with carbon fibre ones can reduce the car weight by approx 60 percent. This 60 percent reduce in weight would decrese the car’s fuel consumption by 30 percent and would cut the emissions of greenhouse gases by 10-20 percent. Displacement Displacementis the volume of air the engine can consume in a single revolution. It is generally denoted in litres. The more air the engine can move in, the more fuel it can burn. Thus a small compact bike engine will be more efficient than a truck’s engine. Compression ratio Most gasoline (petrol) engines have the compression ratio calculated purely from the geometry of the mechanical parts(geometriccompression ratio). 10:1 (premium fuel) or 9:1 (regular fuel), with some engines reaching a ratio of 12:1 or more. The greater the compression ratio the more efficient is the engine, in principle . Higher compression-ratio conventional engines in principle need gasoline with higher  octane  value .High octane value gives the fuel the tendency to burn nearly instantaneously (known as  detonation or knock) at high compression conditions. Fuel intake The carburetor system is adapted for the fuel intake. The carburetor contains jets that push the gas into the combustion chambers. The amount of fuel that can flow through these jets depends completely on the amount of air that can be pulled into the carburetor . The main issue with obtaining the best performance using a carburetor is that it cant monitor the air to fuel ratio for each individual cylinder. Fuel injection systems on the other hand are becoming more popular for best performance from the engines. The main benefits to using direct injection is that the amount of fuel and air can be perfectly released and then injected into the cylinder according to the engine load conditions. The electronics used in the system will calculate this information and constantly adjust. This type of controlled fuel injection results in a higher power output, greater fuel efficiency and much lower emissions. The main issues is that these systems are sophisticated and will cost much more than a carburetor. In the past years direct injection systems haveincreased the efficiency of the engines equipped with this fueling system up to 35% Oxygen If there is not enough  oxygen  for proper combustion, the fuel will not burn completely and will produce less energy. Relatively, an excessively rich air fuel ratio will increase pollutants from the engine. The fuel burns in three stages. Firstly, the hydrogen burns to form water vapour. Second, carbon burns to carbon monoxide and finally, the carbon monoxide burns to carbon dioxide. This last stage produces most of the power of the engine. If all of the  oxygen  is consumed before this stage, engines power is reduced. To increase the amount of oxygen, we need to increase the air intake. One way is through forced induced intake. A compressor can be added to force a larger charge .This can be done by mechanically driven supercharging or exhaust driven turbo charging. Mechanical Resistance Type of resistance car manufacturers are concerned with, called mechanical resistance, which has more to do with a vehicle’s mechanical components other than the tires. Mechanical resistance is described as the amount of effort it takes to move each individual piece of the vehicle’s drivetrain. The automatic transmissions generate more resistance than their manual counterparts. Mechanical resistance usually accounts for about a 15 percent drop in power from what the engine produces to what actually makes it to the pavement. Which means if an engine produces 100 horsepower, then only about 85 of those horses make it to the ground. An engine has many moving parts that produce  friction. Some of these friction forces remain constant while some of these friction losses increase as engine speed increases, such as piston side forces and connecting bearing forces Synthetic lubricants, light weight materials and tighter manufacturing tolerances can all contribute to less mechanical resistance in a vehicle. Aerodynamics At high speeds, and on exceptionally windy days,air resistance(the forces acted upon a moving object by the air also defined asdrag) has ­ a tremendous effect on the way a car accelerates, handles and achieves fuel mileage. Engineers have developed several ways ofreducing it. For instance, more rounded designs and shapes on the exterior of the vehicle are crafted to channel air in a way so th ­at it flows around the car with the least resistance possible. Some high-performance cars even have parts that move air smoothly across the underside of the car. Many also include aspoileralso known as arear wing to keep the air from lifting the cars wheels and making it unstable at high speeds. CONCLUSION Even after years of its discovery in the 19th century, gasoline (petrol) engines account for the most used engines currently ,much ahead of its diesel counterpart which is evident enough to denote our dependency on petrol. However petrol as we know is a limited resource. the rate at which it replenishes is way much lower than the rate at which we are consuming it .Moreover burning of the fuel causes pollution. Keeping that in mind and following the context of my study, I feel it is a great move by president Obama to order the vehicle industry to double the gross fuel economy of their vehicles by the year 2025

Sunday, January 19, 2020

To Kill A Mockingbird: Scene Analysis :: essays research papers

  Ã‚  Ã‚  Ã‚  Ã‚  An important scene found in the movie To Kill A Mockingbird is a scene concerning Mr. Tate recoiling upon the outcaste, Boo Radley, and unraveling a new perception of friendship. Atticus Finch (played by Gregory Peck), his daughter Jean-Louise Finch, also known as Scout (played by Mary Badham), and Boo Radley (played by Robert Duvall) all play an important role in the scene. As scout relates what had happened, she notices a man in the corner of the bedroom behind the door. She identifies the mysterious man as the one who grabbed Mr. Ewell and carried Jem home when she says, â€Å"Why, there he is Mr. Tate. He can tell you his name . . .† The sheriff, Mr. Tate, moves the bedroom door revealing in the light a frightened, gentle, and pale Boo Radley. And as he conveys a loving look, Scout gazes at him and smiles. In the meanwhile, Atticus had already introduced Scout to Boo. Then, Scout and Boo hold hands and walk over to the side of Jem’s bed.   Ã‚  Ã‚  Ã‚  Ã‚  The challenge of taking a novel and translating it into film falls into the work of the screenwriter. The Academy Award winning screenplay was faithfully adapted by screenwriter Horton Foote from the 1960 novel of the same name, To Kill A Mockingbird. For the most part, Foote utilizes Harper Lee’s words. There is, however, one noticeable formality seen in the movie and not in the book. This formality takes place when Boo appears and Atticus states, â€Å"Miss Jean-Louise . . .† Her name does not appear this way in the book but does in the movie in order to exert a certain idealistic fervor of the Finch household that belongs in every household that adults should be respectful and well-spoken.   Ã‚  Ã‚  Ã‚  Ã‚  A screenplay is entirely useless unless if there are actors to bring it to life. When Mary Badham leans against the bedpost and wraps her hands around it, she is implying that, at least at first, there is reason for Scout to fear Boo. But then Mary Badham puts her hand out towards Boo effectively inviting him back into society. And when the young six-year-old actress smiles, Robert Duvall (playing Boo) immediately enters a relaxed state which demonstrates the character’s affection and trust of children. During this time, Atticus (played by Gregory Peck) pulls out a handkerchief as a sign of nervousness, and also to imply that men feel very uncomfortable during emotional situations.

Saturday, January 11, 2020

Jasmine Revolution Essay

Leadership or Tyranny? Summary: Within just 28 days, Zine El Abidine Ben Ali had no alternative but to step down from his 23-year presidency in Tunisia. A single spark set by Mohamed Bouazizi turned out to be a prairie fire across the whole country. Economic Growth Paradox Although the economy of Tunisia has been growing steady at an average rate of 5% for the past 23 years, the unemployment rate has been standing at over 10% since 2003, which is indeed alarmingly high. The rate is double for the young Tunisians, and even higher for the fresh graduates. A recent survey has shown that the unemployment rate stands at 25% and 44% for male graduates and female graduates respectively. If the economy is growing every year, why are there so many people out of job and struggling to survive against serious inflation? What is going on behind the scene? Surrender to Dictatorship In addition to the economic factors, the political situation in Tunisia has played a crucial role in this Jasmine Revolution. The Tunisians have been silent for years: minimal (if any) freedom of speech, deprivation of other political rights and stringent censorship over information and the press. Rampant corruption at the top tier level of the Ben Ali regime, as revealed by Wikileaks, is another burning issue. On the other hand, the Tunisians had to confront the unreliable and abusive police force from the government. Instead of being protected by the local police force, Bouazizi (who was operating as an unlicensed hawker) had his produce confiscated and his subsequent complaints entirely ignored, which eventually led to his self-immolation. Transactional Leadership The exchange relationship between the Ben Ali government and the citizens in Tunisia did not seem to be balanced. Prior to a series of protests and demonstrations and subsequent abdication of Ben Ali, the Tunisians had been resigned to the dictatorship of Ben Ali in exchange of a decent life. However, are the Tunisians getting what they are supposed to obtain? Undeniably, Tunisia has become one of the most stable countries in Arab. True, the slow yet steady economic prosperity and gradual increase in basic health care and education have made the Tunisians look better-off than their Libyan and Algerian counterparts. Nonetheless, they are also under constant threat of unemployment, corrupt officials and violent police force instead of what guarantees a decent life – law and order. Media in Play? While some critics have also partially attributed this revolution to Internet social media, Twitter and Facebook in particular, caution should be exercised in order to avoid playing up the actual influence of social media. No doubt, the speed of information transmission has been greatly enhanced with the introduction of the Internet. In the case of Tunisia, some have named it as â€Å"Twitter Revolution†. However, all social media are better seen as a vehicle or a catalyst of the protests and subsequent overthrowing of Ben Ali. In other words, they are not the sole enablers of such revolution. After all, the crux lies with the fact that when the leader realises his self-interests and benefits at the expense of the interest of the other party, such transactions can no longer be deemed as satisfactory or fair in the eye of the exploited party. What’s Next The single spark in Tunisia has already started a prairie fire in Egypt, with the flame spreading to Libya and China at a great speed. How should the leaders faced with similar dilemmas react? Adopting an even more high-handed approach on the people helps very little at best, and aggravates the problem further at worse. Stricter censorship and control over the information flow to the citizens might sound plausible, yet people can always find means to overcome such barriers. On the other hand, people do not seem intimidated by the dire consequence of their protests – arrest and torture. The self-immolation of Bouazizi is a case in point to show the ‘make-or-break’ determination of the people when pushed to the dead alley. Fair Deal If the transactional relationship is to be maintained, the leaders should identify, understand and respond to the true needs of people. Marginalizing any segment of the society is the last thing to do – frustration and disappointment of the people can evolve into a fatal blow to any regime. If people’s basic welfare were not well taken care of, could the government rest assured that social peace would be maintained? What can go hand in hand with the above is that the leader should create a vision for the people and motivate the people to pursue and actualize the same version, not for themselves only but for others as well.

Friday, January 3, 2020

Hiv And Aids News And Updates New Strain Of Hiv

Critical Summary Draft: Our chosen article is titled â€Å"HIV and AIDS News and Updates: New Strain of HIV Found in Cuba Which Can Develop Into a Full-Blown AIDS in a Span of Only 3 Years† written by Steff Lyn Smetham. It was published on November 5th, 2015 on the Crossmap online website. The article was written to inform the readers on a newly discovered strain of HIV, which develops faster than the average known types of HIV. This article mentioned many recently studied concepts including, the rate of disease progression, CRF19’s involvement in the AID’s rapid progression (AID’s-RP), the adverse effects of RANTES defense molecules, and proper HIV treatment. The general consensus is that the average rate of disease progression takes approximately 5 to 10 years to progress into AIDS, however, it is quite complicated to pinpoint the rate due to many factors. 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