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Automobile Engines

Feb 09, 2017

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  • Automotive Engines

    By: Andrew Chasin

    1

  • Abstract Automotive engines are very complex machines that work in order to create

    power for the automobile. This is done through engine strokes and combustion, which

    are the essentials in knowing how the engine actually works. Although, not all engines

    are the same, there are many different engines, some of which arent covered here

    because of their complexity. In this report, one will learn how the engine works, how the

    power is created and transferred, the differences of various engines, how superchargers

    and turbochargers increase power and about engine performance. Some concepts of

    thermodynamics are used in order to aid in the description of engine strokes. All in all,

    even without any knowledge of automobiles, one can come to understand how engines

    work through reading this report.

    2

  • Table of Contents

    Literature Survey Narrative 4

    List of Figures 5

    Engine Strokes 6

    Engine Types 7

    Combustion 8

    Engine Performance 9

    Turbochargers & Superchargers 10

    Intakes & Miscellaneous Parts 11

    Conclusion 12

    Recommendation for Further Study 13

    Bibliography 14

    3

  • Literature Survey Narrative I decided to choose automotive engines once I realized vehicle dynamics may

    have been too difficult. I had no experience with automotive engines prior to writing this

    report nor did I have any knowledge of engines. It took me a while to get the ball rolling

    on this report due to the fact that I didnt know anything. I decided to go to my Formula

    SAE advisor who then explained how it all worked with diagrams and thermodynamic

    concepts. I then looked further into these topics, which are the subheadings, and was

    able to delve deeper into the topics to master my overarching topic. The book

    Introduction to Internal Combustion Engines helped bring everything together

    considering there are so many different parts of the engine that do their own jobs. Once

    I learned engine strokes, the rest of the engine basically helps aid in that process which

    made it less difficult for me.

    4

  • List of Figures

    5

    Figure 1.1Figure 1.2

    Figure 2.1 Figure 2.2

    Figure 3.1 Figure 3.2

    Figure 4.1

  • Engine Strokes

    There are several types of engines, two of them are 4 stroke and a 2 stroke engines.

    Most other engines follow the same format, having multiple strokes in order to create

    power for the car. The four strokes in an engine are intake, compression, expansion or

    power stroke, exhaust. This 4 stroke procedure is usually seen in V-Type engines, not

    in diesel engines. A V-Type engine requires a spark plug above the combustion

    chamber to ignite the gasoline when a diesel engine does not. The first stroke in an

    engine cycle is the intake. This is where the air/fuel mixture travels through the intake

    valve into the combustion chamber. The second stroke is compression, where the

    piston is forced upward by flywheel in the crankcase. In addition to this movement, the

    camshaft is located near the fly wheel and its what converts rotational motion into linear

    oscillating motion which is what moves the piston up and down. The third stroke is

    called expansion or the power stroke. This is where most of the power is created, the

    spark plug ignites the compressed fuel and drives the piston downward. The exhaust

    stroke is the final stroke and comes at the end of the power stroke. With the downward

    motion of the piston, the exhaust valve opens up and while the piston goes back up

    compressed fuel/air mixture goes out. This results in the cycle starting back over.

    Similar to this is the 2 stroke engine, it does all 4 steps much like the 4 stroke but only in

    2 steps. 2 stroke engines are usually more powerful than 4 stroke engines. This is

    because the 2 stroke engines have a power stroke every 2nd stroke and complete their

    cycle faster than the 4 stroke engine. The first stroke in the 2 stroke engine is the intake

    and power. This is when the intake valve is opened by the upward force of the piston.

    Since the piston is going upward, the fuel/air mixture from the previous cycle explodes

    in the combustion chamber in order to create power. Then the piston is driven

    downwards, while this happens the waste from the explosion goes out as the exhaust

    part of the cycle and the new fuel/air mixture is compressed. Its easy to tell that the 2

    stroke is more powerful considering the cycle happens much quicker.

    6

  • Engine Types There are numerous types of engines, such as V4-V8, diesel, HEMI, inline, etc. The

    most common engine type seen throughout everyday life is the V4 or four cylinder

    engine. Each cylinder has their own 4 or 2 strokes stated in the previous section. The

    more cylinders in the engine means the more cycles the engine can go through and the

    more power strokes will occur resulting in more power (Stone, 1985). The difference

    between the V-type engines are the amount of cylinders it has. For example, a V4

    engine will have 4 cylinders opposed to a V8 engine having 8 cylinders. The V4-V8

    engines all have spark plugs which ignites the fuel. Meanwhile, diesel engines dont

    have a spark plug, the diesel fuel has a different chemical makeup which enables it to

    explode at a specific temperature and pressure. Non-diesel engines use whats known

    as petrol or gasoline which explodes with the help of the spark plug. Non-diesel engines

    can time their engine to begin accelerating exactly when the spark plug explodes the

    gasoline in order to gain the most amount of power at the start. In most cars, the

    amount of liters in the engine are usually advertised. There is a specific ratio as to what

    amount of air and gasoline are in the mixture that enters through the intake valve. The

    usual ratio, air to petrol, is 15 to 1 (InfoSpace LLC, 2015). The liters are referring to how

    much air is let into all of the pistons. For example, if an engine is said to have 5.4 liters,

    that means the engine is able to let 5.4 liters of air into all four pistons after 2 revolutions

    of the crankshaft. Obviously, the more air let into the engine means the more power will

    be created, so the more liters in the engine means that the engine is generally more

    powerful than those with less. There are also many different types of engines, one of

    which being V shaped. V shaped engines have usually 6 cylinders with 3 on each side

    and one opposite the other at an angle of about 120 degrees. As one piston on one side

    goes up the other has the opposite motion.

    7

  • Combustion Combustion is what creates the power from the

    power stroke. Theres a lot more to it than just a

    timed explosion, there are processes such as

    the otto cycle and the diesel cycle that occur

    that are crucial in engines. The otto cycle uses

    the 4 stroke engine cycle in order to show how

    pressure and volume increase and decrease in

    order to create power (Hall, 2015). As one can

    see in the figure, the intake stroke increases

    volume, then the compression stroke

    decreases the volume by increasing the amount

    of pressure. This can be more understood as

    Boyles law, where pressure and volume are

    inversely proportional. The combustion then

    happens rather quickly while the temperature and

    pressure increase. Thereafter, the gas expands

    causing an adiabatic process where the

    temperature and pressure will decrease without

    the loss of heat; energy is only transferred as

    work (Thermal Science, 2011). The diesel cycle

    differs from the Otto cycle due to the fact that the

    diesel cycle doesnt require a spark plug.

    8

    Figure 1.1

    Figure 1.2

  • Engine Performance Horsepower and torque are two things that

    are often advertised in new car commercials

    or car ads. Horsepower is supposed to gauge

    how powerful the car is and how fast it can

    accelerate. This relates to engines because

    the more powerful the engine is the more

    horsepower it will put out. For example,

    generally a V8 engine will put out more

    horsepower than a 4 cylinder engine.

    Horsepower increases as the number of

    revolutions per minute increase as seen in

    figure 2.1.Horsepower is calculated by the equation

    HP = where HP is horsepower, RPM is

    revolutions per minute, and T is torque. (Simple

    Motors, 2015). This equation can also be used

    to convert horsepower to torque and torque to

    horsepower. When racing, one wants to keep

    the engine near the peak horsepower in order

    to maximize acceleration. Designers of high

    end super cars are often faced with the

    challenge of increasing the power to weight ratio because the higher the ratio, the faster

    the car. Torque is another aspect of engine performance thats talked about a lot, and

    its defined as the rotational motion from the internal combustion engine (Craig, 2014). A

    car engine creates torque by the rotational motion of the crankshaft previously stated.

    As stated previously, the crankshaft turns rotational motion into linear oscillating motion

    of the piston through

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