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Title: Carranti Term Paper Automobile Engines

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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 aren’t 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 didn’t 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

Figure 1.1
Figure 1.2

Figure 2.1

Figure 2.2

Figure 3.1

Figure 3.2

Figure 4.1

5

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 it’s 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. It’s 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 don’t
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 what’s 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. There’s 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

Figure 1.1

decreases the volume by increasing the amount
of pressure. This can be more understood as
Boyle’s 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 doesn’t require a spark plug.

Figure 1.2

8

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

figure 2.1.Horsepower is calculated by the equation
HP =

RPM*T

where HP is horsepower, RPM is

5252

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

Figure 2.2

challenge of increasing the power to weight ratio because the higher the ratio, the faster
the car. Torque is another aspect of engine performance that’s talked about a lot, and
it’s 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 the connecting rod. There are various types of torque in an
automobile, although engine torque is what gets everything moving.

9


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