Automotive Engines

By: Andrew Chasin

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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.

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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

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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.

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List of Figures

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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 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.

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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.

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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

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.

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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 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.

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Figure 2.1

Figure 2.2

RPM*T

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Turbochargers & Superchargers Turbochargers are placed into cars in order to increase horsepower and to increase the

efficiency of the engine. Also, turbochargers do not significantly increase weight so it

makes sense as to why turbochargers are

found in most sports cars. In short, a

turbocharger will compress the air prior to

entering the cylinder through the intake

valve, resulting in more air in the cylinder

which ultimately correlates to the car

receiving more power (InfoSpace LLC,

2015). This may seem like a no brainer to

add this to one’s car if they want to increase power.

Although, there is a drawback to adding a

turbocharger to a car. The turbine in the turbo spins

because of the exhaust flow which increases back

pressure during the exhaust stroke in a cylinder. This

means the engine must work harder in order to get

the fumes through the exhaust valve which causes a

slight decrease in power from all cylinders. Another

downside of having a turbocharger is a concept

known as “turbo lag”. This refers to the delay in power

because the turbine needs to start spinning once the

exhaust fumes start flowing and once it does the car

lunges forward. In essence, turbochargers are mainly for that

quick extra boost in acceleration or horsepower, they don’t aid in increasing top speeds.

Turbochargers and superchargers accomplish the same goal of increasing power in

different ways. A supercharger uses fuel because it’s connected to the crankshaft by a

belt, although there is no lag.

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Figure 3.1

Figure 3.2

Intakes & Miscellaneous Engine Parts The intake of a car does exactly what it sounds like, it sucks in air. There are 3

categories of intakes, cold air, short pipe, and ram air. Obviously each type of intake has

it’s ups and downs, although they all share a common goal of getting as much air in

through the intake valve as possible.

Different intakes may give you more power

or even make you're engine sound better.

All intakes generally want to take in cold

air because cold air is less dense than hot

air, therefore you can get more air in

through the intake if it’s cold rather than

hot. This is where the short pipe intake

comes in. It has a high flow filter and is

efficient at high RPMs, but with this it

sacrifices inhaling hot air radiating from the

engine (Cars Direct, 2012). On the other hand, a cold air

intake draws air away from the engine components so it’s not heated by the engine,

making the air denser which means the engine will produce more power. A ram air

intake is similar, but this intake has a special air collector that forces extra air into the

cylinders when the car moves forward (Cars Direct, 2012). Another aspect of intakes is

the amount of air is flowing in through it. The velocity and pressure that the air is flowing

at does matter because of the inverse relationship of the two. This is seen in the

dynamic pressure equation p = 1/2pv^2 which describes how the air moves through the

valves (NASA, 2015). The air flow is often manipulated in race cars in order to decrease

pressure or temperature depending on whether they’re looking for more acceleration or

torque.

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Figure 4.1

Conclusion When looking at an engine work, one must look at each piece individually in

order to see how the entire engine works. Each piece does it’s own job, whether its

converting rotational motion to linear oscillating motion, or opening the intake valve, all

the engine parts work together to create power for the automobile. The main engine

type seen in everyday driven automobiles is the 4 stroke engine because of its

efficiency. The otto cycle is also discussed in order to help explain the four strokes and

to see how power is made based off of pressure and volume. The intake is also crucial

to an engine because the ratio of gasoline to air is essential in determining how much

power will be produced. In essence, automobile engines may look complicated,

although once one takes a closer look, it isn’t incredibly difficult to understand.

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Recommendation For Further Study The first place to start for further study would be looking at either drivetrains or

automatic versus manual transmissions. “The Automotive Transmission Book” by

Robert Fischer would be a great place to start one’s research as it tells how the

automatic transmission works and how the engine works along with it. Basically any

other part of the car would be a great place to start considering one now sees how the

engine creates power. One can now see how that power is transferred to other aspects

of the car in order to create motion. Also, one can see what happens to the engine when

the car is in park, neutral, etc. This will lead the reader to becoming more car say

because they’ll be able to compare different components of the cars and see how they

work together.

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Bibliography Hall, N. (Ed.). (2015). Ideal Otto Cycle. Retrieved November 8, 2015, from https://www.grc.nasa.gov/www/k-12/airplane/otto.html

V.A., K. (2015, October 15). Adiabatic Conditions. Retrieved November 25, 2015, from http://www.thermopedia.com/content/290/

Stone, R. (1985). Introduction to Internal Combustion Engines. Basingstoke: Macmillan.

"What does 2.4 liter mean in the context of an engine?" 23 July 2001. HowStuffWorks.com. <http://auto.howstuffworks.com/question685.htm> 10 November 2015.

Nunni, R. (n.d.). Chassis Weight and Dimensions. Retrieved November 8, 2015, from http://alison.hine.net/gpl/grehelp/tables.htm Calculations. (n.d.). Retrieved November 29, 2015, from http://simplemotor.com/calculations/

Horsepower and Torque. (n.d.). Retrieved December 5, 2015, from http://craig.backfire.ca/pages/autos/horsepower

Cutler, C. (2015, February 3). Turbocharger vs. Supercharger - What's The Difference, And Which Is Better? Retrieved November 28, 2015, from http://www.boldmethod.com/learn-to-fly/systems/turbocharger-vs-supercharger-differences-and-which-is-better/

Turbododge.com. (n.d.). Retrieved December 8, 2015, from http://www.turbododge.com/forums/f4/f15/357413-cold-air-intake-installation-question-4.html

**Sources for figures are included above**

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