Mazda Training manual - part 230

 
2 – BASIC OPERATION 

 

5

Piston Engine Fundamentals

TC010-05-01S

In a car or truck, the engine provides rotating power to drive the wheels. This power is 
transferred to the wheels through the transmission and driving axle. The source of this 
rotating power is the energy released when fuel burns in the engine’s cylinders. 
 
This section provides an overview of how the engine converts 
energy from burning fuel into power that drives the vehicle’s 
wheels. 
 
 
 
OBJECTIVES

 

 
 
After completing this section, you will be able to describe how: 
 
• 

The cylinders and pistons convert energy from burning fuel into power. 

 
• 

The crankshaft converts up-and-down motion into rotational (turning) motion. 

 
• 

The flywheel stores energy for a smooth transfer of power. 

 
• 

The four-stroke cycle operates. 

 
• 

Valves control intake and exhaust in a cylinder. 

 
• 

Engines are classified by their design characteristics, including: 

 

- Cylinder 

configuration 

 

- 

Valve train type 

 

- 

Bore, stroke, and displacement 

 

- 

Compression ratio

 
2 – BASIC OPERATION 

 

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Piston Engine Fundamentals

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FIGURE 1. 
Power is 
developed by 
burning fuel in a 
cylinder.

 

 

Burning 
mixture of air 
and fuel 
 
Piston 
 
Cylinder 

 

Crankshaft

 

 
 

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

HOW POWER IS DEVELOPED

 

 
Figure 1 shows how the energy from burning fuel is converted into rotating 
power. In an engine, a piston is closely fitted into a hollow cylinder. The 
cylinder has free space at the top, where a mixture of air and fuel is 
inserted. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

The air-fuel mixture is ignited, and the burning gases from the mixture 
expand, creating very high pressure. This pressure pushes down on the 
piston, causing it to move down in the cylinder. 

 

The process shown in Figure 1 is how the engine produces power. 
Everything else on the engine is designed to control this process, harness 
the power, and transmit it to the wheels. 
 
 
 
Harnessing Power

 

 

To harness this power, the up-and-down movement of the piston is 
changed into a turning (rotary) motion by connecting the piston to a 
crankshaft, 

as shown in Figure 1. 

 
 

 

 

 
2 – BASIC OPERATION 

 

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Piston Engine Fundamentals

TC010-05-01S

The engine’s cylinders are arranged to fire one after the other. In this way, 
some pistons are always supplying power to the crankshaft while other 
pistons are moving up into their cylinders. To keep the crankshaft rotating 
smoothly, it is connected to a flywheel, which is a heavy round plate that 
turns with the crankshaft. See Figure 2. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Because of its weight, the flywheel tends to keep turning smoothly even 
though power is applied in spurts by the pistons. The end of the crankshaft 
is also connected to the vehicle’s transmission to continue the power flow 
through the drive train to the wheels. 

 
 
 

Controlling Combustion

 

 

The process of burning the air-fuel mixture in the cylinder is called 
combustion

. The combustion process in an engine requires four steps: 

 

1.   Admit the proper mixture of air and fuel into the cylinder. 

 

2.   Squeeze (compress) the mixture so it will burn better and deliver 

more power. 

 

 
 
 
 
 
 

FIGURE 2. The 
flywheel Keeps the 
crank- shaft 
turning smoothly.

 

 

Piston

 

Crankshaft

 

Flywheel

 

 
 
 
 
 

 

 

To transmission 

 
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Piston Engine Fundamentals

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FIGURE 3. 
Valves and a 
spark plug help 
control 
combustion in 
the cylinder. 
 

Intake valve 
Spark plug 
Exhaust 
valve 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

3.   Burn the air-fuel mixture. 

 

4.      Remove the burned gases from the cylinder so intake, compression, 

and combustion can be repeated. 

 

As Figure 3 shows, each cylinder has several parts that help control the 
combustion process: 

 

• An 

intake valve 

lets the air-fuel mixture into the cylinder. 

 

• A 

spark plug 

ignites the air-fuel mixture. 

 

• An 

exhaust valve 

lets the burned gases out of the cylinder.