How Car Engines Work: Internal Combustion Explained

By Longwayeducation.com

Here, you will learn about the vital roles that key components – from pistons and camshafts to fuel injection systems – play in keeping the engine running.

Introduction

The car engine is the cornerstone of modern land transportation, converting chemical energy into efficient kinetic propulsion. These structurally advanced machines are classified as internal combustion engines and utilize an integrated heat exchange mechanism, where the oxidizer and fuel source are burned within a specific combustion chamber. This chemical reaction generates high-temperature, high-pressure gases that exert a direct linear force on reciprocating pistons, which is then converted into rotational motion via a central crankshaft to propel the vehicle forward.

The development of modern automobile engines has historically relied on rigorous mechanical engineering frameworks. Conventional car designs impose a precisely regulated four-stroke combustion cycle—comprising intake, compression, combustion, and exhaust strokes—to maintain operational efficiency and thermodynamic performance. To systematically evaluate performance, contemporary research utilizes computational thermodynamic models to analyze fluid dynamics, friction limits, and heat transfer. In response to global environmental challenges, current academic and industry models are driving the automotive sector toward higher compression ratios, cleaner fuel injection technologies, and hybrid powertrains designed to reduce greenhouse gas emissions while maintaining structural integrity.

An internal combustion engine (ICE) is a heat engine that burns fuel using an oxidizer. Image source: Shutterstock.com

Combustion Engine

An internal combustion engine is essentially a sophisticated energy converter. It harnesses the chemical energy stored in liquid fuels (such as gasoline or diesel) and converts it into heat through combustion, then into mechanical energy to power the car’s wheels. Most modern cars use a four-stroke, four-cylinder engine. Here is a detailed explanation of the engine’s components and the process that keeps the car moving. To understand the combustion process, it’s helpful to know the main components within the engine block:

The Core Components

Cylinder: The straight, cylindrical chamber where all the combustion processes take place.
Piston: A sealed metal component that moves up and down inside the cylinder.
Connecting rod: A rigid arm that connects the piston to the crankshaft.
Crankshaft: A rotating shaft that converts the linear (up and down) motion of the pistons into rotary motion.
Valves (intake and exhaust): Precisely vented valves at the top of the cylinder that open and close to allow the fuel-air mixture to enter and the combustion gases to exit.
Spark plug: A device that produces an electric spark to ignite the fuel-air mixture (in gasoline engines).

The Four-Stroke Cycle

The vast majority of cars rely on a four-stroke cycle. The term “stroke” refers to the movement of the piston from its highest point (top dead center) to its lowest point (bottom dead center) or vice versa.

1. Intake Stroke

The cycle begins with the piston at the top of the cylinder.

What happens: The intake valve opens, and the crankshaft pulls the piston downward.
Result: This downward movement creates a low pressure inside the cylinder. Similar to pulling a syringe, it draws a mixture of fresh air and atomized fuel into the cylinder.

2. The Compression Stroke

Once the piston reaches the bottom of the cylinder, the intake valve closes tightly, preventing air from entering the combustion chamber.

What happens: The crankshaft’s thrust forces the piston to the top of the cylinder.
The result: Because the valves are closed, the air-fuel mixture has no way to escape. It is compressed into a small space at the top of the cylinder (the combustion chamber). This compression makes the mixture more flammable and easier to ignite efficiently.

3. The Combustion/Power Stroke

This is where the process begins. The piston is at its highest point, and the air-fuel mixture is under immense pressure.

What happens: The spark plug produces a powerful electric spark. This spark ignites the fuel, causing a rapid and controlled explosion (combustion).
The result: The explosion generates tremendous heat, causing the gases to expand violently. This immense pressure forces the piston down the cylinder.

The above stroke is the only stroke of the four-stroke engine that generates the power needed to rotate the crankshaft and propel the car.

4. The Exhaust Stroke

After power is generated, the cylinder fills with used, unusable exhaust gases.

What happens: The piston reaches the bottom of the cylinder, the exhaust valve opens, and the crankshaft’s thrust pushes the piston back up one last time.
The result: The rising piston acts like a vacuum, sweeping the used exhaust gases out of the cylinder, through the exhaust manifold, and into the exhaust pipe.

Once the piston reaches the top of the cylinder and the exhaust valve closes, the intake valve opens again, and the entire process repeats. At highway speeds, this complete cycle occurs 25 to 50 times per second in each cylinder.

Keep In Mind

The engine cannot run if the valves open at the wrong time or if the spark ignites too early. A timing belt or chain is used to control the synchronization.
The crankshaft (driven by the pistons) is connected to the camshaft, which is located above the cylinders. The camshaft has oval-shaped lobes that drive the valves to open and close in perfect harmony with the piston positions.

Supporting Systems

Mechanical parts cannot operate independently; they rely on several vital supporting systems to ensure their safe and efficient operation:

Fuel and Air System: This system mixes the exact amount of gasoline and oxygen required for combustion and typically delivers it to the cylinder or intake manifold via fuel injectors.
Ignition System: This system delivers high-voltage electricity to the spark plugs at precisely the right moment.
Lubrication System: This system circulates engine oil throughout the engine. Without oil, friction between metal parts would generate immense heat, potentially causing the engine to seize within minutes.
Cooling System: This system uses a mixture of water and antifreeze (coolant) that is pumped through channels in the engine block to absorb excess heat and dissipate it via the radiator.

Gasoline vs. Diesel: The Key Difference

Although both are internal combustion engines, they ignite fuel in different ways:

Gasoline Engines	Diesel Engines
These rely on a spark plug to ignite the compressed air-fuel mixture.	These do not have spark plugs. Instead, they compress air very high (at a much higher compression ratio than gasoline engines) until the air is hot enough to ignite the diesel fuel as soon as it is injected into the combustion chamber.

Sources

Heywood, J. B. (1988). Internal Combustion Engine Fundamentals. McGraw-Hill Book Company.
Pulkrabek, W. W. (1997). Engineering Fundamentals of the Internal Combustion Engine. Prentice Hall.
Stone, R. (1994). Introduction to Internal Combustion Engines. Macmillan.
Ganesan, V. (2012). Internal Combustion Engines (4th ed.). Tata McGraw-Hill Education.

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