What Is an Internal Combustion Engine?

Two hands touch an engine surrounded by metal parts — We've come a long way since the first internal combustion engine. Elena Popova / Getty Images

Unleashing the power that drives our vehicles and fuels our world, the internal combustion engine is a marvel of engineering. By harnessing controlled fuel explosions, this four-stroke engine seamlessly converts energy into powerful mechanical motion, propelling us forward with unprecedented efficiency.

From the exhilarating rumble of a sports car to the thunderous roar of an airplane taking flight, this invention transformed transportation, shaping the very fabric of our modern way of life. Its impact resonates far and wide, across the roads and skies that connect us all.

What Is an Internal Combustion Engine?

An internal combustion engine is a type of heat engine that is widely used in various applications, particularly in transportation. This engine acts as the primary power source for automobiles, motorcycles, airplanes, boats, and many other machines.

The engine works by turning the stored energy in fuel into useful energy that makes these machines move. It does this by carefully controlling explosions that create force, which then powers the engine's parts and makes everything work together.

Picture the internal combustion engine as a powerful muscle that converts the energy stored in fuel into motion, driving vehicles and machinery. Just as our muscles use energy from food to move our bodies, the engine uses controlled explosions to transform fuel's energy into mechanical energy, propelling machines forward.

This forceful energy conversion from fuel helps vehicles and machinery do their jobs and get us where we need to go.

Mechanics and Components

The internal combustion engine consists of several key components working together to produce power:

The cylinder provides a sealed chamber where combustion actively occurs.
The piston moves up and down with a graceful reciprocating motion.
The crankshaft takes charge, converting the piston's linear motion into active rotational motion.
The valves, including intake and exhaust valves, actively control the flow of the fuel-air mixture and the expulsion of exhaust gases.
Finally, the spark plug actively generates a spark to ignite the fuel-air mixture, setting the entire performance in motion. These components work together, actively producing the powerful and coordinated performance of the engine.

The Four-Stroke Cycle

Most internal combustion engines use a four-stroke cycle, which includes the intake, compression, combustion and exhaust strokes to convert fuel into mechanical power efficiently.

During the intake stroke, the piston moves downward, creating a vacuum that draws the fuel-air mixture into the cylinder.
In the compression stroke, both valves close, and the piston moves upward, compressing the mixture.
The spark plug ignites the compressed mixture in the combustion stroke, resulting in a rapid explosion. The high-pressure gases from combustion push the piston downward in the power stroke, generating mechanical work.
Finally, the exhaust valve opens in the exhaust stroke, allowing the piston to expel the spent gases.

To better understand this process, think of the four-stroke cycle of the internal combustion engine as a musical performance.

The intake stroke acts as a conductor bringing in the fuel-air mixture. The compression stroke builds up excitement, just like the rising anticipation in the audience. The combustion stroke creates an explosive burst, similar to the climax of the music. Lastly, the exhaust stroke releases spent gases, like the smooth fade-out of the music.

Together, these strokes work in harmony to power vehicles, creating a symphony of motion.

Types of Internal Combustion Engines

There are three main types of internal combustion engines, each of which has its own unique characteristics and applications:

Gas engines, also known as gasoline engines, are commonly found in cars. They work by igniting a fuel-air mixture with a spark plug. The intake stroke creates a vacuum, drawing in the mixture. During the compression stroke, the mixture is compressed, and when ignited, combustion occurs, generating power. Sometimes called a spark ignition engine, a gas engine is known for its quick throttle response, high-revving nature and smooth operation.
Diesel engines, on the other hand, are heavy-duty workhorses found in trucks and buses. They operate differently from gas engines. In a diesel engine, air is highly compressed, and fuel gets injected directly into the hot, compressed air. This creates controlled combustion without the need for a spark plug. Diesel engines offer exceptional fuel efficiency, high torque output and rugged durability, making them ideal for demanding tasks.
Turbines are used in aircraft engines, power plants and ships. They don't have pistons like gas and diesel engines. Instead, they use a continuous flow of air or combustion gases. The intake process compresses the air, and when fuel is added and ignited, rapid combustion occurs. The resulting high-pressure gases flow through turbine blades, spinning them rapidly. This spinning motion is harnessed to power the engine or generate electricity. Turbines offer a high power-to-weight ratio, quick acceleration and reliability, making them essential for aviation and power generation.

Combustible Engines and the Industrial Revolution

The invention of the internal combustion engine significantly impacted the Industrial Revolution. Several inventors played roles in the engine's development, but Nikolaus Otto was credited for creating the first internal combustion engine in 1876. But it may only have been possible with advancements from Belgian engineer Jean Joseph Étienne Lenoir decades earlier.

In 1859, Lenoir created an engine that used a mixture of coal, gas and air, ignited by an electric spark. His engine was the first commercially successful internal combustion engine, used primarily in stationary applications.

Although it had limited efficiency, it was a crucial stepping stone in advancing engine technology. Lenoir's pioneering work laid the groundwork for subsequent innovations by inventors like Otto, leading to the more efficient and practical internal combustion engines we have today.

Before Otto's invention, the industrial landscape primarily relied on steam power. Steam engines were cumbersome, required large infrastructure, and were predominantly stationary. Then the combustion engine came along and introduced a portable and efficient source of power, completely revolutionizing transportation.

The engine's compact size and portability enabled it to be incorporated into vehicles, such as automobiles and locomotives, leading to unprecedented mobility and the rapid transportation of goods and people. This advancement in transportation greatly facilitated trade, expanded markets and contributed to the growth of cities and urbanization.

Over in the manufacturing world, the engine's widespread adoption in industrial machinery and equipment revolutionized laborious processes. It powered machines and tools, increasing productivity and efficiency, and pushing the whole industrial sector forward.

Internal vs. External Combustion Engines

Internal combustion and external combustion are two different methods of harnessing energy from fuel.

Internal combustion refers to the process where fuel combustion occurs within the engine itself. Fuel, typically a mixture of air and a hydrocarbon, is ignited inside a combustion chamber, resulting in controlled explosions. These explosions generate high pressure and temperature, which drive the movement of pistons, ultimately converting the energy into mechanical work.

On the other hand, external combustion involves burning fuel outside the engine to produce heat. This heat is then transferred to a working fluid, such as steam or a gas, which expands and drives a piston or turbine. Examples of external combustion engines include steam engines and Stirling engines.

This article was created in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.