How an Internal Combustion Engine Works (and Future Outlook)

Internal combustion is based on the idea that you can create lots of energy when you burn gasoline in a small enclosed area. When you are able to harness the expanding gas that comes from this process, then you have created the core of an internal combustion engine (ICE). From there, the energy from this gas is converted into motion.

Virtually every car that you see on the road uses a four-stroke combustion cycle to create motion from gasoline. Keep reading to understand (and see) how a typical internal combustion engine works as well as what the future holds as it goes up against the rise of electric vehicles.

4 stroke cycle engine

Related: Diesel Engine vs Gasoline Engine

How a 4-Stroke Engine Works

The four-stroke engine process is also known as the Otto Cycle. A German engineer named Nikolaus Otto was the first person to invent and patent a four-stroke gas engine. Each step in the process is named with the word stroke in it; intake stroke, compression stroke, power stroke, and exhaust stroke.

It is important to understand the term Otto Cycle because it is different than the combustion cycle that diesel engines used known as the “Diesel Cycle.” This cycle is also a four-stroke process, but the details of how each process works are different than the Otto Cycle.

how a gasoline engine works

Below are the four unique processes for combustion to take place in a typical gasoline engine.

See Also: What Happens If Your Put Gasoline in a Diesel Engine?

#1 – Intake Stroke

intake stroke

The intake stroke is the first part of the internal combustion process and is basically the aspiration or breathing of the engine. What happens is there’s a connecting rod that connects the piston to the crankshaft.

The piston moves from the top to the bottom once the intake valve opens up. From there, the piston allows gasoline and air to get into the engine from the cylinder.

The intake stroke occurs when the gasoline mixes with the air. There doesn’t have to be a lot of gasoline for this to work either. Just a small drop of gasoline mixed together with air will create the stroke.

  • Intake Valve = Open
  • Exhaust Valve = Closed

#2 – Compression Stroke

compression stroke

After that, the piston moves upwards and compresses the mixture of air and gasoline to give it a more powerful effect. This is known as the compression stroke.

  • Intake Valve = Closed
  • Exhaust Valve = Closed

#3 – Power Stroke

power stroke

The piston eventually makes it back to the top after compressing the air and gasoline mixture. Once it does, a spark is discharged by the spark plug which causes the gasoline to ignite.

There is a mini-explosion inside of the cylinder where the gasoline charge is still active. This is known as the power or combustion stroke.

  • Intake Valve = Closed
  • Exhaust Valve = Closed

#4 – Exhaust Stroke

exhaust stroke

After the explosion, the piston falls back down to the bottom and causes the exhaust valve to open up. All of the exhaust that was created in the cylinder starts to leave through the exhaust valve and comes out of the car’s tailpipe.

The engine has now gone through one rotation of the four-stroke combustion cycle.

  • Intake Valve = Closed
  • Exhaust Valve = Open

The cycle keeps repeating over and over again as you put your foot on the gas pedal to accelerate the vehicle. If there was a problem with any one of these strokes then it would prevent the whole combustion cycle from happening. Either that or it would gradually damage the components of the engine.

Some cars may have slight differences in this process, like with the number of cylinders it has. But the overall concept is still the same.

See Also: How a Common Rail Diesel Engine Works

The Future of Internal Combustion Engines

Despite the increased popularity of electric vehicles, most experts believe internal combustion engines still have a role to play in the future (at least for the next couple decades). There are several key areas of development that will shape their ongoing use.

Advanced Combustion Modes

Engineers are working on newer, more efficient ways to burn fuel that could boost efficiency. These include homogeneous charge compression ignition (HCCI) and lean-burn gasoline engines. These advanced combustion modes could potentially improve fuel economy by 25% or more.

Lower Emissions

Stricter emissions standards will drive refinements to exhaust gas treatment and filtering systems. Gasoline particulate filters, for example, could lower particulate emissions to near zero levels to meet tightening health-based air quality regulations.


Vehicle weight reductions through the growing use of aluminum, magnesium, and carbon fiber components could lead to 15-20% fuel economy improvements for internal combustion engine vehicles.

Hybrid Powertrains

The integration of electric motor-generators and battery packs into gas-electric hybrids can significantly improve fuel efficiency, with some hybrids achieving 50 mpg or more. Mild hybrids are a lower cost option expected to continue their gain on market share.

Hydrogen and E-Fuels

Future ICEs may increasingly rely on hydrogen, propane, and e-fuels to lower carbon emissions. These alternative fuels can help ensure ICEs remain relevant, especially in motorsports, long-distance driving, and commercial applications.

In total, the maximum feasible efficiency gain for internal combustion engines is estimated to be 30-50% in the coming decades. This, combined with synthetic zero-carbon fuels, could enable gas engines to play a meaningful role in a low-carbon transportation future.

Mark Stevens

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