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How does a Car Engine Work?

By Carol Francois
Updated May 23, 2024
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A car engine is also known as an internal combustion engine, and is designed to use small, controlled explosions to create the power necessary to move the vehicle. This type of engine is used in lawnmowers, motorcycles and other motorized devices. There have been many improvements on the design to improve efficiency and power, but the car engine is really a very simple device.

All automobile engines are designed to use a four stroke combustion cycle. The four strokes are the intake, compression, combustion and exhaust. These strokes are repeated in quick succession to generate power. All parts of the combustion cycle take place within an enclosed car engine.

To understand how a car engine works, picture a windmill. The arms of the windmill are moved by the force of the wind. As the wind moves the arms, the windmill creates power that can be used to move heavy grinding stones or generate electricity.

The automobile engine works in a very similar way. Instead of wind, a small, controlled explosion forces the piston, or "arms," of the engine to move. When the energy from the explosion is almost worn out, another explosion occurs, forcing the pistons to move again. This recurring cycle generates the power needed.

The piston is a metal rod that is connected by a crankshaft to the connecting rod. During the intake cycle, the intake valve opens and the piston moves down, to start the cycle. This motion brings a cylinder full of air and a small amount of gas into the engine.

In the compression cycle, the piston moves up and reduces the space of the air and fuel. The smaller the space, the more powerful the explosion will be. The seal on this space must be airtight, so that no energy is lost.

At the top of the cycle, the spark plug releases a spark that explodes the gasoline. The power of the explosion forces the piston down. If the spark does not occur at the right moment, the explosion does not happen.

At the bottom of the stroke, an exhaust valve opens so that the waste gas from the explosion can leave the engine. This gas is moved down through the pressure of the recurring explosions to the catalytic converter and muffler. The air is cleaned of the larger pollutants and the exhaust exits the vehicle through the tailpipe.

The speed of the cycle determines the speed of the vehicle. When the driver increases the amount of gas going to the engine, the engine pistons increase their movement. This faster pace results in an increase in the speed of the combustion cycle.

The spark plugs play a critical role in the car engine, as they provide the spark that initiates the explosion. Spark plug designers continually try to improve on this design. The more sparks that can be issued by the spark plug within a short period of time, the greater speeds the engine can achieve.

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Discussion Comments

By anon263380 — On Apr 24, 2012

I feel as if there should be more information on how engines work. I asked how do car engines work and everything but what I asked for came up!

By anon175452 — On May 12, 2011

my dad used to own a mustang all white..a sleeper, he redid the engine so that it had true dual exhaust. he took out everything that blocked the exhaust, which gave it more speed, because it was able to release the waste quicker and easier. in the article i think they need to explain more on what everything is, not just how it works and makes it move. for example explain the pistons, the muffler, the carborater, the transmission and how everything works together.

By anon110412 — On Sep 11, 2010

There is another new engine design that may be even better than the Scuderi. The Doyle Rotary. It is also a Split Cycle engine but it has eliminated the valve train and reciprocating motion. The Tour engine is also pretty cool.

By Amphibious54 — On Jun 19, 2010

@ ValleyFiah- I read about that engine as well. The company that designed the engine, Scuderi, unveiled the prototype at the IAA Car Show in Frankfurt, Germany. Their website has a great video showing how the engine works. This is what I got from it.

The engine intake’s fuel and air on cylinder one’s downstroke, compresses it, and transfers it to cylinder two on the upstroke. The spark plug fires in cylinder two at top dead center, just as the connecting valve is opened. This forces piston two down and creates negative pressure, drawing in the rest of the compressed fuel and air on the downstroke. The exhaust is then expelled during cylinder two’s upstroke, just as the first returns to its intake cycle.

By ValleyFiah — On Jun 19, 2010

@ Georgesplane- I read about a new prototype combustion engine that is undergoing testing called the Scuderi Engine. It is a modern variation on a split cycle combustion engine that uses two pistons and cylinders linked together to complete the four cycles.

Cylinder one is responsible for the intake and compression of fuel and air. Cylinder two is responsible for the combustion and power/exhaust cycles. The two cylinders are linked by a tube and two valves that allow the compressed fuel and air to be passed back and forth. The benefit of this type of system is that it allows for all four cycles to be completed in one revolution of the cam shaft; theoretically doubling the efficiency of a comparable engine.

By Georgesplane — On Jun 18, 2010

This article did a very good job at describing how a gasoline combustion engine works, but a diesel combustion engine is a little different. Diesel engines do not use spark plugs to ignite the fuel like a gasoline engine does. Instead diesel engines ignite the fuel by compressing air.

Compressed air becomes heated which in turn ignites the diesel fuel. The colder the air the greater the compression needed to ignite the diesel fuel. A diesel vehicle’s ECU will change the amount of compression based on an air temperature sampling allowing combustion in colder climates.

Injectors for diesel engines are also different than their gasoline counterparts. Diesel injectors must withstand the immense heat and pressure inside of the compression chamber; all while maintaining a fine spray pattern. Furthermore, gasoline engines inject the fuel just prior to the intake stroke, while diesel engines inject fuel at the top of the compression stroke. Diesels are still combustion engines but the properties of the different fuels require different techniques to achieve combustion.

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