How an Engine Works

Have you ever wondered what's really going on under the hood of your car? It makes a lot of sound and can create some serious power, but what is actually happening under there? The first time you pop the hood of your car, it can look pretty intimidating. There's a big hunk of metal, lots of strange wires and hoses everywhere, and some things you probably can't even identify. Well wonder no more! Let's take a look at the process that occurs inside that huge hunk of metal we call the engine.

First of all, some background information. The purpose of an internal combustion engine is to convert fuel (gasoline) into power (motion). We do this by burning the fuel. The engine is a means of creating tiny controlled explosions to burn the gasoline and harness the power from the explosion, hence the name, "internal combustion engine." There are many different types of internal combustion engines, including rotary, diesel, and many others. But for now, we'll stick to the basic gas-powered engine.

Most engines run on a four-stroke pattern. Those strokes are Intake, Compression, Combustion, and Exhaust. This process occurs thousands of times per minute in order to create the power needed to move a car. Let's take a look at this process (parts of the engine are explained in another page).

Intake Stroke

The intake stroke begins with the piston at the top of the cylinder. The intake valve opens to allow fuel in (most engines today inject fuel by force of injectors for efficiency reasons). The piston moves down to fill the cylinder with air to mix with the gasoline.

Compression Stroke

In the compression stroke, the piston moves back up towards the top of the cylinder to compress the air and fuel mixture. This compression will make the explosion more powerful once the sparkplug ignites the mixture.

Combustion (Power) Stroke

The combustion stroke is where the piston is at the top of its stroke, and the spark plug ignites the air and fuel mixture to cause an explosion. This explosion forces the piston back down. This is the force that is ultimately spinning your wheels and moving the car.

Exhaust Stroke

Once the piston has reached the bottom of its stroke, the exhaust valve will open to force the exhaust gasses to leave the cylinder. The piston moves back to the top of the cylinder to force the exhaust out and get into position for the next explosion. The exhaust will go out of the valve, through the catalytic converter and eventually out the tailpipe. Then the cycle begins again.

A 4 stroke engine, like the one described, has one power stroke for every two revolutions of the crankshaft. This is where we get the term RPMs or Rotations per Minute. Imagine this entire cycle occurring at 6000rpm! That's a lot of miniature explosions, and a lot of power!

Check out the next article to get a better understanding of what parts help to make this process happen.

Special thanks to IndyCarz (http://www.indycarz.com/threads/tech-basics-part-2-the-four-stroke-cycle.141585/) for the pictures.