How Does a Car Engine Work?

Before you can repair your car engine, you'll need to know how it works, including fuel injection, expansion, and the stroke sequence.

How Does a Car Engine Work?
Fuel Injection
A mixture of gasoline and air travels from the intake manifold into all the cylinders of your engine. You control the amount of air by how much pressure is on the accelerator when you're driving. According to, the best ratio of air to gasoline in your engine is 14.7:1. This is because gasoline is much heavier than air by weight, so it only takes a small amount. Also, oxygen and gasoline are extremely combustible, but gasoline is even more so. Too much gasoline would be dangerous and could cause an explosion or a fire.
When the air-gasoline mixture is in the cylinder, the spark plug ignites it, causing it to expand and combust with great force. The expansion drives down on the piston, which is attached to the crankshaft. The crankshaft is attached to the gears and axle which cause the back wheels of the car to rotate. The more gas you send into the pistons, the faster this process happens. It's measured in revolutions per minute, or how many times your tires make a full rotation in a minute.
The Stroke Sequence
Most engines are four-stroke, meaning their pistons make four motions in a single power cycle: First, the air mixture injects into the cylinder, forcing the piston down for one rotation. When the piston moves up again, the mixture is compressed. The spark plug fires, causing the compressed mixture to expand. The final stroke occurs when the fumes exit through the exhaust pipe. There are three engine configurations: inline, V-shaped and flat. Inline engines have all the cylinders in a straight line, with the crankshaft below it. V-shaped engines have the same setup, but the cross-section is shaped like the letter V. Flat engines' cylinders are horizontally placed in two rows, with the crankshaft between them.
Automobile Engines - Short Course on How They Work

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