Question: How does fuel make cars move

Nathan Quinlan answered on 6 Feb 2015:

Hi there

Most cars burn petrol or Diesel fuel in an internal combustion engine. All these engines are based on the principle that air expands when you heat it. You can easily do an experiment to look for this expansion effect – crush a table-tennis ball and drop it in very hot water, or take a partly inflated balloon and move it between hot and cold water, and see what happens.

So if you want to make an engine, how do you harness that effect? First you have to heat the air, and the quickest way to do that is to burn something in it – so the petrol or Diesel gets mixed with the air and ignited. The air (suddenly very hot) expands and pushes on a part called the piston. The piston pushes on some other parts to make a shaft rotate. The rotating shaft drives some gears in the gearbox and finally they drive the wheels of the car go around. But all that power engine just comes from air.

There are lots of details that have to be designed in to make that all work, of course. This whole process with the expanding air happens about 25 times a second in four different cylinders. There are valves that open and shut at just the right time to let air into the engine, and release the air after fuel is burnt, so that it goes out the exhaust. There are systems to mix the fuel with the air, and in petrol engines there are spark plugs to light the fire. The gearstick in the car arranges the gears (cogs) in the gearbox to change the behaviour of the car. Cooling, lubrication, bit of this, bit of that.

Lots of internet people have explained this much better than I can. And they have pictures. Try these engine animations and howstuffworks.com for starters.