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Asked by paul and james to Áine, Ciarán, Eoin, Lydia, Victoria on 18 Nov 2014.
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Lydia Bach answered on 18 Nov 2014:
Hey,
The fuel and air mix are in the cylinder which contains a piston, when the piston rises to the top of the cylinder it compressors the fuel and air mix. When the piston reaches the very top of its stroke a spark plug fires causing the fuel to combust and forcing the piston back down the cylinder.
In cars multiple cylinders fire at different times turning a crank – that results in power for the engine.
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Ciarán O'Brien answered on 18 Nov 2014:
Explosions!
A car engine is part suction pump, part explosion test chamber. When you start a car, you use electrical power from the battery to get the engine moving, but once it starts it can keep itself powered.
Ok, so the engine has these cylinders on a crank shaft. When the cylinders move up and down, they make the crankshaft rotate, and that drives the wheels of the car.
On the first cycle of the cylinder, it sucks in air from the atmosphere and a small amount of petrol from the fuel tank, and then compresses them both. Then a sparkplug makes a tiny spark to ignite the mixture. Boom, explosion! The explosion forces the cylinder back down, rotating the crankshaft and causing the suction part to draw in more air and petrol for another explosion.
Just the one cylinder doing this would be very unbalancing, and the engine would wobble a whole load making cars much less reliable. But with some clever engineering and perfect timing of spark plugs, engines can use several cylinders, some sucking in air and petrol while the others are exploding, and that balances out a lot of the vibrations, and the extra cylinders generate more power for the crankshaft as well, making for a more powerful car.
Here’s an animation that can explain what it all looks like:
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