What is the chemistry behind how combustion engines work?
In: Chemistry
The ideal gas law tell us that 1 mole of a substance occupies 24 liters of volume as a gas at room temperature and pressure. At higher temperatures, like an engine, it wants to spread out and take up more space.
A mole is the atomic weight of a substance in grams.
A mole of petrol is about 114 g, but with a density of 0.7 cm/g this will occupy about 80 cubic centimetres, or 0.08 litres.
Turning liquid petrol into gas suddenly increases the volume it wants to occupy by at least 300 times.
A petrol engine takes in liquid petrol mixed with oxygen and uses a spark to explode it while the piston is in the top position. Making the cylinder as small as possible.
This exploding petrol suddenly wants to occupy hundreds of times more space, creating huge pressure, shoving the piston out of the way to create the space it wants.
The other end of the piston is attached to a crank shaft that ends up spinning as a result, giving you a power output drive shaft, that also returns the piston to the top position. Repeat a few thousand times a minute.
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