Eli5: Why do automobiles operate with diesel or petrol but not with water?
In: Physics
Once upon a time they did… kinda. Steam powered engines use expanding water vapor to drive pistons, but the heat to turn the water to steam was normally a coal or wood fire in the boiler.
In the future, they may be… kinda. Hydrogen fuel cells have been developed that burn hydrogen and discharge water instead of noxious fumes, but the race is on between pure electric and hydrogen cells, and right now it’s looking like electric will win simply bc the infrastructure is already there.
It could be argued they are right now… kinda. The electricity for an electric car comes from somewhere, and if your electrical grid is powered by a dam… well then your car is powered by the stored potential energy of a massive amount of water.
You need something that is flammable. In a car engine, fuel vapor is injected into pistons. The vapor is exploded which forces the piston up and the piston on the opposite end down. These explosions happen rapidly pushing the pistons up and down. These pistons are connected to a shaft which spins and is connected to the axeles which spin the wheels.
Water can’t create these high pressured explosions.
There have been cars run on water in the past. The very first cars in fact were steam powered and there have been experimental cars which use a process called electrolysis to extract the hydrogen from water to use in a combustion engine, but these cars aren’t as practical and efficient as standard fossil fueled combustion cars. If you want to use a combustion engine it’s best to use something that’s highly flammable from the start.
Water is not a fuel.
In the context of fuel, you can think of water as being the unusable ash produced by burning hydrogen.
You can use electrolysis to break water apart into hydrogen and oxygen, but it takes more energy to do that then you will get back from burning them again. This is why we can’t just invent a car that uses a tank of water to make its own fuel.
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