Eli5: Why do automobiles operate with diesel or petrol but not with water?

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Eli5: Why do automobiles operate with diesel or petrol but not with water?

In: Physics

Because water is not a fuel source. You can use the hydrogen and oxygen that water is composed of as a fuel source, but it takes just as much energy to split the molecule using electrolysis as you get out of it when you burn the hydrogen and oxygen back together in to water.

Water is not flammable. In order to have combustion, you need a fuel source, oxygen and an ignition source. Water is none of them.

As much as I know about combustion engines and hydrogen, I have encountered so many different reasons as to why they never took off.
So I’m following to see if there is a proper answer. Fingers crossed.

Internal combustion engines use fuels that explode so that small explosion drives the pistons in the engine.

Water doesn’t readily expel its energy like that. The energy required to break the bonds of the water molecule are much higher than the energy it would release.

Vehicles with traditional engines use a chemical process called combustion to generate power.

They take a fuel molecule and react it with oxygen to release heat and generate pressure.

Now consider water – H2O. It already contains oxygen – it’s actually mostly oxygen by weight. It’s not combustible, it’s hydrogen that has already been combusted.

You can’t burn it again, so no more energy can be realistically extracted from a water molecule unless you have something much more dangerous than oxygen around to react it with.