Eli5: Why is fuel/petroleum the liquid that makes cars run? What’s happening inside the car with this specific liquid that makes it go that can’t happen with other liquids?
In: Technology
You can make cars work on other liquids (ethanol for instance). But it has to do with the amount of caloric energy in the liquids, the density of the liquids, etc. Petrol/gasoline isn’t terribly dense (so it isn’t heavier/more viscous), and has a very high caloric energy value (it burns better than say, water, which has no caloric energy). It also has a relatively low combustion temp (ie, how hot something needs to be to catch on fire, hence why you can light it on fire with a spark rather than needing an already lit flame to burn it).
All of these combine to make it the BEST, but not the ONLY fuel for cars.
The piston pulls fuel and air into the cylinder, and when the piston moves up, it compresses the fuel/air mixture, then the spark plug lights causing the flammable mixture to explode, pushing the piston down and sucking the exhaust out of the exhaust valve.
Diesel fuel runs different in diesel motors, but that’s a basic example of how a gas engine works
Petroleum isn’t unique – it just needs to be a flammable liquid. The power of an engine comes from burning (exploding, actually) that flammable liquid. The explosion pushes a metal rod that turns the wheels. This happens over and over – lots of small explosions – to keep the metal rod moving and the wheels turning. The rumble sound the engine makes is the sound of all those explosions.
While you can use different flammable liquids to make an engine run, our cars require petroleum because they were designed for it. If you used a different liquid you need a slightly different design. Diesel is another common fuel for engines (used for large trucks, usually) and it requires a slightly different engine design. But the basic principle is the same.
Are you asking why some liquids are combustible and other liquids, like water, do not burn in the presence of a spark?
The liquid is aerosolized inside the cylinder, air (oxygen) is pulled in and a spark fires which causes the fuel air mixture to combust and push against the piston and the process repeats.
There are certainly other liquids that are combustible but not every one has the same energy content. Ethanol, for example, burns but you cannot go as far with the same amount.
Explosions! Your car works because of thousands of controlled explosions per second!
Fuel and air are brought into the cylinders, then ignited with a spark plug. The result is a tiny explosion. This explosion pushes a piston, which turns the crankshaft. When the power from this crankshaft is sent to the wheels, it makes your car move.
Petrol is used purely because we know the mixture we need to create an explosion the size we need, but engines can also be tuned to use other liquids like ethanol.
Fun fact: M1 Abrams tanks have jet engines that compress air so much that any combustible fuel can be used.
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