If gasoline combustion is just a heating method for the air to expand and cause pressure then why can't we find another way to heat the air in the engine during the "combustion" stage? Have people tried?
As juhist said, just about every remotely feasible fuel has been tried in the history of motorized transport. Petrol and diesel became popular because:
- they're easy to use
- they're reasonably safe
- they're available in enormous quantities, enough to fuel close to a billion cars.
- they can be made cheaply,
- they have high enough energy density to not take up large amounts of space.
Ever since the first oil crisis in the early 1970s, people have been trying to find an alternative to petrol and diesel. Lots of potential solutions have been tried, but they all failed at at least one of the above criteria. The electric car revolution of the past few years is the first time an alternative has been found that satisfies 1-3 and can get close enough on criteria 4 and 5.
Yes, people have tried. For example, in addition to gasoline, you can use diesel. You can use alcohols (ethanol, methanol). The fuel doesn't even have to be a liquid: you can use natural gas. All of these fuels have been used in cars. Probably the most exotic fuel is wood gas, which requires a separate unit to convert wood into syngas.
The fuel doesn't even have to be injected inside the engine like what is done in internal combustion engines. In that case, this is called external combustion engine. Probably the most notable external combustion engine is the Stirling engine. However, external combustion engines have a low power to weight ratio, making it unlikely that external combustion engines would be used in passenger cars.
"If gas is just a heating method for the air to expand and cause pressure" - it is not.
The combustion products also increase the pressure in the enclosed volume, see the Ideal gas law:
pV = nRT
Both n and T are increased by the combustion; V remains the same at the moment of combustion, so p has to increase.
It is a balance.
You attempt to keep combustion chamber temperatures higher and increase efficiency of the gas. In a typical engine around 40% of that potential is lost due to cooling alone. You loose over 30% right out the exhaust which is why you are seeing turbochargers used to increase efficiency. The other 10% is frictional losses leaving you with the magic 20% (give or take a few percent) efficiency we currently have.
If you go to high then the piston rings have trouble lubricating the cylinder walls and you have increased wear.
Now the fuel type out of it you still need to lubricate the cylinder walls. There have been ring designs to increase the efficiency of the gas but none has yielded any reliable results.
Once again it is a balance. There have been attempts at exotic rings and cylinder selves to increase the thermal efficiency of many types of volatile fuels. But the end result is that the combustion chamber perfers a temperature level that we currently run at.
Running a engine "hot" provides increased thermal efficiency. Recovering the exhaust through turbochargers increases the efficiency. Both have been done already getting us a few ticks above 20%.
The next step is to eliminate frictional losses further. That is currently being done(in F1/racing circuits) and should become available in high end cars in a few years trickling down to mainstream cars later with the use of free valve/ solenoid computer controlled actuated valves. . . They will allow for increased control of the exhaust timing and tuning increasing the efficiency of turbochargers. The electronic valves will also allow for more controlled air fuel intake. The days of oil actuated valves at varying rpm ranges will be gone replaced by millisecond precision as the engine and transmission demand it for the condition. While the heat inside the cylinder will not increase any time soon having greater control of the valves themselves will lead to increased compression within the cylinder and increased pressure providing better use of whatever fuel is filled into the tank.