* Fossil fuels: Like gasoline, diesel, and natural gas, which are burned to release heat energy.
* Biofuels: Like ethanol and biodiesel, which are derived from organic matter and also release heat when burned.
Other potential sources of thermal energy for engines include:
* Nuclear energy: Nuclear reactors can produce heat to drive steam turbines, which can then power engines.
* Solar energy: Solar thermal systems can collect and concentrate sunlight to produce heat.
* Geothermal energy: Heat from the Earth's core can be used to generate steam and power engines.
The type of thermal energy source used depends on the specific type of engine and its intended application. However, chemical energy from fossil fuels remains the most common source for internal combustion engines.
