in essence any heat engine, which is the heart of a machine or a working element. has to be fueled.

for that in any case it needs a source of energy. that very source of energy has to be something other than a mechanical energy source. i.e. a source that supplies energy through means like spring or a powered shaft , motor, should,nt be considered the power source.

a power source is ideally heat and sometimes electricity.

in most engines used in vehicles the ultimate source of energy is chemical energy .

heat energy is the intermediate state. this heat energy pressurises a fluid, that can be vaporized gasoline created during combustion or steam. fluid under high pressure and temperature is capable of driving a cam/piston / turbine.

the power of any engine fundamentally depends on the amount of heat energy generated at the source, which in turn depends on the temperature of the source.

the fluid coming out of the pump ( turbine / piston cylinder) is lower in energy than the fluid that enters the pump.

this means , the loss is completely converted to useful mechanical work , or power.

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