Fuel is mixed with air, compressed then ignited.
It is burnt.
Firebox
Fuel compressed and burnt
No the fuel is burnt inside the engine, hence the term "internal combustion"
the energy between the bonds of the fuel in the engine.
A thermic reaction resulting from the use of a form of fuel.
Steam engine: external combustion (the fuel is burnt in the boiler and the steam led through pipes etc to the power cylinder(s). Diesel (and petrol and gas): internal combustion - the fuel is burnt in the cylinder. Otherwise they are all Heat Engines.
Engine cylinder head valves admit the air/fuel mixture and release the burnt gases.
The intake manifold routes the fuel/air mixture to the cylinders or just the air on a modern fuel injected engine. The exhaust manifold routes the burnt fuel gases out of the engine into the exhaust system.
It is the burnt product after the oxygen and fuel are mixed and used to power the engine.
Incomplete combustion in an engine indicates that all of the fuel has not been burnt. Incomplete combustion can cause clogging and damage to the valves in the engine of a car.
A rocket engine is a reaction engine as the fuel is burnt the thrust created pushes the rocket forward. Newton's 1st law in action; for every reaction there is a equal and opposite reaction.