Answer:
Heat is produced
Step-by-step explanation:
In a combustion engine there is a chamber in which the combustion of fuel occurs in the presence of an oxidizer. This combustion generates heat is produced which expands the gases and the gases moves the pistons or rotor present in the chamber. These pistons are then connected with system that moves a vehicle or turbine.
Here the fuel i.e. chemical energy is being converted into heat which is then being converted into mechanical energy. Thus following the law of conservation of energy and mass.