Question

explaining the role of combustion
why is combustion of fuel necessary for heat engines to do work?

Explanation:

Heat engines operate based on the second law of thermodynamics. Combustion of fuel is a chemical reaction that releases a large amount of thermal energy. This thermal energy creates a high - temperature reservoir. The heat engine then uses the temperature difference between the high - temperature reservoir (from fuel combustion) and a low - temperature reservoir (usually the environment) to do work. Without the combustion of fuel, there would be no significant temperature difference to drive the thermodynamic processes (such as expansion of gases in a piston - cylinder arrangement in a gasoline or diesel engine) that result in work output.

Answer:

Combustion of fuel is necessary for heat engines to do work because it provides the thermal energy that creates a high - temperature reservoir. The heat engine utilizes the temperature difference between this high - temperature reservoir (from fuel combustion) and a low - temperature reservoir (e.g., the environment) to drive thermodynamic processes (like gas expansion) which result in work output, as per the second law of thermodynamics.