What is the primary function of the engine in a truck and coach?

The primary function of the engine in a truck and coach is to convert fuel into mechanical energy to power the vehicle. This process occurs through internal combustion, where fuel is mixed with air and ignited, causing a series of controlled explosions that push the pistons. These pistons then turn the crankshaft, ultimately generating the necessary power to move the vehicle. This conversion of chemical energy stored in the fuel into mechanical energy is fundamental to the operation of all combustion engines used in vehicles, providing the necessary force for acceleration and motion.

The other options relate to important functions within the vehicle but do not define the core purpose of the engine. While providing electricity to onboard systems, cooling the engine, and filtering exhaust gases are all critical aspects of vehicle operation, they serve as support systems rather than the primary role of the engine itself.