Prime Movers For Motor Vehicles

The motion of all vehicles requires the expenditure of a certain quantity of mechanical energy, and in motor vehicles the system that supplies such energy (in most cases an internal combustion engine) is on board. The lack of an adequate prime mover is the main reason that mechanical vehicles could be built only at the end of the industrial revolution, and enter mass production only in the Twentieth Century, in spite of attempts dating back to ancient times.

For a mechanical vehicle to be built, a prime mover able to move not only itself, but the vehicle structure and payload as well, was needed. Remembering that the power needed to move the mass m at the speed V on a level surface with coefficient of friction (sliding or rolling) f is equal to P = mgfV , it is easy to conclude that the minimum value of the power/mass ratio of a prime mover able to move itself is

EquationSource$$\frac{P}{m}=\frac{gfV}{\eta\alpha}$$

((22.1))

where α is the ratio between the mass of the engine and the total mass of the vehicle and η is the total efficiency of the mechanism which transfers the power and propels the vehicle.