Power System Optimization for Passenger Cars

Statistical studies show that each power system from a milliwatts rating (batteries and mechanical springs) to a megawatts rating (steam and gas turbines) has optimum (minimum) weight per horsepower, minimum volume (box) per horsepower, and minimum fuel consumption (maximum brake thermal efficiency) within a limited range of output. In the case of heat engines, the basic parameters involved are the maximum efficiency of the ideal thermodynamic cycle, which is about the same for all heat engines, and the losses due to heat transfer and fluid friction. Also involved are maximum heat flux, and mechanical friction at moving surfaces. This paper discusses the effect of size on such parameters as surface-to-volume ratio (heat loss) and wetted perimeter to cross section area (fluid friction) and the effect of these parameters on power system performance- From these considerations, one must come to the inevitable conclusion that the amount one can scale a system up or down is definitely limited, e.g., steam turbines or even gas turbines for a passenger car (100 HP or less) are more than likely out of the allowable range for optimum performance.