A METHODOLOGY FOR DETERMINATION OF OPTIMUM ENGINE SIZE FOR BEST FUEL ECONOMY

A procedure is described for determining in advance the optimum engine size for best fuel economy in a specific vehicle with defined driving performance (expressed by acceleration time from 30 mph to 60 mph in highest gear). A specific fuel consumption map is described with only two normalized parameters; load-dependent and zero-load fuel consumption. The effects of cylinder volume and specific power output on fuel consumption are discussed, under the basic assumption that acceleration performance of every engine displacement/axle ratio combination is identical. The study confirms the generally accepted fact that reduced driving performance will result in improved fuel economy. It is also concluded that lowering the numerical axle ratio will not yield maximum fuel economy unless engine size is also reduced, and that reducing the acceleration capability beyond a certain point will yield only marginal further increases in fuel economy.