Fuel consumption per revolution is approximately a linear function of work output per revolution, for power levels less than about two-thirds of the power at wide-open throttle. Thus
where
N is engine speed,
Pf is fuel energy rate (kW), and
Pb is power output (kW). The approximation is relatively good for engine speeds typical of regulatory driving cycles. The parameters α and
b are studied using engine measurements conducted in the late 1970s. The parameter values are rather uniform, with averages α = 0.29
V, where a is in kJ/rev and
V is displacement in liters, and
b = 2.45 (dimonsionless). Engine maps for more modern engines show, that the parameter a has declined. Several applications are discussed: especially simulation of vehicle fuel use, and creation of a figure of merit for fuel use by engines.