Fig. 6 shows fuel consumption as a function of relative air-fuel ratio with addition of 0%, 10% and 20% H2 at 1400 rpm, MBT, and a compression ratio of 8. Fuel consumption that depends on thermal efficiency is defined as the mass flow rate per hour, and it may depend on the increase of brake power rather the increase of fuel quantity. The reason for lower fuel consumption with increased hydrogen addition compared to LPG combustion would be the fast flame propagation velocity of hydrogen.