NO x emissions ought to depend on the fast combustion of hydrogen fuel and the higher maximum temperature and pressure of NO x emissions on the addition of hydrogen compared to that of pure LPG combustion depend on the flame temperature of hydrogen fuel that is higher than LPG fuel, and the higher maximum temperature in the cylinder as compared to LPG combustion. But the amount of NO x emissions are high in the addition of 10% hydrogen at around c = 0.9-1.15 as compared to the pure LPG fuel.