Improvement of Lean Burn Characteristics with Ozone Addition in a Diesel Micro-pilot Natural Gas Engine

Ozone (O₃) was introduced into the intake air in a natural gas fueled engine ignited by micro-pilot of diesel fuel, to utilize the reactive O-radicals decomposed from the O₃ for the promotion of the combustion and for improvements in the thermal efficiency and exhaust emissions. Experiments were carried out in a single cylinder engine to elucidate the effects of the ozone addition under the lean burn conditions. A supercharger was employed to increase the intake air amount and vary the equivalence ratio of natural gas. The experimental results showed that the O₃ addition has a limited effect on the ignition of the diesel fuel injected near top dead center, while the heat release during the flame propagation in the natural gas/air mixture was increased at the lower equivalence ratio of natural gas. Further the ignition of natural gas was promoted, resulting in the increase of the combustion efficiency and the degree of constant volume heat release. The cooling loss and the NO_x emissions decreased due to the leaner burn achieved by the supercharging. Overall, the indicated thermal efficiency and the exhaust emissions can be improved by the supercharging combined with the O₃ addition.