Improvements in thermal efficiency and exhaust emissions with ozone addition in a natural gas-diesel dual fuel engine

Abstract

Here, ozone (O₃) was introduced into the intake air in a natural gas fueled engine ignited by diesel fuel, a natural gas–diesel dual fuel engine, to utilize the reactive O-radicals decomposed from the O₃ for the promotion of the ignition and for improvements in the thermal efficiency and exhaust emissions. The engine experiments were performed over a range of equivalence ratios of the natural gas in a single cylinder engine. The timing of the pilot injection of the diesel fuel was varied from early in the compression stroke to near top dead center to examine the changes in the effects of the O₃ addition on the ignition and combustion with the pilot injection timing while varying the O₃ concentration. The results showed that the combination of the O₃ addition and the early pilot injection is a means to improve the thermal efficiency and unburned emissions with a small amount of O₃. Further, the improvement in the thermal efficiency and the reduction of the unburned hydrocarbons with the O₃ addition are more pronounced for lower equivalence ratios of natural gas, while the O₃ addition has a limited effect on the thermal efficiency and the unburned hydrocarbons for higher equivalence ratios of the natural gas.