A study of the effect of post injection on combustion and emissions with premixing enhanced fueling strategies

An empirical investigation was carried out in a compression ignition engine to characterize the effect of the post injection timing on the post injection power production, the exhaust temperature, and the exhaust gas composition. Due to the potential emission reduction benefits of alternative fuels, numerous fuel injection strategies were investigated, including direct injection diesel, dual fuel diesel and ethanol, dual fuel diesel and butanol, and direct injection butanol. For all of the tested fuel injection strategies, the results indicated that the engine power output, the exhaust gas temperature, and the exhaust gas composition were very sensitive to the post injection timing. For producing additional power output, a relatively early post injection timing was the most suitable and the power output gradually declined when the post injection timing was delayed. A relatively early post injection timing was also preferable for raising the exhaust gas temperature. For generating highly reactive species, such as hydrogen and reactive light hydrocarbons, the results suggested that an intermediate post injection timing was the most suitable. Furthermore, a late post injection timing was the least desirable due to a very low contribution to power output, a minimal increase in the exhaust gas temperature, and a very low amount of reactive species in the exhaust gas. In general, the alternative and dual fuel injection strategies resulted in reduced nitrogen oxide emissions, reduced smoke emissions, and reduced exhaust gas temperatures compared to the traditional diesel fuel injection. For the alternative and dual fuel tests, it was found that an early post injection was able to reduce the hydrocarbon and carbon monoxide emissions relative to the quantity without a post injection.