The modification of the fuel injection rate in heavy-duty diesel engines. Part 1: Effects on engine performance and emissions

An experimental study has been performed on the effects of injection rate shaping on the combustion process and exhaust emissions of a direct-injection diesel engine. Boot-type injections were generated by means of a modified pump-line-nozzle system, which is able to modulate the instantaneous fuel injection rate. The interest of the study reported here was the evaluation of the effective changes produced in the injection rate at different engine operating conditions, when the engine rotating speed and the total fuel injected were changed. In addition, the influence of these new injection rates was quantified on the global engine performance and pollutant emissions. In particular, the focus was placed on producing “boot-like” injection rate shapes, with the main objective of reducing NOx emissions. Results show how this system is capable of achieving boot-type injections at different boot pressures and boot durations. Also, even though the general trend of the system is to reduce NOx and to increase soot and fuel consumption, emissions and performance trade-offs can be improved for some specific boot shapes. On the contrary, the modulation of the injection rate showed to be ineffective at medium engine load, since the increase in soot was greater than the relative decrease in NOx. The analysis of the modifications produced by these strategies on the combustion process, and on the rate of heat release are the base of a second paper.