Particle matter emission control and related issues for diesel engines

The particulate matter is probably one of the most critical issues of the diesel engine emissions. After years of research, people begin to understand it further, with respect to its impact on the environment and human health, its formation mechanism inside and outside the diesel engine, and most importantly, the methods to control its formation. This study has focused on the particulate matter emission control in diesel engines. It started with the application of two closely coupled Diesel Particle Filters (DPFs), consisting of an assistant DPF and a main standard honeycomb DPF, to replace the standard Diesel Oxidation Catalyst (DOC) + DPF system, commonly applied on diesel engines these days. This new after-treatment system showed a great potential to be adopted in the future, not only for the tighter emission regulations but also for the great cost reduction of the total after-treatment system by the reduction of the main DPF’s size and weight and more options of other cheaper materials. The back pressure problem revealed in the experiment was then studied through a one dimensional model simulation and its influence to the engine performance was discussed. Fuel injection parameters which are related with the engine performance and emissions were also investigated in the study. After careful calibrations, a single injection induced Partially Charge Compression Ignition (PCCI) combustion was achieved, in which mode, NOx and smoke emissions were reduced by more than 80% compared with using the normal multiple injections. Following that, the non-volatile particulate emissions under the pilot injection’s impacts were studied and the key parameters of the pilot control such as fuel quantity and injection timing were examined. The particulate number concentrations and size distributions were investigated under different engine operation conditions and the results illustrated how a pilot injection alongside a main injection could influence particulates and what these effects were closely related to. The research continued with the investigation of bio-fuels on the particle emission reduction, when 10% alternative diesel fuel blends (Rapeseed Methyl Ester (RME) and Gas-to-Liquid (GTL)) were used. They indicated that without any modification to the engine, adding selected alternative fuels, even at a low percentage, could result in a noticeable reduction of the particle numbers, both in the total and the non-volatile parts; however, the number of nucleation mode particles could increase in certain cases. It was also revealed that the engine suffered very high numbers of the nucleation mode particulates during warming up.