Experimental Study of Post Injection Scheduling for Soot Reduction in a Light-Duty Turbodiesel Engine

This experimental study involves optimization of the scheduling of diesel post injections to reduce soot emissions from a light-duty diesel engine. Previous work has shown that certain post injection schedules can reduce engine-out soot emissions when compared to conventional injection schedules for the same engine load. The purpose of this study is to investigate the impact of post injection scheduling for a range of engine conditions on a light duty multicylinder turbodiesel engine (1.9L GM ZDTH). For each engine operating condition, a test grid was developed so that only two variables (post injection duration and the commanded dwell time between main injection and post injection) were varied, with all other conditions held constant, in order to isolate the effects of the post injection schedule. Results have identified two distinct regimes of post injection schedules that reduce soot emissions. In one regime, the post injection timing is critical, with the size of the post injection having only a minor effect on the results. This "close-coupled" regime reduced soot by up to 22%, with reductions in fuel consumption of up to 3%, but at the price of a 7% increase in NOx. In the other regime, the size of the post injection is critical, with the timing of the post injection having only a minor effect on the results. This "long-dwell" regime reduced soot by up to 40% and NOx by up to 5%, but with no significant improvement in fuel consumption and up to 13% increases in total hydrocarbons.