Effects of post-injections on diesel engine emissions and efficiency at low load using design of experiments

A design of experiments and regression analysis are used to investigate the influence of engine operating conditions on post-injection efficacy. The study targets emissions of engine-out soot and NOx, as well as fuel economy and is performed on a typical heavy-duty diesel engine at a relatively low load. The regression models indicate the presence of a strong correlation between available oxygen, reduction in engine-out soot and optimal post-injection scheduling. This observation strengthens the suggestion that enhanced late-cycle mixing of fuel and oxidizer is an important contributor to the soot reduction capabilities of post-injections. Decrements in both NOx emissions and fuel consumption are established for a particular post-injection scheme, although an intricate synergy with EGR rate was found, emphasizing the importance of careful scheduling of a post-injection event.