Effects of injection strategies and EGR on catalyst heating operation and engine – Out emissions on a diesel engine

Achieving catalyst light – off temperatures during the engine – warm up period has been a challenge for medium – and heavy – duty diesel engines, and catalyst heating operation using one or multiple post injections has been identified as a viable solution to achieve the light – off temperatures faster. This study investigates the effect of post injection timing, main and post injected quantities on the tradeoff between exhaust temperatures and engine – out HC emissions by performing experimental investigations on a single cylinder, medium – duty diesel engine. This study also presents optical data obtained using high – speed natural luminosity imaging and IR imaging, to further understand the phenomena that affects the HC emissions – exhaust temperature tradeoff. The optical data obtained provide a comprehensive understanding of in-cylinder phenomena occurring during catalyst heating operation, whereas prior literature is heavily focused on the engine – out emissions and after treatment devices. Results obtained from this study showed that even a small post injected quantity (2 mg) improved exhaust enthalpy significantly and helped maintain exhaust temperatures in excess of 200 ° C, which is beneficial for catalyst heating. The engine – out HC emissions also reduced significantly (even in excess of 70 % at early post injection timings) with the addition of a post injection. It was observed that post injection timings between 18 and 22 CAD aTDC yielded an optimum tradeoff between HC emissions and exhaust temperatures. The optical data showed that higher main – post quantity ratio helps reduce HC emissions significantly with minimal penalty in HC emissions due to faster penetration of combustion in the squish region and due to the increased local equivalence ratios, which are a result of higher injected quantities.