Measurement of the Effect of Injection Rate and Split Injections on Diesel Engine Soot and NOx Emissions

This study was conducted to develop an understanding of how rate-shaped and split injections can affect the soot and NOx emissions of a heavy-duty diesel engine. The tests were performed on a single cylinder version of the Caterpillar 3406 production engine, modified to accept an electronically-controlled, high-pressure common-rail injection system that offers a very high degree of flexibility in injection timing, split injections, and rate shaping of the initial injection. The engine was instrumented for particulate measurements with a full dilution tunnel, and CO, CO2 and NOx emission meters. Cylinder pressure was used to study heat release rates, and the response to changes in the injection scheme. The results show that rate-shaped injection, when optimized for lowest BSFC, does not appreciably affect pressure rise or peak cylinder gas pressures. Split injections, however, allowed peak pressures to be reduced by more than 45%, and have a significant effect on the overall rate of pressure rise. The emission measurements showed that split injections have a trend of reduced NOx as the quantity of fuel in the first injection is reduced, without particulate emissions increasing rapidly. Furthermore, it was determined that split injection better utilizes the air charge and allows combustion to continue later into the power stroke than for a single injection case, without increased levels of soot production. This indicates that pulsed injection may provide a means to reduce particulate emissions, and allow for reduced NOx from controlled pressure rise.