Strategy for Mode Transition between Low Temperature Combustion and Conventional Combustion in a Diesel Engine

Mode transition between low temperature combustion (LTC) and conventional combustion was performed by changing the exhaust gas recirculation (EGR) rate from 60% to 0% or vice versa in a light duty diesel engine. The indicated mean effective pressure (IMEP) before mode transition was set at 0.45 MPa, representing the maximum load of LTC in this research engine. Various engine operating parameters (rate of EGR change, EGR path length, and residual gas) were considered in order to investigate their influence on the combustion mode transition. The characteristics of combustion mode transition were analyzed based on the in-cylinder pressure and hydrocarbon (HC) emission of each cycle. The general results showed that drastic changes of power output, combustion noise, and HC emission occurred during the combustion mode transition due to the improper injection conditions for each combustion mode. Therefore, a strategy for smooth combustion mode transition was developed by controlling the injection parameters such as injection timing, injection duration, and the number of injections on a cycle-by-cycle basis. As a consequence of gradually retarding the injection timing, gradually decreasing the injection duration, and adding a pilot injection, the differences in power output and combustion noise between the periods before and after mode transition were reduced by up to 100% and 225%, respectively, compared to those values for the case without controlling the injection parameters.