Fuel adjustment to achieve a smooth net indicated mean effective pressure during mode switching from homogeneous charge compression ignition to conventional diesel compression ignition in a transient hydrocarbon emissions study

Abstract

For diesel homogeneous charge compression ignition engines, combustion is unstable during the mode-switching process because of an unfavourable evaporation environment, especially at low speeds. Unusual fluctuations in the net indicated mean effective pressure and a spike in the transient emissions occur in the transitional cycles between modes. In this study, first, experiments were performed to characterize the hydrocarbon emissions during the combustion mode-switching process between homogeneous charge compression ignition and conventional diesel compression ignition. The results showed that the hydrocarbon emissions decreased as the speed increased at a constant load. When the load increased at a constant speed, the hydrocarbon emissions decreased. A spike in the hydrocarbon emissions during the transitional cycles was observed at 1000 r/min when mode switching from homogeneous charge compression ignition to compression ignition. Second, based on the spike phenomenon, a method of fuel adjustment was proposed to eliminate the fluctuations in the net indicated mean effective pressure and the spike in the hydrocarbon emissions in the five transitional cycles. Finally, by regulating the fuel adjustment coefficient in the five transitional cycles, the spike phenomenon of the transient hydrocarbon emissions was eliminated, and the fluctuations in the net indicated mean effective pressure decreased. The coefficient of variation in the net indicated mean effective pressure decreased to 2%.