Simulation Analysis of Early and Late Miller Cycle Strategies Influence on Diesel Engine Combustion and Emissions

Based on the working model of a diesel engine, the influence of 2 Miller cycle strategies-Early Intake Valve Closure (EIVC) and Late Intake Valve Closure (LIVC) on the combustion and emissions of diesel engine was analyzed. Then the working condition of each Miller cycle strategies on the engine under the rated speed was optimized through the adjust of the valve timing, boost pressure and the injection timing. The research found that both delaying and advancing the closure timing of the intake valve can decrease the pressure and temperature during compression stroke, prolonging the ignition delay. However, due to the decrease of the working media inside the cylinder, the average in-cylinder temperature and soot emissions will increase, which can be alleviated by raising the boost pressure and the resulting compensation of the intake loss. The study found that together with increasing boost pressure and delaying injection timing, both EIVC and LIVC can reduce the NOx and soot emissions simultaneously. The simulation results show that while keeping the peak firing pressure the same as the original machine, M-50 together with constant peak firing pressure boosting and a 6^oCA injection delay can decrease the BSFC by 1.21%, the NOx emissions by 22%, and the soot emissions by 58.1%, while M100 together with constant peak firing pressure boosting and a 4^oCA injection delay can reduce BSFC by 1.56%, the the NOx emissions by 12.96%, and the soot emissions by 54.75%.