Numerical investigation of direct injection stratified charge combustion in a natural gas-diesel rotary engine

To further improve the performance of diesel rotary engine, a novel natural gas-diesel rotary engine was proposed and studied in this paper. Based on a spray experimental setup, the diesel spray characteristics under diesel rotary engine working conditions were obtained and analyzed. Thereafter it was used to validate the spray model for diesel rotary engine modeling and simulation. The effect of different natural gas blending ratios on mixture formation and combustion process in the natural gas-diesel rotary engine were investigated. Simulation results showed that for fuel-air mixing process, the natural gas movement process was susceptible to the airflow motion. However, the diesel distribution range was obviously enlarged under the influence of high-speed unidirectional flow. At assisted ignition timing, the stratified distributed diesel made the combustion process mainly occured at the front and middle of the combustion chamber. Besides, the flame propagation speed was accelerated with natural gas blending ratio increasing, which effectively improved the total combustion rate. Compared to single-fuel mode, when natural gas blending ratio increased to 20%, the maximum combustion pressure increased by 24.17%. Meanwhile, soot and CO decreased obviously, but NO and CO2 also increased.