Experimental and numerical study the effect of combustion chamber shapes on combustion and emissions characteristics in a heavy-duty lean burn SI natural gas engine coupled with detail combustion mechanism

With the computation ability boomed, the CFD coupled with detailed combustion mechanism has been widely used in natural gas engines to investigate the combustion and emissions characteristics. Further optimization of combustion chamber (CB) is needed more than ever for increasing the tumble and swirl ratio to achieve the reasonable in-cylinder flows and enhance the turbulent intensity in the heavy-duty lean burn SI natural gas engine, particularly in the vicinity of the spark plug. In this paper, four detailed three-dimensional full-size combustion chambers were built and redesigned according to real combustion chamber of the heavy-duty lean-burn SI natural gas engine by industrial computed tomography, including detailed intake port and exhaust port. Then these cases simulated by the commercial CFD code coupled with detail combustion mechanism, and validated against the experimental data. The simulation results showed that the CB #1 displayed the best performance, followed by CB #2, while original CB was located between CB #2 and CB #3 from the behavior of the in-cylinder pressure, hear release rate, combustion phasing, swirl ratio, turbulence flow and flame propagation. By means of using the higher turbulence combustion chamber in the lean-burn SI natural gas engine, the combustion rate dramatically increased, and thereby shortening the combustion process, which was conducive to the spark kernel formation and development, and the late turbulence flame propagation throughout the combustion chamber. In addition, the turbulence flow dramatically stretched, distorted, and wrinkled the flame front, and thereby increasing the flame deformation and combustion area, and accelerating the combustion rate.