抄録
An experimental investigation was performed to analyze the effects of EGR rate and turbulence flows on the combustion and flame propagation characteristics of methane (CH_4) - air gaseous mixtures in a constant-volume optically accessible combustion vessel (CV). In this study, combustion pressure data is analyzed in detail for ignition delay and combustion duration, with high-speed schlieren imaging analyzed for flame propagation characteristics. Experimental results showed that the peak combustion pressure decreased as the EGR rate increased. The slope of the pressure rise is lower with a higher EGR rate, resulting in a longer time to reach the maximum pressure compared to 0% EGR. The combustion performance of 20% EGR revealed a near misfire phenomenon, meaning it is difficult for the 20% EGR gas to achieve stable combustion performance under a quiescent condition. The rate of growth of the flame kernel decreased with an increase in EGR, and hence the flame size of 20% EGR case was the smallest at every given time. The influence of turbulent flow on the combustion characteristics showed that the combustion duration was significantly shortened for all EGR rates with compared to the results of quiescent combustion cases.
