Study of the influences of blending different proportions of propane into methane on combustion characteristics at the knock threshold by using RCM

A spark-ignited Rapid Compression Machine (RCM) has been used to investigate the influences of the different proportions of methane-propane mixtures on the combustion characteristics at knock threshold operating condition. First, the threshold operating points of the mixtures have been obtained and the results indicated that the piston driving pressure reduces from 142 bars to 90 bars as the propane content in the mixture increases. As a spark plug was fitted in this RCM, the optimum spark timing was also investigated. It was established that spark timing should be set synchronize with the piston at TDC, due to the free movement of the piston. In most RCMs, piston can move toward TDC following the equilibria of forces due to the absence of con-rod. Finally, knock intensity of the different mixtures has been studied. Pre-heating system in RCM with and without trace heating system; effects of flow-rate and lambda variations on peak pressure, ignition delay time and ARR; threshold operating conditions of pure methane, 90% methane and 10% propane, 80% methane and 20% propane, 70% methane and 30% propane; effect of driving pressure on the knocking intensity for mixture of methane and propane for heavy and light knockings are presented in the article.