Research is widely conducted on air-diluted and EGR-diluted combustion of natural gas that contains no sulfur and less carbon. This study focused on a relationship between the laminar burning speed of methane-diluted mixtures and their heat release rate. In order to analyze the laminar burning speed with high accuracy, we measured the temperature of in-cylinder gas using an infrared absorption method. Using the data obtained, the pressure, temperature, and dilution ratio, we constructed a formula to predict the laminar burning speed with high accuracy. It has been experimentally shown that mixtures with nearly laminar burning speed of equivalence ratio and EGR ratio combination and the same ignition timing have the similar heat release rate.
