The interest in natural gas engines as an alternative to diesel engines has intensified as crude oil prices have risen and global environmental regulations have become more stringent. Natural gas engines can improve thermal efficiency through lean combustion, owing to combustion of a wide range of fuels; meanwhile, the low carbon content of the fuel reduces CO2 emissions, which is crucial in reducing greenhouse gas emissions. Natural gas engines also exhibit excellent fuel economy and low fuel costs. Unlike crude oil, natural gas is widely distributed worldwide and offers an advantage in terms of supply and demand. As a result, the demand for gas engines is increasing rapidly. Therefore, many marine engine manufacturers have developed micropilot-type gas engines that inject diesel fuel only for ignition.