Abstract: A method and system for more safely operating a diesel engine in a methane-rich environment, such as a mine. The method includes providing a diesel engine having an air intake, a combustion chamber, and an exhaust. Methane-rich air is introduced into the engine through the air intake and mixed with diesel fuel, which is combusted. The exhaust gases are introduced into a converter comprising a bed of silica. The converter generates highly reactive hydroxyl radicals that are attracted to the combustion temperature at the cylinders. The hydroxyl radicals form supercritical water in the cylinders, and eliminate soot formation, increases engine efficiency, and reduce top combustion temperature. The disclosed methods and systems significantly reduce pollutants and the risk of explosions within or near the diesel engine. The methods and systems also result in single phase emissions, whether or not operated in a methane-rich environment.