Combustion, Emissions, and Performance Studied in Dual-Fuel Engine Tests: From the standpoint of production costs, converting a conventional reciprocating engine is a significant advantage over developing a fuel cell. Yet technological problems such as backfire and abnormal combustion under high load are issues requiring practical solutions.On the other hand, operating a gasoline engine on both gasoline and hydrogen has been found to increase thermal efficiency. These results were obtained in an engine operating on premix gasoline and premix hydrogen. Nowadays, a direct-injection gasoline is commonly available on the market. Thus, researchers at the Japan Energy Corporation (JOMO) tested a 0.499-liter DI spark-ignition engine with a mixture of port-injected hydrogen and direct-injected iso-octane to characterize combustion, engine performance, and exhaust emissions. The chapter include 10 pages, 2 tables, and 8 figures.