A hydrogen engine-fuel system is being developed as an alternative for powering underground mining machinery. A diesel was converted to a spark-ignited hydrogen engine and operated with a metal hydride, solid-state hydrogen storage system.Performance and emissions data show that hydrogen can be used as an ultralow emission fuel for underground mining. A special method of fuel control has overcome abnormal combustion problems frequently experienced with hydrogen fuel. The turbocharged, after-cooled engine maintains NOX emissions (the only significant pollutant) below 0.7 gram per kilowatt-hour. Power and fuel consumption are comparable to the naturally aspirated, prechambered diesel version of the engine.Hydrogen fuel is released from a metal hydride storage container by heat from the engine coolant. Through proper design, hydride containment can limit the leakage of hydrogen, in a worst-case accident, to acceptable levels.