Sandia National Laboratory is developing from first principles a hydrogen fuelled internal combustion engine for driving an electrical generator that can be utilized either as a stationary power set or the auxiliary power unit in a hybrid vehicle. The intent is to take advantage of hydrogen＇s unique fuel characteristics and the constant speed characteristics of generator sets to maximize thermal efficiency while minimizing emissions. The current experiments utilize a flat cylinder combustion chamber shape with two ignition points at high (14: 1) compression ratio. Emissions and indicated thermal efficiency measurements with fuels of hydrogen, natural gas and a blend confirm low emissions and high thermal efficiency. CFD modelling done by Los Alamos National Laboratory (Los Alamos, NM) using their KIVA code is helping to further direct variations in the experimental design space.