A combustion engine of a given displacement will develop less power when running on hydrogen compared to gasoline or natural gas operation due to less heating value of the fuel air mixture in the combustion chamber. This drop in output exists for external mixing of hydrogen and air prior to intake valve closure. However, external mixing does not require intricate engine modification. Without substantial investment, supercharging is an effective method to increase the output of a hydrogen engine which uses the simple technique of external mixing of hydrogen and air.
AVL stationary type research engine was used to investigate the percentage gain in output and thermal efficiency, knock limited combustion air ratios, NO emission and combustion characteristics at different supercharging pressures. The performance of the supercharged hydrogen engine is also compared with that of naturally aspirated hydrogen engine.
Results indicate that compared to naturally aspirated hydrogen engine the output increases as much as 233 % and the percentage increase in indicated thermal efficiency is 29 % at a combustion air ratio of 2.0 and speed of 1200 rpm. By supercharging the hydrogen engine, NO emission increases and knock limit sets in at combustion air ratio leaner than that of naturally aspirated engine. Reduced spark plug gap and better insulation of ignition system are necessary to avoid the ignition failure at supercharged condition of hydrogen engine.