Abstract
Legislation will limit fleet average CO2 emissions for vehicle manufacturers in the future. A number of technologies can use hydrogen as an energy carrier, with the internal combustion engine being the most mature technology. Also hydrogen fuelled internal combustion engines have advantages of being less expensive than fuel cells, the ability to run bi-fuel, to run on different load control strategies, and to have an efficiency much higher than the gasoline engine. In the literature quite a number of papers have reported efficiencies of engines operated on hydrogen. Efficiencies are given for dedicated and non-dedicated engines, for different load control strategies, for different engine settings (compression ratio, ignition timing, air-fuel ratio, injection timing etc…). An overview of these results is given in this paper. However, the authors found no published reports of direct efficiency comparisons, i.e. measurements on the same engine, on gasoline and on hydrogen. Therefore a gasoline engine was converted to bi-fuel operation, by mounting a hydrogen fuel system and gas injectors (port fuel injection). In this paper, results are presented of the brake thermal efficiency (BTE) of this bi-fuel hydrogen/gasoline engine at several engine speeds and loads. Results on hydrogen are compared to results on gasoline. Also efficiencies are compared for the different load strategies of hydrogen: wide open throttle, lean burn and throttled stoichiometric strategies. These results confirm the efficiency results reported in the literature, that the brake thermal efficiency of a hydrogen engine exceeds that of a gasoline engine over the entire speed and load range. At low loads, important for everyday driving, the efficiency gains of hydrogen compared to gasoline are particularly high (up to 60% relatively). At high loads, NOx emissions control incurs an efficiency penalty but the BTE is still higher for hydrogen. At high loads, efficiencies will be even higher for dedicated hydrogen engines (direct injection).
Keywords: Hydrogen, Efficiency comparison, SI engine