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Effects of Supercharging, EGR and Variable Valve Timing on Power and Emissions of Hydrogen Internal Combustion Engines
Abstract:
Hydrogen-fueled internal combustion engines equipped with port fuel injection offer a cheap alternative to fuel cells and can be run in bi-fuel operation side-stepping the chicken and egg problem of availability of hydrogen fueling station versus hydrogen vehicle.
Hydrogen engines with external mixture formation have a significantly lower power output than gasoline engines. The main causes are the lower volumetric energy density of the externally formed hydrogen-air mixture and the occurrence of abnormal combustion phenomena (mainly backfire).
Two engine test benches were used to investigate different means of compensating for this power loss, while keeping oxides of nitrogen (NOx) emissions limited. A single cylinder research engine was used to study the effects of supercharging, combined with exhaust gas recirculation (EGR). Supercharging the engine results in an increase in power output. The combination with EGR permits stoichiometric operation and thus low NOx emissions because of the resulting high aftertreatment efficiency. Furthermore, the power output can be varied through the supercharging pressure and the EGR percentage, enabling throttle-less operation and thus higher engine efficiencies.
A four-cylinder production gasoline engine was converted to bi-fuel operation and was used to study the effects of continuously variable intake valve timing on power output, efficiency, emissions and the occurrence of backfire when operated on hydrogen. The engine efficiency on hydrogen is compared to gasoline operation.