Improving the performance of a gasoline engine with the addition of hydrogen–oxygen mixtures

The limited fossil fuel reserves and severe environmental pollution have pushed studies on improving the engine performance. This paper investigated the effect of hydrogen–oxygen blends (hydroxygen) addition on the performance of a spark-ignited (SI) gasoline engine. The test was performed on a modified SI engine equipped with a hydrogen and oxygen injection system. A hybrid electronic control unit was adopted to govern the opening and closing of hydrogen, oxygen and gasoline injectors. The standard hydroxygen with a fixed hydrogen-to-oxygen mole fraction of 2:1 was applied in the experiments. Three standard hydroxygen volume fractions in the total intake gas of 0%, 2% and 4% were adopted. For a given hydroxygen blending level, the gasoline injection duration was adjusted to enable the excess air ratio of the fuel-air mixtures to increase from 1.00 to the engine lean burn limit. Besides, to compare the effects of hydroxygen and hydrogen additions on the performance of a gasoline engine, a hydrogen-enriched gasoline engine was also run at the same testing conditions. The test results showed that the hydroxygen-blended gasoline engine produced higher thermal efficiency and brake mean effective pressure than both of the original and hydrogen-blended gasoline engines at lean conditions. The engine cyclic variation was eased and the engine lean burn limit was extended after the standard hydroxygen addition. The standard hydroxygen enrichment contributed to the decreased HC and CO emissions. CO from the standard hydroxygen-enriched gasoline engine is also lower than that from the hydrogen-enriched gasoline engine. But NOx emissions were increased after the hydroxygen addition.