Investigating combustion enhancement and emissions reduction with the addition of 2H2 + O2 to a SI engine

Document Type

Conference Proceeding

Publication Date


Publication Title

SAE Technical Papers


This research involved studying the effects of adding small amounts of hydrogen or hydrogen and oxygen to a gasoline fuelled spark ignition (SI) engine at part load. The hydrogen and oxygen were added in a ratio of 2:1, mimicking the addition of water electrolysis products. It was found that the effects of hydrogen addition (∼ 2.8% of the fuel by mass, ∼ 60% by volume) decreased as the fuel/air equivalence ratio approached φ = 1. When operating at φ < 0.8, the torque, indicated mean effective pressure (imep) and NO emissions increased and cycleto-cycle variation decreased with hydrogen addition. The improvements in engine performance and increase in NO emissions were related to a faster burn rate shown by a decrease in burn duration with the addition of hydrogen. Further, the addition of hydrogen only and hydrogen and oxygen in a ratio of 2:1 were compared. The extra oxygen had little effect on engine performance other than an increase in NO exhaust concentration ∼ 500 ppm. Under the conditions tested, the power necessary to generate the hydrogen on board through electrolysis was greater than what was gained from the engine.