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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 cycle-to-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.

The effects of the addition of small amounts of molecular and atomic hydrogen/oxygen on laminar burning velocity, pollutant concentrations, and adiabatic flame temperatures of premixed, laminar, freely propagating iso-octane flames are investigated using CHEMKIN kinetic simulation package and a chemical kinetic mechanism at different equivalence ratios. It is shown that hydrogen/oxygen additives increase the laminar burning velocities. Increased hydroxyl (OH) concentrations resulted in reduced carbon monoxide (CO) emissions in every stoichiometric ratios investigated. Additives also increased the adiabatic flame temperature of iso-octane/air combustion, thereby causing increased NOx concentrations for all additives at all stoichiometries.