Abstract: This paper experimentally investigates the emission performance of a hydrogen-enriched gasoline engine.The experiment is carried out on a spark-ignited gasoline engine equipped with a hydrogen port injection system at a constant engine speed of 1 400 r/min.Test results show that properly increasing excess air ratio is beneficial for reducing the engine HC,CO,and NOx emissions.CO emission increases with the hydrogen volume fraction in the intake at stoichiometric conditions.However,at lean conditions,the addition of hydrogen is effective in decreasing CO and HC emissions.HC and NO_x emissions are reduced with decreasing spark advance.With the increase of the intake manifolds absolute pressure,HC and CO emissions are reduced.