This　paper　compared　the　effects　of　hydrogen　and　hydrogen　oxygen　blends　(hydroxygen)　additions　on　the　performance　of　a　gasoline　engine　at　1400　rpm　and　a　manifolds　absolute　pressure　of　61.5　kPa.　The　tests　were　carried　out　on　a　1.6　L　gasoline　engine　equipped　with　a　hydrogen　and　oxygen　injection　system.　A　hybrid　electronic　control　unit　was　applied　to　adjust　the　hydrogen　and　hydroxygen　volume　fractions　in　the　intake　increasing　from　0%　to　about　3%　and　keep　the　hydrogen-to-oxygen　mole　ratio　at　2:1　in　hydroxygen　tests.　For　each　testing　condition,　the　gasoline　flow　rate　was　adjusted　to　maintain　the　mixture　global　excess　air　ratio　at　1.00.　The　test　results　confirmed　that　engine　fuel　energy　flow　rate　was　decreased　after　hydrogen　addition　but　increased　with　hydroxygen　blending.　When　hydrogen　or　hydroxygen　volume　fraction　in　the　intake　was　lower　than　2%,　the　hydroxygen-blended　gasoline　engine　produced　a　higher　thermal　efficiency　than　the　hydrogen-blended　gasoline　engine.　Both　the　additions　of　hydrogen　and　hydroxygen　help　reduce　flame　development　and　propagation　periods　of　the　gasoline　engine.　HC　emissions　were　reduced　whereas　NOx　emissions　were　raised　with　the　increase　of　hydrogen　and　hydroxygen　addition　levels.　CO　was　slightly　increased　after　hydrogen　blending,　but　reduced　with　hydroxygen　addition.　(C)　2011　Elsevier　Ltd.　All　rights　reserved.