CO2　(Carbon　dioxide)　dilution　is　a　feasible　way　for　controlling　NOx　(Nitrogen　oxides)　emissions　and　loads　of　the　internal　combustion　engines.　This　paper　investigated　the　effect　of　CO2　dilution　on　the　combustion　and　emissions　characteristics　of　a　hydrogen-enriched　gasoline　engine.　The　experiment　was　conducted　on　a　1.6　L　spark-ignition　engine　with　electronically　controlled　hydrogen　and　gasoline　injection　systems.　At　two　hydrogen　volume　fractions　of　0　and　3%,　the　CO2　volume　fraction　in　the　intake　was　gradually　increased　from　0　to　4%.　The　fuel-air　mixtures　were　kept　at　the　stoichiometric.　The　experimental　results　demonstrated　that　brake　mean　effective　pressure　of　the　gasoline　engine　was　quickly　reduced　after　adopting　CO2　dilution.　Comparatively,　Bmep　(Brake　mean　effective　pressure)　of　the　3%　hydrogen　enriched　engine　was　gently　decreased　with　the　increase　of　CO2　dilution　level.　Thermal　efficiency　of　the　3%　hydrogen-enriched　gasoline　engine　was　raised　under　properly　increased　CO2　dilution　levels.　However,　thermal　efficiency　of　the　pure　gasoline　engine　was　generally　dropped　after　the　CO2　dilution.　The　addition　of　hydrogen　could　shorten　flame　development　and　propagation　durations　under　CO2　diluent　conditions　for　the　gasoline　engine.　Increasing　CO2　fraction　in　the　intake　caused　the　dropped　NOx　and　raised　HC　(Hydrocarbon)　emissions.　Increasing　hydrogen　fraction　in　the　intake　could　effectively　reduce　HC　emissions　under　CO2　diluent　conditions.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.