Aiming　at　solving　the　difficulties　in　hydrogen　on-board　storage　and　carriage,　a　self-designed　system　was　designed　in　an　SI　gasoline　engine　to　recover　the　exhaust　heat　and　produce　hydrogen　by　the　ethanol　steam　reforming.　The　engine　intake　manifolds　were　specially　modified　so　that　the　produced　syngas　could　be　injected　and　mixed　with　gasoline　simultaneously.　During　the　experiment,　the　engine　was　kept　at　1800　r/min　and　a　manifolds　absolute　pressure　of　61.5　kPa.　The　combustion　and　emissions　performance　of　the　2.5%　syngas-enriched　gasoline　engine　was　compared　with　that　of　the　original　engine　under　various　excess　air　ratios.　The　experimental　results　demonstrated　that　the　enhancement　of　excess　air　ratio　could　improve　the　hydrogen　volume　fraction　whereas　reduce　the　CO　concentration　in　the　syngas.　The　blending　of　syngas　was　beneficial　for　accelerating　the　flame　development　and　propagation,　elevating　the　indicated　thermal　efficiency　and　reducing　the　HC　emissions.　Meanwhile,　the　CO　and　NOx　emissions　were　slightly　increased　after　the　syngas　addition.