The　paper　studied　the　effect　of　syngas　addition　on　performance　of　a　gasoline　engine　at　lean　conditions.　The　engine　ran　at　1800　rpm　and　a　manifolds　absolute　pressure　of　61.5　kPa.　The　spark　timing　for　the　maximum　brake　torque　was　adopted　for　each　testing　point.　The　syngas　volume　fraction　in　the　total　intake　gas　was　fixed　at　0%　and　2.5%.　The　test　results　showed　that　peak　cylinder　pressure　and　indicated　thermal　efficiency　were　enhanced　after　the　syngas　enrichment.　Flame　development　and　propagation　durations　of　the　2.5%　syngas-blended　engine　were　reduced　by　7.2　and　5.7　degrees　CA,　compared　with　those　of　the　original　engine　at　an　excess　air　ratio　of　1.36.　The　coefficient　of　variation　in　the　indicated　mean　effective　pressure　showed　a　noticeable　decrease　after　the　syngas　addition.　CO　and　NOx　emissions　were　slightly　increased　with　the　syngas　enrichment.　HC　emissions　were　first　reduced　and　then　increased　after　the　syngas　blending.　Copyright　(C)　2012,　Hydrogen　Energy　Publications,　LLC.　Published　by　Elsevier　Ltd.　All　rights　reserved.