In　the　view　of　low　thermal　efficiency　and　high　emissions　of　spark　ignition　(SI)　engines,　this　paper　investigated　the　effect　of　hydrogen　blending　at　intake　ports　to　a　SI　engine　on　improving　its　economic　and　emissions　performance.　The　experiment　was　carried　out　on　a　modified　4-cylinder　SI　engine　on　which　hydrogen　could　be　injected　into　the　intake　ports　sequentially　via　an　ECU　based　control　system　and　mixed　with　gasoline　on-line.　The　combustion　and　emissions　characteristics　of　a　hydrogen-blended　IC　engine　were　investigated　under　the　conditions　of　1500　rpm　and　the　stoichiometric　equivalence　ratio　with　four　different　hydrogen　volumetric　fractions　of　1%,　1.5%,　2%,　and　3%.　The　test　results　demonstrated　that　the　average　brake　thermal　efficiency　increased　from　25.12　to　28.35%　and　the　average　coefficient　of　variation　in　peak　in-cylinder　pressure　decreased　from　6.8%　to　3.62%　when　hydrogen　fraction　changed　from　0%　to　3%.　Ignition　delay　and　the　rapid　burning　duration　were　shortened;　the　peak　in-cylinder　pressure　was　increased;　CO2　and　HC　emissions　were　obviously　lower　with　the　increasing　fraction　of　hydrogen　in　the　intake.　However,　NOx　and　CO　emissions　were　also　increased.　In　a　word,　the　addition　of　hydrogen　to　a　gasoline-fuelled　IC　engine　is　a　good　way　to　improve　engine　performance.　Copyright　©　2009　SAE　International.