n-Butanol　is　a　feasible　fuel　candidate　for　spark-ignition　engines.　The　current　paper　carried　out　an　experiment　to　explore　effects　of　hydrogen　addition　on　further　improving　the　performance　of　a　n-butanol　engine　under　the　part　load　and　lean　conditions.　Within　the　test,　the　engine　intake　pressure　and　speed　were　respectively　kept　at　61.5　kPa　and　1400　rpm.　The　volumetric　fractions　of　hydrogen　in　the　total　intake　gas　(hydrogen　+　air)　were　constrained　at　0　and　3%,　respectively.　Under　a　certain　hydrogen　blending　level,　the　global　excess　air　ratio　of　in-cylinder　charge　which　was　changed　from　the　stoichiometric　to　near　the　lean　burn　limit　was　adjusted　by　varying　the　n-butanol　injection　duration.　The　experimental　results　confirmed　that　the　brake　thermal　efficiency　was　heightened　and　the　lean　burn　limit　was　extended　after　the　hydrogen　addition.　Besides,　compared　with　the　pure　n-butanol　combustion,　the　hydrogen　enrichment　enables　the　engine　to　gain　dropped　ignition　delay　and　rapid　combustion　duration.　Moreover,　CO　and　HC　from　the　pure　n-butanol　engine　were　reduced　by　the　hydrogen　addition.　NOx　were　generally　reduced　when　the　excess　air　ratio　was　raised.　This　suggested　that　NOx　from　the　hydrogen-enriched　butanol　engine　could　also　be　controlled　by　lean　combustion.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.