In　this　paper,　the　effects　of　excess　air　ratios　(lambda)　on　nitric　oxide　(NOx)　emissions　of　a　hydrogen-fueled　spark　ignition　engine　in　the　cold　start　period　are　studied.　Cold　start　characteristics　of　hydrogen-fueled　engine　were　investigated　experimentally.　The　study　was　performed　under　different　lambda.　The　experimental　results　showed　that,　when　lambda　declined　from　1.6　to　0.7,　the　peak　engine　speed　within　the　first　6　s　increased　and　in-cylinder　pressure　in　the　first　cycle　raised　firstly　then　decreased　slightly　while　the　flame　development　and　propagation　periods　shortened,　and　the　exhaust　temperature　at　the　6th　s　raised　from　329　K　to　355　K.　In　addition,　NOx　emissions　obviously　decreased,　whereas　hydrocarbon　(HC)　and　carbon　monoxide　(CO)　emissions　caused　by　the　evaporated　lubricant　oil　increased　by　decreasing　lambda　within　the　first　6　s.　(C)　2018　Published　by　Elsevier　Ltd　on　behalf　of　Hydrogen　Energy　Publications　LLC.