High-pressure　gas　direct　injection　(DI)　technology　benefits　engines　with　high　efficiency　and　clean　emissions,　and　the　gas　jet　process　causes　crucial　effects　especially　inside　an　mm-size　space.　This　study　presents　an　investigation　on　the　high-pressure　methane　jet　characteristics　from　a　single-hole　injector　by　analysing　jet　performance　parameters　including　jet　impact　force,　gas　jet　impulse,　and　jet　mass　flow　rate.　The　results　show　that　the　methane　jet　exhibited　a　two-zone　behaviour　along　the　jet　direction　in　the　spatial　dimension　induced　by　high-speed　jet　flow　from　the　nozzle:　zone　1　near　the　nozzle—the　jet　impact　force　and　jet　impulse　increased　consistently　except　for　a　fluctuation　due　to　shock　wave　effects　induced　by　the　sonic　jet　and　no　entrainment　occurs,　and　zone　II　farther　away　from　the　nozzle—the　jet　impact　force　and　jet　impulse　became　stable　when　the　shock　wave　effects　became　weak　and　the　jet　impulse　was　conserved　with　a　linear　conservation　boundary.　The　Mach　disk　height　was　exactly　the　turning　point　of　two　zones.　Moreover,　the　methane　jet　parameters,　such　as　the　methane　jet　mass　flow　rate,　jet　initial　jet　impact　force,　jet　impulse,　and　Reynolds　number　had　a　monotonous　and　linearly　increasing　correlation　with　injection　pressure.　©　2023