Direct　injection　(DI)　technology　imparts　natural　gas　(NG)　engines　with　high　thermal　efficiency　and　reduces　emissions.　Furthermore,　NG　directly　jets　into　the　pilot　flame.　The　interaction　between　the　NG　jet　flow　and　pilot　flame　has　a　significant　influence　on　the　initial　ignition　and　flame　stability.　This　study　investigates　the　effects　of　a　high-pressure　methane　jet　on　the　pilot　ignited　flame,　using　a　constant　volume　bomb　(CVB)　test　rig.　The　interval　between　the　methane　injection　and　the　ignition　determines　the　premixed　flame　and　jet　combustion.　The　high-pressure　methane　jet　flow　collides　with　acts　on　the　pilot　premixed　flame,　which　results　in　two　phenomena:　1)　Flame　quenching:　the　premixed　flame　is　blown　off　by　the　jet;　and　2)　Jet　flame:　the　methane　jet　is　ignited　by　the　premixed　flame.　In　the　jet　flame,　laminar　and　turbulent　flames　co-exist.　The　development　of　the　jet　flame　occurs　in　three　stages:　Stage　I-the　no-jet　stage,　wherein　a　laminar　flame　appears;　Stage　II-the　interaction　stage,　wherein　the　jet　interacts　with　the　premixed　flame,　which　results　in　either　flame　quenching　or　stable　jet　flame;　and　Stage　III-the　stable　stage,　wherein　the　flame　becomes　stable.　(c)　2020　Elsevier　Ltd.　All　rights　reserved.