In　this　paper,　the　flame　evolution　and　pressure　dynamics　of　hydrogen-nitrogen-air　explosions　with　nitrogen　addition　ratio　(χ)　ranging　from　0　to　40　%,　ignited　at　three　different　positions　(“central”,　“back”　or　“front”　with　respect　to　the　vent)　in　a　vented　cylindrical　vessel,　were　experimentally　studied.　Experimental　results　reveal　that　the　coupling　effects　of　χ　and　ignition　position　significantly　affect　the　pressure　curves　and　flame　behavior　within　and　outside　the　vessel.　The　higher　the　χ,　the　smoother　the　internal　flame　captured　by　a　high-speed　schlieren　system.　When　χ＜30　%,　the　maximum　reduced　overpressure　(Pmax)　at　different　ignitions　decreases　with　increasing　χ,　and　the　central　explosion　yields　the　best　suppression　of　Pmax:　when　χ　is　increased　from　0　to　30　%,　Pmax　monotonically　decreases　from　232　kPa　to　38　kPa.　However,　the　differences　in　Pmax　among　the　three　ignition　positions　become　negligible　when　χ　≥　30　%.　The　structure　of　the　pressure　peaks　and　the　types　of　oscillations　measured　near　the　vent　depend　on　the　combinations　of　ignition　location　and　χ.　The　formation　of　a　shock　wave　generated　by　the　external　explosion　and　its　effect　on　the　internal　pressure-time　histories　are　described.　In　general,　for　a　given　ignition,　the　maximum　external　overpressure　(Pe-max)　decreases　with　χ　is　increased.　The　most　pronounced　decreasing　trend　of　Pe-max　is　consistently　observed　in　back　explosions　when　χ　ranging　from　0　to　40　%.　Furthermore,　compared　to　other　ignition　positions,　the　highest　Pmax　is　always　attained　in　central-ignition　with　χ＜30　%;　while　the　highest　Pe-max　is　always　attained　in　back-ignition　with　χ　≤　30　%;　as　χ　≥　10　%,　both　Pmax　and　Pe-max　recorded　at　front-ignitions　are　almost　insensitive　to　χ.　©　2023　Hydrogen　Energy　Publications　LLC