Hydrogen　internal　combustion　engines　(ICE)　will　play　an　important　role　in　reducing　carbon　emissions,　but　low　power　density　and　abnormal　combustion　problems　are　the　main　obstacles　restricting　the　promotion　of　hydrogen　ICE.　Ammonia　is　a　low-reactivity　renewable　fuel.　The　purpose　of　this　study　is　to　study　the　effect　of　different　ammonia-added　volume　fractions　on　hydrogen　ICE.　In　this　experimental　study,　the　combustion　and　emission　characteristics　of　an　engine　fueled　by　a　hydrogen/ammonia　mixture　were　evaluated　at　part-load　operating　conditions.　The　experiment　was　carried　out　on　a　modified　engine,　the　engine　speed　was　1300　rpm,　the　absolute　pressure　of　the　manifold　was　61　kPa,　and　the　volume　fraction　of　ammonia　added　was　5.2%,　7.96%,　and　10.68%,　respectively.　The　test　results　show　that　the　addition　of　ammonia　changes　the　combustion　characteristics　of　hydrogen.　As　the　volume　fraction　of　ammonia　added　increases,　the　flame　development　period　and　flame　propagation　period　are　both　prolonged,　and　the　peak　heat　release　rate　decreases.　The　addition　of　ammonia　increases　the　power　of　the　engine　and　reduces　the　indicated　thermal　efficiency.　At　the　ignition　timing　of　the　maximum　braking　torque,　as　the　volume　fraction　of　ammonia　added　increases,　the　indicated　mean　effective　pressure　and　indicated　thermal　efficiency　increase.　Adding　ammonia　volume　fraction　has　little　effect　on　Nitrogen　oxides　(NOx)　emissions,　and　NOx　emissions　gradually　increase　with　the　delay　of　ignition　timing.　(c)　2022　Published　by　Elsevier　Ltd　on　behalf　of　Hydrogen　Energy　Publications　LLC.