This　paper　aims　to　numerically　investigate　the　effects　of　high　compression　ratio　(CR)　on　the　performance　of　ammonia-hydrogen　engines.　In　this　work,　four　CRs　from　10.7　to　13.7　with　scanning　spark　timing　(ST)　from　28°CA　to　0°CA　BTDC　were　analyzed.　The　main　results　are　as　follows:　As　the　CR　increases,　there　is　a　trade-off　relationship　between　the　dissipation　rate　of　turbulence　and　the　turbulent　kinetic　energy　(TKE).　Initially,　the　TKE　rises　as　the　CR　increases.　As　the　CR　continues　to　rise,　the　tendency　for　an　increase　in　TKE　diminishes,　while　the　turbulent　dissipation　rate　consistently　rises.　Additionally,　there　is　an　escalation　in　heat　transfer　loss.　Therefore,　there　is　a　trend　of　rising　and　then　falling　in　the　flow　velocity　and　turbulence　intensity　with　the　increase　of　the　CR.　Ammonia-hydrogen　flame　propagation　is　susceptible　to　temperature　and　flow　field,　and　a　high　CR　can　improve　ignition　stability,　shorten　combustion　duration,　minimize　cooling　loss,　and　enhance　output　power.　Unfortunately,　the　emission　of　NOx　gradually　rises　as　the　CR　increases.　At　high　CR,　the　combustion　performance　is　optimized　by　adjusting　ST,　and　the　maximum　IMEP　and　ITE　are　4　bar　and　38.3　%,　respectively.　The　ST　for　maximum　braking　torque　(MBT)　should　be　gradually　delayed　toward　TDC　as　the　CR　increases.　©　2023