There　are　few　investigations　on　the　knock　characteristics　of　direct-injection　(DI)　hydrogen　engines,　so　to　reveal　the　influencing　mechanism　of　synergistic　effects　of　the　deep　Miller　cycle　and　oxygen-enriched　atmosphere　on　the　DI　hydrogen　engine＇s　knock　characteristics,　an　experimental　study　was　carried　out　at　1600　rpm　and　wide-open　throttle　conditions.　Overall,　the　Miller　effect　provides　good　suppression　of　combustion　knock　even　at　high　oxygen　concentration　(φO2),　while　the　oxygen-enriched　atmosphere　can　mitigate　the　negative　effects　of　the　deep　Miller　cycle　on　the　combustion　process.　The　results　demonstrated　that　the　Miller　cycle　mitigates　the　excitation　effect　of　elevated　φO2　and　reduced　λ　on　combustion　knock.　For　example,　even　if　φO2　was　raised　to　27.1　%,　the　knock　intensity　(KI)　is　only　close　to　1.0　bar　at　1.6　λ.　It　was　found　that　the　deep　Miller　cycle　achieved　by　regulating　the　intake　valve　timing　to　the　engine　could　further　suppress　the　combustion　knock,　which　may　be　related　to　the　reduced　effective　compression　ratio　and　volumetric　efficiency.　Specifically,　under　the　deep　Miller　effect,　KI　did　not　exceed　0.8　bar　even　when　φO2　was　elevated　to　32.0　%,　indicating　that　knock　was　effectively　suppressed,　although　about　190　cycles　corresponding　to　knock　durations　exceeding　10°CA.　©　2024　Elsevier　Ltd