Knock-free　operation　of　direct-injection　(DI)　hydrogen　engines　at　stoichiometric　and　wide-opening　throttle　(WOT)　conditions　is　attractive,　but　combustion　knock　hinders　the　implementation　of　this　idea,　which　inspires　the　present　study.　In　this　work,　ammonia,　as　a　combustion　inhibitor,　is　added　to　the　DI　hydrogen　engine,　which　is　expected　to　utilize　the　low　reactivity　of　ammonia　and　the　crowding　out　of　the　intake　charge　to　suppress　knock　and　extend　speed　and　lambda　corresponding　to　knock　limits.　All　tests　are　conducted　at　WOT　conditions.　In　Part　1,　lambda　is　1.6,　and　the　speed　corresponding　to　the　knock　limit　is　elevated　from　below　1600　rpm　to　2000　rpm　by　injecting　ammonia.　In　Part　2,　the　speed　is　kept　at　1600　rpm,　and　the　realization　process　of　the　engine　shifting　from　lean　operation　to　stoichiometric　operation　reflects　the　effectiveness　of　ammonia　addition　in　suppressing　knock.　Then,　using　the　critical　knocking　state　as　a　boundary,　dynamically　adjusted　ammonia　injection　enables　the　engine　to　achieve　stoichiometric　operation　and　prominent　power　expansion　at　various　speeds.　Especially　at　3000　rpm,　the　brake　power　varies　from　below　21.0　kW　to　about　44.2　kW.　Furthermore,　the　suppression　mechanism　of　knock　by　ammonia　addition　is　revealed　by　analyzing　the　mapping　relationship　between　combustion　characteristic　parameters　and　knock.