This　study　investigates　the　characteristics　of　gaseous　ammonia　jets　under　an　injection　pressure　of　0.8　MPa　and　an　ambient　pressure　of　0.1　MPa,　using　LES　and　RANS　simulation　approaches　to　inform　applications　of　ammonia　in　internal　combustion　engines.　A　three-dimensional　constant　volume　chamber　model　was　established,　and　the　Dynamic　Structure　model　was　applied　in　LES　modeling　with　AMR　techniques.　The　near-nozzle　transient　structures　were　successfully　captured.　Furthermore,　a　direct　comparison　between　LES　and　RANS　simulation　was　made,　and　main　jet　characteristics　were　investigated.　LES　outperforms　RANS　in　predicting　the　instantaneous　structures　of　ammonia　jets　and　provides　a　more　distinct　visualization　of　oblique　shock　waves　and　diamond-like　shock　cells.　RANS　excels　at　displaying　averaged　features　with　a　smoother　distribution　curve　that　represents　selfsimilar　characteristics.　Additionally,　the　transient　characteristics　of　ammonia　and　hydrogen　jets　were　compared.　The　vortex　formation　and　mixing　process　in　ammonia　jets　occur　at　a　much　slower　rate　compared　to　hydrogen　jets.　Meanwhile,　transient　vortex　ring　behaviors　were　analyzed　in　detail,　including　their　development　tendencies　regarding　initial,　secondary,　and　broken　vortex　formation.　It　is　revealed　that　petal-like　swirling　movements　are　strongly　correlated　with　the　air-fuel　mixing　process.