ABSTRACT This research paper deals with the starting vortex of detonation combustion wave flow field in pulse detonation combustor (PDC). In order to achieve the potential pressure gain from PDC the shrouded ejectors are placed at exit section of detonation tube. Therefore, influence of shrouded ejector position plays a great role on leading vortex and reduction of NOx formation. Furthermore, n-butane (C4H10) and hydrogen (H2) fuel are used for stoichiometric (= 1) fuel-air mixture condition to simulate the thermal and prompt NOx formation at pulse time of 0.022s to 0.030s. The LES turbulence model is used to simulate the unsteady flow field in CFD based fluent platform. The one step irreversible chemical kinetics model analyzed the details of exothermic chemical reaction mechanism inside the combustor. The non-dimensional value of /d = 1.5 geometry position of shrouded ejector is better for leading vortex. So far, pickup detonation wave speed of 2306 ms−1 is obtained at shortest pulse time of 0.028s and this magnitude is higher than C-J velocity. The minimum pollutant number of 0.0000341 is obtained from hydrogen-air detonation, this magnitude is lesser compared to n-butane (C4H10)-air combustion. Furthermore, the maximum combustion efficiency of 85% is obtained from hydrogen-air mixture in detonation combustion process, which is comparatively higher than deflagration combustion process.