The effect of the throat width of plug nozzles on the combustion mode in rotating detonation engines

Rotating detonation engines have been studied due to their better theoretical propulsion performance than that of deflagration-based engines. In this experimental study, the Laval nozzle throat width was varied to study combustion features in rotating detonation engines with different air flow rates and equivalence ratios. The detonation channel had an outer diameter of 100 mm and an inner diameter of 80 mm. Air and hydrogen were injected into the combustor from 60 cylindrical orifices each of 2 mm in diameter and a circular channel with a width of 1 mm, respectively. Four different widths of the plug nozzle were used: 2, 4, 6, and 8 mm. Three dynamic pressure sensors were used to obtain the detonation pressure. A standard speed camera was used to observe the exhaust from the combustion process. The results show that rotating detonation never occurred for a throat width of 4 mm. Rotating detonation waves with high speeds above 2300 m/s were obtained for a throat width of 2 mm. The mode of combustion in the engine was highly dependent on equivalence ratio and throat width. Probabilities of occurrences of longitudinal pulsed detonation increased first and then decreased with the decreased throat width.