Enhanced performance of a constant rate of momentum change (CRMC) ejector: experimental investigation

• Experimental investigation of a constant rate of momentum change (CRMC) ejector using air. • Optimal primary pressure of 225 kPa achieved peak entrainment up to 1.22 at 5 kPa secondary pressure. • Nozzle exit position of 30–50 mm maximized mixing and improved ejector performance. • Three flow regimes observed: choked, unchoked, and reversed, influenced by secondary pressure. • Gas dynamic model closely matched experiments at optimal conditions but underestimated elsewhere. Ejector performance is often limited by shock-induced losses and inefficient momentum transfer in the mixing and diffusion sections. To address these limitations, this study experimentally investigates a Constant Rate of Momentum Change (CRMC) ejector designed to promote gradual momentum diffusion and improved pressure recovery. An open-system CRMC ejector was designed and tested using air as the working fluid under primary pressures of 200–270 kPa and secondary pressures of 0.9–5 kPa. The influence of primary nozzle exit position (NXP) was examined over a range of 0–60 mm to assess its effect on entrainment behavior. Experimental results reveal three operating regimes—choked, unchoked, and reversed flow. Maximum secondary mass flow occurred at a primary pressure of approximately 225 kPa, while the highest entrainment ratios were observed within an optimal NXP range of 30–50 mm. Under choked secondary flow conditions, entrainment ratios reached 0.38 at a secondary pressure of 1.6 kPa and increased to 1.19 at 5 kPa. Beyond the optimal primary pressure, performance declined due to over-expanded primary jets, shock formation, and flow separation. Wall static pressure measurements demonstrated gradual pressure recovery along the CRMC duct, indicating improved momentum transfer compared to conventional ejectors, although complete shock suppression was not observed. Comparisons with an established gas-dynamic model showed that the model generally overestimates entrainment performance but closely matches experimental results near the optimal condition at 225 kPa. Overall, the results indicate that CRMC ejectors provide improved entrainment and pressure recovery when properly optimized, though performance remains influenced by shock formation and mixing efficiency. .