A cold-flow experimental observation of the two-stage impinging type injector for rocket propulsion

Green (low toxicity) liquid rocket propellants have become attractive in recent years due to the features of the low cost and less environmental impact. However, the green propellants, such as kerosene/H2O2, usually have different operational conditions (i.e. relatively high O/F ratio) compared to conventional propellants because of their chemical properties. In this research, a new concept of the two-stage impinging type injector (O-F-F-O) is adopted for investigating the spray mixing at high O/F ratios between 3.75 and 6.25. The impinging distance, jet velocity and impinging angle for the two-stage impinging type injector are design parameters examined, where the impinging angle is more effective at spray atomization and droplet distribution. The PLIF technique is used to measure the droplet distribution so as to identify the spray characteristics. In order to simplify the development process of the injector, the predicted mixture ratio distribution from the individual fuel (F-F) and oxidizer (O-O) sprays by overlapping their averaged images is used to compare with the actual distribution from the two-stage impinging spray (O-F-F-O). At a constant total mass flow rate, results indicate that tendencies towards the variations of the average characteristic velocity (C*) with increasing O/F ratios are similar for outcomes of the prediction and actual measurement. Also, there is obvious flow fields interaction between the fuel and oxidizer sprays and coordinating their relative intensities of sprays well can optimize the mixture ratio distribution of the two-stage impinging spray. Better mixing occurs when the fuel and oxidizer sprays have more similar and uniform distributions.