Combustion Characteristics on a Coaxial-Porous Injector

Abstract

A coaxial-porous injector concept for gas-liquid combustion is proposed as a means of improving the mixing performace of a conventional shear-coaxial injector. The coaxialporous injector discharges a gas jet in the normal direction of the center liquid core, and it is expected that the momentum transfer from the radial gas jet to the axial liquid jet occurs more efficiently than it does with a traditional shear-coaxial injector. To validate the effectiveness of this idea, the combustion performances between the coaxial-porous injector and the shear-coaxial injector were compared by conducting a hot-firing test using nitrous oxide-ethanol combinations as propellant. The momentum flux ratio at the injector tip was selected as a spraying condition index, and the characteristic velocity efficiency was considered as a combustion performance parameter. The coaxial-porous injector demonstrated higher combustion efficiency than the conventional shear-coaxial injector, especially at the lower momentum flux ratio condition. In addition, the comparison of spray images between the shear-coaxial and coaxial porous injector supported the results of the hot-firing experiment quite well. Nomenclature AR= ratio of gas to liquid injection area at the tip A cc = combustion chamber area A G = gas injection area at the injector tip A L = liquid injection area at the injector tip A t = nozzle throat area C * = characteristic velocity J tip = momentum flux ratio at the tip of injector J tip,combustion = momentum flux ratio at the tip of injector in conditions of combustion L cc = combustion chamber length L * = characteristic length G m = mass flow rate of gas L m = mass flow rate of liqud OFR = O/F ratio P cc = chamber pressure tot m= total mass flow rates R G = gas constant of oxidizer ρ G = gas density ρ L = liquid density ρ tip = gas density at the tip of injector T G = gas temperature

Effects of Wall-injection Length on Spray Core and Combustion Performance in a Coaxial Porous Injector

“…The spray from the PRS injector spread wider than the SHR injector due to the radial momentum transfer to the center liquid jet, as observed in the previous cold flow study. 8,12 Although the cold flow spray tests were conducted in an atmospheric condition, the disintegration behavior was quite similar with that of the reactive spray. The disintegration and phase change patterns could be observed more clearly by converting the shadowgraph image to the density gradient magnitude image, as shown in Fig.…”

“…8 The results revealed that the coaxial porous injector configuration showed higher c * efficiency particularly in the low O/F ratio (low momentum flux ratio) condition. Also, the cold flow spray patterns were visualized to find the reason for the difference in combustion performance of the two experimental injectors.…”

“…7 A novel coaxial porous injector concept was suggested to improve the shear coaxial injector in a different way from the coaxial swirl injector. 8 As illustrated in Fig. 1, the geometry of the coaxial porous injector is similar to that of a shear coaxial injector, except that (i) the porous (sintered metal) cylinder encloses the center liquid jet, and (ii) the gaseous jet is injected from the inner surface of the porous cylinder.…”