| The combustion characteristics of bipropellants, including liquid fuel and liquid oxidizer, are studied on scales of droplet separation distance and droplet clouds analytically to provide the bases of bipropellant combustion modeling in the full-scale computer simulation of a liquid rocket engine. Three combustion modes such as normal combustion, conjugate combustion and composite combustion, are identified in the study of a bipropellant doublet system. It is found that the interaction between bipropellants enhances the burning rates of droplets. This result shows a positive impact of bipropellants on the spray combustion in contrast to the reduction of burning rates in single propellant group combustion.;A comprehensive computer simulation code is developed to analyze the sophisticated bipropellant combustion in liquid rocket engines. A bipropellant group combustion model is built in the computer code to facilitate the determination of various combustion modes, including conjugate and normal droplet combustion and gas phase combustion. Physical submodels of the finite transport rates between droplet phase and gas phase are also adopted to account for the interactions between the two phases. An axisymmetric cylindrical liquid rocket combustion chamber installed with two annular ring injectors is selected to demonstrate the capabilities of the present computer simulation code. Two types of injection process are analyzed; one is characterized by a nonpremixed spray process and the other is a premixed spray process. Selected numerical computations are conducted to illustrate the detailed combustion structure, combustion intensity and combustion modes. The sensitivity study of fuel and oxidizer group combustion numbers shows that combustion efficiency is determined by the competing process of normal combustion, conjugate combustion and gas phase combustion. Therefore, the optimal atomization, though not necessarily as fine as possible, can be predicted under various operating conditions. |
