Effect of injection distribution on combustion stability.
Theoretical and experimental studies of injection distribution effects are described. The theoretical treatment consists of a small perturbation analysis based on Crocco's sensitive combustion time lag concept as extended by Reardon. The transverse distribution of the burning rate perturbation is identified with the ratio of the local injection density (weight flow per unit injector face area) to the average injection density for the entire injector. For pressuresensitive combustion, the theory shows that tangential modes are stabilized by decreasing the injection density at the outer periphery of the injector. Adding to the injection at the center tends to destabilize the radial modes. Similar results are obtained for tangential velocity (displacement) effects in spinning modes. The theory also shows that linear tangential velocity effects are inoperative in standing modes and that radial velocity effects are of secondary importance. Experimental data obtained at Purdue and Princeton Universities are shown to agree well with the theoretical results. Recent experience gained from the Gemini Stability Improvement Program is also presented to show, in agreement with the theory, the effectiveness of injection distribution control.