Dark Zones of Solid Propellant Flames: Critical Assessment and Quantitative Modeling of Experimental Datasets With Analysis of Chemical Pathways and Sensitivities

Abstract : The formation of propellant dark zone (DZ) structures in the gaseous flames above many solid propellants has been a subject of recurrent interest at ARL for about 20 years. The DZ structure is controlled by small molecule chemistry. The DZ chemistry is very important in controlling both the flame structure at low pressure (10?100 atm) and burning rates at high pressure (above ~500 atm), even though DZs collapse at higher pressures. We have developed a detailed mechanism to model it, which has been updated many times. For many years, we have promised to provide an extensive review on the subject. This report fulfills that promise, reviews prior work as well as introduces our most recent modeling results, and documents the first quantitative tests of several key assumptions. All relevant experimental literature is critically assessed to identify datasets for testing our model. Comparison of predictions and experimental results shows reasonable agreement; thus, we advocate use of our mechanism. However, the precision of both experiments and predictions is not tight, nor are there many test datasets. Thus, further experimentation is needed, and possibilities that would be of greatest help are briefly discussed. A detailed discussion of the chemistry that controls the DZ structure is presented.