Experimental Techniques to Study the Effects of Nano-Scale Additives on the Burning Rates of Liquid Monopropellants

Abstract

This paper presents the development of equipment and methods used to investigate the combustion behavior of liquid monopropellants with or without additives, with a focus on the authors’ recent work in nano-scale particles as burning rate modifiers in nitromethane. Nano-scale aluminum (100 nm diameter) was used to increase the overall energy of the mixture, while fumed silica powder (0.2 to 0.3 μm aggregate) was used to increase mixture thickness and encourage aluminum suspension. The effects of both added particles on the mixture burning rate were tested at chamber pressures ranging from 3 to 13 MPa, using a technique that functioned without direct observation of the burning front progression. A sensitivity analysis of this new method was performed by varying parameters such as the initial propellant mass and oxygen concentration of the pressurizing gas, proving that this technique is robust enough to remain unaffected by all input variations except the tube wall material. The measured burning rate of neat nitromethane changed significantly between carbon steel and fused quartz walls, but not in similar tests performed on nitromethane mixed with aluminum and silica powders. The close match between the burning rates of neat nitromethane gathered in this study and those taken from other groups proves the utility of this new method, while the consistently measured burning rates of the aluminum and silica mixture prove the versatility of this method when extended to test suspended-particle mixtures.