This paper presents methods used to investigate the combustion behavior of liquid monopropellants with or without additives, with a focus on nanoscale particles as burning rate modifiers in nitromethane. The combined effects of nanoscale aluminum and fumed silica on the burning rate were tested at pressures ranging from 3 to 13 MPa, using a pressure-based technique. Distinct differences in burning rate were observed between burns using a quartz-lined cavity and those employing steel. An analytical model was used to estimate the temperature profiles of quartz, steel, and layered strand burner tubes, indicating that the higher burning rates measured in the steel cavity were likely caused by a combination of heat transfer and catalytic effects. A mixture of 1% silica, 5% aluminum, and 94% nitromethane by weight produced burning rates that were 60–70% higher than those of neat nitromethane across the range of pressures. The close match between the burning rates of neat nitromethane gathered in this study and those taken from other researchers proves the utility of the pressure-based method, whereas the consistently measured burning rates of the aluminum and silica mixture prove the versatility of the method when extended to tests on suspended-particle mixtures.