High-pressure burning rate measurements by direct observation

A new ultra-high-pressure optical chamber has been developed to facilitate direct observation of combustion experiments up to 300 MPa. This chamber features a relatively large 12 L volume for near-constant-pressure burning conditions. Initial experiments using this chamber are reported for the JA2 gun propellant at pressures between 14.1 and 207.7 MPa. Within this pressure range, the propellant has a well-behaved burning behavior resulting in a correlated pressure exponent of 0.91. Results are also reported for liquid nitromethane monopropellant burning rates from 3.6 to 25.7 MPa, which show well-behaved burning behavior below 18.2 MPa with a pressure exponent of 1.15, and a transition to a much higher burning rate with a pressure exponent of 5.87 between 20.6 and 25.7 MPa. This change in burning behavior results from passage to supercritical combustion of the propellant producing hydrodynamic instability from loss of surface tension.