FLAME STRUCTURE AND BURNING SPEED OF JP-10 AIR MIXTURES

Abstract

ABSTRACT The burning speed and flame structure of Jet Propellant (JP)-10 fuel-air mixtures have been studied using two similar constant volumes: a cylindrical vessel with end windows and a spherical chamber. Both vessels are equipped with a central ignition, pressure transducer for measuring pressure rise during combustion process and ionization probes for monitoring flame arrival time. Both spherical and cylindrical chambers can be heated up to 500 K. The spherical vessel can withstand 425 atm pressures while the maximum allowable pressure for cylindrical chamber is 50 atm due to the two windows at end caps. A thermodynamic model has been developed to calculate burning speed using dynamic pressure rise in the spherical vessel. The model considers a central burned gas core of variable temperature surrounded by a preheat zone, an unburned gas shell with uniform temperature and a thermal boundary layer at the wall. The model also includes losses associated with thermal radiation from burned gas to the wall and heat losses to the electrodes and the wall. Measurements in the spherical chamber start when the flame radius is almost half of the chamber radius (about 3.8 cm), where ratio of flame radius to flame thickness is larger than 25, hence curvature and flame thickness effects can be neglected. Shadowgraph photographic observations were made through the end windows in the cylindrical chamber using a high-speed Charged Coupled Device (CCD) camera with variable speed of up to 8000 frames/second. Burning speeds of JP-10 air mixtures have been measured in a pressure range of 1–55 atm, temperature range of 450–700 K and equivalence ratios of 0.7–1. A correlation for burning speed as a function of temperature, pressure and equivalence ratio has been developed.