Boron based gelled fuels are promising candidates for certain future ramjet applications, offering potential improvements in performance and/or safety over conventional liquid and solid systems. For this purpose, a fundamental understanding of combustion of gel droplets is required and several problems of ignition and agglomeration of boron particles have to be solved.
This study addresses the combustion behavior of micro-pyrotechnic clusters of boron suspended in kerosene based gel fuels. The pyrotechnic clusters should ignite in the temperature range between the end of the kerosene evaporation and the liquefaction of boron oxide. This temperature range defines a “dry window” where the boron particles are not submerged in any liquid and their dispersion is not limited by the liquid viscosity and surface tension. Operation within this time frame allows the pyrotechnic reaction to heat up and disperse the boron particles.
The research combines both experimental and theoretical investigations on gel combustion. In the experimental part, pyrotechnic clusters with different oxidizers were tested in order to identify and understand the various ignition and combustion phenomena of gel fuels. In addition to the combustion tests of gel droplets, calorimetric tests of the pyrotechnic mixture were conducted. The theoretical part aims to determine the temperature and pressure profiles inside the burning gel droplet. This allows determining the existence of temperature gradients inside the droplet that produce a “dry window” during the droplet combustion. The existence of a pressure gradient over the droplet outer layer may explain various phenomena, such as secondary atomization, that can break up the droplet into smaller parts and improve combustion efficiency.
