Study On Numerical Simulation For Ignition And Combustion Of Boron Particles Under The Swirl Flow

Boron, with its great advantages in terms of gravimetric calorific value and volumetric calorific value, is an ideal metal additive for Solid Ducted Rocket. It has caused a wide range of research about the ignition and combustion process of boron particle. Due to the fact that the particle stay for a short time in the secondary combustor of Solid Ducted Rocket and is covered by oxide film, which inhibit the combustion of the particles. The swirl flow technology is introduced to improve the residence and the mixing effect of the particles.The new ignition model of boron particle is established by the microcharacteristic of the oxide film under the ambient temperature is 773 K, based on the ignition model of Kuo’s and Ao’s, considering the species at the outside of the film and the reaction in the flame. In the combustion process, surface reaction is adopted when particle is lower than its sublimation temperature(2820K). The two-film model can’t be started unless particle is in larger diameter or in higher temperature. When the particle temperature is higher than its sublimation temperature, the model is combined with surface reaction and droplet combustion. Boiling fraction is accepted to consider the boiling phenomenon when particle reaches its boiling temperature. Based upon the new ignition and combustion of single boron particle, the ignition and combustion model of boron particles under swirl flow is established by using the phenomenon of aerodynamic stripping and the theory of forced convention combustion. The ignition and combustion time which is predicted by this model is in good agreement with previous experimental data.This model has fully considered every situation which will happen during the process of combustion. By numerical stimulation, the result is in agreement with experimental result.The numerical simulation of two-phase flow in the boron-based propellant Solid Ducted Rocket with swirl flow is carried out by the Realizable k?? turbulence model,one-step eddy-dissipation combustion model and the ignition and combustion model of boron particles, which is newly built. The ignition and combustion of boron particles and the combustion efficiency of gas combustion in secondary combustor of Solid Ducted Rocket with four different swirl angles and different pressure, temperature and particle diameter. Finally, the paper comes to conclusions that:1. The total combustion efficiency under swirl flow is higher than no swirl, with the increasing of swirl intensity, the ignition distance of boron particles get shorter.2. Under the situation of co-swirl, with the increasing of swirl angle, the combustion efficiency of gas first decrease then increase. For boron particles, it has the opposite trend to gas. The total combustion efficiency will reach its the highest value when the swirl angle is in the range between 30 degree to 45 degree. The diffusion of particles will improve when increasing the swirl angle.3. Under the situation of counter-swirl, both the combustion efficiency of gas and particle will first increase then decrease with the increasing of the swirl angle. The highest of total combustion will appear when the swirl angle is near 15 degree.However, its highest value is lower than co-swirl. With the increasing of swirl angle,some particles are affected by gas flow and won’t diffuse.4. With the increasing of particle diameter, the combustion efficiency of gas will improve, the combustion efficiency of particle will be first increase then decrease and the particle ignition path will be longer. When the particle diameter is about 8μm, the total combustion efficiency will be best.5. With increasing the air temperature, the combustion efficiency of particle will be improved obviously, while the combustion efficiency of gas will be slightly decreased. But it will have little impact on the ignition path of boron particle.6. Particle diffusion will be decreased under higher ambient pressure in the front of the secondary combustor. With the increasing of ambient pressure, the particle combustion efficiency will be increased, while the combustion efficiency of gas will be be first decrease then increase.