Kenichi Takahashi

Characteristics of aluminum agglomeration at burning surface in AP/AN composite propellants

Aluminum(Al) particles are used composite propellants of a solid rocket for improving performance and combustion stability. However, aluminum particles have a tendency to agglomerate at the burning surface of composite propellants. It is well known that these agglomerated Al particles cause low combustion efficiency. Therefore, it is necessary to study the agglomerate characteristics of Al particles at the burning surface of composite propellants. This study discussed about where the agglomerated diameter is determined and the effect of the burning rate to Al particle diameter distribution. The results were verified by obtaining the Al particle diameter distribution at the burning surface, in the reaction zone and the luminous zone. We clarified that the agglomerate diameter is determined in the reaction zone and it decreases with increasing of the burning rate.

Mass Transfer in the Recirculation Zone of Ducted Rocket

Ramjet induced compressed air to a secondary combustor and mixed with fuel. High thrust was needed to overcome air drug, therefore the diameter of nozzle throat must be large. The flow speed in the secondary combustor was higher than 200 m/s. The residue time in the secondary combustor was shorter than 10 ms, and the mixture gas burned at very short time. To increase combustion efficiency, the reaction rates of metal particles and mixture gas should be high, however mean temperature of mixture gas was 700 K and was impossible to ignite at short time. Local temperature of mixture gas in recirculation zone of the secondary combustor was an important factor to increase reaction rate of mixture gas. The surrounding gas temperature of solid particles in the recirculation zone was higher than mean temperature, and this was possible to become the ignition point. The combustion efficiency of the connected-pipe ducted rocket with the solid particles over 20 parts was larger than that without solid particles.

Agglomeration characteristics of aluminum particles with changing pressure in AP/AN composite propellants

For aluminized AP/AN composite propellant, the relation between the agglomerate diameter and pressure was investigated by observing aluminum particle agglomeration in the reaction zone near the burning surface with changing pressure. When the burning rate increased with increasing pressure in aluminized AP/AN composite propellant, the agglomerate diameter decreased with increasing burning rate. We assumed the agglomerate range as the area of the distributed aluminum particles before agglomeration around the burning surface. When the pressure increased, the burning rate increased. Then the agglomerate range decreased. The agglomerate range changes with the burning rate and varies with the temperature profile in the reaction zone. The agglomerate diameter depends on the burning rate and the agglomerate range with changing pressure.

Effects of the Distance of High Temperature Metal Particles in a Secondary Combustor of Ducted Rockets

A ducted rocket engine induced compressed air to a secondary combustor and mixed with fuel rich hot gas. One of the problems about a ducted rocket was difficult to hold stable combustion in the secondary combustor. It was caused by the temperature of fuel rich hot gas cooled by ram air. Therefore a ducted rocket needed the high temperature region in the secondary combustor. The high temperature region was made by burning metal particles. The distance of high temperature metal particles affected combustion characteristics in the secondary combustor. The combustion efficiency of C* was measured with the direct connected-pipe ducted rocket. The combustion efficiency of C* increased with increasing the distance and reached the maximum value, after then the combustion efficiency of C* decreased with increasing the distance. It was associated with the combustion efficiency of the fuel rich hot gas. We calculated the temperature distribution around the high temperature metal particles by CFD simulation to examine this mechanism in detail.

Velocity and Temperature Distributions Around Metal Particles in the Reaction Zone of AP Composite Propellant

The thrust performance of the solid propellant is improved by adding the metal particles which have good ignition and combustion characteristics. In the reaction zone which is a very thin zone near the burning surface, the metal particles ignite, burn and raise the temperature around them, and the burning rate increases. In order to clarify this mechanism the small solid propellants were combusted and CFD simulations around the metal particles were performed. The temperature histories in the reaction zone, velocity and temperature distributions around the metal particles were obtained. The behavior of the metal particles in the reaction zone was clarified.

Hot Gas Flow around Burning Aluminum Particles near Burning Surface of AP Composite Propellant

In order to clarify the behavior of the burning aluminum particles very near the burning surface, the temperature histories in the reaction zone and the hot gas flow around the burning aluminum particles were studied. The AP composite propellants added the aluminum particles combusted, and the temperature histories near the burning surface in the reaction zone were obtained. The fluctuations caused by the burning aluminum particles were observed in the temperature histories. The detailed hot gas flow around the burning aluminum particle was obtained by CFD simulation of three dimensional model. The small particles maintained high temperature around it, these ignited very near the burning surface, and the small fluctuations raised the gas temperature continuously. It is considered that the burning rate increases as the gradient of the temperature near the burning surface increases. The high temperature area was made around the burning aluminum particle, and the shape of the area was obtained from CFD simulation. The correlation between the hot gas flow and the high temperature area around the particle was very important, and the shape of the area changed with Reynold’s number.