Investigation Of Laser Chemical Propulsion

Laser propulsion is a new concept technique for propulsion. It promotes the aircraft by utilizing the counterforce generated during the injection of gases with extremely high temperature and pressure which formed by interaction between high-power laser and propellant. There is a new concept of laser propulsion, called chemical laser propulsion (CLP) which can greatly enhance the propulsion performance because of the supplement of chemical energy during the propulsion process. The kinetic energy of thruster is converted by not only the laser energy, but also the chemical energy during the chemical laser propulsion process. It can also improve the momentum coupling coefficient and specific impulse, so it can greatly improve the overall propulsion performance of the thruster. It provides a new way for developing laser propulsion technology to application stage.In the present thesis, the following researches, focused on the CLP technology, have been studied.(1) The mechanism research of CLPThe physical process of CLP is divided into two stages by analysing the basic principle of CLP based on the release of chemical energy. The first one is the stage of interaction between high-power laser and propellant, and the last one is the stage of flow field evolution of gases with high temperature and pressure in thruster. The supplement of chemical energy can occur in both the first stage and the last one.The propellants of CLP are divided into energetic propellants and non-energetic propellants. In general, the supplement of a large amount of chemical energy of energetic propellant, which can release chemical energy itself without oxygen provided extra, occurs in the last stage. And that of non-energetic propellant, which needs oxygen provided extra to release chemical energy, occurs in the first stage.The propulsion performance of the propellant has been studied both in1atm atmospheric environment and in1atm nitrogen environment under the constrained conditions by thruster and unconstrained conditions. The results show that there is an exothermic reaction in the propulsion process, occurred with oxygen contained in1atm atmospheric environment. The existence of chemical energy release in CLP has been validated.Based on the molecular spectroscopy analysis, the the final products of the chemical reaction between gas in environment and that, which formed by interaction between high-power laser and propellant with extremely high temperature and pressure, have been ascertained. The final product in vacuum environment is CH2O. The final products with1atm atmospheric environment are CO2and H2O. The chemical reactions in1atm atmospheric environment and the chemical energy released in the reactions have been deduced.The flow field evolution of gases with high temperature and pressure, formed by interaction between high-power laser and propellant, has been obtained by the high speed schlieren experiment and the numerical simulation using Fluent. It has given a very good agreement between simulation and experiment results. The chemical energy and the release rate of chemical energy curves have been given by numerical simulation. It shows that the release intensity of chemical energy depends on how well the product gas is mixed with oxygen in the atmosphere. The release intensity of chemical energy is greater while the gases are mixed more fully.(2) The research of CLP with large energy and thrusterThe numerical simulation of the propulsion performance of cylindrical thruster has been studied. There are two important factors affecting the propulsion performance of cylindrical nozzle thrusters:the length L of thruster and the thruster diameter to laser-spot diameter ratio α. We get the best value of L and a, which is identical with the experimental results. When we use TEA600CO2laser with the energy of519J and the best configuration of cylindrical thruster with POMAl as the propellant, the momentum coupling coefficient and specific impulse is113.2dyne/W and1275.4s, while laser energy coefficient is707%, which is the biggest value reported.The propulsion performance of cylindrical thruster under two repeated pulses has been studied experimentally. The results show the products generated by ablation under the first pulse has no effect on the propulsion performance under the second pulse.(3) The research of chemical laser micro-propulsionWe have designed a baffle torsion pendulum testing system, the measuring principle of which is described, and the measurement error of the system has been analyzed. The effect of the thickness of double base propellant on the propulsion performance has been stydied by using this system. The experimental results show that the momentum coupling coefficient increases with the increase of thickness, while the specific impulse decreases. The effect of laser power density on the release of chemical energy has been studied. When we use semiconductor laser with the power of1.8W and the double base propellant, which is designed ourselves, the momentum coupling coefficient and specific impulse is130.8dyne/W and493s, while laser energy coefficient is316%, which is six times better than the propellant without the release of chemical energy.