Study On Radiation Ignition And Combustion Characteristic Of Solid Propellant By Electrothermal Plasma

In this dissertation, a research has been made on the details of plasma in electrothermal chemical (ETC) launch process, based on the physical phenomenons of its generation, development and interaction with propellants in cartridge. And then the internal ballistics process is also discussed.(1) In terms of electrothermal plasma generation, the pulse forming network (PFN) discharge and metal wire electrical explosion process are mainly discussed. A current calculation model applied to the plasma injector in ETC is developed. And fast Fourier transform (FFT) spectrum analysis method is employed to explore the intrinsic relationship between the loop current and load resistance. Also the load parameters on the influence of peak current in PFN discharge process is discussed.Results show that both experimental and numerical loop current and load resistance are concentrated in the low frequency (0-20Hz). The influence of the load resistance to the loop current mainly presented in RL first-order discharge process, and has no obvious effect in RLC discharge process. The changes of load resistance mainly affect FFT’s phase obviously. When the load resistance has a sinusoidal variation, the relative error of the peak current caused by its frequency, amplitude and initial phase are nearly plus or minus1.0%,1.8%and0.5%, respectively.Both zero and one dimensional calculation model are applied to discuss the physical process in electrical exploding wire. The zero dimensional calculation model is mainly used for verifying and demonstrating the state changes and basic physical process in electrical explosion. And the heat transfer process is considered in the one dimensional model to simulate the development of the transient melting and vaporization waves. The plasma excitation temperature is calculated by the relative line intensities through Andor SR750spectrograph. And the variation characteristic of excitation temperature is also discussed. Results show that the excitation temperature changes obviously at the prophase of pulse discharge, and is relatively stable at the later stage of pulse discharge.(2) The discussion of plasma development in the capillary is carried out from two fields:the capillary ablation and plasma diffusion in the capillary.Based on the capillary ablation shielding effect, an ablation model is employed to calculate the plasma parameters in capillary. And based on the hydrodynamics equations, a nozzle model is also employed to calculate the parameters of mass fluid injected into the cartridge. Results show that the plasma parameters in capillary always have the pulse character. During the discharge period, the capillary ablation mass rate firstly increases then decreases. The capillary’s structure parameters have direct influence to the plasma parameters. And selected the biggish aspect ratio capillary will be beneficial to obtain higher temperature and pressure plasma source. The plasma parameters and ablation mass are both influenced by discharge voltage linearly.(3) The plasma propellant interaction details are discussed from two fields:plasma radiate ignition and propellant statistics combustion.A numerical model of radiation has been employed by using a Monte Carlo method and statistical physics to simulate the process of a capillary plasma source for an ETC launcher. The plasma-propellant interaction when the radiation model is combined with a thermal, model is also discussed. Results show that the strong instantaneous radiation is responsible for the transmission of energy to the propellant grains leading to ignition. The responses of energy flux and propellant grains to radiation are both on the order of picoseconds. The efficiency of energy absorption in the propellant bed always maintains a high level. And the plasma ignition efficiency is mainly affected by the properties of propellant grains within a small field around the plasma injector. This energy skin effect on the propellant grain surface appears to be the main cause of plasma ignition.A propellant statistics combustion model is established to calculate the combustion condition of propellant grains in the cartridge. Calculations indicate that, because the limited effect area of plasma and different location, the propellant grains in the cartridge burned from the near to the distant (relative to the location of plasma injector) successively at the beginning of ignition process. The pressure distribution int the cartridge and burning rate of propellant also have the same spatial distribution characteristics. The high pressure zone gradually increased and extended to the cartridge boundary with the passage of time. Statistical results show that the establishment of the temperature field is prior to the pressure field. This temperature field mechanism is also an important character, which the plasma ignition is superior to the conventional ignition.(4) Based on the classical interior ballistics theory as the assumption of geometric combustion law, combined of PFN discharge characteristics, a practical simplified internal ballistic calculation model of ETC gun is established to calculate and predicte the conventional and ETC launch by using the57mm anti-aircraft gun’s data.Results show that the model can intuitively reflect the interior ballistic process. The conventional launch is conformity with the theoretical data. In ETC launch process, the burning rate of propellant evidently increased by the plasma interaction. The burning time of propellant and the whole launch time are both shorten. The pressure with higher growth caused the shorter peak time and higher peak pressure. Thus, the muzzle pressure and muzzle velocity are both increased. With the increase of injected energy, peak pressure and muzzle velocity are both approximately increased linearly. And the peak pressure curve has a higher gradient.The advantage of simplified model in predicting the interior ballistic parameters is simple method and easy to implement. And a refined model considered more physical process of ETC launch is developed to calculate in the same computational condition. And more details of plasma parameter curves and reference values are obtained. Calculation results of all interior ballistic parameters by the refined model are basically identical with the simplified model.