| The present research experimentally investigates radiative heat transfer from a hydrocarbon capillary-sustained plasma jet, and the role of the radiation during the plasma-propellant interaction. The plasma jet is initiated by exploding a thin metallic trigger wire (∼3.6mg) through a high-voltage electrical pulse. The exploding wire ablates the hydrocarbon capillary, forms a high-temperature, high-pressure electrothermal-chemical (ETC) plasma that emerges in the open-air environment as an underexpanded, supersonic jet. The ETC plasma jet is allowed to impinge over a stagnation plate that holds a variety of diagnostic tools as well as the propellant samples.;The overall objective of this research is to augment the present understanding of the thermophysical and chemical processes involved in the ETC ignition of solid propellants. The particular focus is to deduce the transient variation in radiative heat flux, stagnation pressure, electrical parameters, and plasma jet structure with different capillary and trigger-wire materials, plasma energy levels, and plasma exit port to stagnation plate distance. The effects of trigger-wire mass and capillary diameter are also examined. To understand the role of radiation during ETC ignition, double-base JA2 propellants are exposed to ETC plasma radiation. A variety of measurements are conducted to analyze the gas-phase products generated during the radiative pyrolysis of JA2. These include measurement of transient variation in gas-phase temperature and pressure, identification of gas-phase species, and estimation of species relative mole fractions. To further elucidate the radiative pyrolysis studies of JA2, confined rapid thermolysis of JA2 propellants are also conducted.;A considerable effort is employed to develop thin-film platinum heat flux gages, electrical circuitry, and the corresponding inverse data reduction techniques to estimate the transient radiant heat flux from ETC plasma. A high-speed CCD camera captures the side-view images of the plasma jet. Photodiodes, placed below the plasma jet, identifies the plasma emergence from the exit port and the plasma impingement on the stagnation plate. K-type thermocouples (12mum diameter) are used to measure the gas-phase temperature during radiative pyrolysis of JA2.;Results suggest that the instantaneous value of the transient absorbed radiant heat flux is quite high (∼103 MW/m2), and that the contribution from the UV wavelength region dominates over the visible and IR regions. It is also observed that the radiant flux is material dependent, and that for a given electrical energy level and pulse duration, higher ablation typically leads to lower radiant flux as well as higher stagnation pressure. Radiative pyrolysis of JA2 within a constant-volume chamber suggests that, for moderate plasma energy levels, radiative heating alone may produce a high temperature and pressure of the products evolved into the gas-phase region, but cannot ignite the propellant. Additionally, species produced during radiative pyrolysis of JA2 are found to be different from that generated during standard thermolysis experiments, but that may be expected due to differences in temperatures and pressures in the two experiments. It is possible that the UV radiation from the ETC plasma photolyzes the oxidizers (such as NO 2), and thus reduces the chemical activity of decomposition products, prohibiting ignition of JA2. |
