Solutions to the anode sheath problem have been studied for the case where the electron and plasma temperature is constant and equal. The planar geometry description of steady, low-temperature collisional plasmas permits certain simplifications to the species continuity equations whereby a single, highly nonlinear equation is obtained for the entire region disturbed by the electrode. This equation is given in terms of the electric field and a variable representing the currents. Our formulation includes charged-particle production with a net current flow. Solutions are generated with a nontrivial analytic expression for the electric field of the form: E ( y ) = E,exp{A/(y+a)'}, where a, A, and E, are shape factors. Defects in the approximation can be minimized by identifying the coefficients for the net production of charges U posteriori, thereby yielding largely non-numerical solutions of some validity. Generically, this approach is not restricted to the form of the electric field utilized and other more exact approaches, while expected to refine the numerical values given here, should retain the relationships between parameters basically intact. Meaningful results have been found for nitrogen at moderately high densities [NE loz4 m-'], which at sufficiently IOW currents [JE 100 mA/cm'] are realistic for electron-impact ionization and two-body recombination. This case is completely described by two nondimensional groupings (q and z), which are sufficient to define the sheath and ambipolar regions. The constants A and a are evaluated using information for nitrogen at 6000 K, a case with well documented values, corresponding to degrees of ionization above loa. Other practical discharge gases are also represented in the example. Scaling laws result from our formulation, which allow for relatively quick answers to many single-temperature collisional plasmas at positive probes and anodes.
Anodes display either a glow mode or a constricted mode in plasmas of interest for MHO generator applications. The purpose of this paper is to outline the conditions underlying the existence of anode constrictions or anode spots in conjunction with criteria governing the anode glow. A steady current flowing through velocity and thermal boundary layers is investigated. The sheath and the ambipolar region are considered from an approximation theory viewpoint, and then the nonexistence of a one-dimensional Cartesian or diffuse mode for a nonreacting anode region is shown using the continuum equations for electrostatic probes.
The feasibility of using electrostatic fields as a practical means of altering existing gas-turbine-injector spray characteristics has been investigated. Results indicate that with electrical potentials typical of spark plug voltages, a significant modification of spray characteristics in terms of average droplet size reduction and increased spray cone angles can be produced. This suggests a means of expanding the utility of present combustors either by broadening the operating range for optimum performance with the design or by permitting more attractive combustion of nondesign fuels. A simple retrofit during engine overhaul would allow present combustors to operate with or without electrostatic spray modification. ECAUSE combustion efficiency directly affects propulsive efficiency, substantial effort has been devoted to the development of fuel injectors that produce the optimum droplet size and dispersion pattern in order to maximize the combustion efficiency of each application. As a consequence of the changing market for refined pertroleum products, refiners have tended to alter their jet fuel composition to include heavier fractions. This trend in blending produces fuels of greater viscosity and surface tension, lower vapor pressure, and also results in sprays characterized by larger droplet sizes with altered dispersion patterns. The present work reports on an investigation into the feasibility of using electrostatic fields to modify droplets' size and dispersion patterns in order to reoptimize these quantities when fuels, other than those for which a given combustor has been designed, must be burned.Efficiencies of present combustors are high, and current sentiment is that combustion efficiencies will remain high with alternate fuels. But efficiency does not represent the entire picture in combustion performance. A study done by General Electric 1 evaluating fuel character effects on a turbojet engine (the J79-17C smokeless combustor) indicates that the relative fuel droplet size, i.e., the parameter directly influenced by the injector, has an effect on 1) CO and HC emissions; 2) cold day ground start light off; and 3) altitude relight limits at low Mach numbers. Nondesign fuels produce larger droplets, which tend to worsen the abovementioned effects, and a tech-
This work reports on observations of a diffuse discharge in a turbulent air flow. The discharge power was monitored as a function of velocity and turbulence spectrum in a fixed electrode configuration. The flow direction was also reversed to check on the effect of convection. The flow increased the sparking voltage, and turbulence made the current distribution considerably more homogeneous; the discharge power increased from about l W with no flow to about 250 W with 60-m/sec grid-generated turbulent flow. This turbulence was most intense in the range between l and 10 kHz.
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