Thomas William Megli

Plasmadynamics model for nonequilibrium processes in N2/H2 arcjets

A two-temperature chemical nonequilibrium model is developed for nitrogen/hydrogen (N 2/H2) arcjet thrusters. All viscous flow properties are considered assuming steady, laminar, continuum, and axisymmetric flow. A seven-species N2/H2 plasma composition of molecules, atoms, ions, and electrons is assumed, and a finite rate chemistry model is employed to model collisional processes among the species. Separate energy equations are formulated for the electrons and heavy species. The anode temperature distribution is included, and propellant electrical conductivity is coupled to the plasma properties, allowing for a selfconsistent current distribution. The numerical solution employs the compressible form of the pressureimplicit with splitting of operators algorithm to solve the continuity and momentum equations. Numerical results are presented for a low-power simulated hydrazine thruster. The centerline constrictor region of the arcjet flowfield is predicted to be near thermal equilibrium, whereas a high degree of thermal nonequilibrium is predicted in the near-anode region of the arcjet nozzle. Strong electric fields near the anode produce elevated electron temperatures that enhance ionization levels and electrical conduction through the arcjet boundary layer. Radial diffusion of electrons from the arc core also enhances the near-anode ionization levels. Thus, the nonequilibrium approach is required to accurately model the plasma current distribution.

Optimization Techniques and Results for the Operating Modes of a Camless Engine

Electronic control of valve timing and event duration in a camless engine enables the optimization of fuel economy, performance, and emissions at each engine operating condition. This flexible engine technology can offer significant benefits to each of these areas, but optimization techniques become crucial to achieving these benefits and understanding the principles behind them. Optimization techniques for an 14 - 2.0L camless ZETEC dynamometer engine have been developed for a variety of areas including: Cold Starts Cylinder Deactivation Full Load Idle Transient A/F control The procedure for the optimization of each of these areas will be presented in detail, utilizing both steady state and transient dynamometer testing. Experimental data will be discussed and the principles governing the response of the engine will be explained. Selection criteria for determining an optimum strategy for the different modes will be presented and recommendations Will be discussed. Conclusions will show that a camless engine improves performance, offers significant fuel consumption benefits, improves transient control, and is beneficial in reducing emissions during the cold start and warmed up conditions.