Spark ignited hydrogen/air mixtures: Two dimensional detailed modeling and laser based diagnostics

This study reports a detailed 2-D model which describes the spark ignition of an initially quiescent hydrogen/air mixture. The model includes the compressible Navier-Stokes equations, detailed chemistry and molecular transport in the gas phase as well as heat conduction to the electrodes. The spark is modeled for the phases subsequent to breakdown using the Maxwell equations for quasi-stationary conditions for the electric field. Initial and boundary conditions necessary for the simulations are chosen in accordance with experimental values. Heat conduction to the electrodes and different electrode shapes are investigated. The influence of these parameters on the shape of the initial flame kernel is discussed and compared qualitatively to experimental results. Spark ignition experiments are performed using a highly reproducible ignition system. Shapes of the early flame kernels are monitored by 2-D laser-induced fluorescence (PLIF) imaging of OH radicals produced during the ignition and the combustion process. The investigations are performed for different equivalence ratios. In addition, for a central position within the flame kernel, temperatures are measured at different times after ignition using vibrational coherent anti-Stokes Raman spectroscopy (CARS) of nitrogen. (C) 2002 by The Combustion Institute.