Understanding the Effect of Capacitive Discharge Ignition on Plasma Formation and Flame Propagation of Air-Propane Mixture

摘要

This work is an experimental and computational study to investigate the effect of capacitive discharge ignition (CDI) on plasma kernel formation and flame propagation of air-propane mixture. This paper is mainly focused on the plasma formation and flame propagation characteristics, pressure rise, propagation time, velocity field, and species concentrations. A conventional ignition system is used for comparison purpose. A constant volume combustion chamber with volume of 400 cm(3) is designed for experimental study. This chamber is utilized to visualize the plasma formation as well as the flame propagation induced from two ignition sources. The experiments are performed in a wide range of operating conditions, i. e., initial pressure of 2-4 bar, temperature of 300 K, chamber wall temperature of 350 K, spark plug gaps of 1.0-1.5 mm, discharge duration of 1 ms, discharge energy of 500 mJ, and equivalence ratio of 0.5-1.0. The computational study is performed by ANSYS FLUENT using the partially premixed combustion (PPC) model having the same conditions as experimental study. It is shown that the average peak pressure in CDI increased by 5.79%, 4.84% and 4.36% at initial pressures of 2, 3, and 4 bar, respectively, comparing with conventional ignition. It could be determined that the impact of combustion pressure in CDI system is more significant than conventional ignition particularly in lean mixtures. Consequently, the flame propagation rate in CDI system, due to the large ionized kernel around the spark plug, can be significantly enhanced.