Spark ignition of a bidisperse, n-decane fuel spray

Abstract

The spark ignition characteristics of a bidisperse aerosol were investigated. The purpose of the investigation was to determine the parameter(s) of the droplet size distribution that best correlates the ignition behavior of a spray. Two monodisperse aeeosols, generated by identical Berglund-Liu monodisperse aerosol generators, were used to create the bidisperse spray. A Phase Doppler Particle Analyzer was used to measure the droplet size distribution, droplet flux, droplet velocity and gas velocity at the spark gap. A capacitive discharge ignition system was used to generate the spark which ignited the mixture. Mixtures of oxygen and nitrogen were used as the oxidizing gas instead of air. The results show that the Sauter mean diameter correlates the ignition of the bidisperse sprays very well. The arithmetic, area, and volume mean diameters do not correlate the ignition behavior at all. In fact, in some cases, the arithmetic, area, and volume mean diameters exhibit a trend where the ignition energy decreases with, increasing droplet size. Comparison with monodisperse data also demonstrated that the Sauter mean diameter adequately describes the ignition of the bidisperse sprays. A semi-empirical characteristic time model was used to model the spark ignition of the sprays. The model was extended to include the effects of finite rate chemistry. The model correlated the ignition behavior of the bidisperse spray quite well. The best correlation was obtained by using the Sauter mean diameter consistent with the results of the experimental program.