Abstract
UV-visible flame intensity and extinction measurements were carried out in an optically accessible Diesel engine in order to characterize mixture formation with high temporal and spatial resolution. The liquid and vapor locations were characterized by broadband UV-visible extinction measurements, in order to analyze the species involved during ignition delay and their contribute to pre-flame reactions at autoignition time. The ignition location and time were individuated by radical species like OH and CH, detected by chemiluminescence measurements. The presence of these species was detected in a region characterized by a large amount of fuel almost entirely in the vapor phase and well mixed with air. At autoignition time, the radicals intensities were strongly influenced by the ignition delay. CH and OH intensities increase with short ignition delay and in particular OH concentration is very low at long ignition delay. On the other side, a good correlation between CH intensity and burnt fuel during premixed combustion phase. Understanding the CH chemistry in the engine might allow to follow the formation and destruction of NOx in order to minimize its emission.