AUTOIGNITION CHARACTERISTICS OF DIESEL SPRAYS UNDER DIFFERENT INJECTION CONDITIONS

An experimental study analyzing the complex relationship between exter nal thermo fluid dynamic parameters and the ignition of diesel sprays, as well as flame propagation, is presented. The experiments were perf ormed in a high-pressure, high-temperature system simulating the top d ead center conditions in the combustion chamber of a diesel engine. Th e only simplification with respect to real diesel engines is relative to the aerodynamic pattern. In fact, in this case, the air flux is alm ost quiescent and does not influence significantly the spray evolution or the combustion behavior. The influences of two very different inje ction regimes on the autoignition characteristics of diesel sprays wer e investigated using imaging techniques. In order to perform this anal ysis, a careful choice of injection conditions, obtained with two diff erent types of injection apparatus, was necessary. The spray evolution at both low and high temperatures (at the same air density), the temp oral and spatial distributions of the ignition points, and the flame g rowth velocity were measured for the two cases. Analysis of the result s revealed the specular behavior of the ignition spatial distributions ill the two cases. A first attempt to correlate these different behav iors with the spray-flame interaction is presented, and its implicatio ns are discussed.