抄録
Analysis is made upon the results of CFD combustion simulations of several well characterised diesel fuel spray flame experiments. The experiments are chosen to provide well characterised test cases for three alternate modes of combustion of a diesel spray: 1. a 'classic' mode injection into high (1000K) gas temperature yielding a short ignition delay and rapid transition to a quasi-steady lifted flame structure maintained during the injection event. 2. a short injection into low (800K) ambient gas temperature, long ignition delay with combustion occurring in a part-premixed mode after the end of the injection. 3. an intermediate injection duration at high pressure, low (800K) ambient temperature condition with ignition occurring during the injection and a strong transient combustion continuing until after the end of the injection. A recently developed industry RANS hybrid combustion model (Extended Coherent Flame Model - 3 Zones) is used which takes account of both a propagating (premixed) flame combustion mode in addition to the conventionally assumed diffusion (mixing-controlled) flame used in diesel combustion modelling. The location of and development of a propagating reaction front, obtained from analysis of the progress variable within the model is studied. In the short injection, low temperature (long ignition delay) test cases, the model appears to successfully capture the predominantly partially-premixed combustion mode. In the quasi-steady lifted flame test case, the occurrence of a 'premixed' mode is less prominent however particular emphasis is made in the analyses to identify a 'premixed' mechanism associated with the 'lift-off' phenomena characteristic of contemporary high injection pressure diesel engine combustion.
