Analysis of Premix Flame and Lift-Off in Diesel Spray Combustion using Multi-Dimensional CFD

A detailed analysis is performed upon the results of CFD combustion simulations of several diesel fuel spray flame experiments. Simulations are validated against measurements from a constant volume combustion chamber testcase [9]. Particular emphasis is made in the analyses to identify mechanisms associated with the ‘lift-off’ phenomena characteristic of contemporary high injection pressure diesel engine combustion. A recently developed industry state of the art RANS hybrid combustion model (Extended Coherent Flame Model - 3 Zones) [41] is used which takes account of both a propagating (premixed) flame combustion mode as well as the conventionally assumed diffusion flame mode used in most diesel combustion models. The location of and development of a propagating reaction front, obtained from analysis of the progress variable within the model, is studied in relation to the lift-off behaviour. The entrainment of air upstream of the lift-off is quantified from the CFD simulated field results and compared with values estimated from an empirical model [38] considered in recent experimental studies [34]. The fuel vapour field is also examined and compared with recent field data experiments of fuel concentration [22].