Analysis of Premix Flame and Lift-Off in Diesel Spray Combustion using Multi-Dimensional CFD 2008-01-0968
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 . 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)  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  considered in recent experimental studies . The fuel vapour field is also examined and compared with recent field data experiments of fuel concentration .