An Approach to Incorporate Wall Heat Loss Effects in Flamelet Models for Diesel Combustion

摘要

Spray-Wall interactions in Diesel engines result in modifications of the structure of the spray jet. These modifications have been discussed by the authors in prior publications. Including the influence of the wall when combustion is modeled by employing flamelets is not straightforward. An approach to include wall heat loss effects is discussed in this work. The essential idea is to compute several flamelets with several representative enthalpy defects. The enthalpy defects result from wall heat loss. These defects will vary with time and space in the engine chamber. The average flamelet profile for a given location can then be obtained through a linear fit between the flamelets according to the computed local enthalpy defect. The enthalpy defect is estimated as the difference between the enthalpy in the gas without wall heat loss, which may be approximated as the enthalpy in a flamelet without heat loss, and the gas with wall heat loss. The improved model is applied to model combustion in a Diesel engine. In the application, two flamelets, one without wall heat loss and one with wall heat loss, are considered. Results are shown from computations for the cases without heat loss and with wall heat loss in the flamelet.