Validation of a newly developed quasi-dimensional combustion model - Application on a heavy-duty DI diesel engine

摘要

This work is a part of an extended investigation conducted by the authors to validate and improve a newly developed quasi-dimensional combustion model. The model has been initially applied on an old technology, naturally aspirated HSDI diesel engine and the results were satisfying as far as performance and pollutant emissions (Soot and NO) are concerned. But since obviously further and more extended validation is required, in the present study the model is applied on a new technology, heavy-duty turbocharged DI diesel engine equipped with a high-pressure PLN fuel injection system. The main feature of the model is that it describes the air-fuel mixing mechanism in a more fundamental way compared to existing multi-zone phenomenological combustion models, while being less time consuming and complicated compared to the more accurate CFD models. The finite volume method is used to solve the conservation equations of mass, energy and species concentration. The gas flow field is estimated using a newly developed semi-empirical gas motion model based on the assumption that in-cylinder pressure is uniform. Spray trajectory, fuel vaporization and combustion are simulated using simplified sub-models based on semi-empirical correlations. From this investigation, comparing the calculated with experimental results, it is revealed that the model manages to describe the effect of operating conditions on pollutant emissions (Soot and NO) at least qualitatively and provide a good estimation of the mean cylinder pressure diagram. Moreover the estimation of in-cylinder distribution of temperature, equivalence ratio and pollutants emissions concentrations (Soot and NO), seems to be reliable and in accordance with the conceptual model of diesel combustion. This is encouraging since the model can describe the fuel-air mixing and combustion mechanism, in two different diesel engine designs, without modification.