Numerical assessment of radiative heat transfer impact on pollutant formation processes in a compression ignition engine

Abstract

An imposed solution in the development process of compression ignition engines is the use of numerical research employing Computational Fluid Dynamics (CFD). At the high operating temperatures in compression ignition engines, the radiative heat transfer influences the overall temperature profile and heat transfer, which also affects the formation processes of pollutants. For the radiative transfer calculation in this work, method of discrete ordinates (DOM) employing Finite Volume Method (FVM) is implemented with user functions into the AVL FIRE™ CFD code. The absorptivity and emissivity are described with the implemented Weighted Sum of Grey Gases Model (WSGGM) based on non-isothermal and nonhomogeneous absorption coefficient correlations for carbon dioxide, water vapour and soot. The implemented procedure is extended to work with moving meshes, parallel computing and rezoning procedure, which are needed to account the radiative heat transport in internal combustion engines. Additionally, the focus of this work is on the performed validation of calculated mean temperature, pressure, rate of heat release and emission results against the compression ignition engine experimental measurements. Results with the implemented radiation model showed lower peak temperatures for approximately 10 K, which resulted in around 18% lower nitrogen oxides concentrations, and up to 20% higher soot concentrations at the end of engine operating cycle. The most dominant impact of the radiative heat transfer on soot formation is visible at the crank angles, where peak temperatures occur. The performed parameter study of the piston and head wall emissivity values showed a reduction in mean in-cylinder pressure and NO mass fraction for a less reflective surface. From the conducted parameter analysis of ordinates number, the sufficient accuracy is achieved for simulations with eight ordinates, which resulted in approximately 50% increased computational time. Finally, it may be concluded that the combination of implemented models is useful to predict the heat transfer of internal combustion engine focussing on the radiative heat transport, which can be an important factor for the development of forthcoming internal combustion engines.