Modelling combustion processes in a diesel engine
Diesel engines provide important fuel economy and durability for large heavy-duty trucks, buses, and non-road equipment. The reduction of oxides of nitrogen (NOx) and fine particulate matter emitted with the lean diesel exhaust remains, however, a technological challenge. Engineers are faced with a multi-parameter optimisation problem, where fuel injected at high pressure into the combustion chamber helps reduce the emission of soot, but results in higher levels of nitrogen oxides. Numerical tools with predictive capabilities have been developed during the MINNOX project to provide the means essential for balancing fuel consumption and emission formation. Researchers at laboratories of Volvo Technology Corporation worked towards a more realistic modelling of wall-bounded turbulent flows. This is a necessary prerequisite for the accurate prediction of wall friction and heat transfer, as well as for providing reliable boundary conditions for components' thermal analysis. Sub-models for each flow and combustion process within the engine's combustion chamber were first validated with the use of the in-house Computational fluid dynamics (CFD) flow solver, MERMAID. Covering the effects of heat transfer to engine's pistons as well as exhaust gas recirculation, these were proven to be accurate over a wide range of engine operating conditions. They have also lent themselves to improvements that could ultimately lead to predictions on the build-up of sludge and carbon deposits around pistons as the engine's service life is prolonged. Moreover, the possibility of working independently of a CFD solver was explored, but also well-defined interfaces to commercially available CFD flow solvers, such as the widely used STAR-CD code, were developed,. At the same time, the efficiency and robustness demanded by engineers when performing CFD calculations of flow and combustion processes were kept in mind.
