Coupling Nodal and Multi-Zone Combustion Models to Describe Thermal Diesel Engine Behavior 2008-01-0845

Engine thermal behavior has been solved previously in steady and transient conditions thanks to a lumped capacity model, also called nodal model. But serious shortcomings appear in the heat flux formulation introduced in the model. In this paper, we show that using steady-state maps of heat transfer coefficients to simulate transient thermal response of diesel engines is not sufficient. The heat transfer is strongly influenced by the injection pattern, the intake air conditions and the walls temperatures, which are not taken into account in the previous model. Introducing a single cylinder multi-zone combustion model, a better description of the combustion process and so of the heat release can be obtained. The coupled models are used to describe a 1,9l, 4-cylinder direct injection diesel engine during a warm-up. The results (oil and coolant temperatures) show a good agreement between measures and simulations. This approach offers a great potential for further applications. The coupled models can be used to investigate new engine control strategies in order to improve its warm-up, notably in cold conditions. It also opens the possibility to expand the simulation on emission limits. It is a complete and robust tool to study transient diesel engine behavior.