Development of Highly Premixed Combustion Diesel Model: From Simulation to Control Design

In the context of increasingly stringent pollution norms, reduced engine emissions are a great challenge for compressed ignition engines. After-treatment solutions are expensive and very complex to implement, while the NO_x/PM trade-off is difficult to optimise for conventional Diesel engines. Therefore, in-cylinder pollutant production limitation by the HPC combustion mode (Highly Premixed Combustion) - including Homogeneous Charge Compression Ignition (HCCI) - represents one of the most promising ways for new generation of CI engine. For this combustion technology, control based on torque estimation is crucial: the objectives are to accurately control the cylinder-individual fuel injected mass and to adapt the fuel injection parameters to the in-cylinder conditions (fresh air and burned gas masses and temperature). The main goal is to preserve a precise torque balance during all engine working modes. 1D engine models are an essential tool to improve controller development efficiency, as they allow to easily sweep a large amount of operating conditions and to access accurate information on engine behavior. As a matter of fact, extending the part of the numerical models into the control design process can reduce the algorithm development time and the risks of damaging the prototype hardware.

The contribution of this paper is twofold:

• The design of a 4 cylinder HPC Diesel engine model: A specific validation of the combustion model is achieved for HCCI/conventional dual mode combustion by a study of model accuracy to reproduce the main combustion parameter variations such as SOI, injected fuel mass or burned gas rate. Then, a complete validation campaign on relevant steady state and transient operating conditions show good agreement between engine model behavior and testbed results.
• The use of this model as a crucial support tool for two control development purposes: The validation of an individual cylinder AFR estimator and control using the reliable and available λ-sensor located downstream the turbine as the only measurement is presented. The design of an EGR observer in the intake manifold based on typical vehicle sensors is also achieved.