Development of Model-Based Combustion Control to Ensure Robustness of Emissions, Fuel Consumption and Noise Performances in New Generation Diesel Engine

Abstract

In order to balance low emissions, low fuel consumption and low noise (hereinafter referred to as 'the EM, FC, and noise performances') in diesel combustion, it is necessary to apply optimum multistage fuel injection for EGR target, which is the maximum acceptable volume at each engine speed and load. However, as combustion is susceptible to disturbances when heavy EGR is applied and EGR volume is non-constant during transient operation in actual driving, how to ensure the robustness of the EM, FC, and noise performances is a challenge. We therefore implemented the following combustion control techniques. As for Premixed Compression Ignition (PCI) combustion in an extra heavy EGR region, we developed a system to control ignition timing during transient operation appropriately. In this system, ignition timing is controlled by predicting ignition delay based on in-cylinder temperature and pressure as well as intake oxygen (O2) concentration calculated from an EGR rate. In addition, to deal with a wide EGR range in actual driving, we developed a control system to select multi-stage fuel injection patterns appropriate for PCI combustion or diffusive combustion according to intake O2 concentration calculated from an EGR rate. These model-based combustion control techniques have become one of the key technologies of Mazda new-generation engine, SKYACTIV-D 2.2L. The engine confirms to Euro 6 and Japan's Post New Long Term emissions regulations without NOx after-treatments and also achieves sufficient quietness and low fuel consumption at the top level in its class.