Sangkyu Kim

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 (O 2 ) 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 O 2 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 Japans 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.

Simultaneous improvement of exhaust emissions and fuel consumption by optimization of combustion chamber shape of a diesel engine

In order to achieve clean exhaust gas emissions and high fuel efficiency in diesel engines, a new combustion chamber concept called “egg-shaped piston bowl” was proposed and its effectiveness was validated by engine experiments using a single-cylinder research engine. Numerical simulations of combustion processes and exhaust gas emissions were carried out on different piston bowl geometries using GTT-CHEM code, which is a three-dimensional computational fluid dynamics code coupled with detailed chemical kinetics. In this code, a combustion model taking account of the auto-ignition process of a non-homogeneous mixture and a detailed phenomenological soot model was incorporated. In the detailed phenomenological soot model, particle inception from polycyclic aromatic hydrocarbons, surface growth/oxidation and particle coagulation processes were considered. In addition, to investigate the soot formation characteristics with different piston bowl geometries, experimental measurements by the two-color method were conducted with a constant-volume vessel under high-temperature and high-pressure conditions. As a result of the engine experiments and the numerical simulations, it was confirmed that simultaneous reduction in exhaust gas emissions and fuel consumption was able to be achieved by the egg-shaped piston bowl concept.