As compared with the conventional diesel combustion, Premixed Compression Ignition (PCI) combustion has an opportunity to achieye low fuel consumption and clean exhaust gas simultaneously.However, to improve the stability of fuel consumption, exhaust gas, and combustion noise, it is necessary to control ignition timing appropriately in PCI combustion.We therefore conducted a study to develop a new prediction model to control ignition timing. In this model, an empirical equation of Arrhenius expression including some sub-models and Livengood-Wu integral were applied to consider the in-cylinder condition ofa mixture formed by fuel iajection. The model constants were deterrnined based on the experimental results obtained by Design of Experiments (DOE) so that sutTicient prediction accuracy could be achieved for transient operating condition. By using a mass-produced Engine Control Unit (ECU) employing feed-fbrward control logic based on this model, we confirrned that the ignition timing in the transient operating mode could be controlled rather well by reflecting a predicted ignition delay period to fuel iniection timing. With the controllability of ignition timing, the robustness of engine performances in terms of fuel consumption, exhaust gas and combustion noise could be improved with PCI combustion.

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 autoignition 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.

No abstract

For numerically predicting the combustion processes in homogeneous charge compression ignition (HCCI) engines, practical chemical kinetic models have been explored. A genetic algorithm (GA) has been applied to the optimization of the rate constants in detailed chemical kinetic models, and a detailed kinetic model (592 reactions) for gasoline reference fuels with arbitrary octane number between 60 and 100 has been obtained from the detailed reaction schemes for iso-octane and n-heptane proposed by Golovitchev. The ignition timing in a gasoline HCCI engine has been predicted reasonably well by zero-dimensional simulation using the CHEMKIN code with this detailed kinetic model. An original reduced reaction scheme (45 reactions) for dimethyl ether (DME) has been derived from Curran's detailed scheme, and the combustion process in a DME HCCI engine has been predicted reasonably well in a practical computation time by three-dimensional simulation using the authors' GTT code, which has been linked to the CHEMKIN subroutines with the proposed reaction scheme and also has adopted a modified eddy dissipation combustion model.

No abstract