Potential of emissions reduction by premixed diesel combustion with variable valve timing

A variable valve timing (VVT) mechanism was applied to achieve higher load premixed diesel combustion for low emissions and high thermal efficiency in a light duty HSDI engine. By means of late intake valve closing (LIVC), compressed gas temperatures near the top dead center are lowered, thereby increasing ignition delay to enhance fuel-air mixing. The variability of effective compression ratio has significant potential for ignition timing control. Simultaneous reduction in both NOx and smoke was made possible by the combustion concept applied in this study, which is called Miller-PCI (Premixed Compression Ignition) combustion.