Abstract
This paper proposes a new diesel combustion concept that achieves high thermal efficiency without deteriorating emissions. This new combustion is characterized by the reduction of the heat transfer coefficient through restriction of in-cylinder gas flow using a zero swirl port and a lip-less shallow dish combustion chamber. Since restricting the gas flow generally causes an inadequate mixture of fuel and air, a micro multi-hole injector was adopted to create highly dispersed fuel spray that improves the air-fuel mixture. The temperature gradient near the combustion chamber wall was reduced by moving the combustion area to the center of the combustion chamber. This was achieved because the fuel spray created by the micro multi-hole injector has weak penetration. These improvements reduced the heat flux from the in-cylinder gas to the surface of the combustion chamber wall and improved the cooling heat loss. The heat flux was also analyzed to further reduce the cooling heat loss. This analysis found that providing a taper at the upper portion of the combustion chamber reduced the heat flux generated by the reverse squish flow. By combining all of these elements, namely the low-swirl port, tapered lip-less combustion chamber, and micro multi-hole injector, a 5% reduction in fuel consumption was achieved compared to conventional combustion, without an emissions penalty.
