A New Concept for Low Emission Diesel Combustion (2nd Rep. : Reduction of HC and CO Emission, and Improvement of Fuel Consumption by EGR and MTBE Blended Fuel)

A new concept for diesel combustion has been investigated by means of engine experiments and combustion observations in order to realize a simultaneous reduction of NOx and particulate emissions. The concept is based on pre-mixed compression ignition combustion combined with multiple injection. In this method, some part of fuel is injected at an early stage of the process to form a homogeneous lean pre-mixture, then the remaining fuel is injected at around the TDC in the same manner as a conventional diesel injection. The emissions, ROHR (rate of heat release), and combustion pictures of conventional combustion, pilot injection combustion, and this new combustion concept were compared and analyzed.

Engine tests were carried out using a single cylinder research engine equipped with a common rail injection system. The experimental results showed that the tradeoff relations of smoke and fuel consumption against NOx emissions of this concept was worse than those of a conventional injection or a pilot injection in a high NOx region. However, this concept has advantages of smoke and fuel consumption in the region where the main injection timing is considerably retarded. In order to improve this combustion concept, the effects of EGR and oxygenated fuel were investigated. It was found that EGR had the effect to reduce both NOx and HC emissions and that oxygenated fuel improved emission and fuel consumption. The results of combustion observations were also discussed in order to compare the combustion phenomena.