Fuel Injection Strategy for Clean Diesel Engine Using Ethanol Blended Diesel Fuel

Ethanol is a bio-based renewable and oxygenated fuel, thereby providing potential to reduce the PM emission in diesel engines and to provide reduction in life cycle CO₂. There are several studies which report improvement in the engine performance using ethanol blend fuels. However, most of these studies are carried out using diesel engines with basic combustion control technologies. Therefore, it is doubtful whether a diesel engine fuelled with ethanol blend fuels can compete with the recently developed clean diesel engines. From another point of view, it is important to know whether it is possible to overcome the disadvantages of ethanol blend fuels using modern diesel engines.

The aim of this study is to find strategies for fully utilizing the advantages of diesel-ethanol blends in the recent diesel engines. For this purpose, experiments were performed using a single-cylinder DI diesel engine equipped with common rail injection and cold EGR systems. The results indicate that significant PM reduction at high loads can be achieved using 15∼20% ethanol-diesel blend fuels. Increasing the injection pressure promotes PM reduction. However, weak ignitability of the ethanol blends results in a higher rate of pressure rise at high loads and unstable and incomplete combustion at lower loads. Pilot injection with a proper amount and timing solves the above problems. NO_x increase due to the high injection pressure can be controlled employing cold EGR. The weak sooting tendency of the ethanol-blends allows the use of high EGR rates for a significant NO_x reduction. However, ethanol percentages higher than 20% would require modification in fuel injection system to achieve stable operation. The above finding indicates that low levels of PM and NO_x emissions with no serious fuel consumption penalty, is achievable when the diesel-ethanol blends are used with a combination of the modern combustion control methods.