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Recently, the depression of lubricity ability due to global low-sulfurization of diesel fuels gives bad effect on durability and system of fuel injection pumps. Study on lubricity of low sulfur diesel fuels is important because low sulfur regulation (less than 500ppm by mass) has been enforced in Japan in October, '97. In this study, the following subjects were investigated. Develop a Pump test for the evaluation of lubricity characteristics of diesel fuels Show what kind of bad effect the depression of lubricity of fuels would cause to fuel injection pumps. Investigate the effect of lubricity improvers. As a result, an endurance pump test using a commercial diesel engine showed the diesel fuel with severer desulfurization treatment had greatly reduced the durability of fuel injection pumps, and it became clear that such fuels would easily cause some bad effects to the control system of fuel injection timing.

The effects of fuel properties on exhaust emissions from diesel engines before and after Japanese 1994 regulations were investigated. The test fuels were prepared by blending some solvents and compounds to have no interrelation among fuel properties. NOx emission was affected by cetane number and total-aromatic contents and most influential property on particulate was poly aromatic contents on the 1989 year model engine. However the effect of cetane number and poly aromatics on NOx and particulate were negligible on 1994 year model engine. When the engine was improved more the influences of fuel properties on diesel emissions were smaller.

A constant volume combustion chamber (CVCC) was used to measure the flame speeds for various kinds of liquid hydrocarbon fuels, and an engine test was also carried out to obtain the relationship between combustion characteristics on the CVCC and the engine performance in an SI engine. In the engine test, it was confirmed that the fuel composition significantly affected the combustion stability under lean-burn conditions. From the relationship between the flame speed in the CVCC and the combustion duration in the test engine, we could find out the possibility of various kinds of fuels as the future fuel base.