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I The effect of Cetane Number (CN) of the fuel and the addition of cetane improvers on the cold starting and white smoke emissions of a diesel engine was investigated. Tests were conducted on a single-cylinder, four-stroke-cycle, air-cooled, direct-injection, stand-alone diesel engine in a cold room at ambient temperatures ranging from 25 °C to - 5 °C. Five fuels were used. The base fuel has a CN of 49.2. The CN of the base fuel was lowered to 38.7 and 30.8 by adding different amounts of aromatic hydrocarbons. Iso-octyl nitrate is added to the high aromatic fuels in order to increase their CN to 48.6 and 38.9 respectively. Comparisons are made between the five fuels to determine the effect of CN and the additive on cylinder peak pressure, heat release rate, cold start-ability, combustion instability, hydrocarbon emissions and solid and liquid particulates.

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.