Effects of Fuel Properties on Diesel Spray Behavior under High Temperature and High Pressure Conditions

In order to clarify the state of spray and mixture formation in a diesel engine cylinder, the formation technique of high temperature and high pressure conditions in a constant-volume chamber was developed. This technique reproduces actual cylinder conditions (for example, 5MPa and 873K at TDC in NA engines with a compression ratio of 16) by filling ambience formation mixture into the chamber and pre-igniting the mixture. LIEF (Laser Induced Exciplex Fluorescence) technique was applied to the analysis of vapor-liquid separation as the measurement of spray. However, the light emission from various aromatic compounds by laser irradiation makes it difficult to apply the technique to the evaluation of the actual fuel. Therefore the preparation technique of the fuel for this LIEF technique was developed to have a mixture formation state on fuel properties. Focusing on kinematic viscosity and distillation characteristics, several types of alkanes were blended to approximate the liquid penetration of diesel fuel spray under high temperature and high pressure conditions. Those techniques were used to produce the evaporation characteristics of diesel fuel spray in using light fuel. Then the effect of the early injection of actual fuel on combustion was analyzed. As the result, with the light fuel, as for spray characteristics, liquid and vapor penetrations shorten, spray angle widens, and as for vapor concentration distribution, dense mixture with equivalent ratio above 2 reduces. As for combustion, the visible cylinder inside proved that smoke and bright flames reduce with the light fuel.