Effects of Nozzle Orifice Diameter and Hole Number on Diesel Combustion and Engine Performance

The effects of the diameter and number of nozzle holes on the combustion characteristics of a light-duty diesel engine were investigated. 8- and 10-hole injectors with an orifice diameter of 117 µm and 8-, 10-, and 12-hole injectors with an orifice diameter of 110 µm were examined. In a constant-volume combustion chamber, flame and OH chemiluminescence imaging were employed for measuring the flame penetration, lift-off length, and spray-to-spray interference. The results indicated that, for a small orifice diameter and a large number of holes, the lift-off length and flame penetration were reduced. The interference and overlap of neighboring flames were observed with the increasing number of holes. An experiment involving a 0.5 L single-cylinder diesel engine under low-load conditions was conducted. For the injectors with an orifice diameter of 117 µm, as the number of holes was increased from 8 to 10, the exhaust characteristics and efficiency were improved owing to the higher injection rate, divided fuel quantity per nozzle hole, and wider fuel distribution. However, the injector with an orifice diameter of 110 µm resulted in the opposite tendency; when the number of holes was increased from 8 to 12, the exhaust emissions and efficiency deteriorated owing to flame interference.