The Effect of Non-Circular Nozzle Holes on Combustion and Emission Formation in a Heavy Duty Diesel Engine

Non-circular holes are believed to have a potential in reducing the smoke emissions from a diesel engine by entraining more air into the spray due to the larger surface area exposed between fuel and air. The idea is based on results from investigations of gas jets, where the air entrainment for elliptical jets was increased substantially compared to circular jets. Non-circular nozzle holes were tested in a 2 liter single cylinder heavy duty diesel engine and compared with standard circular nozzle holes. The non-circular holes, which were made with aspect ratios of close to 2:1 and 4:1, have a similar flow rate as the conventional circular holes. Two different angles of the major axis orientation to the injector centerline were used. The engine tests were done at constant speed with both high and low load conditions and were repeated several times. Emissions, fuel consumption and cylinder pressure were measured and are presented together with calculated rate of heat release curves. The results show that the non-circular nozzle holes have a tendency to extend combustion, and the tendency is stronger for the higher aspect ratio. For the aspect ratio of 2:1, the differences in emissions and fuel consumption are small compared with the standard circular shaped nozzle. In the rate of heat release curves for aspect ratio 2:1 it is seen that the delayed combustion is likely caused by spray wall interactions. It is concluded that the hole shape, like those used with the aspect ratio 2:1 nozzles, has a minor impact on the diesel combustion at the tested conditions. The combustion from the aspect ratio 4:1 nozzles which is delayed even further is believed to be caused by spray-wall interactions, but trade off curves for emissions and fuel consumption are similar to those off standard circular nozzles.