The Influence of Pressure in the Nozzle Sac and Needle Lift on Fuel Spray Behavior and HC Emissions in DI Diesel Engines 1999-01-3491

The deviation of fuel spray configuration from hole to hole and from nozzle to nozzle in DI diesel engines is one of the main causes of increased HC emissions at idling and at light load operation. The eccentricity of the nozzle needle, internal flow patterns of fuel, fluctuations of pressure in the nozzle sac, and flow cavitations in the holes are reasons for this deviation. The relationship between the deviation of spray configuration and HC emissions was investigated by using a high pressure chamber and a 6 cylinder direct injection diesel engine. The deviation in the spray penetration from hole to hole is found to be about 15% and there is a 5 to 10% variation in the HC emissions from cylinder to cylinder at idling.

To understand the factors influencing spray deviation, the pressure in the nozzle sac was measured by attaching a small strain gauge at the nozzle tip and the relationship of the pressure in nozzle sac, needle lift, and fuel line pressure was investigated by changing the nozzle specifications and injection parameters. For small nozzle hole areas, high pump speeds, and high injection rates, the pressure in the nozzle sac easily reaches to the fuel line pressure at the holder inlet and deviations in the spray configurations decrease. However, there is at least a 5% deviation in spray configuration from hole to hole even at high pressures in the nozzle sac and high needle lift. The main reason for this deviation would be the assembly of the internal parts of the nozzle, especially the rotation of the spring.