ID 142

Dribble Quantification for Diesel Fuel Injectors

 

Abstract:

Fuel injector dribble is low velocity fuel that leaves the injector sac through the orifices in the form of liga-ments and large droplets after the primary injection event. The volume of fuel leaving the sac after the end of injection represents a significant source of unburned hydrocarbons (UHCs) in diesel engines; therefore, quanti-fying the dribble event is critical to understanding, modeling, and abating the emission of this pollutant. A high-speed dribble imaging diagnostic has been developed to quantify the fuel injector dribble in a constant-pressure unheated vessel via two complementary approaches. Using the first approach, the total dribble is determined by identifying liquid droplets and ligaments in an image, assuming they are axisymmetric oblate or prolate spheroids, and computing their volume. The second approach tracks the liquid fuel flux through a small interrogation region near the orifice exit, allowing the time-varying dribble rate and duration to be meas-ured and total dribble volume to be determined by integration. Simple particle tracking velocimetry (PTV) enables measurement of the average dribble velocity and reconciliation of the two approaches. At 3MPa stat-ic ambient pressure, the dribble event is stochastic, lasting several milliseconds with an average velocity near 3m/s. Results confirm that dribble volume is generally proportional to sac volume and independent of the number of orifices. The developed diagnostic technique enables statistical analysis of dribble behavior, foster-ing understanding of how dribble is affected by sac geometry and operating conditions, thereby enabling design optimization via subsequent simulations of these fuel-born UHC sources.