Nozzle orifice geometry is known to influence the flow inside the nozzle, which in turn affects the spray development, thus impacting combustion and emission processes. In the past, modeling studies have focused on the influence of nozzle orifice geometry on the flow inside the orifice only. This is mainly due to the lack of a suitable primary breakup model.
Argonne engineers, with the help of the KH-ACT model, investigated the influence of nozzle orifice geometry not only on nozzle flow, but on spray, combustion and emission characteristics.
Three different nozzle geometries were investigated (Figure 1):
- Cylindrical (K=0, r/R=0)
- Conical (K=2, r/R=0)
- Hydroground (K=0, r/R=0.014)
Influence of Nozzle Geometry on Spray Penetration
From cavitation simulations it was observed that the cylindrical nozzle was cavitating with patterns reaching the nozzle exit. However, with the conical and hydroground nozzles, cavitation inception could almost be inhibited (Figure 1). The exit density was observed to be about 4 percent lower for the cylindrical nozzle. The turbulence at the nozzle exit was higher for a cylindrical nozzle compared to a conical nozzle. (Figure 2)
The KH model predicts a decrease in spray tip penetration with increase in the Kfactor. This is in disagreement with the experimental trends observed. The KH-ACT model captures the experimental trend accurately, i.e., with increase in the Kfactor, the spray tip penetration increases.
It is well established that imploding cavitation patterns and turbulence patterns from the nozzle destabilize the jet, thus promoting faster atomization which leads to lower spray penetration. Standard primary breakup models like KH are aerodynamics-based and hence do not capture the nozzle flow effects.
Spray and Combustion Characterization
The flame lift-off and liquid lengths vs. time after SOI for the three nozzles were plotted. Consistent with spray penetration trends, the liquid length was shortest for the cylindrical nozzle due to faster liquid breakup and smaller droplets produced with this nozzle. (Figure 3)
However, the lift-off length is smallest for the conical nozzle and largest for the hydroground nozzle. This behavior is related to the amount of fuel injected, vaporization rate, and fuel-air mixing for the three nozzles. Since the rate of fuel injection and total amount of fuel injected were highest for the hydroground nozzle, it formed a richer mixture, implying lower flame base upstream propagation speed. Consequently, the flame was stabilized further downstream for this nozzle. In contrast, the fuel injection rate and total fuel injected were lowest for the conical nozzle, and consequently, the lift-off length was smallest for this nozzle.
This work is supported by the U.S. Department of Energy’s Vehicle Technologies Program under Gurpreet Singh. The University of Illinois at Chicago collaborated with Argonne.
- S. Som, A.I. Ramirez, D.E. Longman, S.K. Aggarwal, “Effect of nozzle orifice geometry on spray, combustion, and emission characteristics under diesel engines conditions,” Fuel 90: 1267-1276, 2011.
- S. Som, A.I. Ramirez, S.K. Aggarwal, E. El-Hannouny, D.E. Longman, “Investigating the Nozzle Flow and Cavitation Characteristics in a Diesel Injector,” Journal of Engineering for Gas Turbine and Power 132: 1-1 to 1-12, 2009.
- S. Som, S.K. Aggarwal, “Effects of Nozzle Orifice Geometry and Primary Breakup Model on Flame Characteristics in Diesel Engines,” 6th Mediterranean Combustion Symposium, Corsica, France, June 2009.