A Numerical Study of the Effects of Spray Angle and Swirl Ratio on Combustion and Emission of Diesel Engines

Ekin F., Kafalı M.


  • Publication Type: Conference Paper / Summary Text
  • City: Kastamonu
  • Country: Turkey
  • Page Numbers: pp.581
  • Istanbul Technical University Affiliated: Yes


During combustion process of a diesel engine inside the cylinder, it is very important that the fuel and
air mix homogeneously. Aerodynamic effects due to air movement are very effective in separating diesel fuel
into droplets and evaporating fuel. This effect is dependent on the fuel spray angle of the injector, the spray
pressure, the nozzle diameter of the injector, and the swirl ratio of air taken into the cylinder.
In diesel engines, the fuel-air mixture is formed in the cylinder. For this reason, homogenizing the mixture and
increasing the combustion efficiency takes place in a limited time frame. On the other hand, it is possible to
damp this disadvantage somewhat by modeling the fuel injection process with the air movement formed in the
cylinder. Especially at high speeds, the duration of combustion takes place in a shorter range. For this reason, the
spray angle and the swirl ratio of the air movement must be optimally adjusted.
In this study, the effects of spray angle and swirl ratio on engine performance and emission values are
investigated numerically. The AVL FIRE CFD software is used to obtain numerical results. The numerical
model generated is compared with the experimental results and validated. The original engine's injector spray
angle is 148 degrees and the swirl ratio is 2.37. Numerical results were obtained by examining the effect of
different spray angles and swirl ratios in this study. The values of 140, 148 and 153 degrees as the spray angle
and the values of 2, 2.37 and 2.5 of the swirl ratio were investigated. 9 different cases were created by obtaining
the binary combinations of all these values. The case in which the experimental conditions are modeled is called
"Reference Case". By comparing the other 8 cases both the Reference Case and among themselves, comments
are made on the most optimum conditions in terms of both emission values and performance values.
Whereas highest values of NOx, SOOT and HC emissions are determined at 140 degrees of spray angle and 2 of
swirl ratio, lowest values are determined 153 degrees and 2.5, respectively. Lowest specific fuel consumption per
unit power in terms of performance values is obtained at 153 degree of spray angle, 2 of swirl ratio. Power and
torque values are found to be very close to each other at all spray angle and swirl ratios. When both emission and
performance values are taken into account one can say 153 degree of spray angle and 2.5 swirl ratio value give
better results compared to the reference motor.