Theoretical and experimental study (linear stability and Malvern granulometry) on electrified jets of diesel oil in atomization regime

1
Theoretical and experimental study (linear
stability and Malvern granulometry) on
electrified jets of diesel oil in atomization
regime

• L. Priol, P. Baudel, C. Louste, H.
  RomatLaboratoire dEtudes AérodynamiquesPoitiers
  ,France
• Laurent.Priol_at_lea.univ-poitiers.fr
• Christophe.Louste_at_lea.univ-poitiers.fr

2
Summary

• Introduction
• Linear stability theory for charged jets
• Dispersion relation
• Numerical results
• Experiments
• Experimental device
• Experimental results (laser granulometry)
• Conclusion

3
Introduction

• The dynamic of fuel droplets a critical
  importance in the behaviour of liquid fuel
  disintegration in combustion system

• Effects of electric charges, velocity, viscosity
  and electrostatic forces on the stability of an
  electrified jet

• Measurement of the size distribution of droplets
  with Malverns Spraytec

4
Linear stability analysis

• Disturbance on the surface of an axisymmetrical
  liquid jet

5
Linear stability analysis

• Dispersion relation between ? and k, found by
  Reitz1

1 R.D. Reitz and F.V. Bracco, Mechanism of
breakup of round liquid jets, Encyclopedia of
Fluid Mechanics, Gulf Pub., N.J., vol. 3,
pp.233-249, 1986
6
Linear stability analysis

• Dispersion relation between ? and k

7
Numerical treatment of the dispersion relation

• Dimensionless growth rate
• Dimensionless wave number ka
• Initial charge density s0 3 10-4 C/m²

• With electric charges
• Higher growth rate
• Smaller diameter droplets

The electrical charges destabilize the jet
8
Experimental device
9
Electrification system
10
Pressure 70 bars, Potential -30kV
11
Malvern granulometry experiments

• Malvern measures droplets from 1 µm to 250 µm
• Measurements based on Mies diffraction theory
• Real time spray measurement at up to 2500 Hz
• Laser beam diameter of 10 mm

12
Experimental results
Real time evolution of different diameters of
droplets for p80 bars, z40 mm and x0 mm
13

• Dv90350 µm

90 of the total volume is occupied by droplets
which have a maximal diameter of 350 µm
14
Experimental results

• Droplet size distribution for a driving pressure
  of 120 bars at z30 mm, x0 mm (center of the jet)

Volume cumulate distribution ()
Volume of the class diameter ()
Volume cumulate distribution ()
Volume of the class diameter ()
Diameters µm
Diameters µm
Potential 0kV
Potential -25kV
15
Dv75320 µm
Potential 0 kV -25 kV
Volume of class diameter of 20 µm 2.5 5
Volume of class diameter of 200 µm 4 6
Volume of class diameter of 350 µm 12 1
75 of the total volume contain droplets with
maximal diameter of 320 µm
Potential 0 kV -25 kV
Diameter droplet for Dv75 320 µm 160 µm
16
Experimental results

• Droplet size distribution for a driving pressure
  of 120 bars at z30 mm, x5 mm (edge of jet)

Volume cumulate distribution ()
Volume cumulate distribution ()
Volume of the class diameter ()
Volume of the class diameter ()
Diameters µm
Diameters µm
Potential 0kV
Potential -25kV
17
Dv75300 µm
Potential 0 kV -25 kV
Volume of class diameter of 20 µm 6 9
Volume of class diameter of 200 µm 8 1
75 of the total volume contain droplets with
maximal diameter of 300 µm
Potential 0 kV -25 kV
Diameter droplet for Dv75 300 µm 160 µm
18
Conclusion

• Dispersion relation with electrostatic forces
  shows the destabilizing role of the electric
  charges in the jet
• For an electrical charged jet the theory predicts
  a decrease of the droplet mean diameter
• Theoretical results confirmed by experimental
  measurements obtained by laser granulometry

Better atomization of a jet thanks to the
injection of electric charges