Atomizer Research and Selection Process

1
Atomizer Research and Selection Process

• Scott DeClemente, Tim Griffin,
• Evan Claytor, Jon McClure,
• Chris Martin, David Anderson

2
Atomizer Requirements

• Size
• Must be compatible with current design space
• Fuel flow-rate
• Operating Pressure
• Between 300-500 psi
• Droplet size
• Must maintain a droplet size less than 80
  Microns
• Bandwidth
• Greater than 500 hz
• Lifetime
• As long as standard injectors

3
Atomizer Requirements

• Other Considerations
• Flow rate range
• Scaling
• Cost
• Susceptibility to
• Damage, gumming, build up
• Uniform fuel distribution

4
Overview

• Literature Search
• Single Flow Atomizers
• Dual Flow Atomizers
• Comparison Chart
• Top Three Atomizer Choices

5
The first step is understanding the nature of the
beast.
Problem Statement
What makes a design Good? What is the climate in
the industry already? Understanding the industry
orients the Engineers.
Establish Criteria
Generate Ideas
Refine the good, Eliminate the bad
Iterate
TEST THE IDEA
STRATEGY!
Solution
6
A multitude of resources yielded diverse results.
Almost no specific information Helped establish
list of atomizer types

• Web (corporate sites)
• Research Publications
• Patents
• Texts
• Corporate Catalogues

Reliable, geometry-specific data Helped establish
typical performance
No performance information Offered a good feel
for how current designs work
General performance overviews with research
data Helped establish industry standards and
terminology
Establish possibility of adaptation or
modification of current designs Establish
up-to-date industry standards
7
We identified a number of existing atomizer
designs.
8
Single Flow Atomizers
Plain Orifice Atomizer Simplex Atomizer Electrosta
tic
9
Plain Orifice Atomizer
Simple nozzle Creates pressure drop
10
Graphical Results
11
Analytical Approach
(Fluent,2003)
12
Goal Comparison
Positives Small Light Easy to fabricate Easy
to modify Cheap to build Competitive droplet
sizes
Lengthlt30mm Outside Dialt15mm
Negatives Cant independently control SMD and
mass flow Large pressures are needed for SMD
70g (Delavan,2003)
Removable nozzle tips (delavan,2003)
Driving force for SMD
40-80microns
13
Simplex Atomizer
Plain orifice with addition of swirl pot Swirl
pot creates shear layers Layers break into
smaller droplets
14
Graphical Results
(Vandsburger, 2003)
15
Analytical Approach
do - most probable droplet size Ks
wavelength Oh Ohnesorge number
(Fluent, 2003)
16
Goal Comparison
Lengthlt30mm Outside Dialt15mm
Positives Small Light Easy to fabricate Easy
to modify Cheap to build Competitive droplet
sizes
Negatives Cant independently control SMD and
mass flow Large pressures are needed for SMD
70g (delavan,2003)
Removable nozzle tips (delavan,2003)
Driving force for SMD
40-80microns
17
Electrostatic Nozzles

• Atomize by inducing a charge in the fluid.
• Provide very small, easily controllable drop
  sizes
• SMD(1-100µm)
• Low droplet coalescence
• Used most commonly for painting and metallic
  powder formation

CFDRC Electrostatic atomizer
18
Analysis of Electrostatic Nozzles
Dielectric constant is the most important
factor of atomization
Electrostatic atomizer(Lee)
19
Twin flow atomizers

• Air assist
• Plain jet air blast
• Simplex air blast
• Pre-filming
• Piloted

(Delavan)
20
Air assist atomizers use small quantities of air
at high velocity.

• Two classes

(Lefebvre)
(Lefebvre)
Internal Mixing
External Mixing
21
Performance of external air assist
SMD under 30 microns SMD modulation Mass flow
modulation Fuel Supply Pressure
(Lefebvre)
22
External air assist nozzles are readily available.
23
Size and modification
(Delavan)
(Delavan)
24
Dual Flow Atomizers

• Plain Jet Air Blast
• How it works?
• Shear Forces between colliding air flow and fuel
  flow
• Goal to maximize contact area between fuel flow
  and air flow
• High velocity air relative to low velocity fuel
• Low Fuel Pressure Relative to Pressure Swirl and
  Air Assist Atomizers
• Main Mechanisms of Atomization
• Air Velocity, UA
• Air to Liquid Ratio, ALR
• Dynamic force, ?AUR2
• Air Density, ?A

25
Dual Flow Atomizers

• Plain Jet Air Blast
• Experimental Data
• SMD range between 30 and 90µm with Kerosene as
  fuel
• Effective air velocities between 60 and 300 m/s
• Over 120 m/s there is little added effect of air
  velocity
• Analytical Results
• SMD range between 20 and 65µm

26
Dual Flow Atomizers

• Plain Jet Air Blast

27
Dual Flow Atomizers

• Plain Jet Air Blast

28
Dual Flow Atomizers

• Plain Jet Air Blast

29
Simplex-Airblast Atomizers combine pressure swirl
with airblast technology.

• Fuel is injected tangentially in inner chamber.
• Angular momentum drives the fuel into a conical
  sheet.
• The liquid sheet is impinged upon by high
  velocity air.

30
Airblast technology offers multiple knobs to turn.

• SMD is a function of both air velocity and fuel
  flow!

Air Flow?
Air Vectoring?
Lefabure
31
Dual Flow Performance of the Piloted air blast
nozzle

• High relative fuel velocity
• Improved performance at startup and lean blowout
  over other air blast nozzles
• Can contain the basic features of any dual flow
  nozzle

32
An pre-filming air-blast atomizer shears the fuel
stream with an air flow to increase atomization

• The addition of the external air stream past the
  sheet produces smaller droplets than without the
  air

The flow-rate of the of air stream may be
controlled to alter atomization characteristics
33
An pre-filming air-blast atomizer shears the fuel
stream with an air flow to increase atomization
34
Effervescent atomizers inject a super-heated
fluid into the main liquid flow
F. Schmidt 2002

• The fuel mixture phase changes to vapor quickly
  and breaks up the stream into small droplets with
  a wide dispersion angle

35
The criteria used for judging nozzle viability

• Sauter Mean Diameter
• Geometry
• Availability
• Independent SMD/fuel flow modulation
• Relative fuel supply pressure
• Ease of modification
• Ease of fabrication

36
Relative comparison between atomizers
Weighting Factor 2 2 2 2 1 3 2
Atomizer SMD Geometry (size) Availability Independent SMD/Fuel flow Modulation Relative Fuel Supply Pressure Ease of Modification Ease of Fabrication
Plain Jet Air Blast 3 2 2 2 3 3 3
Plain Orifice 2 3 3 0 2 3 3
Simplex 2 3 3 0 2 3 3
Simplex Air Blast 3 2 2 2 3 3 3
Air Assist 3 1 1 2 2 2 2
Piloted Air Blast 3 1 1 2 3 1 1
Pre-filming air blast 3 1 2 1 3 1 1
Effervescent 3 1 1 1 1 1 1
Electrostatic 3 3 2 3 1 1 1

37
Relative comparison results
Atomizer Total Pts Final Rank
Plain Jet Air Blast 36 1
Plain Orifice 33 3
Simplex 33 4
Simplex Air Blast 36 2
Air Assist 25 6
Piloted Air Blast 21 8
Pre-filming air blast 22 7
Effervescent 18 9
Electrostatic 28 5
38
Conclusion

• Top three atomizers based on relative comparison
• Plain Jet Air Blast
• Simplex Air Blast
• Plain Orifice
• Questions?