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Atomizer Research and Selection Process

Atomizer Research and Selection Process

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Atomizer Research and Selection Process

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  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 Electrostatic

  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 Length<30mm Outside Dia<15mm Negatives Can’t 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 Length<30mm Outside Dia<15mm Positives Small Light Easy to fabricate Easy to modify Cheap to build Competitive droplet sizes Negatives Can’t 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) External Mixing Internal 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 Fuel Flow Air Flow • 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, ρAUR2 • Air Density, ρA

  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. MOMENTUM • 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 • The fuel mixture phase changes to vapor quickly and breaks up the stream into small droplets with a wide dispersion angle F. Schmidt [2002]

  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

  37. Relative comparison results

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