Spray Technology

Sprays are used in many industrial processes, and understanding spray trajectories and evaporation rates is crucial to their proper implementation. Southwest Research Institute (SwRI) offers a broad spectrum of services associated with characterizing and modeling sprays in industries, such as:

• Manufacturing
• Refineries
• Agricultural
• Medical

Experienced engineers, chemists, and scientists, complemented by state-of-the-art instrumentation and unique test facilities, are teamed to provide a responsive resource for any spray-related problem. SwRI offers a wide variety of spray services. Those services discussed in this brochure include:

• Spray characterization
• Spray modeling
• Atomizer design
• Spray consultation

Spray Characterization

Spray characteristics greatly affect the evaporation or congealing rate of spray droplets. To determine optimum spray characteristics under varying conditions and atomizer configurations, SwRI engineers evaluate and measure factors such as:

• Droplet size and spray shape
• Droplet velocities
• Spray jet cone angle
• Spray and droplet penetration rate

To measure these characteristics, SwRI uses state-of-the-art laser-based systems, high-speed film and video cameras, and laser-strobe photography as part of a wide spectrum of spray instrumentation capability.

• An Aerometrics phase-Doppler particle analyzer acquires droplet size, velocity, and liquid volume flux distributions with high spatial resolution, and resolves sizes from 1 to 2,000 micrometers with a dynamic range of 35 at any setting.
  
  
• A Malvern model 2600 laser-diffraction particle-sizing instrument determines droplet size and liquid volume fraction along the laser's line-of-sight through the spray, and resolves sizes from 1 to 1,200 micrometers with a dynamic range of 100 at any setting.
  
  
• A Hycam-II high-speed movie camera provides full-frame framing rates up to 11,000 frames per second and quarter-frame framing rates up to 44,000 frames per second.
  
  
• A Kodak Spin-Physics high-speed video camera allows full-frame framing rates up to 2,000 frames per second and sixth-frame framing rates up to 12,000 frames per second.
  
  
• An Nd:YAG laser strobe provides high-energy, six-nanosecond pulse duration to freeze spray motion, enabling high-resolution photography.
  
  
• A copper vapor laser, when synchronized to high-speed cameras, maintains high-energy pulses at 10 kHz rate, freezing the spray motion and permitting very high framing rates.

Air pressure and temperature play key roles in determining spray angles, droplet sizes, and velocities. Sophisticated test facilities enable Institute staff members to study spray phenomena such as penetration, evaporation, and breakup over a broad range of pressures and temperatures. SwRI spray facilities include:

• Low-turbulence ambient spray chamber
  This spray facility passes a low-turbulence airflow, adjustable from 0.1 to 1.0 meter per second, through a 0.3-meter square test chamber. The chamber uses a bellmouth and two honeycomb flow straighteners to smooth the airflow. A chilled metal screen condenses the spray from the airstream.

Using the Institute's high-pressure, high-temperature apparatus, engineers study burning diesel sprays to evaluate spray characteristics such as jet cone angle and penetration rate.

• High-pressure, high-temperature flowing gas facility
  This facility permits spray tests at air pressures from 0.1 to 1.5 MPa (1 to 15 atm), air temperatures from 35° to 800°C, and air mass flows up to 1.1 kg per second. Flowing gas allows use of optical spray diagnostics without the spray contaminating the viewing window.

To evaluate spray atomization, scientists use high-pressure, high-temperature flowing air spray chambers that minimize problems of spray collection on the chamber windows.

• High-pressure, high-temperature static gas apparatus
  Capable of reaching air pressures of 8.3 MPa and temperatures of 550°C, the Institute's high-pressure static gas apparatus is particularly suited for diesel spray evaluation. SwRI engineers have studied diesel injection systems, including unit injectors and pump-line-nozzle systems, at injection pressures up to 300 MPa.

Fuel sprays are studied at realistic pressures and temperatures in this high-pressure, high-temperature apparatus.

• Subatmospheric pressure flowing gas facility
  Some systems inject fuel sprays into air below atmospheric pressure. This facility allows characterization of these sprays under realistic conditions, providing pressures down to 34 kPa absolute (one-third atm).

Atomizer Design

Institute staff members design atomizers to meet a variety of requirements, including:

• Air-assist injectors for automotive port fuel injection and gas turbine combustors
• Rotating discs for spray drying explosives
• Rotating wheels for atomization of coal-water slurries

Spray Consultation

SwRI engineers and scientists offer expert consultation on a wide range of spray topics. Previous projects include:

• Fuel injection in spark-ignition, compression-ignition, and gas turbine applications
• Spray drying of detergent additives and explosives
• Spray congealing of plastics and explosives

Extensive facilities such as this high-pressure, high-temperature laboratory allow SwRI engineers to evaluate and diagnose spray problems for real-world applications in a timely manner.

Spray Modeling

SwRI engineers use sophisticated software programs to predict the reaction of sprays at different pressures and temperatures. These algorithms include:

• TESS^TM predicts trajectories and evaporation rates of dilute sprays. This commercially available model, which includes liquid properties for water, alcohols, and hydrocarbon fuels, is used to predict polydisperse droplet-size distributions and changes in distribution caused by droplet evaporation and the loss of droplets due to wall collisions.
  
  
• JETMIX is an Institute-developed model that simulates fuel jet performance in diesel engines, predicting fuel-air mixing and jet penetration rates.

SwRI characterizes sprays from all types of spray nozzles and fuel injectors for a wide variety of applications, including:

• Gasoline fuel injectors
  • Port fuel injectors
  • Throttle body injectors
  • Direct in-cylinder injectors
    
    
• Diesel fuel injectors
  • Unit injectors
  • Common rail injectors
  • Jerk pump injectors
    
    
• Gas turbine fuel injectors
  • Pressure swirl atomizers
  • Air blast atomizers 
    
    
• Fuel atomizers for burners and boilers
  • Pressure swirl
  • Y-jet
    
    
• Atomizers for industrial processes
  • Pressure atomizers
  • Spray drying
  • Spray congealing
    
    
• Agricultural spray nozzles
  • Pressure atomizers
  • Fan jet atomizers
  • Air-assist (twin-fluid) atomizers
    
    
• Nebulizers for medical applications
  
  
• Spray nozzles for residential and personal applications
  • Room fresheners
  • Hair sprays
  • Aerosol filter efficiency tests

This brochure was published in February 1998. For more information about spray technology, contact Ryan Roecker, Manager, Engine, Emissions and Vehicle Research Division, Southwest Research Institute, P.O. Drawer 28510, San Antonio, Texas 78228-0510, Phone (210) 522-3195, Fax (210) 522-2019.

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