Volume 5, Number 2     March/April 1997

  Small Business/SBIR

Phase Doppler Particle Analyzer
Measures Where Other Devices Cannot

NEW MEASURING DEVICE AT NASA'S LEWIS RESEARCH CENTER is developing environmentally friendly engines that give off fewer emissions. The Phase Doppler Particle Analyzer (PDPA) can optically determine the size and velocity of spherical particles, such as fuel and water, without interfering with flow. Older measurement techniques required intrusive probes that changed the environment.

Dr. Valerie Lyons at Lewis said a goal in new gas turbine development is to reduce pollutant emissions from the combustor. "If you optimize the mixing of the fuel and air in the combustor, considering fuel drop sizes and velocities and their evaporation rates, you can reduce emission of nitrogen oxides, carbon monoxide and unburned hydrocarbons," she said. "Nitrogen oxides are of particular interest lately because of their capability to react at high altitudes to destroy ozone molecules."

	Left: Aerometrics Inc. developed the Phase Doppler Particle Analyzer via a contract with Lewis Research Center. The system consists of a laser and an optical system. Below: It receives scattered laser light from the flow.

The first PDPA was developed by Aerometrics Inc. of Sunnyvale, California, in 1983 through a Small Business Innovation Research (SBIR) contract with Lewis Research Center. The system consists of a laser and an optical system, which transmits the laser beam into the flow to be measured, then receives scattered laser light from the flow and interprets the size and velocity data using a personal computer with custom software.

Customized computer software interprets data on size and velocity of scattered laser light received via the optical system.

Greg Payne, Aerometrics technical support engineer, said, "Since the PDPA is an optical technique, it can be used in areas where other measuring tools cannot. The Phase Doppler Particle Analyzer can be used anywhere someone needs to measure small, round particles, like in fuel injection systems, medical nebulizers and bubbles in water."

Mark Klem of NASA Lewis said the PDPA "can measure the drop size in sprays. You have to know the drop size to determine how long combustion will occur: When the droplet burns up, combustion is over."

How can the Phase Doppler do all of this and not get in the way? According to Aerometrics, the PDPA method is based on light scattering interferometry. Measurements are made in a small, nonintrusive optical probe volume defined by the intersection of two laser beams. As particles pass through the probe volume, they scatter light from the beams and create an interference fringe pattern. A receiving lens at an off-axis collection angle projects part of this fringe pattern onto detectors, which produce a Doppler burst signal with a frequency proportional to the particle velocity. The phase shift between the Doppler burst signals from the different detectors is proportional to the size of the spherical particles.

This development by Aerometrics can measure particle size and velocity simultaneously in the probe volume. It requires no calibration because the particle size and velocity depend only on the laser wavelength and optical pattern.

For more information on the Phase Doppler Particle Analyzer,
contact Greg Payne at Aerometrics, Inc. Call 408/738-6688.
Or contact Dr. Valerie Lyons at the Lewis Research Center. Call 216/433-5728.
Or contact Mark Klem at Lewis. Call 216/977-7473.
Please mention you read about it in Innovation.