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Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

A Diagnostic Technique for Particle Characterization Using Laser Light Extinction

[+] Author and Article Information
Kris Barboza

Department of Mechanical Engineering,
Virginia Tech,
Blacksburg, VA 24061
e-mail: krisbarb@vt.edu

Lin Ma

Department of Aerospace Engineering,
Virginia Tech,
Blacksburg, VA 24061
e-mail: linma@vt.edu

K. Todd Lowe

Department of Aerospace Engineering,
Virginia Tech,
Blacksburg, VA 24061
e-mail: kelowe@exchange.vt.edu

Srinath Ekkad

Department of Mechanical Engineering,
Virginia Tech,
Blacksburg, VA 24061
e-mail: sekkad@vt.edu

Wing Ng

Department of Mechanical Engineering,
Virginia Tech,
Blacksburg, VA 24061
e-mail: wng@vt.edu

Contributed by the Controls, Diagnostics and Instrumentation Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 28, 2015; final manuscript received April 12, 2016; published online May 17, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(11), 111601 (May 17, 2016) (10 pages) Paper No: GTP-15-1466; doi: 10.1115/1.4033468 History: Received September 28, 2015; Revised April 12, 2016

Increased operations of aircraft, both commercial and military in hostile desert environments have increased the risk of micro-sized particle ingestion into engines. The probability of increased sand and dust ingestion results in increased life cycle costs in addition to increased potential for performance loss. Thus, the ability to accurately assess the amount of inlet debris would be useful for engine diagnostics and prognostic evaluation. Previous engine monitoring studies were based on the particle measurements performed a posteriori. Thus, there exists a need for in situ quantification of ingested particles. This paper describes the initial development of a line-of-sight optical technique to characterize the ingested particles at concentrations similar to those experienced by aircraft in brownout conditions using laser extinction with the end goal of producing an onboard aircraft diagnostic sensor. By measuring the amount of light that is transmitted due to the effects of scattering and absorption in the presence of particles over a range of concentrations, a relationship between particle diameters and the laser light extinction was obtained. This relationship was then used to obtain information on diameters and number densities of ingested particles. The particle size range of interest was chosen to be between 1 and 10 μm and the size distribution function was assumed to be lognormal. Tests were performed on polystyrene latex spheres of sizes 1.32 μm, 3.9 μm, and 5.1 μm in water dispersions to measure diameters and concentrations. Measurements were performed over multiple wavelengths to obtain information on the size distribution and number density of particles. Results of tests presented in this paper establish the validity of the laser extinction technique to provide real time information of ingested particles and will serve as an impetus to carry out further research using this technique to characterize particles.

Copyright © 2016 by ASME
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References

Figures

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Fig. 1

Interaction of light with a small particle describing the phenomenon of scattering and extinction

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Fig. 2

Q¯ at two distinct wavelengths versus diameter for increasing distribution widths (indicated in the direction of arrows). Refractive index is taken as m = 1.6143 at λ = 450 nm and m = 1.5633 at λ = 7000 nm for the polystyrene particles.

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Fig. 3

Ratio of Q¯ using 450 nm and 7000 nm lasers at five distribution widths (standard deviations) using polystyrene particles. Note that ripple structure fluctuations of average extinction efficiencies occur at distribution widths close to 1.

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Fig. 4

Variation of R versus distribution width for a diameter of 8 μm using a combination of 450 nm and 7000 nm lasers resulting in a distribution width prediction of 1.2

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Fig. 5

Schematic representation of experimental setup

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Fig. 6

Flow chart illustrating the measurement technique utilized

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Fig. 7

Diameter versus concentration measured compared with actual values for sampled polystyrene particles

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Fig. 8

Concentration measured using 450 nm light for 1.32 μm particles

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Fig. 9

Concentration measured using 635 nm light for 3.9 μm particles

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Fig. 10

Concentration measured using 450 nm light for 5.1 μm particles

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Fig. 11

Standard deviation versus ratio of transmissivities for 5 μm particles

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Fig. 12

Particle size distribution for 1.32 μm polystyrene latex

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Fig. 13

Particle size distributions for 3.9 μm polystyrene latex

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Fig. 14

Particle size distributions for 5.1 μm polystyrene latex

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Fig. 15

Particle diameter measured for the mixed sample

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Fig. 16

Particle concentration measured for the mixed sample with mean diameter of 1.89 μm

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Fig. 17

Particle concentration measured for the mixed sample with mean diameter of 4.3 μm

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Fig. 18

Dependence of diameters measured on refractive index fluctuation

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Fig. 19

Dependence of concentration measured on refractive index fluctuation

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Fig. 20

Ratio of extinction efficiencies for combinations of 635 nm, 450 nm, and 7000 nm lasers using water aerosols

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Fig. 21

Ratio of extinction efficiencies for combinations of 450 nm and 7000 nm lasers using silica dust

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Fig. 22

Ratio of transmissivity R versus diameter using 635 nm and 450 nm laser for a standard deviation of 1.033

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Fig. 23

Ratio of transmissivity R versus diameter using 450 nm and 10,000 nm laser for a standard deviation of 1.033. Note the reduction in the number of possible diameters compared to Fig. 23.

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