Method and system for particle characterization and identification

Abstract

Disclosed herein is a novel, compact optical particle identification and characterization system and method of use within both gaseous and liquid media. The system can implement both elastic and inelastic light scattering techniques simultaneously under the same sensor platform. By separating the sensing components from the electro-optical unit and using optical fibers for interconnection, only the sensing components need to be exposed to the environmental conditions. This reduces the design constraints on the electro-optical unit and permits the incorporation of optical components into the sensing probe that can withstand high-temperature, high-pressure, and corrosive environments. Thus, the system can be used in benign, moderate, and harsh environments.

Claims

1. A system for optically detecting particles and determining their constituent composition while simultaneously measuring size distributions and mass concentrations in a flowing gas or a liquid, the system comprising: one or more sensing probes each consisting of one or more light source pathways and one or more sensing pathways, where each source pathway directs an ultraviolet, visible, or infrared light beam through optional beam-shaping optics and into one or more detection zones and each sensing pathway collects light scattered from particles in the detection zones with optional collection optics and relays those optical signals to the electro-optical unit; one or more electro-optical units that house one or more ultraviolet, visible, or infrared light sources, one or more detectors, an optional spectrometer, corresponding light source, detector, and/or spectrometer control, optic components, processing electronics, and a signal classifier for each electrical signal, where each detector converts the optical light scattering signal generated by particles passing through the detection zones into a pulsed electrical signal whose amplitudes depend on the particle size, particle shape, and particle composition and each signal classifier provides a plurality of size channels into which the measured pulsed signals are classified, and signal processing hardware to convert the classified pulsed signals into particle statistics including particle distribution, total particle volume, average particle size, average particle surface area, particle mass concentration, and material identification; and one or more optical fiber connections between the sensing probes and electro-optical units.

2. The particle identification and measurement system described in claim 1 where only one sensing probe and one electro-optical unit are used.

3. The particle identification and measurement system described in claim 1 where only one light source and/or one, two, or more detectors and/or a spectrometer are included.

4. The particle identification and measurement system described in claim 1 where one light source and one detector are coupled on two separate optical fibers or only one optical fiber with the use of a fiber coupler.

5. The particle identification and measurement system described in claim 1 where either multi-angle light scattering, multi-wavelength light scattering, or Raman scattering spectroscopy or a combination thereof are used to identify the particle composition.

6. The particle identification and measurement system described in claim 1 deployed with multiple light sources which may have same or different emission wavelengths.

7. The particle identification and measurement system described in claim 1 wherein the signals from two or more detectors are summed, differenced, or ratioed to provide material identification, noise cancellation, or other signal processing and interpretation.

8. The particle identification and measurement system described in claim 1 where a notch filter or dichroic filter separates the light and guides the elastic scattering component to a detector and the inelastic scattering component to a spectrometer.

9. The particle identification and measurement system described in claim 1 where the signal classifier is a multichannel pulse height discriminator or signal analyzer which provides a plurality of size channels numbering from 1 to 16,777,216 channels.

10. The particle identification and measurement system described in claim 1 where the interconnecting optical fibers for one sensor probe are all contained within one optical fiber cable.

11. The particle identification and measurement system described in claim 1 where light along the optical paths in the sensing probe is spatially beam shaped to achieve a defined performance at the sensing location.

12. The particle identification and measurement system described in claim 1 where each optical path has its own set of optical elements to shape the beam or optical elements are shared on multiple optical paths.

13. The particle identification and measurement system described in claim 1 where the sensing probe is capable of withstanding pressures between 0 psia (0 MPa) and 250 psia (1.7 MPa) or more.

14. The particle identification and measurement system described in claim 1 where the sensing probe is capable of withstanding temperatures between 100 F. (73 C.) and 570 F. (300 C.) or even possibly higher.

15. The particle identification and measurement system described in claim 1 where the outer housing of a sensor probe comprises a predetermined shape, wherein this predetermined shape is generally cylindrical and may include one end threaded to secure the sensor probe to a mounting location.

16. The particle identification and measurement system described in claim 1 deployed multiply or in a distributed fashion where the system could share common light sources or multiple detectors.

17. A method for optically detecting particles and determining their constituent composition while simultaneously measuring the size distributions and mass concentrations in a flowing gas or a liquid, the method comprising: providing a sensing probe in one or more locations, wherein each sensor probe consists of at least one light source pathway and at least one sensing pathway, where each source pathway directs one or more ultraviolet, visible, or infrared light beams through optional beam-shaping optics and into one or more detection zones and each sensing pathway collects light scattered from particles in the detection zones with optional collection optics and relays those optical signals to the electro-optical unit; providing one or more electro-optical units in one or more locations, wherein each electro-optical unit houses one or more light sources, one or more detectors, corresponding light source, detector, and/or spectrometer control and processing electronics, and a signal classifier for each electrical signal, where each detector converts the optical light scattering signal generated by particles passing through the detection zones into a pulsed electrical signal whose amplitudes depend on the particle size, particle shape, and particle composition and each signal classifier provides a plurality of size channels into which the measured pulsed signals are classified, and signal processing hardware to convert the classified pulsed signals into particle statistics including particle distribution, total particle volume, average particle size, average particle surface area, particle mass concentration, and material identification; and providing one or more optical fiber connections between the sensing probes and electro-optical units.

18. The method of claim 17 applied to monitoring particle flow in a gas turbine engine to provide early warning and protection from excessive dust ingestion.

19. The method of claim 17 applied to monitoring the effectiveness of a filtration system by measuring the particle concentration before and after filtration.

20. The method of claim 17 applied to contamination monitoring of liquid media such as water, oils, or lubricants and gaseous media such as air or industrial gases where cleanness is of concern.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1 shows the particle identification and measurement system concept with sensor probe, electro-optical unit including light sources and detectors, and interconnecting optical fiber(s).

[0019] FIG. 2 illustrates an example of a specific flush-mounted implementation of the particle identification and measurement system with one laser light source and three optical detectors. A flush-mounted implementation allows for minimal flow field disturbance such as for engine flows.

[0020] FIG. 3 describes both elastic scattering and inelastic scattering with an energy-level diagram (upper) and a spectral plot (lower).

[0021] FIG. 4 displays the unique Raman spectra for a few selected compounds.

[0022] FIG. 5 illustrates example computer simulations of the effect of refractive index on the ratio of scattering intensities from two receivers at different angles.

[0023] FIG. 6 illustrates the refractive index variation with wavelength for a few selected compounds. Some compounds are relatively invariant while others vary significantly.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The above, as well as other objects and advantages of this disclosure, will become readily apparent to those skilled in the art from reading the following description of an embodiment of the invention. The description and drawings illustrate exemplary embodiments of the invention and serve to enable one skilled in the art to make or use the invention and are not intended to limit the scope of the invention in any manner. With respect to the methods disclosed and illustrated, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical.

[0025] As used herein, the terms first, second, third, and fourth may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components.

[0026] The present disclosure uses an in-situ approach wherein a sensor probe separates the light source(s), detector(s), and electronics from the harsh measurement zone by using an interconnecting optical fiber cable. Some of the interconnecting optical fibers transmit the light source(s) to the detection zone and may also simultaneously transmit the measured scattered light back to the detectors through either a single cable connector or multiple connectors. The optical fiber configuration can range anywhere from multiple single-core fibers to one multi-core fiber to a single single-core fiber with multiplexed data to any combination thereof. Individual optical fibers can be either multi-mode optical fibers, single-mode optical fibers, or polarization-maintaining optical fibers, as determined by the requirements of the sensor system and the system may include any combination of these optical fibers. If desired, the sensor probe could be mounted flush to the process wall and have a single connector. The sensor probe contains beam-shaping optics, collection optics, optical apertures, and optical fibers, all of which can be designed to survive high temperature environments, since only optical components and no electronic components are included in the sensing probe. For applications with spatial variation in particle characteristics and materials, such as engine dust ingestion, multiple sensors could also be placed at multiple sensing locations.

[0027] The fiber-based probe design is flexible and allows implementation of single or multiple light sources and single or multiple optical detectors at the same time. FIG. 1 illustrates in schematic form, a sensor system 100 for accomplishing the invention. More specifically, there is provided an electro-optical unit 110 connected via optical fibers 120 to a sensor probe 130 to measure the particles in a particle-laden flow 140. An entire sensor system may also include one or more electro-optical units 110, one or more optical fibers 120, one or more sensor probes 130, and may interrogate one or more particle-laden flows 140. The electro-optical unit 110 may include one light source 101 or multiple light sources 102 and one detector 105 or multiple detectors 106 along with any additional optical components necessary to control the light transmitted from the light sources and to control the processing of the light returned into the detectors. The sensor probe 130 consists of only optical components to control the light transmitted to and from the particle-laden flow 140. The sensor probe 130 may include single or multiple pathways for both transmitted light 125 and returned light 126. Interconnection with optical fibers provides the advantage of flexible sensor mounting and placement while only exposing the sensor probe to harsh environments with moderate or high temperature and pressure, such as found in a gas turbine engine. Furthermore, this design allows a 1n (or even mn) coupler to be used if more light sources, more detectors, and/or more locations are monitored. In addition to design requirements such as dust size and range, flow rate or particle velocity, and concentration limit mentioned above, typically, sensor calibration for dust size quantitation is also required.

[0028] FIG. 2 shows an example implementation of this invention with one light source and three optical detection pathways. This example permits complimentary material identification by simultaneously using MALS and RSS, and characterization of particle size, distribution, and concentration. More specifically, a sensor probe 240 is connected to an electro-optical unit 200 using an optical fiber cable 220. A light source 202 transmits light through an optical fiber 213 to a directional fiber coupler 214 if the transmitted light shares a single fiber with the returned light. That fiber coupler transmits the light via optical fiber 215 to a first optical fiber connector 217 that is at the exterior of the electro-optical unit 200. Optical fiber connector 217 and all other optical fiber connectors in the system may consists of single or multiple fiber cores and may also consist of more than one connector. Similarly, optical fiber cable 220 may consist of single or multiple fiber cores and may also consist of more than one cable. A second optical fiber connector 218 connects to fiber connector 217 and transmits the light source through an optical fiber core in the optical fiber cable 220 to a third optical fiber connector 222. A fourth optical fiber connector 223, on the exterior of the sensor probe 240, connects to fiber connector 222 and transmits the light source into the sensor probe 240 via optical fiber 232. It should be noted that any pair of optical fiber connectors (217 and 218 or 222 and 223) may be replaced by a continuous section of optical fiber, removing the ability to separate the optical path at that location. The light leaving optical fiber 232 may either be directly transmitted or may be reshaped using optical components 235, such as lenses. The transmitted light then passes through a window 237 to a sensing location 250 in the particle-laden flow 251. The spatial beam-shaping performed in 235 is done to achieve a defined performance at 250 and is known to those skilled in the art. In this illustration, the sensor probe 240 is mounted flush to a wall 245 which confines the particle-laden flow 251. Whether the sensor probe is mounted flush is dependent on the application and is readily apparent to those skilled in the art. All elements of the sensor probe 240 are contained within an outer housing 239 with openings for the fiber connector 223 and window 237. The body of outer housing 239 may also have a predetermined shape, such as a cylinder with a threaded end 241, configured to secure the probe into existing locations in the measurement application.

[0029] Particles in the sensing location 250 return scattered light back into the sensor probe 240. The first scattered light passes into optical fiber 232 either directly or by passing through optical components 235. Similarly, the second scattered light passes into optical fiber 233 either directly or by passing through optical components 234. The spatial beam-shaping performed in 235 and 234 also achieves a defined performance at 232 and 233 for collected light and is known to those skilled in the art. Light entering optical fiber 232 passes back through the optical fiber cable 220 and enters optical fiber 215 using the same pathway as the transmitted light. In the directional fiber coupler 214 the returned scattered light is separated from the transmitted light and sent into optical fiber 211 and on to detector 205. Any method, known to those skilled in the art, can be used to separate the transmitted and returned light when they share the same fiber, for example polarization rotation or directional coupler. Light entering optical fiber 233 is directed sequentially through the fourth optical fiber connector 223, the third optical fiber connector 222, the optical fiber cable 220, the second optical fiber connector 218, the first optical fiber connector 217, and into optical fiber 210 where it is separated using optics 208 and then passed on to detector 206 and spectrometer 207. The light separation by optics 208 may consist of any separation method including combinations of beamsplitters, wavelength dispersion, wavelength rejection, or wavelength selection elements. Example elements of 208 may include a beamsplitter, notch filter, long-wave-pass filter, or dichroic filter and are known to those skilled in the art. The components of the electro-optical unit 200 are controlled by a controller/processor 201 which provides voltage control, current control, and signal control to light source 202, detector 205, detector 206, and spectrometer 207 and also processes the signals from detector 205, detector 206, and spectrometer 207. The controller/processor 201 may also include individual control elements or signal processing elements at each component.

[0030] An example of processing hardware that may be included in 201 is a signal classifier. The signal classifier is an electronic device such as a FPGA- or DSP-based multichannel signal analyzer that classifies particles based on the pulse height of their scattering signal and is known to those skilled in the art. Based on the pulse amplitude of the detector signal created by a passing particle, the diameter of the particle can be classified. The classified diameters are then processed into particle characteristics such as particle size distribution, particle load rate (also known as total number concentration and similar), and particle mass concentration. For engine applications, the particle identification and measurement system may be interfaced with an engine control unit to provide both engine health management and early warning of periods of excessive dust ingestion.

[0031] It should be obvious to those skilled in the art, that many variations on FIG. 2 are possible. Additional or fewer light sources, detectors, fibers, and connectors may be included in the sensor probe 240, the electro-optical unit 200, and the optical fiber cable 220. Additional sensor probes 240, electro-optical units 200, and optical fiber cables 220 may also be included in a complete particle measurement system, especially for measurements at multiple distributed locations. The location of one optical fiber with respect to another optical fiber within the sensor probe can also be flexible. For example, optical fiber 232 and optical components 235 could be adjacent to optical fiber 233 and optical components 234, to build a compact probe. Alternately, a prescribed distance could separate the optical fibers and components, to examine different aspects of the particle light scattering. Additionally, various elements can be combined to optimize part count and aid in assembly. For example, some optical elements in 235 could be combined with optical fiber 232 to make an optical fiber focuser or an optical fiber collimator. Additionally, window 237 may be combined with other optical elements in 235 or 234 to convert the window into a focusing lens or a beam spreader. A single sensor probe 240 may also have multiple sensing locations 250, which may require additional fibers 232 and/or 233 and additional beam-shaping optics 234 and/or 235. Pairs of optical fiber interconnections, such as 222 and 223, may also be replaced by continuous optical fibers, removing connectivity but improving signal transmission and/or averting possible connection contamination.

[0032] Each of the elastic scattering and inelastic scattering techniques can be implemented individually or simultaneously in a sensing system consisting of a sensor probe 240, electro-optical unit 200, and an optical fiber cable 220. Since the optical fiber cable 220 and the sensor probe 240 are merely optical conduits which can operate over a wide range of wavelengths, the type of scattering being sensed depends on the light source(s) 202 being transmitted into the fiber cable 220 and the detector(s) 205, 206, 207 that receive the light from the fiber cable 220. Thus, the electro-optical unit 200 determines the type of scattering being measured. Implementing only one type of scattering is straightforward. Implementing more than one type of scattering with one laser source is demonstrated in FIG. 2. Implementing more than one type of scattering using different light sources requires either coupling of those light sources 202 into a single optical fiber 215, or multiple optical fibers 215. If multiple optical fibers 215 are used, then the subsequent optic elements must also be similarly multiplied. For example, if fiber 215 is duplicated then there needs to be an additional fiber within fiber cable 220, an additional optical fiber 232, and possibly additional optical components 235.

[0033] Both elastic and inelastic scattering techniques are described in FIG. 3 using an energy-level diagram (known as a Jablonski diagram for molecules) and a spectral plot (amplitude vs. wavelength). For both elastic and inelastic scattering, incident light 300 increases the energy of a molecule from an initial state to a virtual state. For elastic scattering, the molecule scatters light 301 back at the same wavelength as incident light 300. Depending on the proportion of particle size to incident light wavelength, elastic scattering is also sub-categorized by different scattering regimes. The Rayleigh scattering regime occurs for particle diameters much smaller than the light wavelength, the Mie scattering regime occurs for particle diameters of similar order as the light wavelength, and the geometric scattering regime occurs for particle diameters much greater than the light wavelength. For inelastic Raman scattering, the molecule scatters light back at different wavelengths. For scattering light energy 302 less than the incident light energy 300, or a scattering light wavelength 312 longer than the incident light wavelength 311, it is termed Stokes Raman scattering. Conversely, for scattering light energy 303 greater than the incident light energy 301, or a scattering light wavelength 313 shorter than the incident light wavelength 311, it is termed anti-Stokes Raman scattering.

[0034] For RSS, only one light source and one collection fiber are required, and the returned light is routed to a spectrometer which typically includes an array of detectors to measure the spectrum of the scattering. To implement RSS in FIG. 2, optics 208 would be an optical filter to significantly reduce the incident light source contribution into spectrometer 207. That optical filter could be a notch filter, long-wave-pass filter, dichroic filter, or similar and is known to those skilled in the art. Optionally, optics 208 could reflect or transmit light into detector 206 for elastic scattering measurements and simultaneously transmit or reflect light into a spectrometer 207 for inelastic scattering measurements. Also, in FIG. 2, the laser source 202 could be a continuous-wave source or a pulsed laser source. FIG. 4 demonstrates the unique spectral signatures for compounds of quartz 401, gypsum 402, and dolomite 403. All molecules have unique signatures and comparison of a measured spectrum must be made to a library of known spectra to determine the material. If only a few specific molecules are being interrogated, the array of detectors in a spectrometer may be replaced by discrete detectors that only receive light from Raman peak location(s). It should be noted that compact, palm-sized spectrometers are commercially available to keep the entire particle measurement system compact.

[0035] For MALS, the particle scattering is measured at two or more different angles and for different refractive indices the ratio of the responses is different. Only a single light source is necessary for MALS, but at least two collection fibers must be used to return the scattered light from different angles. Each collection fiber can then be routed to a detector for measurement. FIG. 5 shows an example of computer simulations for the ratio of scattering intensities between two receivers at different collection angles. The different curves 501, 502 and 503 are the intensity ratios for different refractive indices. In FIG. 5, theoretical simulations based on Mie theory for refractive indices of 1.33 (501), 1.51 (502), and 1.66 (503) are shown. These different ratios allow the determination of the refractive index of the particle which is a unique property of a material. There are many possible combinations of the measured intensities that allow distinction of the refractive indices. Along with the ratio of two intensities, other mathematical processing, such as addition and subtraction of intensities, can provide alternative means of determining the refractive index. In FIG. 2, MALS would be performed using laser source 201, detector 205, detector 206, and the light entering fibers 232 and 233 would come from scattering at different angles.

[0036] For MWLS, the particle scattering is measured at two or more different wavelengths and can be used to identify materials with a strong wavelength-dependent refractive index. FIG. 6 shows the wavelength-dependence of the refractive index for some representative materials. Taking examples of water 601 and silica 602, there is very little wavelength dependency, but for aluminum 603 and magnetite 604, the refractive index varies significantly with wavelength. For MWLS, it is possible to use only one collection fiber to return all wavelengths of light, but two or more light sources at different wavelengths must be used. The returned light must be separated into the individual wavelength components and then routed to at least two detectors using wavelength dispersion or wavelength selection elements with methods known to those skilled in the art. The light source 202 in FIG. 2 must be replaced by at least two light sources coupled together into one optical fiber 213 or by light sources introduced into separate optical fibers. Careful choice of the light wavelengths is important for MWLS. For example, if 0.5 m and 0.65 m light wavelengths were chosen, then magnetite 504 would show no difference in response.

[0037] This written description uses examples to disclose the invention and enables any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The claims define the patentable scope of the invention, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.