CA1318517C

CA1318517C - Asymmetric purge air system for cleaning a lens

Info

Publication number: CA1318517C
Application number: CA000576367A
Authority: CA
Inventors: Richard J. O'brien; Douglas C. Myhre
Original assignee: Rosemount Inc
Current assignee: Rosemount Inc
Priority date: 1987-09-04
Filing date: 1988-09-02
Publication date: 1993-06-01
Anticipated expiration: 2010-06-01
Also published as: DE3889732D1; EP0378575A4; WO1989002069A1; EP0378575A1; JPH03500205A; DE3889732T2; EP0378575B1; US4836689A

Abstract

ABSTRACT OF THE DISCLOSURE
A purging air flow system for passing air over a lens to keep it clean and free from particulate contaminants and also for providing a positive flow of air away from the lens has baffles which cause a flow across the lens that is not symmetrical to avoid a dead air or stagnation zone in the center of the lens . The air supply used for such purging is controlled adequately so the flow changes direction and particles are removed from the main flow of purge air by inertial separation prior to the time the air contacts the lens . Such air entrained particles might otherwise deposit on the lens . A flow control orifice also may provide a secondary flow to carry the particles separated from the main flow out of the flow passageway .

Description

1 31 ~5 1 7 ASYMMETRIC PURGE AIR S~STEM
FOR CLEANING A LENS
BACKGROUND OF THE IMVENTION
1. Field o~ the Invention.
05 The pre~ent invention relates to a sy~te~
for purging contaminants from the lens of an instrument, such as a radiation pyromet0r.

2. Description of th!3 Prior Art.
Radiation pyrometer~ are widely used for detecting temp2ratures in applications such as gas turbinee, and the Rtandard pyrometers sense radiation ~hrough a window or lens that is nor~ally mounted in a tube that opens through a housing into a turbine rotor chamber.
One of the requirements is that the pyrometer lens be Xept clean and free o particulate contaminants, Particles deposited on the lens can reduce the energy to the sensor and thereby cau~e inaccurate temperature measurement~. Several purge air aesigns have been developed to keep particulate contaminants from the lens and the sighting tube, but most have limitations in normal u~e, for example when the pyrometers are to be mounted with the siyhting tube facing in an upward direction where gravity will cause particles to ~all down onto the lens and the flow is not sufficient to purge the particles. In some designs, a particle laden cornpressor air supply is used to "scrub" the surface of the lensO that i6, pa~s over the surface of the lens. Significant ~ 131851-/

particle deposition on the lens occurs as the result of the contaminants fro~ the purge air flow contacting and adhering to the lens as the air passes - over the surface.
Other designs provide an air curtain spaced from the lens that is intended to keep the flow of air in a direction to move the particles away from the lens, but during starting and stopping of the turbine in an aircraft, particularly when the pyrometer lens surface is facing upwardly, particles precipitate and accumulate on the lens surface.
SUMMARY OF THE INVENTION
_ The present invention relates to a pur~e air system ~or passing a flow of fluid over a window o a combustion instrument to keep it clean and free from particulate contaminants which af~ect the radiation transmissive characteristics of thQ window, by providing an asymmetric 10w of purge air across the lens to avoid creation of a dead zone or stagnation zone in the center of the lens where particles could come to rest. The present asymmetric flow system is useful with any purge system but preferably the fluid supply used for such purging is controlled adequately to first remove particles from the purge air which might oth~rwise affect the lens prior to the time the air or fluid is passed over the lens. The purge air also is controlled to maintain an adPquate flow velocity to insure that particles that are removed from th~ lens remain entrained and are carried outwardly away fro~ the pyromete~ lens.

-2a-Accordingly therefore the present invention provides an instrument for sensing radiation representative of a parameter in a particle suspension and for providing an output indicative of the parameter, the instrument receiving a supply of pressurized fluid, comp:rising: port means disposed on the instrument and opening to the parameter source for receiving the radiation; sensing means coupled to the port means for sensing the received radiation and for providing the output; window means disposed between the port means and the sensing means for transmittiny the radiation therethrough and for shielding the sensing means from the particle suspension, the window means having a window surface with a central axis normal to the window surface, for transmitting radiation to the sensing means exposed to the suspension; and purge means disposed in the instrument for receiving the pressurized fluid and having openings arranged around the circumference of the window surface for directing flo~s o~ the pressurized fluid having an axially asymmetric flow pattern onto the window surface, generating an unstable flow pattern of the pressurized fluid on the window surface such that particles are removed from substantially all of the window surface.

In the present invention, compressor air in a jet engine is used for purging. At least the heavier particles carried by the compressor air supply are separated out of the purge air by causing 131~517 a change in direction of airflow immediately prior to its passage over the lens and by preventing stagnation zone~ from forming 02l the lens or window by having an asymmetrical flow pattern radially 05 inward from the outer edge of t11e lens. The separation eliminates that source of contamination that is present, usually during ground engine operations, when ambient air (u~ed in the compre ~or) can carry dust particles and other particles~ ~he asymmetrical flow pattern causes a shifting of any flow stagnation point on the lens surface so that substantially no location on the lens t~nds to collect particles because the purge air moves or flows across the entire surface~
When æmall particles such as particles formed of an organic material with an adhe ive surface come to rest on a pyrometer lens surface they will tend to be firmly attached to the lens by adhesion forces between the particles and the lens~
The present device provides for a moving air flow that can be controlled so that an adequate air velocity passes across the lens to reentrain deposited particles and prevent stagnation ~ones where the smallex particles may tend to collect.
Many factors are involved in the adhesion forces, and whether or not a particle adheres to the lens, depends on particle size, particle bounce or rebound energy, and the surface propertiea of a particle and a lens. The air velocity in the sight tube that is provided by the purging system and the absence of stagnation or dead air zones also overcomes the adherence of the particles.
The present invention serves to insure that the purge air that is used has gone through an 131(3~17 inertial separation step 60 larger particles such as molten solid particles that may Euse to the lens upon contact are separated prior to ]passing over the lens. It is found that it i8 very difficult to 05 reentrain submicron particles. The shifting of the flow pattern across the lens without causing a dead zone of no flow reduce~ the likelihood of such sub~icron particles being e~ected out of the flow.
Removal of large particles ~rom the purge air greatly aids in keeping the lens free from depositc.
The present system provides a simple mechanical arrangement for scrubbing the lens or window to control the amount of flow o~ compres~or air past the pyrometer lens to purge the lens and reentrain particles that may have been deposited as well as maintaining a positive pressurP in the sight tube to avoid depositing particles. The purge air changes direction significantly just prior to pa~sage over the len~, for inertial separation of larger particles, and the asymmetrical flow causes a shifting of air flow across the entire lens to prevent dead air zones where particles tend to accumulate.
BRIEF ~ESCRIPTION OF THE DRAWINGS
Figure 1 is a fragmentary vertical Rectional viaw through a portion of a typical turbine compres~or, and showing a sectional view of a radiation pyrometer having a purge system made according to the present invention installed thereon;
Figure 2 is an enlarged vertical sectional view of the sight tube portion and pyrometer lens of the device shown in Figure l;
Figure 3 is a sectional view taken generally along line 3--3 in Figure 2;

1 3 1 ~5 1 7 Figure 4 i8 an enlarged vertical sectional view of a modified form of the invention; and Figure 5 is a sectional view taken on line 5--5 in Figure 4.
05 DETAILED DESCRIPTIO~ OF THE PREFERRED EMBODIME~TS
.. . . . .. ..
A typical radiation pyrometer indicated generally at 10 is adapted to be mounted in a gas turbine, a~ in a jet engine, including a turbine housing ll, and an outer ~hell or wall 13, which together define a compressor bypass passageway indicated at 14 that receives air under pres~ure from the inlet compressor (before combustion) and i8 filled, therefore, with air at a pressure above atmospheric pressure, and above that of a combustion suspension which is within the turbine chamber indicated generally at 20 on the interior of the housing or case 11.
Turbine blades schematically indicated at 22 are mounted on a suitable rotor 22A. ~le temperature of the turbine blades 22 i 6 to be measured by the pyro~eter 10 in order to insure that the design operating temperatures are not exceeded, but yet to permit the turbine to operate at or near its most eficient operating temperature or another de~ired temperature.
The case 11 has a port indicated generally at 25 opening to a pas~qageway 24 in the case ll which houses a sight tube as~embly 26. The sight tube assembly 26 is made to support the pyrometer barrel 27 in a suitable location, so that the pyrometer lens indicated at 28 i~ positioned axially center0d on the axis of the sight tube aRsembly 26 and in position to receive radiation from the turbine blades 22 through the port 25. Sight tube 26 fits slidingly in t ~ l ~5 1 ~

passageway 24 to allow for movement due to thermal expansion and contraction betwe~en case ll and wall 13.
~ he opposite end of the pyrometer 10 has a flange 30 that is mounted to wall 13 in a desired 05 manner. The pyrometer lO includes optical fiber cable 12 which receiveq radiatiion from the turbine blades 22 which passes through the lens 28~ The optical fiber cable 12 i8 0~ conventional design and convey~ the radiation to radiation sensing mean~ 15, which senses the radiation conventionally, ~uch as with silicon photodiode~ and optical filters, and produces an output 16 indicative o~ the temperature of the turbine blades. The diameters of the window or lens 29 and barrel 27 are determined by the requirements of the optical fiber cable 12 and the spacing between the end of the cable and the turbine blade in a conventional manner.
me problems that have been out-~ined in relation to the depositing of materials on the pyrometer lens are pre~ent in most pyrometer 6y~tems where a lens or radiation transparent window is open through an open port into a turbine chamber. Any depo~its on *he lens or window degradeq the pyrometer performance and attenuates the radiation signals being received, and thus makes the temperature indicationæ le~s reliable. In the fir t form of the invention shown in Figures l, 2 and 3, it can be seen that in oxder to supply purge air, a series of passageway~ are provided for permitting air from the chamber 14, which is under pressure, to pass across or purge the lens 28 of particulate contaminants.
The sight tube assembly 26 includes an outer conduit or tube memb~r 35 that has a tapered transition section 36 e~ctending from a barrel portion 37 (which 13I~517 fits into passageway 24) to a pyrometer receiving sleeve 38 of laryer diameter than the barrel 37a The tube 35 defines an annular passageway indicated at 39 between the interior o~ the sleeve 38 and a second 05 smaller sleeve 42, which i5 concentric with the ight tube assembly 26 and fits arount~ an annular surface 43 of the pyrometer barrel 27. Sleeve 42 is fixed in place and forms a flow control ~leeve for controlling and directing purge air flow. 'rhe lens 28 of the pyrometer is of an ordinary design, and it closely fits within the interior of the sleeve 42. I~e structure of pyrometer 10 inoluding the ~ight tube assembly 26 concentric about sleeve 42 provide~ a rugged, vibration-resistant passageway for purge air flow.
The passageway 39 is an annular passageway, as shown in Figure 3. A plurality of air inlet openings indicated at 50 are provided in the sleeve 38 of the tube 35. These openings 50 are spaced around the periphery to carry pressuri~ed compressor air present in the chamber 14 into th~ passageway 39. As seen in Figure 2, the openings 50 have axes 55 that are inclined relative to the longitudinal axis 54 of the sight tube assembly 2~ to create direction change and turbulance as the air enters passageway 39. Par~icles pre~ent in the compressor air entering openings 50 may be found to impact on an outer surface of sleeve 42. Some of these particles may be deflected off the outer surface of sleeve 42 and carried w:ith the purge air flow along passageway 39. Other particles, such as small particles formed of organic material having surfaces with adhesive properties may adhere to the outer surface of sleeve 42. The particles adhered to the outer surface of sleeve 42 can adhere together amd agglomerate into a larger particle which i later Iscrubbed off by tha purge air flow and carried by t,he purge air flow along passageway 39. The compres~or presæure at 05 openings 50 is greater than that in the turbine chamber 20, and thus there will be flow in passageway 39 as indicated by the arrows 52 parallel to the longitudinal axis 54. The ~low control sleeve 42 'nas a plurality of opening~ 57 ~as shown in Figure 2 through the wall thereof that are in transverse alignment with the surface 28A of the lans 2~. The openings 57 are large and cause air in passageway 39 to flow into the interior passageway 42A of sleeve 42 and out to the interior o tube 26 forming a passageway for flow to port 25.
The abrupt change in direction of air flow, as it enter6 the internal passageway 42A of sleeve 42 through openings shown generally at 57, as indicated by the arrows 62 causes inertial particle separation. The heavier particles, such as those larger than a few microns, suspended in the air flowing in passageway 39 will tend to be separated out of the air flow before the flow enters the interior 42A of the sleeve 420 The flow through openings 57 moves past lens 28 and in particular across the lens surface 28A. The smaller particles, such as particles smaller than a few microns, that move past the lens 28 tend to remain entrained in the air flow and are not effectively dapoæited on the lens. The smaller paxticles have insufficient momentum to penetrate a boundary layer 28B of purge air formed at the lens surface 28A.
The outer surface of sleeve 42 can be cylindrical along its length as shown in Figure 1, but inertial particle separation and the flow through openings 57 ean be further enhanced by ~haping the outer surface of sleeve 42 with a shaped annular surface 59 as shown in Figure 2. Optional shaped 05 surface 59 haq an airfoil cro~s section which provides a desired reaction orce in the moving purge air which induces a large ~low through openings 57.
As the air flow repres~ented by the arrow 62 flows across the surface 28A of the lens 28 (or radiation window), it tends to scrub the ~urface 28A
with relatively clean air because the larger particles (such afi molten metal particles, dirt, etc.) are separated out by inertial ~eparation caused by the sharp turn in direction of air flow at openings 57. This flo~ across the lens also tends to reentrain particles already deposited on the lens.
The posi~ive flow due to the pressure dif~erence between cham~ers 14 and 20 keeps particlea that are within the interior chamber 42A of cleeve 42 moving and carries the particles out through the internal passageway in direction along the axis 54 toward the port 25. The sleeve 42 forms part of the flow conduit for air flow from the lens 28 to port 25.
However, with symmetrical radial inward flow, there is a stagnation zone likely to form near the axis 54. There is essentially no flow at this spot on the lens, so particles can precipitate and deposit on the lens.
The improvement shown herein is the control of flow through the openings 57 to prevent stagnation zones from forming on the center of the lens or window surface. As can be seen in FigurP 3, the openings 57 are made so that they are not symmetrical with respect to the central axis 5~ of the lens 28.

131(,517 The opening~ 57 at the periphery of the lens or window compriRe two large openings or ports 57A and 57B, as can be seen in Figure 3, separated by a support web 58A. The openings 57A and 57B have 05 central radial axes that are sy}nmetrical with respect to a bisecting plane of the ~upport web 58Ai Additional purge flow opening~ or ports 57C
and 57D are ~eparated from the openings 57A and 57B
by support webs 58A and 58C, an~ the openings 57C and 57D in turn are separated by a support web 58D. The positioning of the support webs is such that the radial inward air flow rom each opening i 8 not opposed by an equal size opening directly opposite from it, but rather the openings are asymmetrical~
In other words, the axes normal to the tangent plane at the center of each opening (bisecting axes) of some o~ the peripheral openings are not a common axis with another opening on the opposite side of the lens or window. Thu8, flow from at least one of the openings or ports does not have a diametrically opposing flow, thu~ in uring a flow across the center of the lens. When the flows are balanced, a central stagnation region is caused where the opposing flows merge. The asymmetrical flow causes a ~hifting, turbulent flow rather than a dead air space in the center which occurs when balanced radial flows are present.
The purge air flow therefore i6 off center, and part of the air will tend to scrub across axis 54 rather than stagnate in the center, to insure that there is adequate movement for removing and keeping particles entrained. The pressure changes occurin~
keep the regic~n of minimum flow on the lens shifting.

1 3 1 ~35 1 /

The openings can be made as asymmetric as pos6ible. In general the openings are positioned ~uch that the flows will change direction and shift across the ~urface of the len~ without causing a 05 stagnation point, to scrub off particles and to keep su~pended particles from being deposited~
The openings 57A and 57B are quite large, as can be seen, while the openings 57C and 57D are smaller. That generally will mean that there is a different air velocity flow through the openings 57C
and 57D than that through openings 57A and 57B.
Openings 57A and 57B further aid in shifting low flow regions across the surface of the lens. The flow is not stable but forms a pattern which i8 un~table and tends to shift and move across the entire surface of the lens or window.
The total flow from openings 50 into openings 57 is controlled by an annular flow control and restriction orifice indicated generally at 65 formed between the inner surface of the transition portion 36 oP the outer end 66 of the sleeve 42. The annular control and restriction orifice 65 causes a minor flow indicated by the arrows 69 from pa~sageway 39 past the end surface 66 of the sleeve 42 into the transition section 36 where the flow will join with the flow represented by the arrows 62 from the interior passageway 42~ of the sleeve 42. The size of flow control orifice 65 is set to a desired dimen~ion by placing a removable shim over the end of sleeve 42 and then sliding tube assembly 26 back over pyrometer barrel 27 until the tapered section 36 contacts the skin. The tube a~sembly 26 is then welded to pyrometer barrel 27 and the shim is removed. The total flow ~hen goes through the center 1 31 (35 1 7 portion of the outer barrel 37 outwardly into the turbine chamber through the port 25. The minor flow through the flow control orifice! will carry particles separated by the inertial action of changing 05 direction o~ the air a8 it enters through openings 57 on out through the passageway 39. ~he6e particles are carried through the narrowing end of passageway 39 (where air velocity increases) and into the transition ~ection 36, which al~o i9 a constricting section causing greater air velocity. The particles will be carried out and away from the lens 28. The ~elocity of the purge air flow increase6 through transition ~ection 36, thus minimi~ing back flow in transition section 36 and barrel 37 which would otherwiæe draw suspended combustion particles from turbine chamber 20 into tube assembly 26. The converging section 36 functions as an aerodynamically ~haped nozzle which minimizes back flow and contamination of barrel 37 with combustion particles.
The particulate contaminants that are present in the compressor air, ~uch as molten metal particles, oil mist and the like, are separated out before the flow goes past the lens. The inertial saparation insures that the lens is kept clean and purged adequately in use.
The flow of purge air out of port 25 into turbine chamber 20 forces combus~ion gases and particles in turbine chamber 20 away from port 25, thus minimizing contamination of lens surface ~8A by combustion particles. The flow of purge air through the pyrometer 10 also coolæ pyrometer 10 to extend the use of the pyrometer in the high temperature environment in case 11.

A second form of the E~resent invention i8 #hown in Figure~ 4 and 5, and incorporates the principle of inertial separation by change o~
direction of the air, as well as asymmetrical purge 05 air flow across a radiation window or lens. A8 ~hown in Figure 4, a turbine housing 75 has a port 76 leading into a rotor chamber 77, and a sight tube assembly 78 is provided in a paa~ageway 79 that opens to the port 76. In this form o~ the invention, as shown ~chematically, a gland or nut 80 i~ used for holding the sight tu~e assembly 78 in poaition in the housing 75. The sight tube assembly 78 is adapted so that it will mount a standard radiation pyrometer 82 in position as previously explained. The pyrometer 82 has a window or lens 83 at its end to receive radiation from turbine blades (not ~hown) which pass in front of the port 76.
The pyrometer ~ystem al~o includes a radiation sensor 130 w~ich is disposed to receive the radiation entering the pyrometer along axis 93 ~nd pa~ing through lens 83. Radiation sensor 130 is of conventional design and may include photodiodes and optical filters. Leads 132 couple signals from sensor 130 to processor 134 which calculates an 25 output 136 indicative of a temperature in chamber 77.
In this form of the invention, the sight tube assembly includes a tube or barrel 85i which has a first interior annular passageway shown at 86 formed around a ~low control guide sleeve assembly 87 which is positioned in conduit or barrel 85. The passageway 86 opens into a smaller diameter passageway 92 that in turn opens into the chamber 77, and the axis of the sleeve, indicated at 93, is parallel to t:he axi~ of the passageway 79. The flow control sleeve as~embly 87 includes an outer tube 94 that receives an end portion 95 of ~he pyrometer a~sembly 82 to hold it centered on the axi~ 93.
The tube 94 in turn is made with a locating 05 hub 96 that, aR ~hown in Figure 5, i8 made to fit within the pas~ageway 86 of the tube 85/ but the outer surface of hub 94 is trimmed off wlth chordal plane~ or cuts indicated at 99 to provide axial flow passageways 100 along the interior of the passageway 86 toward the outlet passayeway 92. ~s ~hown in Figure 5 there are four such passageway~ 100 defined. The outer surface of the hub portion 96 is used for locating and positioning tube 94 in proper location.
Also, aR shown in Figure 4, the inner surface of the hub portion 96 is provided with a plurality of axially extending slots or passageway~
indicated at 104. The interior ~urface of hub 94 is cylindrical and receives and supports a further purge air flow control exhaust tube 107 which is axially aligned and concentric with the axis 93. The flow control tube 107 has an inlet end 108 spaced downstream from the outer surface 83A of the lens 83 by a gap 109. Fl.ow control tube 107 has an interior exhaust passageway, and at its outer end has a tapered outer flow control surface 110. An exhaust port 111, which is of smaller diameter than the rest of the passageway defined by the tube 107 is provided at the outer end of flow control tube 107. The flow control surface 110 cooperates with an annular inwardly extending shoulder 115 formed at the outer end of chambex 121 in barrel 85. The inner edge of shoulder 115 and ~urface 110 define an annular outlet flow control orifice 116.

~ 1 3 1 ~ 5 The barrel 85 has lateral facing inlet openings 118 at its outer end, and these passageway6 118 are open to the compressor bypas~ chamber of the turbine, so that air under presl3ure is admitted as 05 indicated by the arrows 119, into the pa~ageway 86.
Becau6e the pressure in the com]?re~sor bypass chamber in which the openings 118 are located i~ higher than the pressuxe in chamber 77, air will flow along the passageway 86 as indicated by arrows 120. ~his air will ~low through the passageways 100 (see Figure 5) along portions oF the hub 96 into the i~terior chamber 121. Cha~ber 121 is defined between the flow control tube 107 and the interior of the barrel ~5.
The annular outlet flow control orifice 116 tends to restrict the flow of air out through this chamber 121 to the outlet passageway 92. Thus the air flowing from passageway 86 throu~h passageways 100 will be caused to flow through the axial passageways 104 toward ad~e 108 which defines gap 109 surrounding the lens surface 83A. The arrows 122 illu~trate the 180 degree~ change of ~irection of flow re~uired as the purge air flows from pas~ageway6 100 into pasgageway~
104 The pa~sageways 104 shown in Figure 4 end in openings or ports 104A and 104B shown in Figure 5 which are positioned on opposite sides o~ a radial plane on which Figure 4 is taken, and there are passageways forming ports 104C, 104D, and 104E, that are formed to direct the flow of air ~rom passageways 104 radially toward the lens or window 83. I~e ends of the passageway~ 104 form the inwardly facing ports or openings 104A - 104E at the periphery of the lens or window. The flow through passageways 104 moves through opening 10~, past the end 108 of the tube 107 and is thus directed inwardly acro s the lens or 131~17 window surface 83A. The 10w then moves out through the center of tube 107. The ports 104C, 104D, and 104E are not symmetrical abou~ the cen~ral axis 93 and the bisecting axes of these openings do not 05 coincide with the axes of a directly opposite opening.
The flow tube 107 closes off the inner surfaces of the pa~sagewaye 104. The inlet end 108 of flow control tube 107 as stated iB RpaCed downstream from the outer ~urface 83A of the lens or window 83 and the opening 109 defines the axial length o~ ports 104A - 104E. The interior passageway of the tube 107 forms an exhaust passageway that carries flow from the openings or ports 104A ~ 104E
across the opening or gap 109. The purge air exhausts through the ports 104A - 104E to form a radial purge flow adjacent the window or lens 83, in asymmetrical configuration, so that the air flow is not completely b~lanced and does not center or stagnate with respect to the central axis 93 of the window or lens 83. ThP ports 104A - 104~ form purge means that provide an unstable flow of the purge fluid onto the lens surface 83A, so that the ~low will not stagnate in any one region on the surface, but will be unstable, and flow from at least one of the ports will scrub aCro~Q axis 93 to insure that the particles are carried out through the inner passageway of the tube 107.
The asymmetrical flow from the periphery onto the lens shows that the purge means can be made to provide flow that is sufficiently unbalanced or un table to keep a stagnation zone from forming. The percentage of unstable or unbalanced flow can be varied, dependin~ on pressure and the opening sizes~
The ports are made so that there is a qu~stantial 1 ~ 1 85 `1 7 magnitude of flow of fluid across the central axis region adjacent to the central axis of the window or len~. The asymmetric flow provides for a circulating or moving Yone of lowest flow speea so that all of 05 the surface area of the window or lens that i8 being purged will be covered with some flow of air in a cycle to insure that particles are kept moving.
As shown, the bisecting axis o~ at least one of the plurality of peripheral openings has a radial bisecting axis that does not coincide with the axis of another window on an opposite side of the lens~
As stated, the larger particles which are in the chamber 121 are carried by the secondaxy flow out past the tapered surface 110 and through the ori~ice 116 into the passageway 92, a~ indicated by the arrows 125. The purge air that has scrubbed lens surface 83A flows out opening 111 and join the flow coming through orifice 116. me particles that remain entrained are carried wi~h the airstream into the chamber 77. The window or lens surface 83A iq purged with air tha~ has been subjected to inertial separation so large par~icles carried by the purge air are removed.
In both forms of the invention, inertial separation of particles from the compressor air flow is achieved by causing an abrupt change in air flow direction of at lea~t substantially 90 degrees to separate out larger particles shortly prior to passage of the asymmetric flow of air across the pyrometer lens or window. The inertial separation minimizes potential contamination caused by the purge air and the asymmetrical flow insures that all regions of the pyrometer window or lens are kept free o~ particles.

I ~ 1 8~ 1 7 The pyrometer disclosed herein provides a more reliable mea~ure of a turbine blade temperature and thus allows a turbine engine to be operated at a higher power level at which the turbine blade 05 temperature approaches a selected design temperature for the turbine blades.
While the invention has been shown and described Eor use on a pyrometer, uses on other combustion instruments which make radiation measurements in a contaminated atmosp~ere ~uch as a combustion ~uspension will be apparent to those skilled in the art. The purge air sy~tem described herein may be used, or example, on a light-off detector which optically senses the presence of flame in a turbine engine or afterburner. The purge air system described herein may also be used on optical sensing sy~tems for sensing the clearancs between a turbine rotor tip and a ~urbine housing, or an optical system for sensing rotor speed. The present invention may also be u~ed in radiation transmis~ion meters for us~ in power plant smokestacks or die~el engine exhausts.

.

Claims

1. An instrument for sensing radiation representative of a parameter in a particle suspension and for providing an output indicative of the parameter, the instrument receiving a supply of pressurized fluid, comprising:

port means disposed on the instrument and opening to the parameter source for receiving the radiation; sensing means coupled to the port means for sensing the received radiation and for providing the output; window means disposed between the port means and the sensing means for transmitting the radiation therethrough and for shielding the sensing means from the particle suspension, the window means having a window surface with a central axis normal to the window surface, for transmitting radiation to the sensing means exposed to the suspension; and purge means disposed in the instrument for receiving the pressurized fluid and having openings arranged around the circumference of the window surface for directing flows of the pressurized fluid having an axially asymmetric flow pattern onto the window surface, generating an unstable flow pattern of the pressurized fluid on the window surface such that particles are removed from substantially all of the window surface.

2. The instrument of claim 1 wherein the purge means comprises ports disposed adjacent to the window surface for providing radial flow of the fluid onto the window surface

3. The instrument of claim 2 wherein the port means are positioned radially around the window surface such that at least one port providing substantial flow is positioned so its central radial axis is non-coincidental with the central axis of other ports.

4. The instrument of claim 2 wherein the window surface has a central region disposed in the center of the window surface and spaced away from the ports and wherein the radial flow of the fluid is controlled to have an asymmetric magnitude such that there is substantial flow of fluid over the central region of the window surface.

5. The instrument of claim 4 wherein the radial flow has a low flow zone where generally opposite direction flows meet on the window surface and which zone moves with respect to the window surface.

6. The instrument of claim 4 wherein the radial flow has a low flow zone where generally opposite direction flows meet on the window surface and which zones moves with respect to the window surface.

7. An instrument for sensing radiation representative of a parameter in a particle suspension and for providing an output indicative of the parameter, the instrument receiving a supply of pressurized fluid, comprising:

port means disposed on the instrument and opening to the parameter source for receiving the radiation; sensing means coupled to the port means for sensing the received radiation and for providing the output; window means disposed between the port means and the sensing means for transmitting the radiation therethrough and for shielding the sensing means from the particle suspension, the window means having a window surface for transmitting radiation to the sensing means exposed to the suspension; and purge means defining a plurality of radially spaced ports around the periphery of the window surface and means for providing a flow of the pressurized fluid inwardly from the ports toward center portions of the window surface, the ports being asymmetrical for providing an unstable flow of the pressurized fluid onto the window surface such that particles are removed from substantially all of the window surface.

8. The instrument of claim 7 wherein; the ports are separated by a pluraity of walls and at least two of the walls having different annular length to provide the asymmetric flow.

9. The instrument of claim 7, and passageway means for the pressurized fluid formed to cause an abrupt change in direction of flow to inertially separate particles from the pressurized fluid prior to flow of the pressurized fluid through the ports.