NASA CASE NO. LAR 14997-1

PRINT FIG.

NOTICE

The invention disclosed in this document resulted from research in aeronautical and

space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for

licensing in accordance with the NASA Patent Licensing Regulation (14 Code of

Federal Regulations 1245.2).

To encourage commercial utilization of NASA-owned inventions, it is NASA policy

to grant licenses to commercial concerns. Although NASA encourages

nonexclusive licensing to promote competition and achieve the widest possible

utilization, NASA will provide the necessary incentive to the licensee to achieve

early practical application of the invention.

Address inquiries and all applications for license for this invention to NASA Patent

Counsel, Langley Research Center, Code 143, Hampton, Virginia 23681-0001.

Serial No.: 08/141,294

10/19/93 LaRC

(NASA-Case-LAR-14997_l) 0PTZCAL

FLAHEOUT DETECTOR Patent

APplication (NASA. Langley

Research Center) 12 p

G3/35

N94-29368

Unclas

0003656
NASA Case No. LAR 14997-1 

AWARDS ABSTRACT 

OPTICAL FLAMEOUT DETECTOR 

It is necessary to detect a flameout to guard against an unplanned combustor 

flameout and reignition during operation. By detecting the flameout quickly and 

limiting the quantity of fuel allowed to enter the combustion chamber after a 

flameout is detected, the magnitude of a detonation is limited to acceptable 

levels if a reignition of the unburned fuel occurs. Present flameout detectors 

include optical systems and temperature sensing devices. The optical devices 

are ultraviolet detectors which sense UV radiation generated by combustion in 

the 200 -300 nm range such as Geiger-Mueller or Edison tubes which provide 

response times of 150 milliseconds to 30 seconds. The temperature sensing 

devices include thermocouples which are immersed in the flame to sense the 

flame temperature. These devices provide response times of 200 - 300 

milliseconds. In addition to having slow response times, these systems are 

unable to survive the high pressures and widely varying temperatures within 

some combustor environments. 

The present invention is a device for detecting a flameout in a fuel-supplied 

combustion chamber is provided which includes a pair of optical detectors 

optically coupled to a pair of fiber optic probes. The ultraviolet optical detector, 

preferably a photomultiplier tube, provides a measurement of the change in 

intensity of a flame within the ultraviolet region of the light spectrum. The 

visible light optical detector, preferably a silicon photodiode, provides a 

measurement of the change in intensity of a flame within the visible region of 

the light spectrum. The fiber optic probes have a field of view between O0 and 

16O and are located within the combustion chamber to couple each optical 

detector to the light source. In the preferred embodiment, the fiber optic probes 

are fused silica optical fibers encased in a stainless steel sheath and an epoxy 

resin is inserted in between the optical fiber and the steel sheath at one end and 

a silicon RTV is inserted in between the optical fiber and the steel sheath at the 

other end. The measurements taken by the optical detectors are evaluated to 

determine if a change in intensity has occurred within the flame and, if a change 

has occurred, a signal is provided indicating a flameout. 

Inventors: Stephen E. Borg James W. West 

Address: 824 Redgate Avenue, No. 7 51 4 Shelton Road 

Norfolk, VA 23507 Hampton,, VA 23663 

Employer: NASA LaRC NASA LaRC 

Robert M. Lawrence Samuel E. Harper, Jr. 

51 0 Chapel Street 406 Merry Oaks Dr., No. 120 

Hampton, VA 23669 Newport News, VA 23602 
Inventors: 

Address: 

Evaluator: Fredrick A. Kern 

Serial No.: 0811 41,294 

Filed: October 19, 1993 

David W. Alderfer 

109 Eastwood Drive 

Newoort News, VA 23602 
LAR 14997-1 - 1- PATENT APPLICATION

OPTICAL FLAMEOUT DETECTOR

Origin of the Invention

5

10

The invention described herein was jointly made in the performance

of work under a NASA contract and by employees of the United States

Government and is subject to the provisions of Section 305 of the National

Aeronautics and Space Act of 1958, as amended, Public Law 85-568

(72 Stat. 435; 42 U.S.C. 2457).

Background of the Invention

1. Technical Field of 1;he Invention

15 The present invention relates generally to flameout detectors for

monitoring the presence of a flame and more particularly to an opticalbased flameout detector.

20

2. Discussion of 1;he Related Art

Flameout detection systems are well known in the art. It is

necessary to detect a flameout to guard against an unplanned combustor

flameout and reignition during operation. By detecting the flameout quickly

and limiting the quantity of fuel allowed to enter the combustion chamber

25 after a flameout is detected, the magnitude of a detonation is limited to

acceptable levels if a reignition of the unburned fuel occurs. Present

flameout detectors include optical systems and temperature sensing

devices. The optical devices are ultraviolet detectors which sense UV

radiation generated by combustion in the 200 -300 nm range such as

30 Geiger-Mueller or Edison tubes which provide response times of 150
LAR 14997-1 -2- PATENT APPLICATION

milliseconds to 30 seconds. The temperature sensing devices include

thermocouples which are immersed in the flame to sense the flame

temperature. These devices provide response times of 200 - 300

milliseconds. In addition to having slow response times, these systems are

5 unable to survive the high pressures and widely varying temperatures

within some combustor environments.

It is accordingly an object of the present invention to provide an

optical flameout detector having a response time less than 100

milliseconds..

10 It is a further object of the present invention to provide an optical

flameout detector able to withstand pressures up to 28 MPa (4000 psi).

It is an additional object of the present invention to provide an

optical flameout detector able to withstand temperatures up to 1700°C

(3100°F)

15 It is yet another object of the present invention to accomplish the

foregoing objects in a simple manner.

Additional objects and advantages of the present invention are

apparent from the drawings and specification that follow.

20 Summary of 1;he Invention

A device for detecting a flameout in a fuel-supplied combustion

chamber is provided which includes a pair of optical detectors optically

coupled to a pair of fiber optic probes. The ultraviolet optical detector,

25 preferably a photomultiplier tube, provides a measurement of the change in

intensity of a flame within the ultraviolet region of the light spectrum. The

visible light optical detector, preferably a silicon photodiode, provides a

measurement of the change in intensity of a flame within the visible region

of the light spectrum. The fiber optic probes have a field of view between

30 0 ° and 16 ° and are located within the combustion chamber to couple each
5

LAR 14997-1 -3- PATENT APPLICATION

optical detector to the light source. In the preferred embodiment, the fiber

optic probes are fused silica optical fibers encased in a stainless steel

sheath and an epoxy resin is inserted in between the optical fiber and the

steel sheath at one end and a silicon RTV is inserted in between the optical

fiber and the steel sheath at the other end. The measurements taken by

the optical detectors are evaluated to determine if a change in intensity has

occurred within the flame and, if a change has occurred, a signal is

provided indicating a flameout.

10 Brief Descrip!;io..n of the Drawings

15

Fig. 1 is a view of the interior of the combustion chamber;

Fig. 2 is a cross-sectional view of the fiber optic probe; and

Fig. 3 is a block diagram of the optical flameout detector.

Detailed Description of 1;he Invention

A unique device for detecting flameouts is described in detail below.

The device is generally applicable to any combustion chamber or furnace in

20 which a flameout followed by reignition of unburned fuel could cause

catastrophic damage. This device optically detects if a flameout has

occurred, and, if so, shuts down the main fuel supply to the combustion

chamber or furnace, limiting the amount of unburned fuel which would

collect in the combustion chamber after normal combustion has stopped.

25 By limiting the quantity of unburned fuel to below the flammable limit, a

reignition, deflagration and detonation are not possible.

The optical flameout detection system is designed to respond to

gross changes in combustor light levels. Light intensity is monitored in

two spectral bands by two independent optical detectors 26. A

30 photomultiplier tube makes optical measurements in the ultraviolet portion
LAR 14997-1 -4- PATENT APPLICATION

of the spectrum from 200-600 nm, and a silicon photodiode covers the

visible region from 400 - 1100 nm.

The optical detectors 26 are located outside the combustion

chamber 10 and are optically coupled to the light energy radiated from

5 air/methane combustion with two fiber optic probes 12. The fiber optic

probes 12 are 6 m (20 ft.) in length and are designed specifically for

operation in the high pressure (28 MPa, 4000 psi) oxidizing environment

within the combustion chamber 10. They are comprised of a single, 690

micron diameter, fused silica optical fiber 22 encased in a one- sixteenth

10 (0.062) inch diameter stainless steel sheath 18. A standard grade, two

part epoxy resin 24 cured with Di-n-Butyl Phthalate is inserted through fill

hole 23 of steel sheath 18. An optically transparent liquid silicon 20 (GE

Silicones Part number 655) is inserted between the optical fiber 22 and the

steel sheath 18 through fill hole 25. The silicon has the following

15 properties: a temperature range from 500°F to -166°F, specific gravity of

1, thermal coefficient of expansion of 33.0 x lOScm/cm°C, index of

refraction of 1.435 and thermal conductivity of .11 Btu/hr. ft2"°F/ft The

fiber optic probes 16 are aimed to look transversely across the flow of

gases at a region of the combustion chamber 10 wall roughly 15 inches in

20 front of the spray bar. The fiber optic probes 12 do not have focussing

optics, and are able to see events occurring within a 16 degree conical

field-of-view. Selection of this optical path permits the detection system to

respond quicker to a potential flameout by being able to see movement of

the flame front 32 down the combustion chamber 10 as the flame 32

25 leaves the direct field-of-view 14. This limited field-of-view 14 allows the

system to react much more quickly in detecting a flameout as compared to

other detector systems having a 180 ° field-of-view. If the flame 32 leaves

the limited field of view 14, a flameout is detected.

The detector outputs are conditioned and used to activate a logic

30 circuit which determines whether a flame ON/OFF condition exists within
LAR 14997-1 -5- PATENT APPLICATION

the combustion chamber 10. Characterizing the detection system's 28

response to the various combustor light levels associated with different

flame intensities - pilot, boost, and main-flame - was achieved through

experimentation. In order to generate a main-flame "ON" indication from

5 the detection circuitry, the detector outputs must exceed a preset minimum

value corresponding to a low level boost flame. Once this voltage level is

reached, a FLAME ON condition is signalled to the facility control system.

Conversely, if the detector outputs drop beneath a minimum value, then a

FLAME OFF condition is realized. A FLAME OFF signal from the detection

10 system 28 will be used to initiate a rapid shut down of the main fuel

supply by the facility control system 30.

The basis of the flame detection circuitry is a non-inverting amplifier,

a voltage comparator, and two relays - one normally open (NO), and one

normally closed (NC). The amplifier conditions the output from the

15 detector for the fixed voltage comparator. Variation of the amplifier gain

will change the minimum detector output voltage required to generate a

state change in the fixed voltage level comparator. A 2-1 comparator turn

ON/OFF voltage ratio has been designed into the comparator circuitry to

guard against false triggers from reflections within the combustion chamber

20 10. When a change in state of the comparator does occur, a

corresponding change in state of the NO/NC relay combination will also

take place. The relay combination is the flameout detection system's

trigger that will be monitored directly by the facility's control system 30.

Design of the comparator/relay combination will insure that a "FLAME

25 OFF" signal is generated in the event of a power/component failure.

Although our invention has been illustrated and described with

reference to the preferred embodiment thereof, we wish to have it

understood that it is in no way limited to the details of such embodiment,

but is capable of numerous modifications for many mechanisms, and is
LAR 14997-1 -6- PATENT APPLICATION

capable of numerous modifications within the scope of the appended

claims.
LAR 14997-1 ._._" PATENT APPLICATION

OPTICAL FLAMEOUT DETECTOR

Abstract of the Disclosure

5 A device has been developed which monitors the presence of a

flame within a combustion chamber. The optical flameout detection

system responds to gross changes in combustor light intensity, which is

monitored in two spectral bands. A photomultiplier tube makes optical

measurements in the ultraviolet portion of the spectrum, and a silicon

10 photodiode covers the visible region. The detectors, located outside the

combustion chamber, receive the light energy radiated from the

combustion process through fiber optic probes designed to operate in a

high pressure environment. The optical fibers are aimed diagonally through

the center of the injector at the combustion chamber wall downstream of

15 the injector. The probed observe events occurring within a narrow conicalshaped field of view so that the system can quickly detect longitudinal

movement of the flame front away from the injector. If a change in

intensity of the flame is detected, the fuel supply to the combustion

chamber is shut off, limiting the amount of unburned fuel in the

20 combustion chamber which could reignite.
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