A sensing device comprising an O2 sensor, a pump, a compressor, and a heater is provided to quickly sense the amount of O2 in a combustion product gas. A sample of the combustion product gas is compressed to a pressure slightly above one atmosphere by the compressor. Next, the heater heats the sample between 800 C and 900 C. Next, the pump causes the sample to be flushed against the electrode located in O2 sensor 6000 to 10,000 times per second. Reference air at approximately one atmosphere is provided to the electrode of O2 sensor. Accordingly, the O2 sensor produces a voltage which is proportional to the amount of oxygen in the combustion product gas. This voltage may be used to control the amount of O2 entering into the combustion chamber which produces the combustion product gas

Davis, William T.

Puster, Richard L.

Singh, Jag J.

English

NASA Technical Reports Server

United States Patent [191 
Singh et al. 
[ill Patent Number: 4,911,898 
[45] Date of Patent: Mar. 27, 1990 
1541 DEVICE FOR QUICKLY SENSING THE 
AMOUNT OF 0 2  IN A COMBUSTION 
PRODUCT GAS 
[75] Inventors: Jag J. Sin& William T. Davis, both 
of Yorktown; Richard L. Puster, 
Hampton, all of Va. 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 165,945 
[22] Filed: Mar. 9,1988 
Related U.S. Application Data 
[63] continuation-in-part of Ser. No. 823,830, Jan. 29, 1986, 
abandoned, which is a continuation-in-part of Ser. No. 
633,178, Jul. 23, 1984, abandoned. 
[51] Int. Cl.4 ............................................. GOlN 27/30 
[52] U.S. Cl. ........................................ 422/62; 422/98; 
422/111; 422/126; 436/55; 436/137; 436/143; 
431/12; 431/76 
Field of Search ..................... 422/62, 83, 58, 108, 
422/111, 126; 436/55, 137, 143; 431/12, 76; 
252/372 
[58] 
[561 References Cited 
U.S. PATENT DOCUMENTS 
4,187,486 2/1980 Takahashi et al. ............. 436/137 X 
4,225,559 9/1980 Achari et al. ................... 436/137 X 
4,298,573 11/1981 Fujishiro ......................... 436/137 X 
4,744,954 5/1988 Campbell et al. ..................... 422/98 
4,770,758 9/1988 Suzuki et ai. ..................... 422/98 X 
Primary Examiner-Barry S. Richman 
Assistant Examiner-Lynn M. Kummert 
Attorney, Agent, or Firm-George F. Helfrich; John R. 
Manning; Charles E. B. Glenn 
A sensing device 50 comprising an 02 sensor 22, a pump 
37, a compressor 19, and a heater 21 is provided to 
quickly sense the amount of 0 2  in a combustion product 
gas. A sample of the combustion product gas is com- 
pressed to a pressure slightly above one atmosphere by 
compressor 19. Next, heater 21 heats the sample be- 
tween 800" C. and 900" C. Next, pump 37 causes the 
sample to be flushed against electrode 32 located in 0 2  
sensor 22 6OOO to 10,ooO times per second. Reference air 
at approximately one atmosphere is provided to elec- 
trode 32 of 0 2  sensor 22. Accordingly, 0 2  sensor 22 
produces a voltage which is proportional to the amount 
of oxygen in the combustion product gas. This voltage 
may be used to control the amount of 0 2  entering into 
the combustion chamber 10 which produces the com- 
bustion product gas. 
[571 ABSTRArn 
7 Claims, 2 Drawing Sheets 
CALIBRATION 
REFERENCE 
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1 
DEVICE FOR QUICKLY SENSING THE AMOUNT 
OF 0 2  IN A COMBUSTION PRODUCT GAS 
ORIGIN OF THE INVENTION 
The invention described herein was made by an em- 
ployee of the U.S. Government and may be manufac- 
tured and used by or  for the Government for govern- 
mental purposes without the payment of any royalties 
thereon or  therefor. 
This application is a continuation-in-part of co-pend- 
ing application Ser. No. 823,830, tiled Jan. 29, 1986, 
which is a continuation-in-part of abandoned applica- 
tion, Ser. No. 633,178, filed 7/23/84. 
TECHNICAL FIELD OF THE INVENTION 
This invention relates to sensing the amount of a 
specific gas in a combustion product gas and more par- 
ticularly to sensing the amount of oxygen in a combus- 
tion product gas. 
BACKGROUND OF T H E  INVENTION 
quick sensing and subsequent controlling of the 
amount of oxygen (02) in a combustion product gas is 
necessary in various situations. For example, most en- 
gine test facilities in the U.S. use vitiated (oxygen en- 
riched) combustion products expanded to either sub- 
sonic, supersonic, or hypersonic speeds to test and vali- 
date engine operation. To conduct nominal Mach 7 
flow wind tunnel testing of air-breathing propulsion 
systems, the oxygen content of the combustion product 
flow gas must be equivalent to the oxygen content of 
the air. Too much oxygen may damage the engine; too 
little oxygen will result in reduced impulse. Also, this 
sensing of the amount of 0 2  in the combustion product 
gas must be accomplished in a time interval smaller than 
the flow delivery system response and in a time frame 
that is a small fraction of the run time. Run times are 
often approximately 20 seconds. 
Current 0 2  sensing devices d o  not have response 
times which are quick enough to be utilized during such 
small time periods They are usually designed for use in 
boiler operations or steady state industrial processes 
where time is not of the essence. Currently available 
sensors have a response time of approximately five sec- 
onds. A sensor system response time of at least a quarter 
of a second is required in the above application. Such a 
sensor response time approximates real time since the 
response time of the valve controlling the amount of 0 2  
in the combustion chamber is about 0.25 second. 
Accordingly, it is an object of this invention to 
quickly sense the amount of oxygen in a combustion 
product gas. 
It is a further object of this invention to achieve the 
object in order to control the amount of oxygen in the 
combustion product to maximize efficiency and mini- 
mize pollution. 
Other objects and advantages of this invention will 
become apparent hereinafter in the specification and 
drawings which Follow. 
SUMMARY OF T H E  INVENTION 
According to the present invention, the foregoing 
and additional objects are obtained by providing a de- 
vice for quickly sensing the amount of oxygen in a 
combustion product gas. A test sample from a combus- 
tion product gas is pressurized, heated, and introduced 
into a product gas cavity of an 0 2  sensor. A heated 
ceramic electrolyte disc coated with platinum elec- 
trodes serves as a shared wall between this product gas 
cavity and a reference air cavity. This disc generates a 
voltage output which is proportional to the partial pres- 
5 sure difference of the 0 2  in both the product gas and the 
reference air which are introduced at one atmosphere 
and normal to  opposite sides of the disc. A vacuum 
pump keeps the product gas moving quickly through 
the product gas cavity, thus allowing a quick sensing of 
10 the 0 2  content of the product gas If necessary, addi- 
tional 0 2  may be introduced into the combustion cham- 
ber or an alarm sounded if an excess of 0 2  is present. 
The quick sensing of the present invention allows essen- 
tially real time control of the additional 0 2 ,  which is an 
l5 essential feature for a vitiated product gas used for en- 
gine testing. 
BRIEF DESCRIPTION OF T H E  DRAWINGS 
FIG. 1 is a schematic diagram of a combustion system 
2o employing the sensing device of the present invention; 
FIG. 2 is an exposed view of the sensing device of the 
and 
present invention. 
25 DETAILED DESCRIPTION OF T H E  
INVENTION 
As illustrated in FIG. 1, a combustion system em- 
ploying a sensing device 50 is shown. Air udder pres- 
3o sure flows through a controlled delivery valve 11 and a 
flow meter 12 into combustion chamber 10; a gas under 
pressure flows through a controlled delivery valve 13 
and a flow meter 14 into combustion chamber 1 0  and 
oxygen under pressure flows through a controlled de- 
35 livery valve 15 and a flow meter 16 into combustion 
chamber 10. The gas flowing through valve 13 may be 
any hydrocarbon gas such as CH4, C2H6, ... C,H,, o r  
any mixture of the preceding. The mixture of gases 
flowing into combustion chamber 10 is burned and the 
product gas of the combustion flow is expanded by 
nozzle 56 into a test section 17. The flow may be sub- 
sonic, supersonic, or hypersonic. A sample of the prod- 
uct gas in test section 17 flows through a probe 47, a 
valve 18, a compression pump 19, a flow meter 20 and 
45 a heater 21 into 0 2  sensor 22. The flow of the sampled 
combustion product is always subsonic with a normal 
pitot type probe 47 and viscous. Accordingly, the diam- 
eter of the tubing through which the gas flows must be 
large enough or the length short enough to avoid volu- 
50 metric choking (a limit to volumetric flow rate for a 
given length and diameter of tubing). Probe 47 must 
have a blunt entrance normal to the sample flow to 
always maintain the sample at subsonic flow rates. High 
enthalpy flows will require a cooled or ceramic probe 
55 47. Cooling may be accomplished by water cooling 
probe 47. 
Referring now to FIG. 2, sensing device 50 compris- 
ing an 0 2  sensor 22, a pump 37, a compression pump 19, 
a heater 21, and reference air is shown. When a sample 
60 of the product test gas flows through valve 18, it is 
compressed to a pressure slightly above one atmosphere 
and has flow energy added by compression pump 19. 
To ensure that the sample enters 0 2  sensor 22 at a pres- 
sure of approximately one atmosphere, an atmospheric 
65 vent 45 which leads to the atmosphere is employed. An 
alternate arrangement would be to use a precision pres- 
sure regulator in lieu of atmospheric vent 45 and a com- 
pression pump 19 with a higher compression ratio. 
. 
4,912,890 
3 4 
Next, the sample is heated by heater 21 to a temperature lower temperature gas from test section 17, the sample 
of 300" c. to 800" c. is heated by heater 21 before it reaches the 0 2  sensor 22 
Next, the sample enters product gas cavity 35 of 0 2  to at least 300" C .  and no more than 800" C. 
sensor 22. The 0 2  sensor 22 consists of a high tempera- "he sample should be flushed normal against elec- 
ture, Y203 stabilized ZrOr ceramic electrolyte disc 30 5 trode 32 from 8400 to 10,OOO times per second to ensure 
coated with porous platinum electrodes 31 and 32. The response time which is less than 0.2 second for the entire 
Platinum electrodes 31 and 32 are Porous enough to combustion system. The 0 2  sensor 22 has a response 
permit ready diffusion of 0 2 .  The disc 30 and electrodes time of 30 milliseconds. Therefore, it is apparent that 
31 and 32 are enclosed in a cylindrical enclosure 33 with the elements shown are important to achieve the system 
disc 30 dividing enclosure 33 into product gas Cavity 35 10 response since the 02 sensor 22 is relatively fast but 
and reference air cavity 34. Reference air is introduced delivery and control ofthe sampled gas must be done as 
into reference air cavity 34 through valve 23 at a pres- shown. The test gas is from 800" c. to 3000" C. The 
sure of nearly one atmosphere and comes into contact could not survive direct impingement of high 
l 5  collects the gas and.cools it to an acceptable level be- electrode 32. 
The O2 22 produces a Output E fore compression pump 19 is encountered. "he required electrodes 31 and 32 which is given by the following flushing- is accomplished by a vacuum pump 37 and equation: compression pump 19. Product gas cavity 35 has a cir- 
cumferential slot opening 38. In one embodiment of the 
present invention, product gas cavity 35 has a volume of 
slightly less than one cubic centimeter and circumferen- 
tial slot opening 38 ha a width of 0.5 mm and is located 
where A is a mathematical constant, T is the tempera- approximate~y o.5 mm from electrode 32. The sample 
nearly one atmosphere before entering product gas electrode 31, P2 is the partial pressure of oxygen on 25 electrode 32 and C(P) is the cell constant determined by cavity 35. Next, the sample is pumped out of product calibration with known gas mixtures at known pres- gas cavity 35 and through circumferential slot 38, cylin- sures. Usually operation at 1 atmosphere ( r t 2  percent) drical enclosure 33, flow meter 36, water trap 46, and a is desired since increasing cell pressure increases the 
ZrO: sensor output. It is apparent from equation (1) that 30 system exit at a rate Of 'Oo0 cubic centimeters per sec- 
when the partial pressures of the gas from test section 17 ond to 107000 ccm'sec by pump 37* According1y* the 
sure, the voltage output E will not be directly propor- o.20 seconds. 
tional to the difference of the two partial pressures. The 
H ~ ~ ~ ~ ,  ,-(PI must be determined. This calibration to FIG. 1, Or sensor 22 produces a voltage E continu- 
should be done daily since atmospheric p o ~ ~ u t i o n  ously ad enables the combustion system to respond to 
changes the calibration slightly each day. T~ do this sample change in 0.2 seconds. This system response is 
sphere pressure is applied through a valve 27, flow Jo in a real time update to the 01 valve controller. It is 
meter 20, and heater 21 to 0 2  sensor 22. consequently, possible to have faster response with short lengths of 
the partial pressure of calibration air is compared to the tubing and very compact systems. This voltage E passes 
partial pressure of reference air and if the flow rates of through control circuit 25, which subtracts the output 
flow meters 20 and 24 are the same the output E of Or of potentiometer 29 and controls the controller (15a) for 
sensor 22 will be C(P). Referring Once again to FIG. 1, 45 valve 15. Large valves usually have a response time Of 
this output is measured by a voltmeter 28. Then the 0.25 second Or slower. AcCordindY, the 0.20 second 
slider of potentiometer 29, with a voltage v applied to response time Of  the sensing device 50 results in sensing 
it, is adjusted to apply c ( p )  to control circuit 25. Con- device 50 operating in essentially real time relative to 
trol circuit 25 subtracts the output of potentiometer 29 the control valve 15. If the control valve 15 is relatively 
from the output of 0 2  sensor 22. Next, mathematical 50 large, then one-fifth second is adequate If the system is 
constant A is determined by introducing a reference gas small, building the components as compact and as small 
of known pressure, temperature, and mixture through as possible is necessary. If the amount of sensed 0 2  
valve 27, flow meter 20, and heater 21 to 0 2  sensor 22. exceeds a predetermined amount, visual and audio 
Once output voltage E is obtained, equation (1) may be alarm 26 may be excited and the amount of 0 2  flowing 
easily solved for A. 55 into combustion chamber 10 is decreased by control 
Referring once again to FIG. 2, the voltage E pro- valve 15. Likewise, i the amount of sensed 02is less than 
duced across electrodes 31 and 32 is extremely sensitive a predetermined amount, the amount of 02 flowing into 
to disc 30 temperature. Henbe, it is important that the combustion chamber 10 is increased by control valve 
temperature of disc 30 be maintained at a high level 15. Thus, the amount of 0 2  in the combustion product 
between 800" C. and 900" C. An optimal temperature is 60 gas is quickly sensed and controlled to the desired 
843" C. To maintain such a temperature, a NiCr/NiAl valve. For example, it is essential when testing engines 
thermocouple 39 monitors the temperature of disc 30. that the flight conditions be duplicated and that the gas 
The output of thermocouple 39 is compared with a set have twenty-one percent molar concentration of 02. 
voltage in a voltage controller 40 to produce an error An important feature of this invention is its ability to 
signal which is used by voltage controller 40 to produce 65 be used at a wide range of Mach numbers from 0 to 8 
a voltage across a heating coil 41 to maintain the tem- with gas temperatures from 800" C. to 3000" C. The  test 
perature of disc 30. In  order to avoid an increase in gas is regulated to simulate various flight altitudes as 
sensor response time caused by the cooling effect of the well. The unique arrangement shown will always adjust 
with 31* The contact with temperature, ultra-fast combustion products The probe 
E = .ATIn- PI + C(p) ( I )  
P? 
ture Of disc 30* is the partial pressure Of Oxygen On gas is compressed by compressor 19 to a pressure of 
and reference air are compared at the same total pres- response of the sensing device 50 is less than 
Such a quick response time for a Of the 
reason is that the cell constant C(P) is not equal to zero. 35 amount of in chamber lo. Referring now 
valve 18 is closed and clean calibration air at one atmo. usually much faster than most control valves resulting 
5 
4,911,890 
the sample gas to a sea level reference. The present 
invention may be used at altitudes ranging from 0 to 
above 130,000.feet as simulated by a propulsion type 
wind tunnel. 
What is claimed is: 
1. A device for quickly sensing the amount of oxygen 
in a combustion product gas produced in a combustion 
chamber comprising: 
a means for obtaining a sample of the combustion 
product gas; 
a means for compressing the sample to a pressure 
slightly greater than one atmosphere; 
a means for heating the sample within a temperature 
range from 300" C. to 800" C; 
. a cylindrical enclosure; 
a product gas cavity inside said cylindrical enclosure; 
a reference air cavity inside said cylindrical enclo- 
sure; 
a means for providing reference air to said reference 
air cavity at a pressure of approximately one atmo- 
sphere; 
a ceramic electrolyte disc which is coated on both 
sides with platinum electrodes with sufficient po- 
rosity to permit diffusion of the oxygen present in 
the reference air and test sample gas, is positioned 
as a shared wall between said product gas cavity 
and said reference air cavity, and produces a volt- 
age output; 
a means for heating said disc from 800" C.; 
a means for flushing said compressed and heated 
sample through said product gas cavity and im- 
pinging said sample against said platinum electrode 
in the product gas cavity approximately 8400 to 
10,ooO times per second; 
a means for sensing the voltage output of said disc 
which is proportional to the amount of oxygen in 
5 
10 
15 
20 
25 
30 
35 
6 
the sample and therefore the combustion product 
gas according to the following equation: 
, E= ATln(PI/Pr) + C(P) 
where E is the voltage output produced by the platinum 
electrolyte disc, T is the temperature of said ceramic 
electrolyte discs, PI is the partial pressure of the oxygen 
in the reference air against one side of said disc, P2 is the 
partial pressure of the oxygen in the sample gas against 
the other side of said disc, A is a mathematical constant, 
and C(P) is the disc constant. 
2. The device of claim 1 including a combustion 
chamber for producing the combustion product gas 
sample and regulating the amount of oxygen into the 
combustion chamber which produces the sample in 
response to said voltage output. 
3. The device of claim 1 wherein said means for flush- 
ing comprises a vacuum pump which pumps the sample 
through said product gas cavity, through a water trap, 
and through an exit. 
4. The device of claim 3 wherein said vacuum pump 
provides a flow rate of the products gas ranging from 
approximately 6000 to 10,ooO cubic centimeters per 
second and said product gas cavity has a volume of 
approximately one cubic centimeter. 
5. The device of claim 1 wherein the combustion 
product gas produced flows at a supersonic rate and 
said means for obtaining a sample is a probe with a blunt 
end which is normal to the flow to ensure a subsonic 
flow to said means for compressing. 
6.  The device of claim 5 wherein said probe includes 
water-cooling means. 
7. The device of claim 5 wherein said probe is com- 
posed of a ceramic material. 
* * * * *  
40 
45 
50 
55 
60 
65 


Device for quickly sensing the amount of O2 in a combustion product gas

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