A method and device is provided for a quick, accurate and on-line determination of heats of combustion of gaseous hydrocarbons. First, the amount of oxygen in the carrier air stream is sensed by an oxygen sensing system. Second, three individual volumetric flow rates of oxygen, carrier stream air, and hydrocrabon test gas are introduced into a burner. The hydrocarbon test gas is fed into the burner at a volumetric flow rate, n, measured by a flowmeter. Third, the amount of oxygen in the resulting combustion products is sensed by an oxygen sensing system. Fourth, the volumetric flow rate of oxygen is adjusted until the amount of oxygen in the combustion product equals the amount of oxygen previously sensed in the carrier air stream. This equalizing volumetric flow rate is m and is measured by a flowmeter. The heat of combustion of the hydrocrabon test gas is then determined from the ratio m/n

Puster, Richard L.

Singh, Jag J.

Sprinkle, Danny R.

English

NASA Technical Reports Server

United States Patent 1191 
Singh et al. 
[ i i ]  Patent Number: 4,761,744 
1451 Date of Patent: Aug. 2, 1988 
[54] METHOD AND DEVICE FOR 
DETERMINING HEATS OF COMBUSTION 
OF GASEOUS HYDROCARBONS 
[75] Inventors: Jag J. Singh, Yorktown; Danny R. 
Sprinkle, Newport News; Richard L. 
Puster, Hampton, all of Va. 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[73] Assignee: The United States of America as 
[21] Appl. No.: 933,962 
[22] Filed: Nov. 24, 1986 
[51] Int. Cl.4 ...................... G06F 15/46; GOlN 25/22 
[52] U.S. Cl. .................................. 364/500; 236/15 E; 
364/557; 364/571; 374/36; 431/13; 431/76 
[58] Field of Search ....................... 431/9, 115, 13, 76; 
374/36, 37; 364/500, 557, 571; 236/15 E 
~561 References Cited 
U.S. PATENT DOCUMENTS 
2,743,609 5/1956 Schuller ................................ 374/36 
4,329,873 5/1982 Maeda ................................... 374/37 
4,337,654 7/1982 Austin et al. .......................... 374/37 
4,359,284 11/1982 Kude et al. ........................... 374/37 
4,362,499 12/1982 Nethery ................................ 431/76 
4,386,858 6/1983 Kude et al. ........................... 374/37 
4,492,559 1/1985 Pocock .................................. 431/76 
4,433,922 2/1984 Bohl et al. ............................. 374/36 
4,500,214 2/1985 Calvet et al. .......................... 374/36 
4,511,262 4/1985 Arcara .................................. 374/36 
4,565,788 1/1986 Milovidov et al. ................... 374/37 
4,576,570 3/1986 Adams et al. ..................... 236/15 E 
Primaiy Examiner-Parshotam S. La11 
Assistant Examiner-Kevin J. Teska 
Attorney, Agent, or Firm-George F. Helfrich; John R. 
Manning; Charles E. B. Glenn 
[571 ABSTRACT 
A method and device 15 is provided for a quick, accu- 
rate and on-line determination of heats of combustion of 
gaseous hydrocarbons. First, the amount of oxygen in 
the carrier stream air is sensed by oxygen sensing sys- 
tem 20. Second, three individual volumetric flow rates 
of oxygen, carrier stream air, and hydrocarbon test gas 
are introduced into burner 19. The hydrocarbon test gas 
is fed into burner 19 at a volumetric flow rate n mea- 
sured by flowmeter 18. Third, the amount of oxygen in 
the resulting combustion products is sensed by oxygen 
sensing system 20. Fourth, the volumetric flow rate of 
oxygen is adjusted until the amount of oxygen in the 
combustion product equals the amount of oxygen previ- 
ously sensed in the carrier stream air. This equalizing 
volumetric flow rate is m and is measured by flowmeter 
16. The heat of combustion of the hydrocarbon test gas 
is then determined from the ratio m/n. 
2 Claims, 4 Drawing Sheets 
0 2  
CARRIER 
STREAM 
AIR 
CARRIER 
HYDROCARBON 
REFERENCE 
GAS 
https://ntrs.nasa.gov/search.jsp?R=19880019618 2020-03-23T20:06:27+00:00Z
U.S. Patent 
30 
20 
10 
Aug. 2,1988 
o CALCULATED 
' 
- 
n r 
70 
ON 
+ -
50  
Sheet 1 of 4 4,761,744 
A 
E)= 3*'6 
0 EXPERIMENTAL 
0 CALCULATED 
X(02) =0.2095 
- 
Y q/ ON , , , 
x * 
IO I5 20 5 
II 
=VALUE 
n 
a 0  
n 
>r 
c - 
Y ON 
x + 
+ 
- 
Y 
x 
& 
Y- + 
c 
yl 
I - 
Y 
c 
Y ON
X * 
II 
a 
FIG. 1 
EXPERIMENTAL I 
-/ 
0 2.5 5 .O 7.5 10.0 
m 
ZVALUE 
FIG. 2 
U.S. Patent Aug. 2,1988 Sheet 2 of 4 
0 cu 0 - 
4,761,744 
U.S. Patent Aug. 2,1988 Sheet 3 of 4 4,761,744 
A 
I .2 
I .o 
.8 
.6 
.4 
.2 
0 
3 
- X I 0  
X(02) = 0.2095 - 
- 
- 
- 
- 
IO 12 14 
?VALUE 
FIG. 4 
- 
1.4 
\ 
s 1.2 
A 
L 
1.0 
0 & .8 
3 * .6 2 
0 
0 .4 
LL 
O .2 
0 CXH2,+2HYDROCARBONS 
GAS MIXTURES 
X(0,) = 0.2095 
I I I I I I I 
2 4 6 8 IO 12 14 
m VALUE 
FIG. 5 
U.S. Patent Aug. 2,1988 Sheet 4 of 4 4,761,744 
1 
4,76 1,744 
2 
used for a mixture of hydrocarbon gas and inert gases 
such as nitrogen and helium. 
Other objects and advantages of this invention will 
become apparent hereinafter in the specification and 
SUMMARY OF THE INVENTION 
METHOD AND DEVICE FOR DETERMINING 
HEATS OF COMBUSTION OF GASEOUS 
HYDROCARBONS 
ORIGIN OF THE INVENTION 
5 drawings which follow. 
The invention described herein was made by According to the present invention, the foregoing 
and used by Or for the Government for governmental 10 ratio of m/n, where m is the volumetric flow rate of 
or therefor. the hydrocarbon test gas, flowing at the volumetric rate 
of n, is burnt such that the mole fraction of oxygen in 
the resulting combustion product gases equals that in 
to the heats of combustion of the hydrocarbon test gas. 
First, the amount of oxygen in the carrier stream air is 
ees of the Uas. Government and may be manufactured and additional objects are obtained by measuring the 
purposes without the payment Of any thereon oxygen needed to enrich the carrier stream air in which 
TECHNICAL FIELD OF THE INVENTION 
more specifically to a method and device for &termin- 
ing heats of combustion of gaseous hydrocarbons. 
This invention relates generally to G h h e t e r s  and 15 the carrier stream air. This m/n value is directly related 
determined. Second, three individually controlled flows 
of carrier stream air, oxygen, and a hydrogen test gas 
BACKGROUND OF THE INVENTION 
An accurate determination of the heats of combustion 20 are fed into a burner and result in combustion product 
of various hydrocarbons is necessary in a variety of gases. The hydrocarbon test gas is fed into the burner at 
applications. For example, the production Of simulated a volumetric flow rate of n. Third, the amount of oxy- 
test media in wind tunnels for hypersonic vehicle stud- gen in the resulting combustion product is sensed. 
ies requires a knowledge ofthe hydrocarbon properties. Fourth, the volumetric flow rate of oxygen flowing into 
Also, natural gas suppliers often mix gas Supplies from 25 the burning is adjusted until the amount of oxygen 
different sources. Since these mixtures must meet mini- sensed in the resulting combustion product is equal to 
mum federally mandated Btu standards, a determination that previously sensed in the carrier stream air. The 
of the heat of combustion for the mixture is necessary. equalizing volumetric flowhate of oxygen is m. The 
Currently, this determination occurs off-line in a labora- heat of combustion of the hydrocarbon test gas is then 
tory. 
Several methods are currently utilized to determine BRIEF DESCRIPTION OF THE DRAWINGS the heats of combustion for gaseous hydrocarbons. One 
method, known as water-flow calorimetry, transfers FIG. 1 is a graph showing the relationship of the heat 
heat resulting from hydrocarbon combustion to water of combustion constant A to m/n for Pure saturated 
and then measures the resulting temperature rise of the 35 hydrocarbon gases; 
water, which is proportional to the heat of combusion. FIG. 2 is a graph showing the relationship ofthe heat 
Disadvantages of water-flow calorimetry include a of combustion constant A to m/n for a binary mixture 
lengthy response time due to the relatively high thermal of hydrocarbon gases; 
resistance of water and inexact data due to heat losses to Of the heat 
the Another method 
volves catalytically burning air and hydrocarbon gas of 
30 determined from the ratio m/n. 
FIG* 3 is a graph showing the 
40 of combustion constant A to m/n for a mixture of hy- 
drocarbon and inert gases; 
known volumetric flow-rates and then measuring the FIG. is a graph showing the Of the heat 
amount of oxygen utilized by This mea- of combustion to m/n for several hydrocarbon gases; FIG. 5 is a graph showing the relationship of the heat 
of combustion to m/n for several mixtures of saturated 
hydrocarbon and inert gases; and 
FIG. 6 is a schematic diagram of the device for deter- 
sured amount of oxygen is proportional to the heat of 45 
combustion of the hydrocarbon gas. One disadvantage 
of this method is that some prior knowledge of the 
sufficient oxygenic content to completely oxidize the 
hydrocarbon gas, which necessitates some knowledge 5o 
of the composition of the hydrocarbon gas. Second, 
gas is required to select the optimal catalyst. 
Accordingly, it is an object of this invention to pro- 
vide an accurate method and device for measuring the 55 
heats of combustion of hydrocarbon gases which re- 
quires no prior knowledge of the hydrogen gas. 
It is a further object of this invention to provide an 
accurate method and device for measuring the heats of 
combustion of hydrocarbon gases which may be 60 
quickly performed. 
It is a further object of this invention to provide an 
accurate method and device for measuring the heats of 
combustion of hydrocarbon gases which may be per- 
formed on-line. 65 where 
It is a further object of this invention to provide an 
accurate method and device for measuring the heats of 
combustion of hydrocarbon gases which can also be 
hydrocarbon gas is needed. First, the air used must have mining heats of combustion of hydrocarbon test gases. 
DETAILED DESCRIPTION OF THE 
INVENTION 
gas sample in oxygen enriched air can be written as 
follows~ 
[(Air) + m(02)  + nflC,Hy) + n(1 - f)f-+/(Air) + 
Some Of the Of the hydrocarbon A general expression for the combustion of a natural 
(1) 
nfx(C02)  + +-fv (H2O) + 
0 2  + n ( l  - A I  + heat 
(C,H,+I)=Test gas 
C,H,=Effective hydrocarbon in the test gas (for 
saturated hydrocarbons, y = 2x + 2), 
4,761,744 
3 4 
I = Non-combustible impurities in test gas, would be C1.5H5.0, giving m/n=3.81 for 
f=Combustible fraction of test gas, X(02)=0.2095. If this mixture also contained an incom- 
I=Volumetric flow rate of carrier stream air, bustible impurity, the corresponding m/n-value would 
m=Volumetric flow rate of oxygen, and be lower, as indicated by equation (4). Referring now to 
n=VOlumetric flow rate of hydrocarbon test gas. 5 FIG. 3, A is seen to be a function of m/n for f= 1 for test 
The mole fraction of oxygen in the Products OfeWa- gases containing several saturated hydrocarbons as well 
as non-combustible gases. Again, the uniqueness of cor- 
relation between A and m/n is evident. 
Because m/n-values for various test gases containing 
10 saturated hydrocarbons are related to their chemical 
composition, they can serve as the basis for direct deter- 
minations of their heats of combustion. Table I below 
summarizes the gross heats of combustion of several 
pure saturated hydrocarbons. 
TABLE I 
tion (1) is: 
(2) 1 
1 
0.2095 1 + m - 5 (4 x + y)  
1 + nfx ++fi + [ m  - f(4.x + y )  + n(1 - A  
0.2095 1 + m - f (4 x + y)  
I +  m + n + nf(-+) 
c 
15 
X(02) = 
- 
Heat of Heat of Combustion 
m/n Combustion [ _(kct;Fl) ] 
Hydrocarbon X(02) = 0.2095 (kcal/mol) 
2o CH4 2.795 212.80 76.14 
C2H6 4.825 372.82 77.21 
c3HS 6.855 530.61 77.40 
GHiz  10.915 845.10 77.43 
where 
X(Oz)=Mole fraction of oxygen in the combustion 
products. 
If X(02)=0.2095, we obtain: C4Hio 8.885 687.65 77.39 
0.838 (1 - + fl4x + 1.2095 Y) 
3.162 n = - m 
C6Hi4 12.945 1002.55 71.45 
(3) 25 
Referring now to FIG. 4, the heats of combustion 
(kcal/mol) vs. m/n values for several selected hydro- 
carbons are shown. Referring now to FIG. 5. the heats 
I f f= 1 (i.e., the test gas has no non-combustibk imPu- 
rities in it), equation (3) reduces to: 
I 
30 of combustion vs. m/n values for mixtures containing 
4x + 1.2095 y - E (3af selected saturated hydrocarbons and non-combustible 
gases is shown. It is apparent that the heats of combus- 
tion of various gases are directly related to their corre- 
If, on the other hand, f = O  no combustible frac- sponding m/n nerefore, determination of m/n 
mination of its heat of combustion. 
Referring to Table I and equation 3(b)p the following 
relationship between heats of combustion and m/n has 
been derived: 
3.162 - n 
is present in the test gas)* equation (3) reduces to: 35 for the hydrocarbon test gas provides an on-line deter- 
0.2650 = E (3b) 
Generalizing equation (3) for non-standard air, we 40 obtain: AW = Ao+Al(m/n)+ A ~ ( ~ / I I ) ~  + A3(m/n)- 
+A4(n~/n)~ 
4X(OZ)(l - n +A4x + (1 + X(0z))yI - (4) - 
4 - m 2 ) l  where 
45 AH” =heat of combustion (kcal/mol), m 
4[1 - X(Oz)] - n Ao= -23.5580, -- 
A 
A1 =89.5119, 
the composition of the hydrocarbon test gas (CxHy+ I) A3=0.1795, and 
and the mole fraction of oxygen in the air used for 50 A4=-0*0051* 
combustion. Constants A v A 4  were determined using a least 
Referring to FIG. 1, the correlation between A and Wares fit to a fourth Power equation expressing AH” as 
m/n is shown. It is apparent that A and m/n are linearly a f~nction of m h .  
related. If f#l, m/n values for various impurity-con- AS illustrated in FIG. 6, a device 15 for determining 
taining hydrocarbon gases will be different from those 55 heats of combustion of various hydrocarbon test gases is 
for pure hydrocarbons* An experimental measurement comprised of an oxygen flow meter 16, a carrier stream 
of m/n will then give f, the combustible fraction in the air flow meter 17, a hydrocarbon test gas flow meter 18, 
test gas. Referring now to FIG. 2, the correlation be- a burner 1% and an oxygen sensing system 20. First, 
tween A and m/n for binary hydrocarbon gas mixtures carrier stream air is directed through air valve 23 and 
is shown. FIGS. 1 and 2 clearly demonstrate that the 60 air conduit 2% to one end of main sensor conduit 28. 
m/n values for gases containing saturated hydrocarbons Both air conduit 22 and main sensor conduit 28 are 
are uniquely related to their hydrogen and carbon con- wrapped with heater tape 26, which is controlled by a 
tents. variable AC voltage source 27 to ensure a temperature 
If the test gas is a mixture of two or more hydrocar- sufficient to avoid condensation of the gases in the con- 
bons, equation (4) can be used to readily calculate the 65 duits. 
m/n-value for the “effective” test hydrocarbon. For The other end of main sensor conduit 28 connects to 
example, for a test gas containing equal mole fractions sensor chamber 30. Sensor chamber 30 contains oxygen 
of CH4and C2H6, the effective equivalent hydrocarbon sensor disc 31. A pump (not shown) is connected to 
A is a constant which obviously depends solely on A2= -2.2580, 
C 
4,761,744 
J 
sensor chamber 30 via a pump flow meter 32. This 
pump allows sample gas to flow through main sensor 
conduit 28 and to come in contact with one side oxygen 
sensor disc 31. This oxygen sensor disc 31 is connected 
to oxygen sensing system 20 and reference gas chamber 
33. A reference gas, standard air, is fed at constant volu- 
metric flow rate by flowmeter 34 into reference gas 
chamber 33 and into contact with the other side of 
oxygen sensor disc 31. An electrical potential is devel- 
oped across oxygen sensor disc 31 from the sample gas 
on one side and the reference gas on the other. This 
electrical potential is read by oxygen sensing system 20 
and is proportional to the amount of oxygen in the 
sample gas. Accordingly, the amount of oxygen present 
in the carrier stream air is determined. 
Next, air valve 23 is closed and sample gas valve 25 is 
opened. Sample gas valve 25 connects one end of sam- 
ple gas conduit 24 to one end of burner conduit 21. 
Sample gas conduit 24 is also wrapped with heater tape 
26, which is controlled by a variable AC voltage source 
27 to ensure a temperature sufficient to avoid condensa- 
tion of the combustion products in sample gas conduit 
24. The other end of sample gas conduit 24 connects to 
main sensor conduit 28. 
The other end of sample gas conduit receives com- 
bustion products from burner 19. Hydrocarbon test gas 
is fed into burner 19 at a volumetric flow rate n con- 
trolled by hydrocarbon test gas flowmeter 18. Carrier 
stream air is fed into burner 19 at a constant volumetric 
flow rate controlled by carrier stream flowmeter 17. 
Oxygen is fed into burner 19 at a volumetric flow rate 
controlled by oxygen flowmeter 16. Initially, oxygen 
flowmeter 16 is closed. The resulting combustion prod- 
ucts travel through burner conduit 21 and ultimately 
contact one side of oxygen sensor disc 31. A pressure 
gauge 29 is connected to main sensor conduit 28 to 
ensure that the previously sensed carrier stream air and 
the combustion products contact oxygen sensor disc 31 
with the same Dressure. Incorrect data can result if the 
5 
10 
15 
20 
25 
6 
gas into a burner to produce combustion products 
containing oxygen; 
sensing the amount of oxygen in said combustion 
products; 
adjusting said flow of oxygen until the amount of 
oxygen in said combustion products is equal to the 
previously sensed amount of oxygen in the carrier 
stream air; and 
calculating the heat of combustion of said hydrocar- 
bon test gas from the following equation: 
AH" =Ao+A1(m/n)+Az(m/n)~+A3(m/n)-  
3 + ~ 4 ( m / n ) ~  
where, 
AH" is the heat of combustion of said hydrocarbon 
test gas, 
m is the volumetric flow rate of said individual flow 
of oxygen which equalizes the amount of oxygen in 
said combustion products with the previously 
sensed amount of oxygen in the carrier stream air, 
n is the volumetric flow rate said individual flow of 
hydrocarbon test gas which is introduced into the 
burner, and 
Ao, Ai, A2, A3 and A4 are constants determined by 
using a least squares fit to a fourth power equation 
expressing AHo as a function of m/n. 
2. A device for determining the heat of combustion of 
a hydrocarbon test gas comprising: 
30 a means for providing a flow of carrier stream air 
a means for sensing the amount of oxygen in said flow 
containing oxygen; 
35 
pressure varies in sensor chamber 30. 40 
Once the resulting combustion products contact one 
side of oxygen sensor disc 31, the amount of oxygen 
present in the combustion products is sensed by oxygen 
sensing system 20 in the manner described above. Oxy- 
gen flowmeter 16 is gradually opened until the amount 45 
of oxygen present in the combustion products equals the 
amount of oxygen previously sensed in the carrier 
stream air. This equalizing volumetric flow rate of oxy- 
gen is m. 
using both the volumetric flow rate n recorded by hy- 
drocarbon test gas flowmeter 18 and this equalizing 
volumetric flow rate m in equation (5).  
The heat of combustion is then quickly determined 50 
What is claimed is: 
1. A method of determining the heat of combustion of 55 
providing a flow of carrier stream air containing 
oxygen; 
sensing the amount of oxygen in said flow of carrier 
stream air; 60 
introducing three individual volumetric flow rates of 
carrier stream air, oxygen, and hydrocarbon test 
a hydrocarbon test gas comprising: 
of carrier stream air; 
a means for introducing three individual volumetric 
flow rates of carrier stream air, oxygen, and hydro- 
carbon test gas into a burner to produce combus- 
tion products containing oxygen; 
a means for sensing the amount of oxygen in said 
combustion products; 
a means for adjusting said individual flow of oxygen 
until the amount of oxygen in said combustion 
products is equal to the previously sensed amount 
of oxygen in the carrier stream air; and 
a means for calculating the heat of combustion of said 
hydrocarbon test gas from the following equation: 
AF =AO+A i(m/n)+~2(m/n)~+A,(rn/n)- 
3+A.+(m/n)4 
where, 
AW is the heat of combustion of said hydrocarbon 
test gas, 
m is the volumetric flow rate of said individual flow 
of oxygen which equalizes the amount of oxygen in 
said combustion products with the amount of oxy- 
gen in the carrier stream air, 
n is the volumetric flow rate said individual flow of 
hydrocarbon test gas, and 
Ao, Ai, A2, A3 and A4 are constants deterhined by 
using a least squares fit to a fourth power equation 
expressing AH" as a function of m/n. * * * * *  
65 


Method and device for determining heats of combustion of gaseous hydrocarbons

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