ON THE MECHANISM OF COLD-FLAME COMBUSTION

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• Document Creation Date: December 22, 2016
• Document Release Date: July 22, 2011
• Sequence Number: 413
• Publication Date: November 21, 1950
• Content Type: REPORT

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CLASSIFICATION CONFIDENTIALCQNFIQENTIAL
CENTRAL INTELLIGENCE AGENCY REPORT
INFORMATION FROM
FOREIGN DOCUMENTS OR RADIO BROADCASTS CD NO.
SUBJECT
HOW
PUBLISHED
WHERE
PUBLISHED
DATE
PUBLISHED
Scientific - Chemistry, cold flame combustion
Monthly periodical
Moscow
May 1948
DATE OF _
INFORMATION 1948
SUPPLEMENT TO
REPORT NO.
THIS IS UNEVALUATED INFORMATION
THIS DOCUM I MT CONTAINS INFORMATION AFFECTI NA' NATIO R,.t DEFENSE
OF THE UNITFO STATES WITHIN THE MEANING OF IJFIONAGI ACT 50
U. S. C.. SI ANO R. AS AMENDED. ITS TRANSMISSION OR THE RIVELATION
OF ITS CONTENTS IN ANT MANNER TO AN UNAUTHORIZED PERSON IS PRO-
HIBITED /T LAW. REPRODUCTION OF THIS FORM IS FROHIEIIID.
Zhurnal Fizicheskoy Khimii, Vol XXII No 5, 1948, pp 561-4,
V. Kondrat'yev, L. Karmilova
Ye. Kondrat'yeva
Inst of Chem Phys
Aced Scl USSR
CTab1e and figures referred to are appended]
The application of a thermo-couple coated with Zn0?Cr203, the heating of
which depends on the catalytic recombination of H atoms, has made It possible
to detect and determine quantitatively the concentration of atomic hydrogen in
H2 f1_7 and CO L2] flames. By means of this method the presence of .atomic
H and its concentration in C2E2 flames were established with a high degree of
probability C2H2 [3J. Our attempts to apply the method to other hydrocarbons
flames was unsuccessful. It was impossible to obtain a stationary flame with
a temperature sufficiently low to prevent a heterogeneous reaction on the sur-
face of the catalyst. For this reason we turned our attention to the study of.
cold flames, where the absence or presence of atomic H is of considerable in-
terest from the standpoint of the flame mechanism.
The mechanism of cold flames observed with hydrocarbons (excluding methane),
aldehydes (excluding formaldehyde), and ethers differs from the mechanism of hot
flames of these substances. The hot flames are characterized by active centers
consisting of free atoms and simple radicals L1J. All experimental data per-
taining to reaction kinetic in cold flames and to the analysis of their reaction
products as well: as the results of spectroscopic analysis indicate that the
active substances in cold flames are peroxides -:td compounds of the complex
radical type.
The results of Gaydon f -5_j7 based on the study of the process N0+ 0.+N02 +h Y
lead to the same conclusion. Gaydon's experiments showed that atomic oxygen is
not present in the inner cone of'a hydrocarbon flame. The analysis of the re-
action products in the inner cone indicates that the mechanism of the reaction
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CoNFmENTIAL CONFIDENTIAL
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ON THE MECHANISM OF. COLD-FLAME COMBUSTION
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CU FlTENT 11 11
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taking place there has certain properties common to cold flames. This raises a
doubt as to the validity of the mechanism of low-temperature oxidation of hydro-
carbons and aldehydes proposed by Elbe and Lewis [6J. The negative results
obtained by the present authors in their attempt to detect atomic hydrogen in
(C2H5)20 and CH3CHO flames also lead to the conclusion that atomic gases are not
present in cold flames.
The experimental methods we employed do not differ from those used in the
study of hot flames. The oxygen enters the displacement flask from the gaso-
meter and the fuel vapor from a vessel filled with liquid fuel. The rate of
delivery is regulated by values. The gasometer shows the consumption of oxygen
and the fuel level in the vessel indicates the consumption of fuel. The composi-
tions O( of the combustible mixtures are determined by means of the following
formulas:
OC- I 2
6 v~fti ~ 4id
where V02, Veth, and Vald are the volumes of oxygen ether vapor and aldehyde
vapor reduced to standard conditions.
In the various experiments with ether, the maximum temperature of the
flame was 210-3600 C, the pressure in the reaction vessel was 15-50 mm of mer-
cury and a was 0.17-0.73. The maximum flame temperature in the case of alde-
hyde (one experiment) was 4200 C with a pressure of 50 mm and OC= 0.39. The
experiments were conducted in such a way that after a stationary flame was ob-
tained (in the stream) the temperature was measured (by means of both thermo-
couples) at various distauces efrom the heated end of the combustion vessel
( e = 0,1,2...........10 cm). Since the temperature increment d T, which was
measured by the difference between the reading of the coated thermocouple and
that of the control thermocouple, was anticipated to be quite small for the cold
flame and since the flow in the stream was not uniform, it was necessary to in-
troduce corrections. These were made by taking a second set of temperature
readings with the oxygen replaced by argon. The difference d T =(.d T) -(d T
was taken as the actual temperature increment. 02 )AR
Our results showed that within the limits of experimental error, which is
20 C, the value ofd T is equal to zero. However, we cannot conclude from this
that atomic hydrogen is completely absent in a cold flame. To substantiate such
a conclusion, it is necessary to evaluate the reaction velocity in the cold
flame since the concentration of the H atoms is directly related to the reaction
velocity.
Our attempts to evaluate the magnitude of the reaction velocity from fuel
consumption produced no reliable results due to the large errors incurred in
measuring relatively small volumes of'liquid which vary little in magnitude one
from another. Therefore, we used an indirect method which we shall describe
below.
The temperature of a stationary flame is directly related to the quantity
4 YV r (Q.is the molecular heat of reaction, the percentage of complete com-
bustion, Vr the volume of fuel vapor delivered per unit time) whit: is a measure
of the quantity of liberated heat. Figure 1 shows the flame temperature t as a
function of 2' v r based on our measurements. The values of temperature in Figure
1 are the averages of readings at t?= 4 cm and
relation between the temperature of the cold flame RndmtheIamount sof heataliber-
ated in it is the same as for the case of CO, we can compute the extent of combus-
tion (`Y) from the following equation:
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r
PE ?T1.AL
which is valid for the same temperature increments in tae flame and the same
reaction tube wall temperature. In each case, the temperature of the wall was
assumed to be equal to that measured with '/-0 (no flame). The heat of combus-
tion of carbon monoxide is 4co - 66,760 cal per mole while the heat of combus-
tion of diethyl ether is Meth - 660,300 cal per mole. It should be pointed out
that since carbon dioxide and water are far from being the sole products formed
in the cold ether flame, the actual heat of combustion of ether under conditions
of a cold flame must be less than the her', of its complete combustion.
Thus the percentage of ether which is burned 7) varies 3.35 to
8.636. The curve showing the temperature as a function of 10 ' from
t r 9eth which is presented in Figure 2 is similar to the analogous curveepor 8Oh \'9c0 110
It follows that our evaluation of the percentage of burned ether is correct. A
similar evaluation for the case of acetaldehyde burning under similar conditions
gives us 7' 22%.
If we assume that for equal reaction velocities ()IV) the concentrations of
atomic hydrogen in cold flames and in the CO flame are the same, we can compute
the corresponding values of temperature increments d T for cold flames provided
we know the value of 7V for each experiment with ether and aldehyde and the
maximum temperature increment4T (in the center of the combustion zone) as a
function of VV for the CO flame. The results of such a calculation are presented
in Table 1.
We can see that the calculated values of L T are several times greater than
the measurement error (20). Since our measurements indicated that within the
limits of experimental error the actual temperature increment is zero, we may con-
clude that atomic hydrogen is either absent in cold flames of diethyl ether and
acetaldehyde or else its concentration is considerably lower than in a hot carbon
aonoxide flame (with the same reaction velocity). If we assume that the heat
balance of thermo-couples in cold flames approaches the heat balance in the CO
flame, and if we make use of the ratio
~N_dT~,dx
P BO,000
w
20, here )514 is the partial pressure of atomic hydrogen, we find, by making d T
PH -
Regardless of which of the two possible conclusions concerning the concentra-
tion of H atoms in cold flames is valid, we must conclude that the H atoms, even
if they are present in cold flames, do not play the same important role that they
do in the mechanism of hot flames.
1. V. Kondrat'yev and Ye. Kondrat'yeva, Doklady Akademii Nauk SSSR, LI, 607, 1946.
2. Ye. Kondrat'yeva and V. KOndrat'yev, Zhurna1 Fizicheskoy Kh#mii, XXI, 769, 1947.
3. Ye. Kondrat'yeva and V. Kondrat'yev, Zhurnal Fizicheskoy Khimii, XXI, 761, 1947.
4. V. Kondrat'yev, Zhurnal Fizicheskoy Khi*'i, XX, 345, 1946.
5. A. G. Gaydon, Proc. Roy. Soc., CLXXXIII, 111, 1944; Trans. Farad. Soc., XLII,
292, 1946.
6. G. Elbe and B. Lewis, J. Amer. Chem. Soc., LIX, 976, 1937.
Table and figures follow)
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CONFIDENTIAL
Expt No
y V AT
Expt. No
yV AT
'50X1-HUM
8
0.095
8
23
0.051
3.5
9
0.079
6
24
0.095
8
0.073
5.5
25
0.126
10
14
0.056
It
26
0.082
6
15
0.063
4.5
28
0.071
5.5
16
o.084
6.5
29
0.071
5.5
17
0.082
6
30
0.068
5
18
0.082
6
,OOT"
0 a2 0.1 a.6 0.8lr.
Figure 1
a 0.2 0f *6 OB/a ,,g
yy
Figure 2 ~ /aaZ!
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