RESEARCH MEMORANDUM
VARIATION OF PRESSURE LIMITS OF FLAME PROPAGATION WITH
TUBE DIAMETER FOR VARIOUS ISOOCTANE-OXYGEN-NITROGEN
MIXTURES
B y Adolph E. Spakowski and Frank E. BelIes
Lewis Flight Propulsion Laboratory
Cleveland, Ohio
NATIONALADVISORY COMMITTEE
FOR AERONAUTICS
WASHINGTON
March 3, 1952
.. .
-
1V
-~
NACA FU4 E52A08
FtESEARCH MEMctRANDuM
VARIATION OF PRESSURE LIMITS OF FLAME PROPAGATION WITH TUBE
By Adolph E. Spakowski and. Frank E. Belles
The change i n t h e p r e s s u r e l i m i t s of flame propagation with tube
diameter for various isooctane-oxygen-nitrogen mixtures
was studied;
t h e e f f e c t s of oxygen concentration upon the pressure limits and concentration limits of flame propagation were also investigated..
.
Lowpressure propagation limits weremeasured. for quiescent
isooctane-oxygen-nitrogen mixtures i n c y l i n d r i c a l glass tubes Kith inside
diameters of 16, 22, 28, and 38 millimeters. Oxygen-nitrogenatmospheres
containing 15.0 t o 49.6 percent by volumeoxygenwere
used.
The data showed t h a t , under the conditions of t h e experiments, no
flame prqpagation is possible for isooctane in oxygen-nitrogen mixtures
containing less than ll t o 12 percent oxygen.
The experiments gave quenchd i s t a n c e s i n terms of c r i t i c a l
diameter for flamepropagation.
For approximately stoichiometric
isooctane-air mixtures, critical
diameter was found t o be proportional
t o the pressure raised to the
-0.91 pzwer. The critical tube diameters
were on t h e average 1.25 times as large as quenching distances obtained
i n connection with ignition-energy experiments.
Forexperiments i n various oxygen-nitrogen atmospheres, t h e logarithms .of t h e maxFnnun flame speeds for isooctane were p r o p o r t i o n a l t o
the critical diheterg.
J
i
~ODUCTION
n
-
The study of conibustion processes and t h e ? r e l a t i o n s t o aircraft
enginescan beapproached i n two general ways:
(a) the study of combusti-on i nt h e engine i t s e l f ; and (b) thestudy of combustion processes
in idealized systeins. A p a r t of t h e program i n t h e second category is
being carried out at t h e W!CA Lewis laboratory and is considereh herein.
5 e eventual aim of all such s t u d i e s i s understanding of t h e complex
conibustion process as it occurs in p r a c t i c a l a p p l i c a t i o n s .
,
2
NACA RM E52A08
8
The e f f e c t s af various proportions of oxygen and i n e r t gases on t h e
conibustion properties of hydrocarbon fuels have been studied by a number
of investigators.Emever,most-ofthesestudies
have involvebgaseous
f u e l s . For example, Blanc,Guest, -Lewis,and von Elbe studied the effect
of oxygen concentration on flammability limits, minimum ignition energies,
and quenching distances of methane; ethane, and propane (reference 1).
Badln, Stuart, and Pease studied t h e e f f e c t on flamespeeds of butadiene
(reference 2 ) . I n thecase of l i q u i d hydrocarbon fuels, a recentinvestigation of t h e minFmum ignition
energies
of irsacctane.-oxy@;en-nitrogen
mixtures has been made by Experiment, Inc., commercial laboratory, under
M A contract.
4
c
N
- mw
.
A research program 'on t h e combustlop properties of isooctane-oxygennitrogen mixtures, ingluding flame-speed measurements, (unpublished) is
a l s o i n progress a t the NACA Lewis laboratory. The e f f e c t s of t h e oxygen
,
'2
on t h ep r e s s n r e - f l m b i l i t y
m t s and concentration02 + prz
f l m b i l i t y limits of t h e s e mixtures is consideredherein.Pressureflammability limit curves were determined i n four glass flame tubes of
16 t o 38 millimeters inside diameter with s i x oxygen-nitrogen
atmospheres
.
."
containing 15.0 t o -49.6percent - e g e n by
?i?r-&"these
data,
quenching distances were obtained in terms of t h e c r i t i c a l tube diameters
f o r flame propagation.-
fraction
vOhi&i.
..
."
=
-
Apparatus.
In this investigation, the
.tube method of determining
pressure-flammability limits was used (references 3 and 4 ) . Special
modifications of the basic apparatus were made to.permit the study of
l i q u i df u e l s .
The equipment i s i l l u s t r a k d i n , f i g u r e 1.
The f u e l metering, m l x i n g , and-storing apparatus consisted of a
4 5 - l i t e r galvanized steel storage tank with sealed stirrer A , . f u e l
capsule B, afr i n l e t I, and precision manmeter C.. Thesecomponentswere
mounted within a glass-walled tank of ethylene glycol, which served as a
constant-temperaturebath.
The batht-erature
was thermostatically
c o n t r o l l e d t o a preset temperature of 58 20.5' C.
The test section consisted of a series of interchangeable glass
flame tubes.
The f o u r flame tubesused in t h i s i n v e s t i g a t i o n were 4 f e e t
long and had inside diameters of 38, 28, 22, and 1 6 milXmetere. Each. . ..
tube was s e a l e d t o a n i g n i t i o n s-ect.ion9 0 -niluliine€-&i%%i"di&ieter- aiid
2 5 centimeters long. The flame tubes were connected t o a 4 7 - l i t e r plenum
chamber through a spherical glass j o i n t and a 25-miUimetgr-bqre stopcock.
In order to prevent
condensation
of l i q u ifdu e l
from the combustible
mixtures, the flame tube and the ignition section w e r e enclosed by a
. .. ..-b
-
NACA RM E52A08
c
3
c y l i n d r i c a l resis,tEtnce-wound furnace. Tbree separate windin@;s were c a l i braked t o give a uniform temgerature of 58O C throughout the length of
t h e flame tube. The furnace was provided with a longitudinal s l i t
1/2 inch wide for visual observation of t h e flames.
The isooctane-oxygen-nitrogen mixtures w e r e ignite+ by paselng a
rapid capacitance spark discharge across pointed stainless-steel electrodes. The maxFmum voltage across t h e gap was 30,000 volts.
-
Preparation of isooctane-oxygen-nitrogen mixtures.
The oxygennitrogen atmospheres used were obtainea commercially i n c y l i n d e r s at
2200 pounds p& square inch gageexcept in the case-of a&. The artificialmixtures contained 15.0, 25.0, 29.4, 34.7, and 49.6 percent oxygen
by volume t o within 20.1percent.
The isooctane used was commercially available knock-rating reference
f u e l with a p u r i t y of 99.6 mole percent. When a c d u s t i b l e mixture Was
prepared, t h e f u e l mixture and the storage tank were first evacuated.
Isooctane vapor was then expanded i n t o t h e t a n k from the fuel. capsule
( s e e f i g . 1) The p a r t i a l p r e s s u r e of the isooctane was read on t h e
precision manometer by meansof a cathetometer accurate t o fo.05
meter. The desired oxygen-nitrogenatmosphere w a s passed through
Anhydrone t o remove w a t e r and Ascarite t o remove carbon dioxide, and then
admitted t o t h e t a n k t o form the desired isooctane-oxygen-nitrogen
mixture as calculated on t h e b a s i s of the i d e a l gas law.
In order t o
insure homogeneity, t h e mixture was s t i r r e d by a vane-type stkrer sealed
i n t o t h e tank. Once a coItibustible m i x t u r e had been prepared as outlined,
leaner mixtures could be
made from it by successive dilutions with the
oxygen-nitrogen mixture.
.
m
m=
i-
The method of determining pressure-flammability limits was b a s i c a l l y
t h e same 88 that reported in reference
4.
'
For a given combustfble mixture, the pressure was found a t which a
flame, propagating upward i n the ignition section,
was just extinguished
at t h e mouth of t h e narrower flame tube. In many of t h e experiments,
extinction of t h e flame w a s observed visually. However, f o r someof
the
canibustible mixtures with
02
Ugh
O2
+
Nz
ratios, the
flame moved s o
rapidly that it was impossible t o determine v i s u a l l y whether it propagated
the length of t h e flame tube or was extinguished a t . t h e mouth. I n these
of t h e flame. me
cases,a thermocouple w a s used t o detect the passage
themnocouple leads were admitted thrqu@;h t h e t o p . o f t h e flame t&e and
the hot junction WBB positioned about 1/2 inch 'above the point where t h e
NACA RM E52A08
4
flame tube widened i n t o t h e ignition section.
The thermocouple was
40-gage chrc?KL-alumel wire, connected by
36-gage ceramic-coated copper
leads t o a rapid-response recording potentiometer.
The operation of this flame detectar was checked with flames on
which visual observations could be made, and good agreement was obtained
between the two types of observation. The location chosen f o r t h e
thermocouple Junction praved t o be such that the potentiometer d i d not
r e g i s t e r a temperature increase i f the flame was extinguished a t the
mouth of t h e flame tube. Lf t h e flameprogressed farther, atemperature
increase was recorded by t h e p o t e n t i m e t e r . It was f o u n d i nt h i si n v e s t i gation, as i n t h e work reported by reference 4, t h a t t h e s e e l a r e r flames
on which visual observations could be made e i t h e r propagated the e n t i r e
length of t h e tube or were extinguished a t t h e mouth of the tube.
The
pressure difference between propagation and extinction was very small,
only 1 or 2 millimeters of mercury. E the flamepropagated, it, of
course, caused the potentiometer t o r e g i s t e r a temperature increase 88
it passed the thermocouple position. Consequently, the pressure limit
could be established in terms of potentiometer scale deflection just as
e a s i l y and precisely as by visual observation. Ln addition, it was found
t h a t the presence of the thermocouple and leads inside the flame tube
had no e f f e c t on the presaure limit.
In the case of the very rapid flames with which the thermocouple
system was designed t o be used, t h e demarcation ( i n terms of pressure)
between propagation and extinction of the flame x88 not so sharp BB it
was for slower flames. It was found t h a t , as flames were observed a t
successively lower pressures, the potentiometer
a t f i r s t experienced a
full-scale deflection with.the passage
of eachflame.
Finally, a test
pressure was reached for which a full-scale deflection was not obtained,
and subsequent tests a t lower and lower t e s t p r e s s u r e s showed smaller
and smaller potentimeter deflections.
Because of t h i s behavior,the
pressure limit for propagation of a fast flame was determined by makin@;
a plot of scale deflection against test pressure, and extrapolating the
resulting.straightlinetozeroscaledeflection.
The pressurecorresponding t o zero deflection was repmted as the pressure limit and wa13
checked by making an a d d i t i o n a l t e s t a t a pressure 1 millimeter of
mercury lower. Zero .scaledeflection was invariablyobtained.
The
precision of t h i s pressure limit was
millimeters of mercury.
*
The pressure a t which t h e f i r s t potentiometer deflection less than
full-scale occurred w a s 5 t o 10 millimeters of mercury greater than the
reported pressure limit. Thus the pressure range of uncertain flame
propagation was much greater than the I- or 2-millimeter of mercury
difference i n t h e pressures of progagation and extinction for slow flames.
However, it is believed that use of t h e procedure described herein led
t o pressure limits for the rapid flames t h a t were consistent with those
obtained visually for- slower flames.
w3I
U
*
I
N
=A
RM E52A08
I
5
A given presswe-limit cWve obtained by measuring t h e l i m i t s for a
s e r i e s of mixtures could be reprduced
on subsequent days with fresh
mixtures. Tbe results of check runs are sham as t a i l e d p o i n t s in
f i g u r e s 2 ( c) to 2(e)
.
Lu
i+
(33
w
Curves of pressure limit against pwcent stoichiometric isooctane
for mfxtures of isooctane i n anatmosphere of 15 percent oxygen and
85 percent nitrogen in tubes of 38, 28, 22, and 1 6 millimeters h i d e
diameter are presented in f i g u r e 2(a)
Figures 2(b) t o 2 ( f ) show similar
data f o r isooctane in olg.'gen-aitrogenatmospheres containing 20.9, 25,
29.4, 34.7, an& 49.6 volume percent oxygen. For a given oxygen concentration, the general effect
of decreasing tube diameter w a s t o r a i s e t h e
minimum pressure f o r flame propagation and t o narrow the concentrationrange of flammability, as has been reported greviously (references 4
and 5)
In gerieral, the c u r v e s show i r r e g u l a r lobes and cross-overs on
t h e r i c h s i d e of stoichiometric (except i n the case of t h e curves for
t h e 15 percent oxygen and -85 percent nitrogen atmosphere), while on t h e
lean s i d e of stoichiometric
they
are
regular. This behavior has been
noted in other cases (references
3 t o 6 ) . The lobes that appear on t h e
r i c h s i d e of s t o i c h i m e t r i c m a y b e i n d i c a t i v e of t h e preEence of cool
flames as described i nr e f e r e n c e 3. In the present
investigation,
however, capacitance sparks were used,xfilch according t o reference 3 a r e
incapable of igniting cool flames.
.
.
#
#
I
For 80 t o 200 p e r c e n t s t o i c h i m e t r i c i s o o c t a n e i n oxygen-nitrogen
atmospheres containing m o r e than 2 5 percent w g e n and i n t h e flame tubes
of 16 and 22 millimeters diameter, the flames propagated so r a p i d l y t h a t
it was impossible t o decide visually haw f a r they traveled.
It was
therefore necessary t o determine the pressure lfmit by t h e thermocouple
techniquedescribed previously. In several instances with the
atmosphere
containing 49.6 p e r c e n t W g e n and 50.4 percent nitrogen, shattering
detonations occurfed at pressures as low as 25 millimeters of mercury.
It i s believed that the high f h e speeds and detonations, with t h e consequent e f f e c t s upon t h e p r e s s u r e - l m t d a t a , were due i n ' p a r t t o the
nature of t h e a p p a r a t u s , p a r t i c u l a r l y t h e r e l a t i v e l y c o n s t r i c t e d
stopcock
(25-mm bore) that connected t h e test section and t h e p i e m chamber.
c
-
The e f f e c t s of v w i a t i o n ih t h e oxygen concentration of oxygennitrogen atmospheres e r e shown &egraphici n figures 3 and 4. For
a given tube diameter, decreasing the
oxygen CORCECItratiOn r a i s e d the
minimum pressure for flame,propagation and nSfrPared the concentration
range of flnmmnbility (figs. 3 and,4 )
It w i l l be noted from figure 2
that both the lean
and t h e r i c h s i d e s of t h e lhit curves become
s u b s t a n t i a l l yv e r t i c a l at a preseure of approxFmately 250 millimeters of
mercury. Figure 3 shows a p l o t of flammability rmge a t this p r e s s m e
6
NACA RM E52A08
against the volume percent of oxygen i n the oxygen-nitrogen atmosphere
for tubes of 16, 22, 28, and 38-millimeter inside diameter. The flnmmab i l i t y range i s defined as the rich l i m t b for propagation ( i n percent
stoichiometric) minus the lean limit ( i n percentstoichiometric).
For
the range of tube diameters considered, f i g u r e 3 i n d i c a t e s t h a t t h e
flammability range for isooctane becomes zero (no flame propagation
possible) i n oxygen-nitrogen atmospheres containing
l l t o 12 percent
oxygen by volume. This conclusion is supported by t h e f a c t t h a t no
propagation
could
be obtained i n 28- and 38-millimeter diameter tubes
i n amixture of 9.4 percent oxygen and 90.6 percent nitrogen.
It should
be emphasized that t h i s limiting oxygen concentration applies only t o
the conditions of this experiment. I n . p w t i c u l c r , t
i markedchange h
the temperature of the experiment would be expected t o change this result.
It is of i n t e r e s t t o n o t e that zero flame speed hrts been p r e d i c t e d ' f o r
isooctane i n an oxygen-nitrogen atmosphere containing less than 1 2 percent oxygen (mpublished NACA data).
DJ
k P
0,
clc
. .
-
-_
.
"
The e f f e c t ofoxygen concentration i n t h e o w e n - n i t r o g e n atmosphere
on t h e minimum pressure for propagation of flame in isooctane-oxygennitrogen mixtures is shown i n f i g u r e 4 for tubes of 16, 22, 28, and
38-millimeter
diameter.
Previous work a t t h i s laboratory on the pressure-flammability limits
of propane-air
mixtures
(reference
4) showed that data such a6 those of
figure 2 y i e l d a c r i t i c a l diameter f o r .flamepropagation.This
critical
diameter w a 8 shown t o be a quenching distance, j u s t a s t h e minimum slit
width for flashback of a Wlnsen flame was shown t o be a quenching
distance by Friedman and Johnston (reference 7 ) . Figure 5 compares t h e
pressure dependencies of c r i t i c a l diameter, obtained from the preeent
work, and of minimum quenching distance of isooctane-airmixtures.
The
minimum quenching distances were obtained i n connection with ignitionenergy measurements made by Experbent, Inc., commercial laboratory, on
NACA contract. The c r i t i c a l diameters a r e seen t o depend upon pressure
r a i s e d t o t h e -0.91 pbwef'determined by calculating the slope of the
l i n e ; t h e quenching distances a l s o depend upon pressure raised t o t h e
-0.91 power. The r a t i o of c r i t i c a l diameter.. .t- o.- quenching
distance
i s 1.25.
This value may be compared with previously reported ratios
of1.35 (reference 7) and 1.43 (reference 4) far'prqeane-air mixtures.
Figure 5 includes s-Ome O f the data of references 1 and 7 on propane-air
mixtures, f o r comparativepurposes.
AB a r e s u l t of previous work, a simple inverse relation has been
found between flame speed and c r i t i c a l diameter o r quenching distance
f o r propane-air mixtures (reference
4).
me r e w t i o n h e l d f o r varying
propane concentration (canstant pressure and. mixture temperature) and
f o r varying mixture temgerature (constant
pressi& and propane concentration). It was found p o s s i b l e t o j u s t i f y t h e inverse r e l a t i o n on a
t h e o r e t i c a l basis (reference 8 ) . The present work provides an opportun i t y t o t e s t t h e r e l a t i o n between flame speed and c r i t i c a l diameter a t
various concentrations ofoxygen i n t h e oxygen-nitrogenmixture.
Figure 6 shows the logarithm of the maximum flame speed for isooctane in
a given oxygen-nitrogen atmosphere p l o t t e d a g a i n s t t h e c r i t i c a l diameter
..
I
"
NACA RM E52A08
7
under the same conditions. The oxygen concentration in the oxygennitrogen atmosphere of t h e mixture is noted beside each point. Pressure
i n all cases.wa8 I atmosphere, mixture temperature w a s 5 8 O C, and
isooctane concentration was 105 percent stoichiometric.
The flame speeds
a r e from unpublished data; the c r i t i c a l diameters are fram the present
work, extrapolated t o 1 atmosphere pressure. The good degree of correl a t i o n shown by f i g u r e 6 indicates that, for the conditions
under which
t h e data a r e p l o t t e d , flame speed. is related t o c r i t i c a l diameter i n the
manner shown by t h e f o l l o w i n g expression:
pf m e-%
where
I L ~ flame
speed
constant
c
dl
0
i
c r i t i c a l diameter
reciprocal of t h e c r i t i c a l
instead of being related t o t h e s-le
diameter. The reasons for t h e changed r e l a t i o n between flamespeed and
c r i t i c a l diameter may l i e i n t h e v a r i a t i o n w i t h oxygen-nitrogen r a t i o of'
sameof t h e f a c t o r s involved. The theory .of reference 8 may prove
capable of p r e d i c t i n g r e l a t i o n (1)as it predicted the reciprocal relat i o n between flame speed and c r i t i c a l diameter i n previous cases.
A
t e s t cannot be made u n t i l s u i t a b l e c a l c u l a t i o n s of adiabatic flame
temperatures and equilibrium concentrations of €kee rawcals, for
isooctane i n various oxggen-nitrogen atmospheres, a r e u
s
& t o evaluate
the theoretical expressions.
From the investigation of t h e v a r i a t i o n of the pressure limits of
flame propagation with tube diameter f o r various isooctane-oxygennitrogen mixtures, the following - r e s u l t s w e r e obtained:
1. For a given oxygen-nitrogen atmosphere, decreashg tube diameter
raiseci the minimum pressure for flame propagation and narrowed t h e concentration-range of f b m m b i l i t y . Fora giventube diameter, decreasing
oxygen concentration i n the oxygen-nitrogen atmosphere produced t h e same
effects
.
2. For the range of tube diameters studied, the flanrmability range
for isooctane became zero (no flame propagation possible) i n oxygennitrogen atmospheres containing ll t o 12 percent oxygen by volume.
NACA RM E52A08
0
3. The data obtained could be interpreted
i n terw of c r i t i c a l
diameter for flame propagation. . Theainimum c r i t i c a l diameter was found
t o depend upon t h e p r e s s u r e r a i s e d t o the -0.91 power. I h e r a t i o of
c r i t i c a l diameter t o quenching distance obtained i n connection with
ignition energy experiments was found t o be 1.25.
4. Flame speed of isooctane in various oxygen-nitrogen atmospheres,
for 105 percent staichimetric isoactane, 1 atmosphere pressure, and
580 C mixture temperature, was found t o b e r e l a t e d t o t h e n e g a t i v e
exponential critical diameter.
1. Blanc, M. V., Guest, P. G., von Elbe,Guenther,
and Levis, Bernard:
Ignition of Explosive Gas Mixtures by E l e c t r i c Sparks. P t 111.
Minimum Ignition Energies apd Quenching Distances of Mixtures of
Hydrocarbons and Ether with Oxygen and I n e r t Gases. Third Symposium
on Combustion and Flame and Ekplosfan Phenmeria, The Williams &
W i u r l n s Co. (Baltimclre), 1949, pp. 363-367.
.
2 . Badin, Elmer J., Stuart, Joseph G., and Pease,Robert
N.: Burning
Velocities of Butadiene-1,3 with Nitrogen-Oxygenand Helium-Oxygen
Mixtures.Jour.
Chem. Phys., vol. 17, no. 3, March 1949, pp. 314316.
.. ..
7
"I
i 3
3. DiPiazza, James T. : L i m i t s of Flammbility of Pure FIydrocarb&-Air
"tures a t Reduced Pressures and Room Temperature. NACA RM E51C28,
1951.
mar& E., and Simon, M o t h y M. : Variation of the Pressure
Limits of Flame Propagation with Tube Diameter for Propane-Air
Mixtures. NACA RM E51303 , 1951.
4 . Belles,
!
I ' 7
)
'
5. Belles, Frank E. : A Preliminary Investigation of Wall Wfects on
'
Pressure-rzlf3.Flmmnbility Limits
of Fropane-Mixtures. - NACA
.
.
RM E 5 0 J l 0 a , 2350.
''
6.Elston, Jean:Influence
des Parois et des Gaa Diluante sur l e s
Domaines d ' Inflammabilitd de 1'FIydrogkne e t duMdthane.Memorial
desServices Chiraiques de l'Etat, vol, 35, 1950, Sec. one, pp. 87132, Sec. two, pp. 87-144.
W A RM E52A08
9
7. Friedman, Raymond, and Johnston, W. C. : The Wall-Quenching of
Flames as a Function of Pressure, Temperature, apd Air-fie1 Ratio.
Jou~.
&pl. Phy~.,V O ~ .21, no. 8, A u ~ . 1950, pp. 791-795.
8. Slmon, Dorothy M., and B e l l e s , Frank E.:
of Flame Quenching for Laminar F l a I I E B .
An Active P a r t i c l e Theory
mAcA RM E5XU.8
NACA RM E52A08
10
Storage tank
Fuel capsule
Precision manometer
D 'Flame tube
E
Plenum
chamber
F
Spark e l e c t r o d e s
(f
D i f f e r e n t i a l manometer
€I Capacitance apark supply
I
Dried 02-N2 mixture i n l e t
A
B
C
va
Figure 1.
-
Apparatus fordetermination
of flammability limit.
11
HACA RM E52A08
n
.
Isooctane, percent stoichicuuetric
(a) Chygen fractton
2,
0.15.
0,
Figure 2.
-
-k
N2
EPfect of tube diameter on preasure Ymit.
NACA €34 E52AO8
12
I
I
I
I
1
0
I s o o c t a n e ,p e r c e n ts t o i c h i o m e t r i c
(b) Oxygen f r a c t i o n
Figure 2.
-
Continued.Effect
,
O?
02
.
+
0.21.
N2
of t u b ed i a m e t e r
limit
on p r e s s u r e
NACA RM E52AO8
Isooctane, percent stoichiometric
(c) Oxygen fraction
Figure 2.
..
-
O2
, 0.25.
0 2 + N2
Continued. Effect of tube diameter on pressure limit.
NACA RM E52A08
14
0
50
100
150
200
250
300
I s o o c t a n e , percent s t o i c h i o m e t r i c
(d) Oxygenfraction
F i g u r e 2.
f
400
, 0.294.
OP
02
350
N2
- Continued. Effect o f tube diameter on pressure limit.
15
NACA RM E52A08
440-
400-
360-
320-
280-
-
. 240-
01
PI
2
E
a
-
m
1
t
200-
s
-
c1
x
4
E
160-
120-
80 -
40-
-
0
100
50
150
200
250
300
350
Isooctane, percent stoichiometric
(e) Oxygen f r a c t i o n
Flgure 2.
-
Continued.
Op
02 i N2
400
, 0.347.
Effect o r tube diameter on pressure limit.
NACA RM E52AO8
16
Isooctane, percent stoichiometric
( f) Oxygen
fraction
O2
02
Figure 2.
-
Concluded.
+
, 0.496.
N2
Effect of tube diameter on pressure Ilmit.
S o l i d symbols
denote nonprop-
0
.10
Oxygen fraction,
Figure 3.
-
.40
.30
.50
.60
02
02 + N2
Effect of oxygen on flammablllty range.
250 millimeters of mercury.
Pressure,
18
c
-
.2
.10
.3
.4
Oxygen f r a c t i o n ,
Figure 4 .
-
.6
.8
1.0
oz
%J+%
Effect of oxygen on minimum pressure
1imi-t.
4v
NACA
R M .
19
E52A08
.
I
Pressure, atm
Figure 5.
- Effect of pressure on quenching distance.
NACA RM E52AO8
20
.
\
5.0
Critical diameter,
-
6.0
mm
F i g u r e 6.
Correlation of critical diameter with flame speed. Fuel, isooctane;pressure
1 atmosphere; f u e l - a i r ratio, 105 percentstolchiometric;
temperature, 58O'C.