February, 1970.
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2
A PRELIMINARY STUDY OF SPHERICAL DETONATION-WAVE SYMMETRY IN STOICHIOMETRIC
HYDROGEN-OXYGEN MIXTURES
by
A. K. Macphers on
.t
•
A PRELIMINARY STUDY OF SPHERICAL
DETONATION-WAVE SYMME.TRY IN STOICIOMETRIC
HYDROGEN-OXYGEN MIXTURES
by
A. K. MacphersEm
Manuscript received January, 1970 •
•
ACKNOWLEDGEMENT
I wou1d 1ike te thank Dr. G. N. Patterson for providing the opportunity to work at the Institute for Aerospace Studies and Dr. I. I. G1ass for his advice and encouragement throughout this study.
This research was funded by the Aerospace Research Laboratory of the U.S.A.F.under contract No. AF 33 (615)-5313 and the National Research Counci1 of Canada.
SUMMARY
A photographic study was undertaken of the detonation wave produced
in a hemispherical chamber filled with a H2-0 2 mixture at high 'initial
pressures (600 psi). The study was ,directed.at the driving processes in
the driver of the UTIAS Implosion-Driven Hypervelocity Launcher.
The shape of the luminous front of hemispherical detonation waves
were photographed,for waves produced in stoichiometrie hydrogen-oxygen
mixtures at initial pressure of between 7 and 27 atmospheres. It was found
that the wave pictures were not reproducible when tests were performedunder apparently identical conditions. Further, the wave front was not always smooth and of ten asymmetrieal.
TABLE OF CONTENTS
"
Page 1.INTRODUCTION
1 2.EXPERIMENTAL INVESTIGATION
.
13.
EXPERIMENTAL RESULTS
14.
CONCLUSIONS
4
REFERENCES
4
FIGURES
1. INTRODUCTION
Examinations of soot patterns have shown (Ref.l) that as the initial pressure of a gas mixture is raised the size of the disturbances formed
de-crease. Thus it is considered that the detonation front becomes smoother
as the initial pressure increases. If this was so, it may be reasonably
thought that the stability and sphericity of point-generated, detonation waves would improve wi th ihcreased ini tial pressure • As most previous work
has been performed at low pressure it was thought that by ~ initial pressure
of 12 atmospheres, stability and sphericity would be ensured. The present
series of results were obtained· as support for the UTIAS Impl,.qsion Dri ven
Hypervelocity Launcher. The techniques used were relatively simple.and as
the work was notdesigned to provide scientific data on detonation waves the
tests were notarranged to produce quantitative data. However, the results
are unique in that there does not appear to be any available data on spherical detonation at such high initial pressures. Also the destructive force pro-duced by the explosion is such that more accurate tests are very expensi ve. 2. EXPERIMENTAL INVESTIGATION
The driving chamber of the UTIAS Hypervelocity Launcher2 was used to
contain the detonation waves generated in stoichiometric hydrogen-oxygen
mixtures. Figure 1 shows the schematic arrangement. Chamber
"c"
is asolidsteel block in which an
8
inch diameter hemispherical cavity is cut. Forthe present experiments a sheet of plexiglass "B" approximately 3-1/2 inches
thick replaced the normal steel plate. A large nut "D" locks "B" and
"c"
together. In the normal firing sequence hydrogen and oxygen we.re admi tted
separately fairly slowly through. the gas inlet to produce a stoichiometric
mixture. The mixture was allowed to settie for about
5
minutes and thenwas igni ted by exploding a short, fine copper wire "A" wi th a potentialof
6
KV.A typical plexiglass plate with wire attached before firing is shown in Figure 2a. A high-speed framing camera was arranged to photograph the
sequence of events. A reference scale was provided by two steel bars 1/2
inch square and 2-1/2 inches apart on the outside of the plexiglass. These
bars also restrained the plexiglass from moving and would show·by permanent
set if substantial distortion of the plexiglass occurred. Af ter about ten
experimental runs there waS no measurable alteration in the posi tion of these
bars. Early experiments, which were perf~rmed without the scale bars are
also included in-- the results.
3. EXPERIMENTAL RESULTS
Figure 3 shows the framing camera pictures obtained when the bars
were used to provide a scale. There are normally
5
fr~es the first in timebeing at the bottom. It can be seen that the bars appear cu~ved, although
as noted above, no change in the dimensions were found af ter 10 runs. The optical effect is due to the light source being cqncentrated at the centre thus the rays going to the outer regions are at a more acute angle to the
glass and are refracted more than those _ near the centre. Hence, even thougtt
the camera was set up initially so that with normal incident light there would be no overlap between frames, this was not achieved due to refraction.
edges. Figure 3a shows that at a time 0.1 ~sec af ter the firing button was depressed (frame 1) the wire has exploded and considerable light output was obtained from the gas. This contention is supported by Figure 3b described
below. Th~exposure time for the first two frames was 200 nanosec, and the
film, as in all the results, 300.0 AEA polaroid. Using the scale prorided by
the distance between the bars at the corresponding radius and assuming no ignition delay, the average velocity of the detonation front is 10,000 ft/sec which is the Chapman-Jouguet value. The wave shape is very asymmetrical, although this could be exaggerated by the refraction effects. The remaining
three frames ,cannot be considered very reliable as the plexiglass may.be
distorting under heat and pressure. It should be mentioned however, that when total failure of the plexiglass did not occur, usually for tests with initial pressure of 200 psia, the inside surface of the plexiglass was
un-marked af ter the experiments. The outside was as shown in Figure 2b but the
cracks stopped short of going right through. Thus i t is possible that the
pictures in frames 3 to 5 may be correct and it requires further
investi-gation to examine this. If so, it appears that ,the gas is hot near the
top and bottom in frames 4 and 5, but cold at the sides, A vertical
elon-gation of the front occurs in frame 2, which ,is apparentlymaintained. Also
horizontal dark lines occur in frame 5, which could be attributed to cold
bands. These are not due to cracks forming in the plexiglass as failure
always occurred along radial lines as in Figure 2b.
To Îlncrease,the turbulence within the chamber and hence improve
mixing, the gases were loaded quickly and fired with a minimum,time delay.
The results are shown in Figure 3b. There was apparently an ignition delay
of about 10 ~sec and between frames 3 and 4 and the wave velocity was
approxi-mately 4,000 ft/sec. A comparison between frames 1 in Figures 380 and 3b,
both taken 0.1 ~sec af ter ignition, shows that the bright gas glow was
not produced in Figure 3b. The exposure time was the same in both cases.
An
interesting feature is the fbrmation of a sharp wedge of light on theright hand side in frames 2 and 3. It does not appear that this is an optical effect as other pictures do not show it. This long ignition is not necessarily related to or typical of the rapid loading and firing
technique. It does show however, that at this initial pressure of 200 psia,
such ',a technique did not assure rapid igni tion and detonation wave production .
The rapid loading and firing technique was used again at an initial pressure of 400 psia and the resultant pictures are shown in Figure 3c.
A great light output was again obtained af ter 0.1 ~sec and even af ter 5.1
~sec the light was being produced over a sufficiently large area such that
the optical distortion of the bars was not excessive. By 10.1 ~sec however,
the light source had decreased in size to a round circle. However, the
exposure in frames 1 and 3 was 200 nanosec and in frame 2, 500 nanosec.
If ,frame 2 had the same exposure as 3 possibly the excessive light output
would not be observed. The problem of setting exposure times is produced by the non-repeatability of results. For example, a setting with the
5 ~sec frame at 500 nanosec worked very weIl on an early test. The average velocity from the origin to frame 3 was 10,000 ft/sec and between frame 3 and 4,7,500 ft/sec. Thus the speed was initially Chapman-Jouguet,
(9,600 ft/sec), but dropped.below later. A significant feature of the
results is the optical distortion in the shape of the hemisphere in frame
5. A flat base has been produced on the picture and this could be explained
..
case the ,edge would be illuminated by light almost normal to the plexiglass, close to the hot spot. Further around,the circumference aw~ frem the spet the illumination would be at amore acute angleand hence refraction woul~ be more important. I t i s alse apparent that a dark line has separated a region frem.the main body of the flame. This could support the view of a local hot spot. Another phenemenon .is that th~ top of, the sphere is not: shown in frames 4 and 5. This could be interpreted as indicating the top is colder than the bottom. Fin~lly thè velocity of the front between frames 4 and 5 was 9,500
ft/sec, i.e.; Chapman~Jouguet. .
A 3/8 inch diameter hemispherical,PETN explqsive pellet in whiçh was embedded an exploding 'wire was used to initiate a mixture at initial pressure 200 psia ~d.the· result is shown in Figure 3d. The aVerage velocity between frames "2 and 3 was ' 7,000 ft/sec and between frames 3 and 4; 3,500 ft/s~c. The second value may ·,not 'be reliable as the shock may have reflected and the.
implosion could alter the result. The first frame at 5 ~sec af ter initiation shows an irregula:r front, but by the second and third frames the wave is more symmetriqal and smoeth. The €lark spot at the centre is due to a plate used to support the detonator. Th~ most significant feature, which applied to all tests with explosive initiators, is the failure to reach Chapman-Jouguet velocities.
The remaining results were obtained during the early stages of testing be fore the external. s caling had been instalied . Al though the wave veloci ties
could not be calcülated accurately certain qualitatively results can be deduced.. Where the wave front is fairly large the fact that (the hemisphere is 8 in. diameter can be used to providean approximate scale. Thus when the guar€led statement is made belaw that "Chapman-Jouguet velocity appeared to b~ obtained" i t isto be remembered that the chamber diameter has been used te provide the scale. At a pressure ef 100 psia it does net appear that detonationoften occurs end a typical result is shown in Figure 4a. Th~ first frame was set at 0 ~sec to coincide with firingand no result was obtained. Even af ter 30 ~sec there was na sign of detonation or eve~ extensive deflag-ration developing. The bright spot . is many times larger than. the wire diameter and is probably.locally excited gas. Nevertheless the plexiglass was shat-tered to at least ·the extent shown in Figure,2b and apparently either a deflagratien or detonati0n wave did occur. It· probably was deflagration as'
detonation veleci ties were only obtained . wh en a rapid. igni tion occurred. Figure 4b shows ' the results at
lBo
psia and i t can be seen 'that a 25 ~s'ec ignitiondelay occurred. Again de fl agrat i on would be postulated and the start of this process is seen in 'frame 5. This result is not typical of this pressure as the resu:lts in Figure 4c, whi,ch were again performed at 180 psia indicate. In both these' cases, 4b and 4c" a ragged flame front was fermed. In 'ad<ai tien, in frames 4 alld 5 of 4c, dark lines ' as in 3a were formed~, It appeared. that a Chapman-Jouguet detonation occurred in 4c. In 'anothe:!;' set .of results ' obtained under apparently identicaJ, con€lit;LlÎma~ 'it ,was found that results similar to4a, were achi~ved. Thus at 180 psia practicaily the,whole range of possible:results were ebtainecl, At ,200 psia initial pressure ,
a ChapP1an..,.J(~)Uguet · det onat i on, apparently.was obtaiined which ·was off-centre,
Fig;ure 4a. It appe,ars to have contac1;;ed the ri~ht hand side first, frame 3 and"a rather unusual bulge was formed . af ter 50 ~~ec near the bettom right hand side. As ,mentioneq, before i t may, be ,unwiseto attempt to interpret the
pic~ures when· théplexiglass could be distorting the rest+lts.
produced some symmetrical waves (Figure 5a). The centre is again obscured due to a circular support for the detonator. Chapman-Jouguet conditions were not achieved. However, a cold region at the bottom appears to be forming in frame 3. This was very pronounced in frame 5. The mark on the left hand side is due to the gas inlet pipe. Using a looped exploding wire inside a PEI'N hemisphere the results in Figure 5b were obtained. Again only deflagration velocities were achieved aud a fairly smooth wave produced. A cold lower part is found in frame 4 although it has disappeared in frame 5. The dark patch on the left
is the inlet pipe. The 5 ~sec picture, frame 1, shows the sideways streaks
detected in Figure 3b frames 2 and 3. Four looped exploding wires were used as au initiator in Figure 3c. From the first frame it can be seen initiation
occurred on the right side. The centre is obscured by the wire holder. By the second frame the wave is fairly symmetrical but moves to the right in the third.
Dark\lines and a cold lower region are again formed. Chapman-Jouguet conditions
were!not apparently obtained.
The final evidence of possibly irregular detonation fronts being ob-tainèd at high pressure is shown in Figure 6. These are pictures of hemispherical
lead liners, 1/8 inch thick and 8 inches external diameter which were placed in
the cavity "c", Figure 1. Holes were formed around the sides at azimuthal angles
between 300 and 60°. These could be interpreted as due to hot spots on the
detonation front. In themselves the results would not be very meaningul but
when viewed with the other data it could be significant. 4. CONCLUSIONS
Although the experirnental conditions were ~ot such that detailed waves
structure could be obtained some conclusions can be drawn with confidence. Under
apparently identical conditions the shape of the luminous region is not repeat-able. At initial pressures of up to 180 ps ia the formation of detonation by au
exploding copper wire cannot be assured however, the higher the initial pressure
the greater the probability.
If detonation does occur intense radiation of applying the potential across the exploding wire. produced the wave can be unsymmetrical and irregular travel with Chapman-Jouguet velocity.
is produced within 1/10 ~sec
Even when detonation is in shape, although it does
There is some evidence th at hot and cold regions may be formed around the circumference although there is a greater tendency to form these at the bottom. The use of explosive charges using PEI'N explosive do not generate a detonation wave, but the deflagration is usually well shaped and symmetrical.
The appearance of dark lines and unusual shapes of hot gases af ter 50 ~sec
require further studies before firm conclusions can be drawn. Furthermore, the exact conditions existing in the driver were not reproduced and conditions under those circumstances may be different.
1. Shchelkin, K. I. Troshin, Ya, K.
2. Glass, 1. 1.
REFER ENC ES
Gazodinamika Goreniya Izdatel'stvo Akademii Nauk, SSR, Moscow, 1963. English translation NASA TT F-231, 1964. Research Frontiers at Hypervelocities, CASI Journ. 13, 9, pp.401-426, 1967.
GAS INLET
---...~~~~
A
o
-~Jt..a
Figure 3. DETONATION WAVES IN STOCHIOMETRIC H2-02 AS SEEN THROUGH PLEXIGLASS WINDOW WITH SCALE BARS 2 1/2 INCHES APART IN FRONT (a) Exploding wire initiator, initial pressure 200 psia, times of frames af ter
ignition ~sec, 0.1, 20.1, 40. 1, 60. 1 and 80. 1.
(b) Exploding wire initiator, initial pressure 200 psia, times of frames af ter ignition ~sec, 0.1, 5.1, 10.1, 20.1.
(c) Exploding wire initiator, initial pressure 400 psia, times of frame af ter ignition ~sec, 0.1, 5.1, 10.1, 15.1, 25.1
(d) 3/8" diam. Explosive initiator, initial pressure 200 psia, times of frames
5
4
3
2
o
b
c
d
Figure 4. DETONATION WAVES IN STOCHIOMETRIC H2-02• EXPLODING WIRE INITIATORS
(a) Initial pressure 100 psia, times of frames af ter ignition Il sec, 0, 5, 15, 25, 30.
(b) Initial pressure 150 psia, times of frames af ter ignition J..lsec, 0.05, 5.05, 15.05, 25.05, 30.05.
(c) Initial pressure 180 psia times of frames after ignition Ilsec, 10, 20, 40, 60, 70.
a
b
c
Figure 5. DETONATION WAVES IN STOCHIOMETRIC H2-02, INITIAL PRESSURE 200 PSIA.
(a) O. 53 in. diam. hemispherical P ETN detonator on exploding wire as in Figure 2. Times of frames af ter ignition ~ sec, 6, 16, 36, 56, 76.
(b) 0.56 diam. hemispherical PETN detonator on semi-circular explosing wire in spark plug. Times of frames after ignition
Figure 6. HOLES IN HEMISPHERICAL LEAD LINER IN CAVITY
"c"
OF FIGURE 1.UtIAS TECHNICA!. NarE NO. 154
Institute for Aerospace Studies, University of T O1'onto
A Preliminary Study or Spherical Detonation - Wave Symmetry in Stoichiometrie
Hydrogen-Oxygen Mixtures
Macpherson, A. K. 4 pages 6 figures
1. Spheriea1 Detonation Waves 2. lIydrogen-Oxygen Detonations 3. Implosions
4. Hyperve10eity Launehers
A photographic study was undertaken of the detonation wave produced in a hemispherical
chamber filled with a li:1-02 mixture at high initial pressures (600 psi). The study was
directed at the driving processes in the driver of the I.I'.crAS Implasion-Driven
Hyper-velocity Launcher. The shape of the luminous front of hemispherical detooation waves
were photographed for waves produced in stoichiometric hydrogen-oxygen mixtures at
ini tial pres sure of between 7 and Z7 atn:cspberes. It was found. that the wave pictures
were not reprc..liucible when tests were performed under apparently id.entical conditions. l'urther, the wave front was not always smooth and orten asymmetrieal.
~
\1rIAS TECHNICA!. NarE NO. 154
Instif:utè for Aerospace Studies, University of T oronto
A Preliminary Study or Spherical Detonation - Wave Symmetry in stoichiometrie
Hydrogen-Oxygen Mixtures
Macpherson, A. K. 4 pages 6 figures
1. Spherica1 Detonation Waves 2. Hydrogen-Oxygen Detonations 3. Implosions
4. Hypervelocity Launchers
A photographic study was undertaken of the detonation wave produced in a hemispherical
chamber filled with a li:1-02 mixture at high initial pressure. (600 psi). The study was
directed at the drlving processes in tbe driver of the UTIAS Imploslon-Drlven
Hyper-velocity Launcher. The shape of the luminous front of hemispherical detOlation waves
were photographed for waves produced in stoichiometrie hydrogen-oxygen mixtures at
initia1 pressure of between 7 and zr atmspheres. It was fown that the wave picture. ""ere not reproducible when tests were performed under apparently identlcal conditions. F'urther, the wave front was nat always smooth and of ten asymmetrieal.
~
Ava'lable copies of this report: are limit:ed. Return t:hil> card to UTIAS, if you require a copy. Available copies of this report: are limited. Return this card to UTIAS, if you require a copy.
\1rIAS TECHNICA!. N\1rE NO. 154
Instif:ute for Aerospacé St:udies, Universit:y of T oronf:o
A Preliminary Study or Spherieal Detonation - Wave Symmetry in Stoichiometrie
Hydrogen-Oxygen Mixtures
.Ma.cpherson, A. K. 4 pages 6 figures
1. Spherical Detonation Waves 2. Hydrogen-Oxygen Detonations 3. Implosions
4. Hypervelocity Launchers
A photographic study was undertaken of the detonation wave produced in a bemispberical
ehamber filled with a li:1-02 mixture at high initial pressures (600 pSi). The study was
directed at the driving processes in the driver of the tJrIAS Implosion-Driven Hyper
-velocity Launcher. The shape of the luminous front of hemispherical detooation waves
were photographed for waves produced in stoichiometrie hydrogen-oxygen mixtures at initial pressure of between 7 and Z7 atn:cspheres. It was found. that the wave pictures were not reproducible when tests were performed under apparent1y identical conditions
Further, the wave front was not always smooth and. aften asymnetrical.
~
\1rIAS TECHNICA!. NarE NO. 154
Insf:ituf:e for Aerospace Studies, Universif:y of T oronto
A Preliminary Study or Spherical Detonation - Wave Symnetry in Stoichiometrie
Hydrogen-Oxygen Mixtures
Macpherson, A. K. 4 pages 6 figures
1. Spherica1 Detonation Waves 2. Hydrogen-Oxygen Detonations 3. Implosions
4 • Hypervelocity Launchers
A photographic study was undertaken of the detonation wave produced in a hemispherical
ehamber filled with a li:1-02 mixture at high initial pressures (600 psi). The study "as
direeted at the driv1ng processes in tbe driver of tbe \1rIAS Imp1osion-Driven
lIyper-ve10city Launcher. The shape of the luminous front of hemispherical detooation waves
were photographed for waves produced in stoichiometrie hydrogen-o:x;ygen mixtures at initial pressure of between 7 Md 27 a.tJIDspheres. It wa.s found. that the wave pictures were not reproducible when tests were performed under apparently id.enticaJ. conditions.
Further, the wave !'ront was DOt always smooth and. aften asymnetrical.
