OLEVEL?!AD

MEMORANDUM REPORT ARBRL-MR-030180O

WINDOWED CHAMBER INVESTIGATION OF

THE BURNING RATE OF LIQUID

MONOPROPELLANTS FOR GUNS

William F. McBratney

DTICELECTE

April 1980 S JUL2 1980 DB

US ARMY ARMAMENT RESEARCH AND DEVELOPMENT COMMANDBALLISTIC RESEARCH LABORATORY

ABERDEEN PROVING GROUND, MARYLAND

C Approved for public release; distribution unlimited.

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The fi..dings in this report are not to be m~ns~rued asan1 official D3-partment'of the Army position, unlessso dUsignatt~d by other cuthoriZed documents.

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Windowed Chazber Invaý..igation of the Burring FinalRate of Liquid Monopropellants for Guns " 6IR. ORO.E PORT IJUUUER

T. AUYTnfl(a) A. -OWTr4AruhR RANi IOUhSEt(O)-

William F. McBratney

S. PERFORMING ORGANIZATION HAit AND AAROA A o VNT. Nq TTSK

US Army Ballistic Research Laboratory a

ATTN: DRDAR-BLP IL161102AH43Aberdeen Proving Cround, MD 21005

11. CQNTAOLL, OFIPIZCNAME AN JADOR KSm it. REPORT DATEUS Army kniament R.esearch andr Development Command A I 1980US Army Callistic Research Laboratory . Er" PGS

ATI': DRDAR-BL • . MUN EU----Aberdeen Proving Ground_. MD 21005"7, M&NITOR1 TM AECY" N•E AMR ADORES•i.f f2Ii•ml t CmoUa hd Off.ce) IS. SECURITY CLASS. (of tA1' mpWet)

UnclassIfied

S.27511 -AwlMEN IE k PI CATION/ o.N-GRA011NGIS. DISTNMMUTIEN STATdkTNT (at this XqmtI

Approved for public release; distribution unlimited.

17. DISTR|UUTION STATEMENT (of eIAho .. alt mited In Blo•ak, If dfffut *m Repst)

1S. SUPPLIEMIENTARY NOTlE3

IS. KEY WORDS (onhme an reversve .eW if necossy amnd Identify by boek ameber)

Liquid Propellant, Burning Rate, surface stability, photographic, NOS-365,OTTO II, NOSET "A"

25• mAMTUAC (•.•h.....ice.im . ...... --. Mm.by by blak , ) ~fdlEquipment and techniques have been developed for the photographic

observation of burning liquid monopropellants at pressures up to 200 MPA. Manydetails of the liquid surface and the reaction zone above it mny be observed.Preliminary photographic runs have been made on OTTO Fuel II, NOS-7b5, andNOSET "A".

OP I W3 EOn I NlET is( oLASI• : " i• • M m • . o v t . o r • i s o m . • zU N Q L A S S I F I E V D

r i Iii TABLE OF CONTENTS

Page

LIST OF ILLUSTRATIONS .. .. .... ...................... ..... 5

I.INTR¶,ULTION .. .. ................ ........................7

II, BACKGROUJND .. .. ................ ........................7

~11. APPARATUS AND EQUIPMENT .. .. .... ..........................8

IV. E~XPERIMENTAL. .. ...... ...................... ............. 8

A. -NOS-.365 -- Polypropylene Straws, Gelled .. .. .... ....... 8B. Hot WalliEffects .. .. .................. ..............12C. NOS-365, H37, 2% Kelzan .. .. .... ......................12D. NOS-3b5, H37, Not Celled. .. .... ......................19E. (M.TO Fuel,1 I.. .. .................. ..................19F. NOSET "A"l..........................................................39

V. CONCLUSIONS. .. .. ................ ........................39

DISTRIBUTION LIST. .. .. ................ ..................45

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LIST OF ILLUSTRATIONS

Figure Page

1. NOS-365, H37, 2% Kelzan, 3 im Polypropylene Straw,20 MPa . .. . . .......... . . . . . . . ... . 9

2. NOS-365, H37, 2% Kelzan, 3 mm Polypropylene Straw,42 MPa . . . . . . . . . . . . . . . . . . . . . . . . . 10

S. NOS-365, H37, 2% Kelzan, 3 mm Polypropylene Straw,62 MPa ........... .. . . . . . ......... 11

4. NOS-365, H37, 2% Kelzan, 6.1 x 1.5 mm Acrylic Cell,

28.6 MPa . . . . . . . . . . . . . . . . . . . . . . . . 14

S. NOS-365, H37, 2% Kelzan, 6.1 x 1.5 mm Acrylic Cell,55 MPa . . . . . . . *...... . . . . . *.. . . is

6. NOS-365, H37, 2% Kelzan, 6.1 x 1.5 m Acrylic Cell,S124 NPa . . . . . . . . . . . . . . . . . . . . . . . . 1

7. NOS-365, H37, 2% Kelzan, 6.1 x 1.5 m• Acrylic Cell,124 ?4Pa . . . . . . . . . .. .. .. .. .. . .. . . 16169 MPa................. . ........... 17

8. NOS-365, H37, 2% Kelzan, 6.1 x 1.5 mm Acrylic Cell,195 MPa . . . . . . . . . . . . . . . . . . . . . . . 18

9. NOS-365, H37 Data Plot, 2% Kelzan ... ........... . . . 20I j10. NOS-365, H37, Not Gelled, 6.1 x .95 mm Glass Cell,

29 MPa........... ... . . . . . .......... . 22

11. OTTO Fuel II, 3.2 x .95 mm Glass Cell, 8.4 MPa,(Meniscus) . ........... ... ..... 23

12. OTTO Fuel II, 6.1 x 1.5 mm Acrylic Cell, 10.3 MPa(Fuse Wire) . . . . . . . ............... 2

13. OTTO Fuel II, 3.2 x .95 imuGlass Cell, 41.4 MPa ... ..... 26

14. OTTO Fuel II, 6.1 x .95 mm Glass Cell, 47 MPa2S(Sloshing) . . . . . . . . . . . . . . . . . . . . . . . 2

15. OTTO Fuel II, 6.0 x 1.5 mm Acrylic Cell, 62 MPa ..... 29

16. OTTO Fuel II, 6.0 x 1.5 mm Acrylic Cell, 82.7 MPa . . . . 32

17. OTTO Fuel II, 6.1 x 1.S mm Acrylic Cell, 129 MPa . . . . . 34

L . ....

j.. . .. . . .. . . .... . , • , . . .,N

LIST OF ILLUSTRATIONS (Cont'd)

Figure Page

18. OTTO Fuel II, 6.1 x 1.5 -m Acrylic Call, 156 MPa . . . . . . 36

19. Burn Rates for OTTO Fuel II ......... ................ 383

20. NOSET "A", 6.0 x .95 mmGlass Cell, 20 MPa . ........ 40

21. NOSET "A", 6.0 x 1.5 mm AcrylVc Cell, 69.6 MPa ........ 42 1

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I. TNTRODUCTION

In conjunction with a program to control and model the combustion

of liquid monopropellants in guns, an effort has been .nade to determine

the pressure dependent burning rate of several liquid monopropellants.Previous work was directed at utilizLng more or less standard strandburner type techniques -- straws, gellation, ignition techniques. 1

'The present report covers some work performed in a windowed chamberto confirm prevAous results and to identify causes of erratic results andnon-planar combustion.

II. BACKGROUND

In order to provide a basis for testing and comparing candidateliquid monopropellantL for gun use, it was desired to determine combustionrates as a function of pressure.

The initial effort was directea at meLsurilg the burning rate inplastic straws filled with the monopropellants. Data reproducibilityand diameter independence were used as crude tests of the planarity of theburning surface in order to develop ignition and shielding techniqdes. 1

Gella'ion was necessary in order to produce stable results with one ofthe candidate propellants.

The lower pressure work with gelled NOS-36S gave data points withappreciable scatter. Inspection of the straw remnants showed signsof decreased thermal output at the lower nressures. The preliminaryinterpretation of these data was that the propellant was decomposingat a relatively low temperature aod therefore not melting the strawout of the way in a consictent manner.

Considering the ease with which a liquid surface may be deformedand the necessarily larger apparent burn rate associated with an increasedsurface area, improved techniques for determining the surface shape weredesired,

Interaction of the pr3pellant with its container and the ignitionsource provide disturbances that will initially alter the surface froma planar shape. Techniques for minimizing these disturbances and studyingthe duration of the disturbance were desired.

W. F. McBratnay, F. Bensinger and W. A2rford, "Stm~nd Combustion Ratesfor Some Liquid Monopropellants at Gun Functioning Pressures," BRLMemorandum Report No. 2658, Aug ?6. (AD#0013130L)

7

III. APPARATUS AND EQUIPMENT

A windowed chamber capable of operating at pressures up to 200 MPa

was obtained and set-up for use in connection with the pre!.surizationapparatus of the BRL strand burner facility.

The chamber has a 15 cm interior diameter and allows a 10 cm opticalpath between the windows which are attached to the end plugs. *The endplugs are provided with plates which may be altered to provide differentapertures. Those apertures used in this series of tests ranged from6 ,%m to 17 mm wide by 37 mm long.

A quartz-halogen lamp was used to back light the samples through adiffuser screen placed within the chamber and near the sample.

A Fastax half frame 16 mm camera operating at approximately 1100frames per second was used for most of the tests in this report. Ekta-chrome 7242 film was normally used.

The samples of liquid propellant were held in polypropylene strawsor in special cells. These cells were of rectangular c.:oss-section anddesigned like spectroscopy cells. Various cell window and spacer mater-ials were tested. Glass microscope slides worked well for some of thetests but tended to ahatter if the combustion was not stable. Acrylicsheet generally gave 3atisfactory results as far as remaining togetherbut would interact with the OTTO Fuel II if the photographic lights wereleft on too long, causing an apparent gel layer to form.

Ignition was achieved by contact with a heated nicl-'ome wire.

IV. EXPERIMENTAL

A. NOS-365 -- Polypropylene Straws, Gelled

One of the observations made during the lower pressure strandburner runs with NOS-365 was that below nu 20 MPa stringy fragments ofthe polypropylene were left after the burn. As pressures were decreasedfurther the portion of the straw remaining increased in size. At suffi-ciently low pressures, most of the straw remained but was thermallydistorted and collapsed. At even lowver pressures the straw was not evendistorted.

With a marginal heat release from the propellant, the melting of the

polypropylene is probably not consistent. Th1is may account for the scatterin the low pressure data.

Figures 1, 2, and 3 show straws during the burn cycle at pressuresof 20 MPa, 42 MPa and 62 MPa, respectively. In Figure 1 at 20 MPa, the

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straw appears to melt and collapse but not burn Off. In the left frame,the formation of a bulbous zone is observed. The top of the Straw appearsto have collapsed in%,ard, giving a restricted orifico. As the burn pro-gresses, the length of the straw remnant above the burn surface increases(Figure 1, left, "' 10 mm; Figure 1, right, N 13 mu).

In Figures 2 and 3, the top of the straw is roughly 7 mmi above theburn front but the higher pressure run in Figure 3 appears to give amore uniform bumn-off with less of the melt thickening observed in Fig-

ure 1.

These figures confirm the suspicion that at the lower pressures themelting of the straw may give erratic data in the standard strand burnerapparatus, where the melting of the fuze wire will be dependent uponthe melting away of the straw to~ allow the hot gas to contact the wire.

In Figure 2, the two frames at the right show a droplet being ejectedfrom the burn zone.

B. Hot Wall Effects

Observation of the non-planar burning of these propellants inrectangular cross section cells reveals one of the mechanisms for highmass burning rates. As the wave-like sloshing of the propellant fromone side of the cell to the other occurs, the call walls in areas thatwere previously uncovered have become heated. When the propellant isdriven back into this region by the wave action, the hot wills reactwith the propellant, forcing the propellant away- from the wall. Thisproduces a relatively large propellant surface area. The films of thiseffect show what appears to be a jetting action of the propellant intoJthe gas zone.

This clipping of the rising portion of the wave may contribute tothe high mass burn rate in at least two ways. The material thrown awayfrom the hot walls has a high mass burning rate due to the increasedsurface area and is rapidly eliminated from participating in the waveaction. This eliminates the material from participating in "normal"stabilizing mechanisms. In addition, the high local mass burning ratewill produce a localized surge in pressure to add to the destabilizingmechapisms. So far, it has been difficult to obtain films of this hot

wall )ffect that are good enough to reproduce a plate illustration.

C. NOS-365, 1137, 2% Kelzan

1. Lower Pressures. Observations on NOS-36S in the transparentcells at pressures of 55 MPa and below show a red zone above the burnfront and ejecta (small droplets) exiting the cell.

12

rTe red zone above the burn front at 28 MPa has the appearance ofa flame of small height, however, at 55 MPa, the red zone has disappearedand the burn zone appears to be an opaque, non-luminous layer. Fromthese data and observations on NOS-365 without gellation, it is probablethat the red zone is caused by NO2 from the decomposition reaction. P.-d.brown fumes are observed at atr.sspheric pressure, and it is r'r, 1'ethat this red zone corresponds to these fumes. 1

At pressures near atmosphoric the decomposition of the NOS-365proceeds into the propellant while generating froth. At higher pressuresthe froth does not form a growing layer but apparently the liquid fromthe froth reaction collects on the reaction front and is blown away asdroplets. These droplets are readily seen in films taken of the reactionnear 28 MPa (Figure 4).

The films taken at 28 MPa and 55 MPa (Figure 5) show reactions thatstart off with relatively flat, horizontal surfaces. As the reactionproceeds, the surface becomes tilted relative to the horizontal. Thismay result in a relatively simple tilted surface as at 28 NPa (Figure 4)or a convex surface consisting largely of two simple tilted portions asat 55 MPa (Figure 5). These observations correlate with the observationsthat the burn surface is convex (N conical) at these pressu:res in poly-propylene straws.

A probable explanation of the mechanism which causes the convoxburn surface at these lower pressures, is given by the observation thatNOS-365 appears to react in a hypergolic manner with the liquid remnantfrom the fizz reaction. 1 Us this remnant liquid is ej-cted from theburn front some of it wLI 1t the walls of the test cell And bereturned to the reaction area along the cell walls causing a higher re-action rate near the walls.

2. Higher Pressures. Photographic runs covering the pressurerange of IOU MPa to 195 MPa show a relatively stable burn surface. Theignition event or the deformity of the initial surface provide earlyburn surfaces which generally approach a flat, horizontal shape as theburn progresses down the sample.

Figures 6 and 7 (124 MPa and 169 MPa) show more typical burns athigh pressure, in which the ignition occurs near one edge of the sample.This causes one edge to lead the other for the early part of the burn,but the surface becomes flat within 0.25 mm across the width of thesample fairly early in the burn cycle.

In Figure 8 (195 MPa), the sample surface has a large depressionnear one side. During the ignition event, the flame propagates intothis depression, producing a large initial deviation from planarity inthe burn surface. The surface does not approach planarity until all butthe bottom one centimeter of the sample has burned away.

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3. Luminosity. In these gelled propellant tests the runs atthe lower pressures do not appear to have luminous areas within thecells. At pressures of 100 MPa and above there appears to be ageneralized low level of luminosity within the sample cell. All of thecell volume above the propellant sample appears slightly luminous at195 MPa. The lumin.sity is softly reddish at 195 MPa. Any laminosityis at least an oider of magnitude less than is observed with a 0.25 mmthick sample of M8 solid propellant.

At these higher pressures there generally occurs a flash of lumin-osity above the cell during the ignition phase. This luminosity occursaround the igniter wire.

4. Results. The data obtained from the photographic runs withNOS-365, H37, 2% Kelzan are plotted in Figure 9 and given in Table I.A reference line for the high pressure region has been taken from Ref. 1for NOS-365, H6, 1.5% Kelzan. The data for the 2% gelled material fallsconsistently below that for the 1.5% gel concentration at the higherpressures. Data on the 2% material of the same propellant lot is beingprepared for publication.

D. NOS-365, H37, Not GelledFigure 10 shows NOS-36S, H37 in a glass cell at 29 MPa. The initial

frame clearly shows the initial surface curvature and the immersion ofthe ignition wire. The following frames clearly show a small wave

traveling to the right and eventually forming a jet up the wall. Numerousejecta droplets are observed in this sequence.

E. OTTO Fuel II1. Low Pressures. At pressures up to the neighborhood of 10 MPa

stable surface curvature is observed during the burn. Apparently thisis due 'o the surface tension of the liquid to cell contact. Figure 11showb the curvature of the front in a glass cell at 8.4 MPa. It appearsthat the surface curvatur' decreases as the pressure is increased butthe data is effected by 'che different cell materials used.

Crude calculations, based on the visible curvature of the front inglass cells in which the increased area is accounted for, give burning

rates which are "close" to those obtained in the strand burner.

During some of the runs at lower pvessures with acrylic cells, someanomalous low uncorrected rate data were obtained. Investigation ledto the conclusion that OTTO Fuel II may be gelled with acrylic plastic.Under normal room conditions, acrylic will dissolve in OTTO Fuel II ata very low rate. However, when exposed to a photo-flood light or asource of heat, an increase of viscosity and finally gellation are fairlyrapidly noted. [Test conditions were a thin layer of OTTO Fuel IIon a sheet of acrylic].

19

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X - PHOTO DATA, NOS 365,2 % KELZAN50

5 - STRAND BURNER DATAINOS 365, 1.5 % KELZAN

3.8 mra POLY STRAWNOS 365 - H61.5 % KELZAN

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Figure 9. NOS-365, H37'Data Plot, 2% Kelzan

20

Table I. NOS-365, H37, 2% Kelzan

P RMPa COMMENT

20 2.17 3 mm polypropylene straw

42 4.24 3 am polypropylene straw

62 2.87 3 mm polypropylene straw

196 6.97 6.1 x 1.S mm cell Acrylic

169 5.55 6.1 x 1.5 = cell Acrylic

124 3.59 6.1 x 1.5 mm cell Acrylic

102 3.0 6.1 x l.S mm cell Acrylic

55 2.7-3.1 6.1 x 1.5 mm Non-Planar Burn

28.6 2.3-2.8 6.1 x 1.5 mm Non-Planar Burn

NOTE: Estimated reading errors of 11 to 5% are to be expected from thephotographic data. This is dependent upon the photographic quality andthe nature of the surface.

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During some of the pxessure runs with thin acrylic cells the fullintensity of the photographic lights was used during adjustment of thecamera and mirrors. This was apparently enough to allow the propellantto dissolve some of the acrylic of the cell walls. Later tests wereconducted with the light intensity reduced until the actual photographicrun was started.

The information that the viscosity of OTO Fuel II may be increaseddrastically by the solution of acrylic plastic should be of use instudying the stability of the combustion at higher pressures. Acrylicmay be utilized as a gelling agent to modify the surface instabilities.

Figure 12 shows the progression of a burn front at 10.3 MPa over apiece e£ submerged fuse wire. The cell is acrylic. In this pressurerange at lea3L, this plate shows that relatively large disturbances maybe imposed upon the burning surface and the surface will stabilize itself,

2. Mid-Pressure Range. The pressure range of 10 MPa to approxi-mately 40 MPa" (Figure 1) covers the transition from surface tension

stabilization to a relatively flat burn surface with small scale distur-bances becoming evident at the higher values.

3* Higher Pressures. In the pressure region above 40 MPa, stronglynon-planar burning has been obtained with the techniques employed tothis date. In these tests the initial surface has been non-planar (sur-iace tension) and the ignition event has been vigorous enough to-stronglydrive the surface in localized areas.

At 46.9 MPa (Figure 14), slightiy asymmetric ignition initiates astrong, sloshing type of wave action. The sequence of photos illustratesthis motion starting at the point on the right side of the cell when themeniscus has been reduced to a minimum by the vertical motion of theliquid. In the second frame, some liquid has moved further upward whilebeing ignited along the walls by the previously heated glass walls. Thisignition has driven the propellant away from the walls and towards thocenter line of the cell, thereby creating a jet of propellant up thecell. This will create a sudden change in surface area and thus pressurein this area which will act to stop the vertical mlotion of the liquidin this area and assist in driving the liquid back down in this region.The rest of the sequence of frames shows the dropping of the liquid withthe resultant large meniscus of liquid on the right side of the cel± andthe corresponding upsurge of liquid on the left side of the cell (• 9 msbetween frames).

Figute 15 (62 MPa) shows the rapid growth of the ignition processand its development into an asymmetric shape. Of special interest inthis sequence is the clear development of the burn front in the firstfew frames. Clearly a meniscus of liquid remains on the wall in bothhorizontal dimensions. The burn-off of this meniscus is clearly seenin later frames.

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Figure 16 (82.7 MPa) shows another example of the sloshing motion.The last frames of the sequence again Clearly show the burning off of awall bound meniscus layer along the center of the cell.

The presence of a meniscus layer on the wall allows the liquid inthe wave to rise up the cell to at least the extent of the meniscus diueto its protection of the wall from the combustion gases.

burn starts out strongly asymmetric due to~ the liquid leaking out Fiue10hw TOFe Ii n cyi ela 2 ~.Tithat a major Portion of the surface is below the ignition wire~. -Le

ignition occurs on the left side of the cell causing a slosh to t"W'ri.ght with a rapid drop of the liquid on the left. This sequence showsI; the surface as being characterized by additional smaller irregularities.The burn progresses in an asymmetric fashion predominantly along oneside of the cell. Small waves move over the burning surface as is shownin the last frame.

Figure 18, OTTO Fuel 11, 6.1 x 1.5, Acrylic, 156 MPa: Ignition by

use of a strip of M8 propellant did not give an fnitially flat surface

due to asymmetric ignition of the MS strip. This provided a slightlyearly LP ignition on the right of the cell and initiates some wavesacross the surface. The depression near the right wall grows at a highrate as at 129 MPa. As the dimensions of this depression increase thevelocity of the tip decreases and small waves travel across this.surface. The), appear to be similar to the small surface waves observedin the NOSET "All run at 70 MPa.

Observation of one of the small surface waves generated near thecenter line shows this peak dividing into two and separating with thegeneration of a depression between them. Apparently, the small ridge-like wave provides a locally high mass burn rate which provides a drivingmechanism to depress the ridge-like structure and drive waves away fromthe area. The area under the former ridge can develop as a majordepression.

4. Results. Table II and Figure 19 show the numerical dataobtained -photographically for OTTO Fuel II. Reference lines for OTTOFuel II taken from Reference 1 are plotted in Figure 19 for comparison.

The higher values obtained at low pressures in the glass cells maybe partly explained by a larger surface tension meniscus obtained inglass cells.

The high values obtained at the higher pressure are, by incpectionof the plates, for strongly non-planar, non-steady surfaces. No attempthas been madie to estimate a correction factor for the large surfacearea.

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'Table II. OTTO Fuel II Not Celled

S~C E L LP W R

MPa mm nuM MATERIAL cm/s-

5.6 6.0 .95 Glass .195

7.0 6.0 .95 Glass .231

9.2 6.0 .95 Glass .276

9.7 6.0 .95 Glass .26S

12.6 6.0 .95 Glass .332

20.1 6.0 .95 Glass .360

46.9 6.0 .95 Glass 1.92

60.0 6.0 .95 Glass 3.73

10.3 6.1 1.5 Acrylic .231

82.7 6.1 1.5 Acrylic 5.08

128.0 6.1 1.5 Acrylic 8.21

156.0 6.1 1.5 Acrylic 9.4

NOTE: Estimated reading errors of 1% to 5% are to be expected from thephotographic data. This is dependent upon the photographic quality and

the nature of the surface.

137

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OTTO FUEL .,° STRAND DATA

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Figure 19. Burn Rates for OTTO Fuel II

38

Further work on ignition techniques and cell material interactionsmay clarify the causes for the disparity in the data at high pressures.

F. NOSET "A"

Figure 20 (20 MPa), 6.0 x .95 mm glass: The sequence of frames inFigure 20 clearly shows the wave action of the liquid. The initialframe shows the start of the sequence with a maximum meniscus to theleft side and the wave minimum to the left. As the sequence progressesthe liquid moves back up aliminating the meniscus and showing the startof a positive wave amplitude. In this sequence as the pcsitive waveis foimed a bubble is formed in the peak region and grows. The bubblefinally breaks, scattering liquid into the gas and leaves streamers ofliquid projecting up. As the upsurge proceeds, additional bubbles areformed and ruptured. The frames in this sequence show the same effectsbeing started along the right of the cell, The formation of the bubblesmay be due to the collection of heated propellant in the regioai of thepeak, giving rise to ignition below the surface. The glass is apparentlynot getting hot enough at this pressure to ignite the sides of thepropellant, as the rising portion of the wave covers glass that hasbeen previously exposed.

Figure 21 (69.6 MPa), 6.0 x 1.5 mm, acrylic: This sequence shows arelatively stable general shape for the non-planar burn front. The"sloshing" observed at lower pressures is not evident. Also the shapeis asymmetric relative to the cell. Small waves propagate over thelarger surface and proceed up along the higher sides of the front. Atthe top of the large shape a streamer (or jet) is -ormed by the smallerwaves.

The velocity of the lowest point is approximately 20 percent largerthan the value obtained for the 6 mm straw samples in the standardstrand buiner tests.

V. CONCLUSIONS

The low thermal output of NOS-365 at lower pressures causes anerratic melting of the straw and will cause additional variability inthe strand burner data for this propellant.

The agreement of the data of Figure 9 above 100 MPa, implies thatthis data from Reference I iE for reasonably planar combustion.

The lower pressure data for the gelled NOS-365 must be correctedfor the characteristic non-pla.arity observed in these tests.

The presence of a stable 3urface curvature in the lower pressuretests on OTTO Fuel II means that the lower pressure data of Reference 1

39

00

14

- N V

'WIT4

40

00

I.M

C.

f4

V)

IV)

.0. 40

410

,,,,,IS~'C

rA

424

-~~-- -* --------.~ r

may be slightly in error. Calculations based on surface are, estimatesfrom the photographic data indicate that it is reasonably accurate,however, further tests should be performed, directed at determining theextent of surface tension effects. A stable curved surface implies thatliquid is being moved to maintain the shape, thus increasing the massburn rate. Without liquid motion the surface should become flat due to

burn-off.

The higher pressure data for OTTO Fuel 11 obtained in these testshas been so strongly noa-planar that it is not especially helpful in

determining the accuracy of the referenced data.

The tests that have been conducted on NtosE "A" show this propellantto be very useful as a photographic subject for this type of test. Theclarity of detail with minimal obscuratiun makes this propellant a good

candidate for studying the sv'rfaca details.

43

rt~,.isAL - L

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