CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
© 2002 American Institute of Physics 0-7354-0068-7/02/$ 19.00
INVESTIGATION OF SHOCK WAVE IMPULSE INFLUENCE ON
SOLID PROPELLANT COMBUSTION
Alexander Yu. Dolgoborodov and Vladimir N. Marshakov
N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 119991, Moscow, Russia
Abstract. The laboratory technique for test of solid propellant combustion under shock wave loading
is described. The explosive generator was used for shock waves formation in propellant sample in
pressure range 100 - 300 MPa. The experiments were conducted in the combustion chamber at
pressure range 1 - 1 2 MPa. HE charge was initiated in 1-1.5 seconds after ignition of the propellant.
For shock pressure in a sample less than 150 MPa, the experimental results have shown that the steady
combustion regime is retained. The shock pressure increasing up to 230 MPa results in product
pressure rise and consequent combustion chamber breakage. The analysis of possible causes of
observed differences in regimes of burning was performed.
bustion chamber. We investigate the samples of
propellant on the base of polybutadiene rubber
filled by ammonium perchlorate and HMX with a
characteristic size of particles of 100-300 um and
fine aluminum particles (5-10 (am). Earlier the
structure of shock wave was investigated for this
propellant [5]. For shock wave formation in samples we used the explosive generator similar described in this work. The scheme of combustion
chamber with explosive generator (EG) is displayed
in Fig. 1.
The combustion camera was made by the way of
thick-walled vessel with volume about 2 litres. The
shock wave impulses with maximum pressure 0.10.3 GPa formed by EG. EG consists of a composite
charge of RDX (lens by a diameter of 40 mm and
weight 15 g and intermediate charge with detonator
in weight 5 g) and thin-walled copper barrel with
water by a diameter of 85 mm. The HE charge was
installed above at centre of a barrel. The barrel was
fixed on a cover of the combustion chamber. The
parameters of a shock wave were adjusted by
variety of height of the barrel with water. The shock
wave from water passed in a propellant sample
INTRODUCTION
In operation on the ground and in flight, a solidpropellant rocket engine may be subjected to shock
loading caused by external shock wave, impacts of
fragments generated by explosions, and directed
high-intensity energy fluxes [1-3]. Duration of these
loads varies from 10'6 to 10~2 s, depending on the
source, and the representative pressure pulses range
from 0.1 kPa*s to 5 kPa*s. Effect of shock wave
impulse on the operating rocket engine can result in
disastrous consequences. Sometimes fire bench tests
are carried out for determination of safe load levels
of operating engine [4]. However realisation of such
tests requires significant costs. The purpose of our
work was to develop a rather cheap laboratory
technique, which would allow investigating the
stability of propellant burning under shock wave
loading in the pressure range 0.1 to 0.3 GPa.
EXPERIMENTAL
For experimental investigation of stability of
composite propellant combustion we used the com-
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The experiments on determination of a shock
wave structure in propellant samples without
burning were previously conducted. For a
measurement of shock wave pressure in samples
were used piezoelectric film PVDF - gauges made
and calibrated in laboratory by Yakushev V.V.
(IPCP RAS, Chernogolovka). PVDF gauges were
placed in two planes: on the contact boundary of the
organic-plastic insert of the chamber and propellant
sample and in a sample on depth of 20-22 mm. The
scheme of experiments is shown in Fig. 2. In order
to prevent of influence of air inclusions on a
structure of a wave of an irregularity between the
insert and sample were filled in with an epoxy resin.
through the organic-plastic insert in a cover of the
combustion chamber. The diameter of the organicplastic insert constituted 90 mm, width of 14 mm.
Propellant samples were produced as truncated
cones by a thickness of 40 mm and diameters of the
basis 50 and 57 mm. Samples are located inside the
chamber and nestled on the organic-plastic insert by
a conic cartridge clip. Ignition of samples was made
from the lower end face by burning products of
powder charge of weight 5 g. On a lateral area of the
chamber there were landing places under the nozzle
block, block of a safety valve and reducing coupling
under the inductive gauge DD-10. The products of
burning were assigned from the chamber through a
nozzle block. The pressure in chamber was
registered by gauge DD-10 with the pressure
indicator ID-21 on the oscilloscope N-117. The
initiation of a HE charge was made in 1-2 second
after ignition of a propellant with the help of
synchronization scheme.
HE charge
copper cylinder wit
PVDF gauge
Computer oscilloscope
Time resolution -10ns
FIGURE 2. Experimental set-up for pressure measurement in
propellant samples. PVDF- piezoelectric film gauges made of polarized polyvinylidene-fluoride with sensing area 5.06 mm2.
FIGURE 1. Combustion chamber with explosive generator
1 - explosive charge, 2 - copper cylinder with water, 3 - cover of
chamber case, 4 - organoplastic insert, 5 - propellant sample, 6 conical cartridge, 7 - protecting cover, 8 - nozzle, 9 - ignition
powder charge, 10 - additional insert of chamber, 11 - block of
safety diaphragm, 12 - orifice in the chamber to adapter and pressure gauge DD-10
EXPERIMENTAL RESULTS
The trial tests were made without combustion of
samples. Samples subjected to shock compression
and were visually studied after a shock loading. Fastening of samples was carried out by two ways. In
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the first case the sample was retained against organic-plastic insert by the plexiglas screen. The
screen had the holes of different diameter. In the
second case the sample was consolidated only on a
lateral area by a special conical cartridge from duraluminum, thus also was given to a sample the conical form. In the latter case it was possible to achieve
absence of separation of a sample from the insert after shock wave loading, and hereinafter this manner
of fastening utilised for researches at combustion.
loosening of a sample in the field of a hole. Inside a
propellant the spalling flaws have appeared. In case
of a pressure increment till 0.23 GPa propellant lost
durability and the corrupting were considerably
magnified, though complete spallation does not
happen.
The experiments on measurement of the profile
of pressure have shown the following. At a stratum
of water of height 148 mm the pressure profile on
contact boundary with the insert was close to the triangular form. The maximum pressure constituted
0.18 GPa. On depth of 21 mm in a sample the main
features of a structure were saved. The maximum
pressure has decreased up to 0.135 GPa. At decrease
of a stratum of water on 50 mm the maximum pressure on depth of 21 mm inside a sample has increased till 0.23 GPa. The pressure profiles are
shown at Fig. 4.
l)
2)
e in propellant sample on depth of 21 n
Pressure in propellant sample on depth of 21 mm
FIGURE 3. Fracture of samples after shock wave loading 1-3 propellant samples pressed from below by plexiglas plate with a
hole. 1- Plexiglas plate with 5 mm hole. Psw = 0.135 GPa. 2Plexiglas plate with graduated hole. Psw = 0.135 GPa. 3- Plexiglas
plate with graduated hole. Psw = 0.23 GPa.
Visual research of samples in all cases has shown,
that the large fragments of a filling material (HMX
and ammonium perchlorate) from a near-surface
layer take off from a sample, and the free surface of a
sample gains spongy structure (see Fig. 3). In case of
availability of holes in the screen in samples the
destructions are observed. Thus the size of
destructions decreases with growth of diameter of
holes. So at diameter of a hole of 5 mm and shock
wave pressure 0.135 GPa there was a full separation
of spalling element by depth up to 2.5 mm. At
diameter of a graduated hole of 18 mm there was a
Time,mcs
FIGURE 4. Shock pressure records in propellant samples. (H height of a stratum of water in the explosive SW generator). 1Pressure on the depth of 21 mm in sample, H=148 mm, Pmax =
0.135 GPa, 2- Pressure on the depth of 21 mm in sample, H=88
mm, Pmax= 0.23 GPa.
The experiences with burning were conducted at
pressure inside the combustion chamber of 1 - 12
MPa. The pressure was regulated by selection of a
nozzle diameter. In Fig. 5 two records of pressure are
870
indicated at shock wave amplitudes - 0.135 and 0.23
GPa. The conducted experiences at a shock load by
amplitude 0.135 GPa as a whole display saving
stability of combustion. After shock wave exit on a
shining surface happens small (approximately up to
0.2 MPa) pattern null of pressure and through 70 100 ms restoring of a former level. A reason of a
pattern null of pressure can be break-up of a part of a
warmed-over stratum from burning surface after
shock wave passing.
under shock wave loading in the pressure range 0.1 0.3 GPa.
There were conducting the tests on combustion
of the composite propellant in the chamber under
shock wave with amplitude from 0.13 to 0.23 GPa.
The experiments conducted in the combustion
chamber under the pressure ranged from 1 to 12
MPa showed the following:
• The shock wave loading of the propellant sample with the amplitude 0.135 GPa did not cause
the combustion failure and resulted only in insignificant (0.15 - 0.20 MPa) short-acting (20 - 70
ms) pressure decrease after which the previous
pressure level restored. This means that steady
state combustion regime was retained.
• Under the same conditions, shock-wave pulse
with pressure amplitude of 230 MPa resulted in
abrupt pressure increase and emergency conditions in the chamber.
In the last case, the abrupt pressure rise could be
caused by several reasons that may be summarised
as following: increasing of total burning area at the
coast of surface disintegration and flame breaking
into the sample; separation of heated-up layer with it
consequent afterburning in the chamber; spalling
fracturing of the sample etc.
The analysis of the pressure diagram suggests that,
as the result of shock wave loading, separation of
burning layer approximately from one third of total
burning surface took place. Burning of this layer and
ignition of the liberated surface caused the pressure
increase in the chamber. More detail analysis of the
phenomenon occurring under shock wave loading
calls for further investigation.
1)
0
0,5
1
^BS MRa, 4^=3.5 nn}
Tim^s
2)
0
0,5
1
Psw^230 IVPa, (Ua^.4 ran
1,5
2
Time, s
REFERENCES
FIGURE 5. Pressure variation in combustion chamber (vertical
arrow shows a moment of shock loading) 1 — shock wave
pressure = 0.135 GPa, 2 - Psw = 0.23 GPa.
1.
2.
CONCLUSION
The experimental procedure for conducting the
laboratory tests on stability of propellant combustion
under shock wave loading has been developed. There
were manufactured and developed explosive
generator, model testing unit, and combustion
chamber for studying combustion of propellants
3.
4.
5.
871
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