Propellants, Explosives, Pyrotechnics 23, 167Ä…171 (1998) 167
Regenerative Liquid Propellant Gun of Caliber 40 mm
G. Zimmermann, E. Gutlin, and G. Klingenberg
È
Fraunhofer-Institut fur Kurzzeitdynamik, Ernst-Mach-Institut (EMI), D-79576 Weil am Rhein (Germany)
È
W. Ch. Bertels
Wehrtechnische Dienststelle der Bundeswehr, WTD 91, D-49716 Meppen (Germany)
Regenerative Flussigtreibstoffwaffe vom Kaliber 40 mm Arme regenerative a propergol liquide de calibre 40 mm
È Â Â Â Á
È Â Â Â Â Â Á
Die vorliegende Veroffentlichung beschreibt Experimente des La presente publication decrit des experiences realisees a l'Institut
Ernst-Mach-Institutes mit einer regenerativen Flussigtreibstoffwaffe Ernst-Mach avec une arme regenerative a propergol liquide de calibre
È Â Â Â Á
 Á
vom Kaliber 40 mm sowie die Ergebnisse von Rechnungen mit einem 40 mm ainsi que les resultats de calculs avec un modele simple
Á Á Á Â Â
einfachen Modell (Lumped-Parameter Modell), die bei der WTD 91 (modele a parametres concentres) effectues au WTD 91. L'arme
durchgefuhrt worden sind. Die Regenerativwaffe enthalt ein Glattrohr regenerative comporte un tube lisse long de 2,53 m et tire un projectile
È È Â Â Â
È
von 2,53 m Lange und feuert ein konventionelles 40-mm Projektil von conventionnel de 40 mm et 0,936 kg. La chambre de combustion
Á Â
0,936 kg Gewicht. Der Verbrennungsraum hat ein Anfangsvolumen possede un volume initial de 219 cm3 et un reservoir de 575 cm3. Un
Á Â Â
von 219 cm3 und ein Reservoir von 575 cm3. Ein System mit zwei systeme compose de deux pistons, un piston central ®xe et un piston
Â
Kolben, ein feststehender Mittelkolben und ein beweglicher Injek- d'injection mobile, est utilise pour l'injection du propergol liquide. Le
tionskolben wird fur die Einspritzung des Flussigtreibstoffes ver- rapport de surface differentiel est de 2:1. L'allumeur pyrotechnique
È È Â
È È È
wendet. Das differentielle Flachenverhaltnis betragt 2 : 1. Der pyro- DM 1101 comportant une charge additionnelle de 6 g de poudre noire
technische Anzunder DM 1101 mit einer Beiladung von 6 g et de 30 cm3 de propergol liquide compose de 80% en poids de
È Â
Schwarzpulver und 30 cm3 Flussigtreibstoff bestehend aus 80 Gew.% nitromethane et 20% en poids de methanol (NM/M 80/20) met le
È Â Â
Nitromethan und 20 Gew.% Methanol (NM=M 80=20) setzt den piston en mouvement et assure l'allumage du jet de propergol liquide
Kolben in Bewegung und sorgt fur die Anzundung des injizierten injecte. L'analyse experimentale du comportement lors du tir repose
È È Â Â
Flussigtreibstoffstrahles. Die experimentelle Analyse des sur les resultats de mesures de pression dans le reservoir, dans la
È Â Â
Á
Schuûverhaltens basiert auf Ergebnissen von Druckmessungen im chambre de combustion et a la bouche, sur l'enregistrement inductif du
Reservoir, im Verbrennungsraum und an der Mundung, auf der mouvement du piston, sur l'interferometrie hyperfrequence (5 GHz) du
È Â Â Â
induktiven Aufzeichnung der Kolbenbewegung, auf der Mikrowel- mouvement du projectile dans le tube et sur la mesure inductive de la
leninterferometrie (5 GHz) der Geschoûbewegung im Rohr und auf vitesse initiale du projectile. Si l'on fait fonctioner l'arme avec une
Â
der induktiven Messung der Abgangsgeschwindigkeit des Projektiles. charge de 550 cm3 de melange de propergol liquide NM/M 70/30
Â
Wenn man die Waffe mit einer Ladung von 550 cm3 der relativ d'energie relativement faible, on obtient des pressions maximales de
ernergieschwachen Flussigtreibstoffmischung NM=M70=30 betreibt, 480 MPa dans le reservoir, de 400 MPa dans la chambre de combustion
È Â
È È Á
so erhalt man Maximaldrucke von 480 MPa im Reservoir, 400 MPa im et de 50 MPa a la bouche du tube. Des oscillations de pression
Verbrennungsraum und 50 MPa an der Rohrmundung. Druck- d'amplitudes allant jusqu'a 250 MPa et de frequence principale 28 kHz
È Á Â
oszillationen mit Amplituden bis zu 250 MPa mit einer Hauptfrequenz se superposent aux courbes. La vitesse initiale est de 950 m/s. Le
von 28 kHz sind den Kurven uberlagert. Die Abgangsgeschwindigkeit modele energetique represente assez bien la puissance mesuree de
È Á Â Â Â Â
È È Ã Â Â Â
betragt 950 m=s. Das Energiemodell reprasentiert recht gut die l'arme. Les calculs peuvent etre utilises pour les etudes parametriques
 Á
gemessene Leistung der Waffe. Die Rechnungen lassen bei entspre- lorsqu'ils sont correctement adaptes a la combustion de gouttelettes.
È Â Á
chender Anpassung an die reale Tropfchenverbrennung Para- Ainsi, on peut par exemple etudier des effets dus a des modi®cations
Á
meterstudien zu. So lassen sich zum Beispiel Effekte studieren, die auf de l'ouverture de tuyere.
È
Anderungen der Dusenoffnung zuruckgehen.
È È È
ber, and 50 MPa at the muzzle. Pressure oscillations are superimposed
Summary
to the pressure recordings which, in the combustion chamber, go up to
250 MPa with a leading frequency of 28 kHz. The projectile launch
The present paper describes experiments carried out with a 40-mm
velocity is 950 m=s. The lumped parameter modeling represents quite
regenerative liquid-propellant gun at the Ernst-Mach-Institut and
well the measured gun performance. It supports gun design and can be
lumped parameter representations of the gun performance developed
used for parameter studies, if properly adjusted to droplet burning. For
at WDT 91. The test ®xture is equipped with a 2.53 m smooth-bore
example, effects caused by variations in the vent area have been
gun tube and ®res conventional 40-mm projectiles of 0.936 kg mass. It
simulated.
has an initial gun chamber volume of 219 cm3 and a reservoir of
575 cm3. A two-piston system, an in-line annular injector with a ®xed
center piston, are used for liquid propellant injection. The differential
1. Introduction
area ratio is 2 : 1. The pyrotechnic igniter (DM 1101 primer) supported
by a priming charge of 6 g black powder combined with 30 cm3 liquid-
The concept of a liquid propellant gun originated in an
propellant containing 80 weight% nitromethane and 20 weight%
methanol (type NM=M 80=20) starts piston motion and ignites the
early 1940er program in Germany, in which mixtures of
injected liquid-propellant jet. Experimental analysis of gun perfor-
nitric acid and kerosene launched a projectile to velocities
mance is based on pressure measurements in the reservoir and com-
of about 700 m=s. Since then various programs have been
bustion chamber as well as at the muzzle, inductive recordings of
injection piston travel, microwave interferometer (5 GHz) measure- or are still under way in the United States, Europe and Asia
ments of in-bore projectile motion, and inductive measurements of
that address the development of liquid propellant gun sys-
projectile launch velocity. When ®ring the gun with a charge of
tems. The historical and extensive treatments of liquid gun
550 cm3 of the liquid propellant type NM=M 70=30, which has a
propellant research and development programs which
relatively low energy content, then maximum pressures are of the
order of 480 MPa in the reservoir, 400 MPa in the combustion cham- spanned over the past ®ve decades are given in two AIAA
# WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998 0721-3115/98/0408Ä…0167 $17.50‡:50=0
168 G. Zimmerman, E. Gutlin, G. Klingenberg, and W. Ch. Bertels Propellants, Explosives, Pyrotechnics 23, 167Ä…171 (1998)
È
Progress Series books(1,2). While recent publications have Studies on liquid propellant (LP) gun technology com-
dealt with the fundamentals(3,4) and addressed speci®cs, menced at the Ernst-Mach-Institut (EMI) in 1980 joining
such as electrical ignition(5) and pressure oscillations(6,7), the LP efforts initiated in 1969=70 by the German Ministry
here we describe investigations carried out with a 40-mm of Defense(2). Research at EMI addressed the mono-
regenerative liquid propellant gun at the Ernst-Mach-Insti- propellant gun with regenerative injection. Various test
tut(8Ä…10). In particular, the combination of gun ®rings at ®xtures were developed and tested, including 20-mm, 28-
EMI(9) and the numerical lumped-parameter simulations of mm, 30-mm, and 40-mm regenerative liquid propellant gun
the ®ring data by WTD 91(10) are described in greater detail. (RLPG) designs(2). The 40-mm RLPG used different
injector techniques, including multi-holes ``showerhead'' or
inline injectors and annual ring injectors(8,11,12). The most
recent design incorporated an annual ring injector with
2. Incentives
improved mechanical strength and sealing(9). Extended
diagnostics permitted a better analysis of the ®ring behavior
The use of liquid propellants in guns is attractive because
supporting numerical simulation(9,10). Prior to describing
of the many advantages associated with a Żuid. For exam-
the results of gun tests and numerical simulations, the
ple, there are potentials due to the high mass or volumetric
experimental is summarized.
energy content of a Żuid. Furthermore, liquid propellants
usually have low vulnerability, there are ®nancial savings in
the production and tradeoffs in storage, transport and
3. Experimental and Numerical
logistics. Of advantage is also that artillery zoning, a pro-
cedure to alter ®ring ranges by changing propellant mass,
becomes easier because it can be controlled by the quantity 3.1 Test Fixture
of liquid propellant metered into the gun rather than by use
of ®xed solid propellant bag charges. However, there are The test ®xture is depicted in the schematic drawing of
also concerns related to the Żuid nature of liquid pro- Fig. 1 showing the actual, recently improved design of this
pellants, such as their potential for spill and leakage, regenerative liquid propellant gun(9). It consists of a
material compatibility, safety, and biological and ecological smooth-bore gun tube of 2.53 m length and a steel block
effects. Also, since gun performance potential is always the that contains the interior injector system. The massy breech
dominant driver early in the research and development screw at the rear holds the assembly together. The rotating
cycle, high energetic liquid propellants were usually used band of the conventional 0.936 kg projectile is reduced in
with the drawback of possible failures in ®ll and gun sys- diameter by a metalworking lathe to adapt it to the caliber
tems. On the other hand, the developer may overcome of the barrel (40 mm) and then loaded to the gun tube. A
concerns of the user, as other issues become more important solid retainer or blow-out disc placed at the base of the
and the design of suitable liquid propellants matures. Such projectile separates the combustion chamber from the gun
issues are, for example, vulnerability, improved safety, and tube. It ruptures at a pressure of about 95 MPa thus simu-
reduced logistic burdens. lating case extraction and engraving forces normally
Figure 1. Schematic drawing of experimental 40-mm RLPG ®xture of the Ernst-Mach-Institut(9).
Propellants, Explosives, Pyrotechnics 23, 167Ä…171 (1998) Regenerative Liquid Propellant Gun of Caliber 40 mm 169
encountered in similar solid propellant gun ®rings. The liquid propellant versions were tested in earlier investiga-
design of the injector system located in the steel block tions with the 40-mm RLPG at the Ernst-Mach-Institut(14).
consists of two pistons, the movable outer differential area
piston and the ®xed center piston. The differential area
3.3 Numerical Approach
piston alters its shape so that it provides space for the
reservoir and separates the combustion chamber and reser-
The numerical simulation of the 40-mm regenerative
voir. The liquid propellant is pumped through the ®ll port
liquid propellant gun system is based on a one-dimensional
into the 575 cm3 reservoir. An igniter port contains the
approach for the system's LP reservoir side and a lumped
pyrotechnic igniter which is triggered electrically and ®res
the igniter charge (DM 1101 ‡ 6 g black power ‡ 30 cm3 parameter model for gas-phase side assuming droplet
burning. This approach suf®ced to match experimental data
nitromethane=methanol NM=M 80=20) into the combustion
and permitted parameter studies on the effect of variations
chamber having an initial volume of 219 cm3. The igniter
in gun geometry on its performance caused; for example, by
discharge causes a pressure buildup in the combustion
variations in the dimensions of the vent or ori®ce(10). A
chamber followed by the onset of injector piston motion so
model representation of the 40-mm RLPG is depicted in
that gun operation ensues. A differential area ratio of 2 : 1 of
Fig. 2, including the (a) movable injector piston, (b) ®xed
the two-piston system providing annular ring or slot injec-
center piston, (c) LP reservoir, (d ) annular ring injector
tion ensures that the force which, after ignition, acts on the
ori®ce, (e) combustion chamber, (f ) gun tube, and (g)
liquid propellant in the reservoir exceeds the combustion
projectile. The volumes considered in the modeling
chamber pressure by multiplying it hydraulically so that
approaches and the corresponding pressure decreases are
injection into the high-pressure gases occurs. As indicated
also indicated in Fig. 2 with a subdivision into three
in Fig. 1, a liner can be placed at the chamber wall repre-
volumes at the LP reservoir side (reservoir, transition part,
senting one of the dissipative approaches that have shown
injector) and into two volumes at the gas-phase side
promise in reducing pressure oscillations(6).
(combustion chamber, gun tube). Numerical simulations
included the motion or travel of both the injector piston and
projectile parts during the ®ring. The force opposing piston
3.2 Liquid Propellant
motion at the LP side considers the exact pressure pro®le
developing in the transition part. Generally, the numerical
Since in Germany gun ®rings were mainly conducted
simulation yielded a close match of experimental data. It
with nitromethane-based liquid propellants and large-cali-
proved further sensitive to dampening effects during initial
ber gun tests were carried out exclusively with the less
piston motion, igniter input characteristics, and to variations
energetic, more benign type NM=M 70=30 consisting of 70
in the dimensions of the vent area. The simulation permitted
weight% nitromethane and 30 weight% methanol(2), the
also an estimate on amplitudes of pressure oscillations by
present investigations with the 40-mm RLPG at EMI used
using a simple phenomenological approach(10).
this type of monopropellant mixture. Its properties are
summarized in Table 1. For comparison, the volumetric
impetus of the more energetic liquid propellant LP 1846, 4. Results
which is based on hydroxylammonium nitrate (HAN), is of
the order of 1330 J=cm3, due to its higher density A pressure recording in the gun chamber is shown in
(1.45 g=cm3) and high impetus (935 J=g) depending pri- Fig. 3. It exhibits a maximum pressure of about 360 MPa
marily on the water content (20%) of this mixture(1). In superimposed by signi®cant pressure oscillations with
view of gun performance, it is desirable to use a high energy amplitudes that go up to 250 MPa. Fast Fourier Transform
propellant at a high loading density. On the other hand, the of the pressure recordings reveal that the main frequencies
water increases corrosion of metal components and thus gun are at about 11 kHz and 28 kHz, Fig. 4. The ®rst-radial
erosion and wear. Therefore, fundamental studies in Ger- mode or leading frequency is at 28 kHz.
many aimed at increasing the energy content of the nitro- Comparisons of experimental (open circle) and modeling
methane-based monopropellants by adding suitable results (straight line) are shown in Fig. 5. Measurement and
additives to the Å»uid(13). Such modi®ed nitromethane-based model representations agree quite well. For example, the
Table 1. List of Physical and Thermodynamical Properties of Liquid Propellant Type NM=M 70/30
LP Oxygen Balance % Density Impetus Flame Volumetric
(20 C) g=cm3 J=g Temperature, K Impetus, J=cm3
NM=M 70=30 72.5 1.040 818 1598 850
Molecular Weight Number of Ratio of Speci®c Co-Volume Heat of
of Products Moles (gas) Heats Explosion
g=mol mol=kg cm3=g J=g
NM=M 70=30 17.952 54.508 1.3956 1.183 2128.2
170 G. Zimmerman, E. Gutlin, G. Klingenberg, and W. Ch. Bertels Propellants, Explosives, Pyrotechnics 23, 167Ä…171 (1998)
È
Figure 2. Model representation of the internal geometry of the 40-mm RLPG.
Figure 3. Experimental combustion chamber pressure versus time.
Figure 5. Comparison of experimental and numerical data.
Figure 4. Fourier transform of pressure oscillations of Fig. 3.
pressures are easily matched and a measured projectile
velocity of 981 m=s compares to a numerical value of
1015 m=s. The initial variation in piston travel between
3 ms to 4.5 ms is attributed to a mass-spring reaction which
can be eliminated by improving the initial ignition=
combustion reaction(6).
The potential of the lumped-parameter model is demon-
strated in Fig. 6. It shows the results of vent area variations
of the annual ring injector (410 mm2, 334 mm2, and
250 mm2) in terms of the obtained chamber pressures. As
expected, the maximum pressure decreases and the half-
width of the pressure pulse increases as the vent area is
Figure 6. Variation of pressure curves with geometry or size of vent
area (numerical results).
scaled down.
Propellants, Explosives, Pyrotechnics 23, 167Ä…171 (1998) Regenerative Liquid Propellant Gun of Caliber 40 mm 171
(5) G. Klingenberg, H. Rockstroh, J.D. Knapton, J. DeSpirito, and
5. Discussion
H.-J. Frieske, ``Investigation of Liquid Gun Propellants: Elec-
trical Ignition of LGP 1846'', Propellants, Explos., Pyrotech. 15,
The few representative results of the experimental and
103Ä…114, (1990).
numerical studies with the 40-mm RLPG indicate the (6) G. P. Wren, T. P. Coffee, J. DeSpirito, J. D. Knapton, and G.
Klingenberg, ``Pressure Oscillations in Regenerative Liquid
potential but also the dif®culties encountered in ®ring
Propellant Guns'', Propellants, Explos., Pyrotech. 20, (1), 225Ä…
regenerative liquid propellant guns. The opportunity for
231, (1995).
tailoring the pressure curve to lower maximum pressures
(7) S. R. Vosen, R. W. Carling, R. E. Rychnovsky, S. K. Grif®ths,
and larger halfwidths thus keeping the desired gun perfor- and R. F. Renzel, ``The Effect of Elastomeric Liners on High-
Pressure Liquid Propellant Combustion Oscillations'', Pro-
mance by optimizing the injector vent area is one of the
pellants, Explos., Pyrotech. 20, (6), 311Ä…321, (1995).
attractive potentials of such liquid propellant guns. On the
(8) G. Klingenberg, ``Untersuchungen von Monergolmischungen im
other hand, the pressure oscillation problem must be
40-mm-Regenerativgerat'', Fraunhofer-Institute fur Kurzzeitdy-
È È
namik, Ernst-Mach-Institut, Weil am Rhein, Germany, Rept.
addressed, because amplitudes up to 50% of mean pressure
E1=92, 1992.
are not acceptable. Furthermore, pressure oscillation
(9) G. Zimmermann and E. Gutlin, ``Meûtechnische Analyse eines
È
amplitudes increase with the energy content of the liquid
Schusses mit der 40-mm-Flussigtreibmittelkanone des Ernst-
È
propellant so that the application of high-energetic liquid Mach-Instituts'', Proceedings 21.Wehrtechnisches Symposium:
Innenballistik der Rohrwaffen; Bundesinstitut fur Chemisch-
È
propellants may be too dif®cult. However, reduction of
Technische Untersuchungen (BICT), Swisttal-Heimerzheim,
pressure oscillations is possible by various ways. Approa-
05.Ä…07. 02., 1996.
ches include(6) (a) mechanical devices to affect the break-up
(10) W. Ch. Bertels. ``Simulation and Validation of Caliber 40-mm
of the liquid jet, (b) chemical methods to increase the Regenerative Liquid Propellant Test Firings'', Wehrtechnische
Dienststelle der Bundeswehr (WDT 91), Meppen, Rept. 13.12.96,
burning rate, and (c) dissipative mechanisms to absorb the
1996.
pressure waves. For example, jet dispersers can dramati-
(11) G. Klingenberg, H. Rockstroh, O. Wieland, R. Rittel, and U.
cally lower the magnitude of the ®rst-radial mode, the
Steffens, ``Untersuchungen an einer Regenerativwaffe vom
Kaliber 40-mm'', Fraunhofer-Institut fur Kurzzeitdynamik, Ernst-
È
dominant acoustic mode in RLPG pressure oscillations, and
Mach-Institut, Weil am Rhein, Rept. 4=88, 1988.
liners in the combustion chamber (see Fig. 1) may absorb
(12) G. Klingenberg, ``Untersuchungen zur Schuûentwicklung bei
pressure waves. Studies on RLPG should continue including
regenerativen Flussigtreibstoffkanonen'', Proceedings 14.Wehr-
È
improvement in the numerical simulation technique.
technisches Symposium: Innenballistik der Rohrwaffen; Bundes-
institut fur Chemisch-Technische Untersuchungen (BICT),
È
Swisttal-Heimerzheim, 08.Ä…10.11.1988.
È
(13) G. Langer, H. Schmid, and W. Koppenhofer, ``Optimization of
6. References
Liquid Gun Propellants Based on Nitromethane=Methanol by
Physical and Chemical Modi®ers'', Propellants, Explos., Pyro-
(1) L. Stiefel (ed.), ``Gun Propulsion Technology,'' Vol. 109, Pro- tech. 17 (4), 185Ä…189, (1992).
gress in Astronautics and Aeronautics, AIAA, Reston, VA, 1988. (14) G. Klingenberg, H. Haas, G. Schulz, and O. Wieland, ``Unter-
(2) G. Klingenberg, J. D. Knapton, W. F. Morrison, and G. P. Wren, suchung von Flussigtreibstoffen mit Additiven zur Oszilla-
È
``Liquid Propellant Gun Technology,'' Progress in Astronautics tionsdampfung'', Fraunhofer-Institut fur Kurzzeitdynamik, Ernst-
È È
and Aeronautics, Vol. 175, AIAA, Reston, VA, (1997). Mach-Institut, Weil am Rhein, Rept. E 20=93, 1993.
È
(3) G. Klingenberg, H. Knochel, and H.-J. Maag, ``Gun Propulsion
Concepts. Part I: Fundamentals'', Propellants, Explos., Pyrotech.
20, (6), 304Ä…310, (1995).
(4) H.-J. Maag and G. Klingenberg, ``Gun Propulsion Concepts. Part
II: Solid and Liquid Propellants'', Propellants, Explos., Pyrotech.
21, (1), 1Ä…7, (1996). (Received March 7, 1997, Ms 7=97)