[email protected]

Propellants, Explosives, Pyrotechnics 9, 91-107 (1984) 91

Experimental Study on the Performance of Pyrotechnic Igniters

G. Klingenberg

Fraunhofer-Institut fiir Kurzzeitdynamik, Ernst-Mach-Institut, Abteilung fur Ballistik (EMI-AFB), D-7858 Weil am Rhein (Germany)

Experimentelle Untersuchung der Leistung von Treibladungsanziin- dern

An speziellen Treibladungsanziindern der Dynamit Nobel AG mit vier verschiedenen Anzundmischungen (a) B-KN03, (b) Schwarzpul- ver, (c) Nitrozellulose und (d) Nitrozellulose/Schwarzpulver-Gemisch wurden Gasdruck, Temperatur und Geschwindigkeit an der Austritts- diise gemessen, um den Energiestrom zu ermitteln. Die Eigenschaften dieser Treibladungsanziinder wurden beim Abfeuern in Luft, in Treib- ladungspulver-Attrappen und in Schiittungen von Treibladungspul- vern untersucht. Es stellte sich heraus, daB der EnergiefluB an der Austrittsdiise entscheidend von der Verdammung abhangt. Beim Abfeuern in eine Schuttung nimmt der Energiestrom zu.

Etude exphimentale des performances d’allumeurs de charges propul- sives

Afin d’Cvaluer les performances d’allumeurs spCciaux de la SocittC Dynamit Nobel et de dtterminer le flux d’tnergie qu’ils sont suscepti- bles de produire, on a mesur6 la pression des gaz, leur tempkrature et leur vitesse d’6jection pour quatre diffkrentes compositions d’allu- mage, P savoir le B-KN03, la poudre noir, la nitrocellulose et un mClange de nitrocellulose et de poudre noire. Les caracttristiques de ces allumeurs ont CtC d6terminCes par des tirs P I’air libre, dans des grains inertes simulant la poudre et dans des lits de poudre. I1 apparaft que le flux d’tnergie P la tuytre de sortie dtpend fortement du confinement. I1 augmente sensiblement lorsque le jet de flamme est eject6 dans un lit de grains inertes ou actifs.

Summary

A special igniter case designed by Dynamit Nobel AG was used for measuring the energy output of four different igniter formulations in terms of gas pressure, flame temperature, and gas velocity in order to study the performance of pyrotechnic igniter systems, and to evaluate the energy flux at the igniter vent. Four igniter systems were defined which consisted of (a) B-KN03, (b) black powder, (c) nitrocellulose, and (d) mixtures of nitrocellulose with black powder. Firings into open air, propellant dummy loads, and propellant beds were carried out with these igniters to obtain their general characteristics. It has been found that the vent characteristics of these pyrotechnic igniters are determined by the confinement conditions used. The energy flux at the igniters vent increased considerably for firings into inert or active propellant beds.

1. Introduction

In order to achieve ignition of solid gun propellants, energy is required as an initial impetus. Pyrotechnic igniter systems venting a mixture of hot, pressurized gaslparticle flows into the propellant bed are usually employed in gun systems. The energy flux at the igniter vent induces ignition of the propellant grains until sustained combustion is achieved(’). In fundamental ignition studies, more information on the vent characteristics of pyrotechnic igniters is therefore desirable.

Basic ignition studies of solid gun propellants in West Ger- many have been coordinated since 1976. A panel of scientists was assembled from ballistic institutes, universities, and pri- vate industry; and a fundamental program was formulated with each group performing specific projects(’). These projects include the - construction and development of a special igniter system

- investigation of the processes occurring at the igniter vent, - studies on the effect of the igniter on the propellant bed, and - ignition modeling.

One of the cooperative tasks of the Ernst-Mach-Institut (EMI-AFB) and the German-French Research Institute (ISL)

0 Verlag Chemie GmbH, D-6940 Weinheim, 1984

with four different igniter compositions,

was to determine the vent characteristics of these igniters in terms of gas pressure, flame temperature, and gas velocities employing optical and pressure measurement techniques, radiative emission-absorption techniques, and a laser doppler velo~imenter(%~). Data were taken firing into open air as well as into inert and active propellant beds evaluating the energy output at the igniter vent for unconfined and confined conditions. In addition, studies on the effect of the igniters o n the propellant bed have been carried out. Prior to describing the experiments which have been conducted, the igniter chamber design is discussed and the selected igniter formulations are reviewed in light of the requirements.

PRESSURE 4

PORT

SUBSEQUENT I FLOW(IGNITER I COMPOSITION 1

PRECURSOR FLOW(INITIAL t IGNITER)

CYLINDRICAL IGNITER VENT

CONICAL PART OF THE NOZZLE

( D = 5 m m )

IGNITER COMPOSITION

TRANSVERSE FLOW CHANNELS

INITIAL IGNITER

ELECTRICAL IGNITION DEVICE

I J

Figure 1. Schematic of special igniter case indicating location of vent pressure (M 1) and flow path for igniter gases.

0721-31 15/84/0306-0091$02.50/0

92 G. Klingenberg Propellants, Exploswes, Pyrotechnics 9,91-107 (1984)

Table 1. Four Igniter Compositions

Code Name Quality Main Loading Heat of Contents Density Explosion

[g/cm31 [JI AZM Boron- Hot,Gas- 953-1 Potassium Poor

Nitrate Y 593 Black Cold, Gas-

Powder Poor

Mv NC- Hot, 'Gas- 7308 Powder Rich NKP-S NC Sulfur- Cold, Gas- 536 lessBlack Rich

Powder Mixture

70.7% KNO, 0.45 793 23.7% B

75% KNO, 0.90 793 10% s 15% C

98% NC 0.65 793

39% NC 0.85 792 47% KNO, 12% c

Table 2. Experimentally Determined Properties of Igniter Mixtures

Code Ignition Gas Heat of Activation Temperature Volume Explosion Energy [KI [cm31 [J'gl [kJ/mol]

AZM 953-1 848 194 6612 105

Y 593 696 208 3051 61.9

M V 7308 495 617 4288 25 1 NC NKP-S536 554 315 3298 I1 "2-C-KNOS

B-KNO,

S-C-KN03

2. Chamber Design and Igniter Formulations

A schematic of the special igniter case designed by Dynamit Nobel AG (DNAG) is shown in Fig. 1. The general objective was to control the internal combustion by means of the flow channels in order to obtain a better defined outflow at the igniter vent, and to load the igniter case with four different igniter compositions. An electrical device first ignites the initial igniter producing hot gases which initiate subsequently the igniter composition contained in the igniter case. The combustion gases pass through the transverse flow channels, merge in the conical part of the nozzle, and escape at the cylindrical igniter vent expanding into the surroundings. However, as revealed by these studies, there are some negative features associated with this Due to the inadequate confinement, part of the gases produced by the initial igniter do not interact with the igniter composition but escape through the transverse flow channels forming a precursor flow at the igniter vent, as indicated in Fig. 1. In addition, the transverse flow channels and the cone-shaped part of the nozzle causes rapid flow expansion within the igniter system enhancing possible condensation reactions which support precipitation of particulate matter at the inner walls and may increase the internal energy. Consequently, the energy output at the igniter vent is dependent on the internal combustion and flow development.

The criteria for selecting four different igniter formulations as defined by the ignition panel were to obtain the following igniter vent characteristics:

hot, gas-poor cold, gas-poor hot, gas-rich cold, gas-rich

In addition, the objective was to obtain one extremely particle-poor and one particle-rich outflow in order to study both the gas and gas-particle ignition. The question of characteriz- ing the igniter formulations was further discussed by the ignition panel, Of the possible parameters, i.e., heat of explosion, activation energy, reaction energy, and reaction enthalpy, the heat of explosion was chosen since it can easily be determined experimentally by a calorimeter. Therefore, it was decided to load the igniter so as to have equal heats of explosion for all four igniter formulations taking into account different loading densities.

To match these requirements the DNAG selected the following four igniter compositions:

Boron-Potassium Nitrate (B-KN03) Black Powder (S-C-KN03) Nitrocellulose (NC) Code: MV 7308 Nitrocellulose-Sulfurless-Black Powder Code: NKP-S-536

as listed in Table 1. To obtain equal heat of explosion of about 793 joules for all

four igniter formulations required apparently rather drastic deviations in the loading densities from 0.9 to 0.45. This results in varying ullages within the igniter composition con- tainer affecting the internal combustion. Thus, the internal effects of the inadequate confinement, rapid flow expansion, and possible incomplete combustion of the igniter composition may affect the energy output at the igniter vent. In particular, an effect on the vent characteristics is to be expected for firings into propellant beds, i.e. for confined conditions.

Experimental determinations of the specific heat of explosion and the activation energy by Brede(2) and Krien@) are shown in Table 2.

For unconfined conditions, Kuthe(') calculated the ther- modynamic data of the four igniter formulations by a thermochemical model using the ideal gas equation. In addition,

Code: AZM 953-1 Code: Y 593

(NC-C-KN03)

CONDENSATION PRODUCTS AT p = 20 MPo

t CONDENSATION

RE ACTIONS . . - BORON-

POTAS S IU M

0 a

1800 2600 8 0

'OOo TEMPERATURE [K]-

NITRATE

Figure 2. Thermochemical calculations at constant pressure of con- densed products in the four igniter formulations.

Propellants, Explosives, Pyrotechnics 9, 91-107 (1984) Experimental Study on Pyrotechnic Igniters 93

he assumed an expansion ratio of 200: 1, and an isentropic expansion in order to evaluate the influence of condensation reactions by a parametric study. Some of the results are shown in Fig. 2 and Fig. 3, which display the concentration of condensation products and the reaction enthalpy versus temperature at constant pressure p = 20 MPa. For B-KN03 with the cooling of the igniter gases a dramatic change of the condensation products occurs with a corresponding change of the reaction enthalpy for temperatures below 2400 K. Apparently, the condensation reactions release energy increasing the internal energy of the flow. For the B-KN03 composition AZM 953-1 a high concentration of condensation products is found to occur with the cooling of the igniter gases during expansion which is associated with an increase of reaction enthalpy . The nitrocellulose composition MV 7308 for a flame temperature above 1800 K shows no formation of condensation products. How- ever, due to the formation of soot particles an increase of the condensation products and a corresponding small change of the reaction enthalphy was found for temperatures below 1800 K, Fig. 2 and Fig. 3.

According to the simple approximations made, this analysis is only capable of predicting the general tendency of the reacting gas-particle flow. A more detailed description of the unsteady flow inside of and at the exit plane of the igniter case awaits the development of a 3-D-2-phase gas dynamic model including the chemistry. Nevertheless, it became obvious that due to the expected flow expansion within the transverse flow channels and the conical part of the igniter nozzle, the igniter vent characteristics will be partly dependent on internal condensation reactions.

3. Experimental

Experiments were performed when firing the four different igniters into open air, inert propellant beds, and a bed of propellant grains type A 5020. Special fixtures were used to permit recordings of the igniter output. About 100 ps after the electrical ignition pulse the first gases arrive at the igniter vent. The jitter of the time between electrical pulse and arrival of the gases was measured to be less than 20 ps. Time zero in

1 , REACTION ENTHALPY AT ~ = 2 0 M P o

2

c s -5000 I-\

Figure 3. Thennochemical calculation of reaction enthalpy at constant pressure (p = 20 MPa) for the four igniter formulations.

IGNITER PHOTOMULTIPLIER

SHUTTER LIGHT PIPE n

TUNGSTEN RIBBON LAMP

INTERFERENCE NEUTRAL DENSITY FILTER

FILTER

Figure 4. Scheme of set-up for spectroscopic temperature measurements.

these experiments is either the electrical ignition or the arrival of the gases at the igniter vent; i.e., about 100 ps after electrical ignition.

3.1. Firings into open air

In order to study the igniter vent characteristics the following experiments were performed:

- Pressure measurements using a PCB gauge at location M 1 (see (Fig. 1), i.e., in-case measurements 2 mm from the end of the igniter nozzle.

- Spectroscopic temperature measurements employing a modified line reversal technique at position x = 2.5 mm in front of the igniter vent.

- Gas velocity measurements by means of a new laser-Dopp- ler-velocimeter , devised by Smeets and George("$ within the gas outflow 2.5 mm in front of the igniter vent.

The employed experimental techniques for spectroscopic temperature and pressure measurements as well as velocity measurements are well established and were used in the field of ballistic studies. They are throroughly documented in References 10 to 14. No further detail will be given here except to mention that in the open air firings a special setup was employed for the modified reversal method to record the radiation flux from the primary flash with and without superimposed radiation of a calibrated tungsten ribbon lamp simultaneously by separating the imaged radiation through light pipes, see Fig. 4.

3.2. Firings into inert propellant beds

Since the internal combustion of the four different igniter compositions must be dependent upon the confinement conditions used, these studies were extended investigating the vent characteristics for firings into propellant beds. Firings into propellant dummy loads were carried out using the device shown in Fig. 5. Propellant grains made of plastics were used in this caliber 20 mm chamber. In order to measure the pressure and temperature within the cylindrical nozzle of the igniter case, a pressure port and optical windows were mounted into the chamber (see Fig. 5) . A line-reversal method employing an Argon laser was used to measure the temperature within the igniter vent. Also, corrections have been made to account for the window c~ntamination(~). A PCB pressure gauge was mounted into the pressure port to perform the igniter exit pressure measurements.

94 G. Klingenberg Propellants, Explosives, Pyrotechnics 9,91-107 (1984)

3.3. Firings into active propellant beds

In order to study the effect of these igniters on the propellant bed the caliber 20 mm chamber was built into a gun system (see Fig. 6).

INERT PROPELLANT 0 3.5 35 - r,

\

rn Figure 5. Test device for firings into inert propellant beds.

The gun chamber was filled with 34.2 g propellant grains of type A 5020 (loading density 0.9). This conventional 20 mm gun propellant is composed of nitrocellulose with small amounts of chemical additives. The four different igniters were fired into this propellant bed. A conventional caliber 20 mm projectile, mounted into the top of the cartridge cas- ing, was further used in order to keep the case extraction force. The projectile has a weight of 120 g and a length of 91 mm. The barrel length of the gun was 1.836 m. PCB- pressure gauges were mounted at locations M 1, M2, M3, and M4, i.e., inside the case of the igniter at its vent and along the gun chamber (see Fig. 6). Pressure histories were measured simultaneously for all four locations M 1 and M4.

As a final test light pipes were mounted inside of the caliber 20 mm gun chamber using the pressure ports M3 and M4; Fig. 7. These light pipes have been placed into the propellant bed A 5020 at two different positions; namely, at the igniter vent, and at an axial distance of x = 35 mm from the igniter

PRESSURE WRTS

E WITH END PORTION

CHAMBER 38 0 cm3 PROPELLANT :34.2 9 A5020

Em LOADING DENSIN: 0 9

Figure 6. Caliber 20 mm gun system equipped with the special igniter.

LIGHT PIPE I

TLANZ f-0 LIGHT PIPE I1

CHAMBER : 38.0 cm3 PROPELLANT : 34.2 g A5020 LOADING DENSITY : 0.9

Mgure 7. Caliber 20 mm gun system equipped with light pipes for emission measurements.


vent. Both light pipes were facing the axial flow. Light emission stemming from the igniter gases and the combustion processes occuring within the propellant bed could be recorded by means of photomultipliers.

3.4. Energy flux at the igniter vent

From the measured flow parameter at the igniter vent, the energy flux at the igniter vent can be calculated using the equation given by Celmins(”) for a cylindrical nozzle:

dE dt

dm -- - m = A e, u, dt

where A = n? denotes the area of the vent, e,, T,, and u, the vent characterictics (e, = f(p)), and C, the specific heat for p = const. Since the pressure, temperature, and gas velocity histories p,, T,, u, versus time are known from experiment, and c, can be derived from thermochemical calculations the energy efflux E can be evaluated. However, one has to be cautious about interpreting the results. Even if the real measured data are used including effects of condensation reactions the role of the gas-particle flows is neglected since Eq. (1) was derived

BORON- POTASSIUM NITRATE BLACK

from gas phase calculations. As we shall see below, the flow- borne particles contribute significantly to the energy flux at the igniter vent.

4. Results

4.1. Firings info open air

Earlier in-case measurements of pressure histories at locations within the transverse flow channels and M l (see Fig. l ) performed by DNAG and EMI-AFB, revealed that a drastic pressure decrease occurs from the transverse flow channels to M1 (igniter vent) indicating the rapid flow expansion in the conical part of the nozzle(3). Table 3 summarizes the results for average peak values of pressure.

Consequently, an effect on the vent characteristics is to be expected, especially in the case of the B-KN03 composition AZM 953-1, consistent with the thermochemical calculations, mentioned above. The results of pressure, temperature, and gas velocity meas-

urements at the igniter vent are shown in Figs. 8 a, b. Since the precursor gases stemming from the initial igniter output arrive first at the igniter vent for to < t 5 30 ps (to = arrival of igniter gases at the igniter vent), the same vent characteristics were obtained with peak values of p = 2 MPa, T = 2700 K to 2800 K, and v = 1600 m / s for all four igniter formulations indicating the effect of the initial igniter gases.

POWER T P [XI [MPoI T p 1 PRECURSOR GASES

[F] 2aoo: IGNITER COMPOSITION

[ M P a ] 2 GASES PRODUCED BY THE

‘”1 3 CONDENSATION REACTION t I‘ Pe

L.r.’~MLOCITY - 900 - 800 1600- - 2

--0s I - -01 , I I I I 1 I I I -

0 200 LOO 0 200 LOO

N ITROCE LLU LOS E NC- BLACK POWDER MIXTURE T P

--Pe

-‘-Ue - [m/sl

----Te U

2500- 1 I ‘-TEMPERATURE

-PRESSURE 2000 - - 8

- - : L ’--- ’\

1600-- - goo

0 200 100

‘\;GAS VELOCITY .- -. ‘.

--0.1 I I I I 1 3

T D r m1 [M-I 2800- .- Pe

U

- 1600

--_- Te --ue [GI 1 - b

2100- 1‘1 :-TEMPERATURE

- t t ?.--.-.-- -_ GAS VELOCITY L --

i - - 2

- aoo 1600- - . I I I

-4 .1 ‘. 0 200 LOO

t (psi - (b) t [ P I - ptnm

Figures 8a, b. Igniter exit pressure, temperature, and velocity versus t.

96 G. Klingenberg Propellants, Explosives, Pyrotechnics 9, 91-107 (1984)

The second pressure increase is associated with the arrival of the igniter composition gases at the igniter vent at t 2 30 ps. Fig. 8 a displays further the effect of condensation reaction occurring inside of the igniter case for the igniter formulation potassium boron nitrate (AZM 953-1). About t = 200 ps after t~ a maximum occurs in the temperature-time history associated with the minima of pressure and gas velocity. This shows the effect of condensation reactions on the flow. Small effects of the condensation reactions were also found in the case of the black powder formulations Y 593 and the NC-black powder mixture NKP-S, while the nitrocellulose produced very little particulate matter during expansion.

A different behavior is displayed in the p,T,u-curves of the nitrocellulose composition MV7308 (Fig. 8 b) indicating that the internal combustion is not complete. The second temperature peak at t = 40 ps first approaches the calculated maximum flame temperature of 2600 K. However, a rapid decrease of T follows, associated with a relatively slow pressure increase and a rapid decrease of gas velocity. The first layer of the previous nitrocellulose is fully ignited and reaches the flame temperature. Due to inadequate confinement the grains (0.3 mm to 0.4 am diameter) move into the flow passage which becomes clogged with individual grains causing a quenching of the reac- t i o n ~ ( ~ , 9.

The calculated energy efflux for 30 5 t I 400 ps is shown in Fig. 9. Considering the restrictions discussed above, for open air firings the “hot” igniter compositions nitrocellulose (MV7308) and B-KN03 (AZM9.53-1) are found to produce higher energy output than the “cold” black powder formations Y 593 and NKP-S. The data in Fig. 8 does not include the effect of the precursor flow coming from the initial igniter device. Table 4 compares the precursor energy (Epr) with the igniter energy (Eig). These were obtained by a time integra- tion of the data in Fig. 8. The igniter energy (Eig) is also compared with the total energy calculated from the thermochemical model (Ec). The effect of the precursor (5 joules) is small compared to the high energy output of the igniter composition gases.

However, measurements performed in the ISL have shown that the particle flow contributes significantly to the energy flux at the igniter vent@).

Table 5 compares the mass efflux of the gases mg with the mass efflux of the articles mp as evaluated from these experiments for the time81 interval1 0 5 t I 400 ps. Also, the ratio of mp to the mass mL of the igniter composition load and the energy contribution of the particles E, ejecting at the igniter

Table 3. Pressure Measurements in Igniter (see Figure 1)

Maximum Gas DNAG (Trans- EMI-AFB Pressure Pressure Obtained verse Channels) (M 1) Decrease to Along Transverse Igniter Vent Channels and Nozzle Vents

AZM 953-1 24.8 MPa 4.8 MPa 1/5 (B-KNOJ Y 593 13.7 MPa 4.8 MPa 1/3 (Black Powder) MV 7308 46.6 MPa 11.0 MPa 114

NKP-S-536 27.0 MPa 3.7 MPa 1 /7 (NC-Black-Powder)

(NC1

2 200

U t %. h -BLACK POWDER 5 ‘oo[ POWDER NC-BLLCK MIXTURE \ 50

Figure 9. Energy flux at the igniter vent for 30 5 t 5 400 ps (particulate matter is not considered).

Table 4. Experimental and Theoretical Values for Igniter Output Energies

Precursor Flow Igniter Flow (Initial Ignition (Igniter Devices) Compositions) Epr EpriEig Eig Ec EigiEc [JI [%’.I [JI [JI [%I

B-KN03 (AZM 953-1) 5 2.8 178 540 33 Black Powder (Y 593) 5 5.7 88 580 15 Nitrocellulose (MV 7308) 5 1.1 458 720 64 Nitrocellulose-Black Pow- 5 7.3 68 565 12 der (NKP-S)

vent as well as the added energy efflux Epr + Eig + Ep is given.

These particles are due to combustionlcondensation reactions occuring within the igniter case and at the nozzle. A considerable amount of particles is produced by the initial igniter (precursor); in particular, for the composition MV 7308. The particle flow contributes about 60 joules to the energy output of the igniter compositions AZM 953-1, MV 7308, and Y 593 while 90 joules are contributed by the particle flow of the NKP-S composition(6, ’I. Apparently, in these open air firings the addition of the particles contribution to the energy efflux does not alter the sequence: MV 7308, AZM 953-1, NKP-S, and Y 593.

4.2. Firings into inert propellant beds

The mean values of the measured igniter exit pressure histories obtained for both the firings into (a) open air, and (b) inert propellant beds are compared in Fig. 10. Apparently, the vent pressure increase considerably when firing into inert propellant beds, i.e., for confined conditions. Concurrently, the average igniter exit temperature increases for confined conditions; Fig. 11.

However, significant deviations in the pressure and temperature data occurred from shot to shot indicating that the internal combustion of the igniter compositions varies considerably


9 -

8 .

t :: s 5 -

P[MPa] t\ AZM 953 - 1 ‘ ‘\ I \ Y - 593

I \

8 ’ P [MPo]

I :: I \ \

k! 5 - I ‘Jb I \

0 100 200 300 400 “us] TIME -

MV 7308

n I \

22

3 4 - w $ L -

E 3 - W

E 3 - 1.

2 - 2 - -. 1 - 1 -

OJ -

16 - W $ 1.4 - v) !$ 12 - a

10 -

8 -

6 -

4 -

2 -

-- --

; ‘\ 1 . I \

\ I

I I

I 0 100 200 300 LOO ‘[us]

TIME -

c 1 0 100 200 300 LOO t[ws] 0 100 200 300 COO tb]

TIME - TIME - Figure 10. Igniter exit pressures versus time for firings into (a) open air, and (b) inert propellant beds.


2800-

I 2600-

2100- cc 3

(L

c a 2200-

t! z w 2000- t

1800-

1600-

4.3. Firings into active propellant beds

First, pressure measurement were made using inert propellant grains in order to test this setup. Also, these additional firings into propellant dummy loads were made to confirm that the scatter of the data is not due to grains that move into the flow passage of the igniter vent clogging the passage with individual grains. This is not the case in these experiments. How- ever, the preliminary measurements confirmed that the igniter vent pressures deviate considerably from shot to shot if confined conditions are used. For example, Fig. 14 shows the results of four tests with the igniter composition nitrocellulose (MV 7308) and the NKP-S composition when firing into inert propellant beds. Time zero (t = 0) in these and the following

Te

Kl 2800-

1 2600 - w 5 2100 -

2 2200 - E

t Q w

I

2000 -

1800 -

AZM 953-1 Te

experiments is the electrical ignition. The same deviations in the igniter vent pressures were obtained when firing into active propellant beds. Figure 15 shows a sequence of pressure recordings at the igniter vent, i.e., four firings for each igniter composition. Obviously, the igniter exit pressure is not reproducible but varies for each firing into the propellant bed. Vari- ations in the arrival of the igniter gases at the igniter vent and in the histories and peak values of pressures are characteristic for the discharge of these pyrotechnic igniters into inert or active propellant beds.

The interaction of the gadparticle flow vented from these igniters into the propellant bed and in the ignition and combustion occurring within the gun chamber was also investi- gated. Figures 16 a, b show for four tests the pressure histories

2800-

2600 -

f 2 L M ) -

k!

If 2000-

!!i

3 2200-

5 I

1800 -

1600 -

11M) -

Te

K]

1600 i

2600 -

t 2100- w (L 2

2200-

E I 2000- W t

1800 -

Y -593

0 100 200 300 LOO 500 0 100 200 3M) L 00 500

TIME - WSI TIME - t [ps ]

MV 7308

PRECURSOR GASES

2*00{ 6 I I

1100

NKP-S

PRECURSOR GASES I

I , I I I 1 ,

0 100 200 300 L 00 Mo 0 100 I O G 396 LOO :m

TIME- t[psl TIME - t [ps]

Figure 11. Igniter exit temperatures versus time for firings into (a) open air, and (b) inert propellant beds.

Propellants, Explosives, Pyrotechnics 9,91-107 (1984) Experimental Study on Pyrotechnic Igniters 99

2200-

2000 -

1800 -

measured at locations M1, M2, M3, and M 4 (see Fig. 6) using the same test numbers as in Fig. 15. For 0.5 < t c 30 ms the pressure increase at M 1 (igniter vent) is due to the arrival of a pressure wave generated by the ignition and combustion within the gun chamber. The first pressure rise at M 2 is caused by the igniter gases arriving at this location. Subsequently, the pressure increases and a pressure wave travels from M 2 to M 4 due to the ignition and sustained combustion establishing within the propellant bed. With increasing igniter exit pressures the ignition delay decreases. The maximum gas pressures amount to about 280 MPa. For example, Fig. 17 shows the peak pressures recorded at location M3. The pressure profiles p versus axial distance x along the gun chamber are shown in Fig. 18. These profiles were derived from the p versus t recordings of Fig. 16.

1bOO -

1400 -

We can now construct the following qualitative picture. When the hot gadparticle flow is vented into the propellant bed an igniter pressure wave moves downstream. The actual ignition of the propellant grains occurs at some distance from the igniter vent, i.e., after the gadparticle flow is decelerated thus permitting the pyrolysis and subsequent sustained combustion of the grains. The combustion of the grains generates the main pressure wave that propagates downstream through the propellant bed attaining a maximum after a few ms. The generation and propagation of the pressure wave is dependent upon the energy efflux at the igniter vent. However, in these tests each firing produces results which are only applicable to ~

the particular test because the igniter output is not reproducible (see Fig. 15). For example, Fig. 19 shows the variations of the igniter exit peak pressures as measured when firing the

"1 TYPICAL A TEHPERATURE + OATA

28004$j a001 Y- 593 AZM 953-1 TYPICAL

I 2mol a O f

2400- 5 t

I z200- I 2000-

1800 . 0 + xo d

1800 { 1600 4 1bOO { ,Loo{ lLOO 4

1 0 100 200 300 Loo 500 0 100 200 300 Loo 500

TIME - t k s ] TIME- tb~]

0 TYPIUL i} OATA TEMPERATURE MV 7308 Te NKP - S

2800{ +j

2400 - 3 I - 2 2200-

Q w

!g 2000-

2L00j A w

A

t o A x t I A "P 9

lbo0l lLOO

I , 0 100 200 300 LOO 500

TIME - t [ps]

1 0 100 200 300 400 500

TIME- t[pS]

Figure 12. Typical igniter exit temperature data as obtained when firing into inert propellant beds.

100 G. Klingenberg

X

3 LL 200- >

8 W 100-

50-

Propellants, Explosives, Pyrotechnics 9, 91-107 (1984)

four different igniter composition types into (a) open air, (b) inert propellants, and (c) active propellants (A 5020). The drastic variations of the igniter vent peak pressures for different firings are quite apparent from Fig. 19. Obviously, the internal combustion in the igniter case is highly dependent

500 0

2000

1000

1 500

X

3 LL

(3

w Z W

> 200 a

10 0

50

20

E AZM 953-1 [ITS J

0 100 200 300 400

lpEprm TIME - 1 [PSI

5000

2000

1000

1 500

X 3

c i 200

3 100

5 W

50

20

E __ k J k ]

upon the confinement condition used. Most severe fluctua- tions of igniter vent characteristics have been observed when firing the composition nitrocellulose ( M V 7308). This particular igniter composition consists of large porous NC-grains of diameter 0.3 mm to 0.4 mm. Therefore, the internal combus-

Y- 593

100 200 300 400 TIME - t [ F J

2000-

1000:

1 5 0 0

X

3

8 200- >

W Z W 100-

50-

NKP-5

20 1 I 0 100 200 300 400

t IPS1 TIME - Figure 13. Energy flux at the igniter vent versus time for firings into (a) open air, and (b) inert propellant beds.


10-

8 -

6-

L -

2-

OJ

Experimental Study on Pyrotechnic Igniters 101

7

tion is already incomplete when firing into open air(3), and its dependency on the confinement conditions is more pro- nounced.

Nevertheless, the results of different tests provide some comparison between the different types of pyrotechnic composition. The correlation between the time integral of the igniter exit pressures versus ignition delay is shown in Fig. 20. Here, ignition delay t2 is defined as the time between the arrival of the igniter flow at its vent and a 10% increase of pressure at locations M2, M3, and M4, respectively. The example shown in Fig. 20 uses the tz-data measured at location M3. It shows once more the scatter of the data for each firing. The same correlations were obtained for the Jpdt or igniter vent peak pressures versus tz, measured at locations M 2 or M 4. Apparently, the “gas-rich’’ igniter compositions nitrocellulose (MV 7308) and the nitrocellulose/black powder mixture (NKP-S) produce higher vent pressures and corresponding shorter ignition delays than the “gas-poor’’ igniter compositions B-KN03 (AZM 953-1) and black powder (Y-593). How- ever, there is no essential difference between the data obtained for the firings with NKP-S and AZM 953-1. This is consistent with the energy efflux at the igniter vent, evaluated for confined conditions (see Table 6).

AZM 953-1

( 0 ) p,,,,, : 11.5 MPh TEST 14

( b ) 8 , : 7.5 I( 10

( C ) : 5.8 8 . ’ 15

(d) .. : 5.9 . . . . 11

”1 p[MR1 Ka

....... ........_..... .-.. ......

o 0.1 0.2 a3 0.4 0.5 0.6 0.7 a8 0.9 1.0 “msl

M l ; TLANZ : B - K W ; TLP: A5020 (34.29) Y-593

(a) pm,, : 10 MPh TEST 30

(b) I * : 7 .. 25

( c ) .. : 6.5 .. ’* 27

(d) - 8 . 3.2 31

M I ; TLANZ : S-C-KN03 ; TLP : A 5020 (3620)

MV 7308

(a) pmax : 50 M R TEST ’ 23

(b) 8 . 42 .* .. ‘22

...................... ,--*:.aq*/;-.yz:x. ..:’-.... I..-..- o 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 as 1.0

t [m51

- ..-. __c 01

M 1 TLANZ : NC; INERT PROPELLANT

NKP-5

p t M k 1 (a) hX : 12.5 M R

(b) : 10.0 (c) : 6.6 * I

(d) 8 . : 4.3 *. 12

t [=I ReP21(1 M 1 TLANZ INC-C-KNO~ ; INERT PROPELLANT

Figure 14. Igniter exit pressures versus time for firings into inert propellant beds using the set-up of Fig. 6 (igniter composition MV 7308, and NKP-S) .

20

10

0.1 0

...-.....- ....... --. ....... ” ....-.-._... . _.....” ..... *- --

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

( 0 ) pmax : 16 MPo TEST 37

( b ) .. : 8 . . . . 19

( C ) .. : 6 . . . . 16

(d) .. : 38 .. x) 12

... ............. -- ........... .......-_ 0 0.1 0.2 0.3 ’0.4 0.5 (16 0.7

0.1 0.8 as 1.0

Figure 15. Igniter exit pressures versus time for firings into active propellant beds (propellant A 5020).

t[m*I IEOS M 1 ; TLANZ : NC-C-KNO, j TLP : A 5020 (34.29)


I PWQI AZM 953-1

TESl 10

10 -

0 05 10 I5 2.0 2 5 30 1 [msl

Am 953-1 1151 t L

Y-593 TESl 25

M L

Y-593 TEST 30

' P S I

Figure 16a. Pressure histories measured at creatives M 1 to

AZM 953-1 lE51 I I

I

25 30 35 LO L5

+=I

AZM 953-1 I t . 1 11,

v-593 TEST 27

1 4

Q 1 2 3 L 30 LO 50 P I

Y-593 TEST 31

P S I

M 4 for firings into active propellant beds (propellant A 5020).


-


. I24 I25 126 127

TEST 1

15

10

5 f 0.1 0

MV 7308 TEST 23

I 1.8 2.0

P S I

MV 7- TEST 39

I 30-

25.

20.

M L

0 a2 0.L 0.6 0.8 1.0 1 2 1.4 16 1.8 2.0 ' P S I

NKP-S WP- s

NKP- s NK P- S TEST 37

M4 L 1.L 1.6 1.8 2.0

TEST. 20 PI*]

10.

8-

6-

0 (12 LIL (16 Q8 1.0 1.2 1.4 1.6 1.8 2.0 0 (12 0.6 0.6 0.8 1.0 1.2 1.1 1.6 18 2.0 - + = I t b l

Figure 16 b. Pressure histories measured at locations M 1 to M4 for firings into active propellant beds (propellant A 5020).

TEST 20 I PI*]

lo]

- .

..Y I I 8-

6-

0 (12 LIL (16 Q8 1.0 1.2 1.4 1.6 1.8 2.0 0 (12 0.6 0.6 0.8 1.0 1.2 1.1 1.6 18 2.0 - + = I t b l

Figure 16 b. Pressure histories measured at locations M 1 to M4 for firings into active propellant beds (propellant A 5020).

104 G. Klingenberg Propellants, Explosives, Pyrotechnics 9,91-107 (1984)

150-

100-

50-

AZM 953-1 TEST 1L

P [ M h I

2501 200 i \ Y-593 TEST 30

0.1 - 0 1 2 3 L 5 6 7 23 2L 25 26 27 28 29 30

MV 7308 TEST 38

I P [ M ~ I

3001 250 n TEST 37

1004 I loo{ I \

Figure 17. Pressure histories at location M 3 (peak pressures) for firings into active propellant beds (propellant A 5020).

Since the performance of a gun is usually measured in terms of the attained launch velocity VO, Fig. 21 shows the vo versus t 2 recordings. The scatter of the data is comparable to that shown in Fig. 20. In the average, however, the “gas-poor’’ igniter composition B-KN03 (AZM 953-1) results in higher launch velocities than the “gas-rich’’ composition nitrocelluloseiblack powder mixture (NKP-S), indicating that a clear correspond- ence between the ignitionlcombustion processes within the gun chamber and the gun performance is difficult to obtain.

First results of the emission measurements are finally shown in Fig. 22. Both the emission E and the corresponding pressure versus t, measured at location M 1 at the igniter vent, are shown on the upper half of Fig. 21 using different magnifi- cations. Significant light emission is observed to occur with the arrival of the combustion pressure wave, i.e., after the ignition wave has interacted with the propellant bed. The onset of light emission on the lower half of Fig. 21 at an axial distance from the igniter vent of x = 35 mm occurs at t = 3.8 ms after to (b = arrival of igniter gases at the igniter vent) and is associated with the arrival of the combustion pressure wave. These preliminary studies show that emission measurements within the active propellant bed provides a mean to study flame spreads and may be even used to evaluate temperature dis- tributions.

5. Summary and Conclusions

The various tests described in this paper have proved useful in initial studies to characterize the ability of pyrotechnic igni-

ters. Experimental techniques have been developed and applied that show an excellent potential for determining the energy flux at the igniter vent. However, each test produces results which are strictly only applicable to the particular geometry and environment of each test. The results of different tests provide some comparison between different types of pyrotechnic composition. For example, the results from the firings into active propellant beds have given quantitative support to the long held view that ignition is favoured by using highly pressurized, hot igniter gases producing high energy efflux at the igniter vent. For these particular caliber 20 mm firings it can be concluded that the “hot, gas-rich, and particle- poor” nitrocellulose MV 7308 igniter composition produce the minimum ignition delay followed by the “cold, gas-rich, and particle-rich” composition nitrocellulose-black powder mixture NKP-S, the “hot, gas-poor, and particle-rich’’ boron- potassium nitrate AZM 953-1 and, with a rather long ignition delay, by the “cold, gas-poor, particle-poor’’ black-powder composition Y 593. These results demonstrate the need for a defined igniter output. However, the goal to produce well- controlled reproducible igniter vent characteristics has not been achieved with this special igniter case. On the contrary, the energy efflux at the igniter vent is highly dependent upon the environment. Apparently, the internal combustion in the igniter case is determined by the confinement. The packed propellant bed at the igniter vent forms a rather undefined boundary changing the vent characteristics for each firing. A confinement should be implemented to improve the performance. Therefore, recommendations are made to alter the igniter device. Recognizing the constraints which have been

Propellants, Explosives, Qrotechnics 9, 91-107 (1984) Experimental Study on Pyrotechnic Igniters 105

AZM 953-1 Y - 5 9 3 MV 7308

NKP-S

M1 M2 M3 ML x[cm]

I ,” 30 a Q

>

0

0

8

x : AIR

0 TLP-INERT

: T L P - A 5 0 2 0

0.1 4 I I I I

AZM 953-1 Y - 5 9 3 MV 7 3 0 8 NKP S

Figure 18. Local pressure profiles within the 20 mm gun chamber. Figure 19. Variations of igniter exit peak pressures for firings into (X ) open air, (0) inert propellant beds, and (.) active propellant beds (A 5020).

outlined above, the new igniter design shown in Fig.23 is proposed. This design avoids the flow channels, and the initial igniter output interacts immediately with the igniter composition. In addition, a burnable burst membrane forms the confinement until the main internal combustion reactions have . 1980. taken place. Thus, a better defined igniter output is to be expected.

6. References A. K. Kulkami, M. Kumar, and K. K. Kuo, ‘‘Review of Solid Propellant Ignition Studies”, AIAAISAEIASME 16th Joint Pro- pulsion Conference, Hartfort, Connecticut, June 30-July 2 ,

(2) U. Brede, “Comparison of Ignition Behavior of Various Primer Mixtures on the Basic of the Interupted Burning Method”, 4th

106 G. Klingenberg

2 -

1-

0.5 -


t pdt

5 J-

0 0 0

b 00

X

X

0

0

0

X

ox

AZM 953-1 0.12 9 BORON-POTASSIUM NITRATE

Y - 5 9 3 0.269 BLACK POWDER

MV7308 0.1859 NITROCELLULOSE

NKP-S 0.249 NC-BLACK POWDER MIXTURE

Q ( X ;

X X

0

0

00

0 0 0

0 0

0.3 7 I I v I I 1 1 1 1 1 1 I ( I ,

1 2 5 10 20 50 loo Figure 20. Integral of igniter exit pressure- IGNITION DELAY - t2 [msl time curve versus ignition delay t2.

0.6

I 880

c U 0 w > I U z 3 U J

w

-I 870

1 + 860 U W

0 E

T

n

850

v o l m l s l 0

x : AZM 953-1 0.12 g BORON-POTASSIUM NITRATE

: MV7308 0.1859 NITROCELLULOSE o : Y-593 0.269 BLACK POWDER

: NKP-S 0.2bq NC-BLACK POWDER MIXTURE

0 x X 0

X

X

0

b X 0

x x 0

0

0 0 0 0 0

0 b

0

Figure 21. Launch velocity of the projectile 0.6 1 2 5 10 20 50 100 IGNITION DELAY - t2 [ m s l v,, versus ignition delay t2. p s - m

International Symposium on Ballistics, Toulouse, France, April 1980.

(3) G. Klingenberg and 0. Wieland, JJntersuchungen der Eigen- schaften von vier Experimentier-Treibladungsanziindern beim Abfeuern in den freien Raum“, EMI-AFB Report No. V 9/79, 1979.

(4) G. Klingenberg and 0. Wieland, ,,Bestimmung der Eigenschaften von vier Experimentier- Treibladungsanziindern beim A bfeuern in Pulverattrappen und Treibladungspulver A 5020“, EMI-AFB Report No. 9/82, Dec. 1982.

(5) G. Klingenberg, “Energy Output of Different Pyrotechnic Igni- ter Systems”, 7th International Pyrotechnics Seminar, Vail, Col- orado, 14-18 July, 1980.

(6) H. Mach, U. Werner, and H. Masur, “Bestimmung von Masse- und Energiestrom des kondensierten Anteils von Anziindschwa- den“, ISL-Report R 106/81, 1981.

(7) G. Klingenberg and H. Mach, ,,Bestimmung der durch das Anziindelement gegebenen Anfangsbedingungen fur die Anziin- dung einer Schiittladung“, EMI-AFB Report No. E 1/82, 1982.

(8) G. Krien, ,,Physikalisch-chemische Daten von Anziindmischun- gen“, Bundesinstitut fur chemisch-technische Untersuchungen (BICT), Swisstal-Heimerzheim, Report 3.0-3/4369/77, 1977.

(9) R. Kuthe, ,,Thermodynamische Berechnungen der Anzundmi- schungen“, DNAG Report 1977.

(10) G. Smeets and A. George, ,,Instantaneous Laser-Doppler Ve- locimeter Using a Fast Wavelength Tracking Michelson“, Rev. Sci. Instrum. 49, 1589 (1977).

(11) G. Smeets and A. George, “Spectrometer for Instantaneous Doppler Velocity Measurements”, J . Phys. E., Sci. Instrum. 14, 838 (1981).

(12) G. Klingenberg and H. Mach, “Investigation of Combustion Phenomena Associated with the Flow of Hot Propellant Gases.

Propellants, Explosives, Pyrotechnics 9,91-107 (1984)

- 7.3 2 - 5.9 g - 4.1. 5

-1.4 5

1

- 2.9 m

m - 0.1 -

C 0 I? E W

-438.8 g -365.7 f -292.5

c

-219.L 2 -1L6.3 - 73.1 2 - 0.1

-

!i ’ 1.b ’ 2 b $0 4.0 5.0 t lmsl I

Light pipe positioned in the igniter vent

- 438.8 -365.7 -292.5 5 -219.L

m -116.3 ’

& - 73.1 .: - 0.1 -

m

C 0

In In .-

._ E w

E l

C 0 In VI

._

._ E W

- 0 1.0 2.0 3.0 1.0 5.0 t [msl

Light pipe a t x = 3 5 m m Vl 1

2.0-

b ’ 1:O 2:O ’ 3.0 1.0 5.0 t Imsl I

IPEPZ211 Light pipe a t x = 3 5 m m

Figure 22. Light emission E within the propellant bed and pressure versus time.


BURST MEMBRANE

MEMBRANE

IGNITER COMPOSITION

MEMBRANE

INITIAL IGNITER

IGNITER CASE

- 1

Figure 23. Igniter system design proposed for basic ignition studies.

I. Spectroscopic Temperature Measurements Inside the Muzzle Flash of a Rifle”, J. Combust. Flame 27,163-176 (1976).

(13) G. Klingenberg, “Investigation of Combustion Phenomena Associated with the Flow of Hot Propellant Gases. 111. Experi- mental Survey of the Formation and Decay of Muzzle Flow Fields and of Pressure Measurements”, J . Combust. Flame 29,

(14) G. Klingenberg, H. Mach, and G. Smeets, “Probing of the Unsteady Reacting Muzzle Exhaust Flow of 20 mm Gun” AZAAI A S M E Third Joint Thermophysics, Fluids, Plasma and Heat Transfer Conference, St Louis, Missouri, June 7-11, 1982, Print

(15) A. Celmins, “Theoretical Basis of the Recoilless Rifle Interior Ballistic Code ‘REGRIFF”’, Ballistic Research Laboratory (BRL), Aberdeen Proving Ground, Maryland 21005, BRL-Rep. No. 1931, 1976.

289-309 (1977).

ASME 82-€IT-34.

(Received February 8, 1983)

[email protected]

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