Hot-Metal Simulating Igniter for In-Bed Thermal 

Initiation of Granular Charges 

by Stephen L. Howard 

ARL-TR-5276 August 2010 

Approved for public release; distribution is unlimited. 
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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5066 

ARL-TR-5276 August 2010 

Hot-Metal Simulating Igniter for In-Bed Thermal 

Initiation of Granular Charges 

Stephen L. Howard 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
ii

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August 2010 

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June–August 2009 

4. TITLE AND SUBTITLE 

Hot-Metal Simulating Igniter for In-Bed Thermal Initiation of Granular Charges 

5a. CONTRACT NUMBER 

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5c. PROGRAM ELEMENT NUMBER 

6. AUTHOR(S) 

Stephen L. Howard 

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622618.H8000 

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U.S. Army Research Laboratory 

ATTN: RDRL-WML-D 

Aberdeen Proving Ground, MD 21005-5066 

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ARL-TR-5276 

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Approved for public release; distribution is unlimited. 

13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

An igniter simulating the effects of penetrating hot-metal fragments into a granular propellant bed was designed, constructed, 

and tested. This primer was designed to facilitate the characterization of the ignition and early-time combustion processes in a 

large-caliber propellant charge confined in a closed chamber which was initiated by an in-bed hot ignition source. The primer 

was used to simulate the situation when charge ignition occurs by a hot fragment that penetrated the chamber wall and 

remained within the propellant bed. Experiments showed that an igniter composed of micron-sized particle thermite powder 

(Al/Fe2O3) surrounded by ball powder propellant contained in a cloth tube initiated simultaneously by multiple electrical 

matches was capable of providing proper ignition stimulus to the propellant charge. 

15. SUBJECT TERMS

ballistic simulator, primers, MIC, thermite, shipping container 

16. SECURITY CLASSIFICATION OF: 

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OF ABSTRACT 

UU 

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OF PAGES 

14 

19a. NAME OF RESPONSIBLE PERSON

Stephen L. Howard 

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Unclassified

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410-278-6098 

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iii

Contents 

List of Figures iv

Acknowledgments v

1. Introduction 1

2. Experimental Development 1

3. Results and Discussion 3

4. Summary 4

Distribution List 5 
iv

List of Figures 

Figure 1. Igniter schematic and photo. ............................................................................................2

Figure 2. Flame development of igniter in open air. .......................................................................4
v

Acknowledgments 

The author would like to express his appreciation to Dr. Lang-Mann Chang for his assistance and 

direction. 
vi

INTENTIONALLY LEFT BLANK. 
1

1. Introduction

There are a number of current efforts in the U.S. Military aimed at achieving insensitive 

munitions compliance. One such effort is the development of venting technologies for metal 

cartridge cases and metal storage/shipping containers of large-caliber propellant charges. The 

design goal is to reduce or eliminate a violent reaction of the propellant charge when it is 

subjected to extraordinary stimuli such as intense heat, impact, or shock. 

For this purpose, a low-impact, hot-metal igniter was designed, constructed, and tested to prove 

its adequacy in providing the stimulus akin to that seen when a hot-metal fragment penetrates 

and reposes in a large-caliber propelling charge inside of a standard shipping container. Design 

metrics included ignition delay, consistent ignition stimulus over the simulated penetration track 

of the simulated hot-metal fragment, and temperature of the reacting ignition materials that 

would be comparable to the myriad of oxidizing metal particles formed upon impact of the fastmoving fragment with the steel shipping container. After the completion of this design study, a 

low-impact, hot-metal igniter was used in a large-caliber propelling charge shipping container 

simulator with exceptional success.1

2. Experimental Development 

Prior art in the simulating of the penetrating and reposing of a hot-metal fragment in a propelling 

charge used a thermite igniter with commercial-off-the-shelf (COTS) thermite powder.2 This 

igniter was very slow (tenths of a second) and non-uniform in providing spatially consistent 

ignition stimulus. At the time of the current development, the COTS thermite powder was not 

available and so a replacement material was designed. The replacement material still used the 

primary components of the COTS material, but the particle size was reduced and the mixing 

process was modified. 

A spherical aluminum powder with an average particle size of 3.0–4.5 μm with a 97.5% metal 

content was mixed with an iron oxide (Fe2O3) powder with an average particle size of 

 –325 mesh (<44 m). The powders were mixed gently in proportions of approximately 1:3 

(Al/ Fe2O3) on a mass basis. Ethyl alcohol solvent was added to wet the paste and the mixture 

was placed in an ultrasonic bath for 30 min. The ultrasonic bath both mixed the powders on the 

 1Chang, L. M. The Response of a Large-caliber Granular Charge in Confinement to an In-bed Thermal Initiation; ARL-CR646; U.S. Army Research Laboratory: Aberdeen Proving Ground, MD, 2010. 

2

Birk, A.; Boyle, V.; Chang, L. M. The Response of MACS Modules in Shipping Configuration to a Peripheral In-bed 

Thermal Initiation; ARL-TR-4013; U.S. Army Research Laboratory: Aberdeen Proving Ground, MD, 2007. 
2

macro scale and tended to help “pack” the Fe2O3 particles around the aluminum particles. The 

solvent was then removed by slow drying. 

This processing should have been sufficient, but since prior art used BKNO3 powder, it was 

requested that a fine powder of BKNO3 be added to the mixture to the 10% level. The BKNO3

had been added to prior art mixtures to facilitate and accelerate the initiation of the thermite 

reaction. However, the change in particle sizes and in processing of the thermite mixture should 

have been sufficient for the requisite initiation. 

With the reacting thermite, the effects of the hot metal particles generated during the fragment 

penetration would be simulated. The next requirement of the igniter was to provide propellant 

ignition similar to that provided by the fast fragment plowing into the grains of the propellant 

bed. During the passage of the fragment through the propellant bed, a portion of the propellant 

grains in its path would be fractured. This “rubble” zone would be more facile to ignite and 

would burn faster than designed due to the greatly expanded surface area. The “rubble” zone 

would only exist along the passage of the penetrating fragment so the “rubble” simulant would 

need to be close to the thermite mixture along the simulated path of the fragment. 

This effect was simulated by placing ball powder propellant (WC855 propellant) around a core 

of thermite powder. Since the simulator will provide data for computer models, the ball powder 

propellant was chosen for its easily-modeled size and known properties. The ball powder was 

placed in a cloth bag so that the gases produced by ignition would easily pass into the main 

propellant bed. The igniter was made to approximately two-thirds length of the diameter of the 

proposed main propellant bed (see figure 1). 

Thermite Powder

Ball Powder

Paper Tube

Electric Match

Cloth Tube

Figure 1. Igniter schematic and photo. 
3

The thermite and the ball powder weighed 15 and 20 g, respectively. Both igniter materials were 

in well-defined confinement zones (paper and cloth tubes), intended to be suitable for interior 

ballistics modeling. Two electric matches were inserted, equally spaced, into the thermite bed 

for initiation of the igniter. The electric matches were wired in parallel and initiated with a 24-V, 

10-ms electrical pulse (prior art used ~5 kV). While the lower end of the cloth tube was sealed, 

the upper end was taped tightly around the electric match lead wires. The overall size of the 

igniter was 10 cm in length and 2.22 cm in diameter, which properly fit into the desired main 

propellant charge. 

High-speed video with a Phantom 5 camera was obtained in order to record the flame spreading. 

The framing rate was set to 10,000 frames/s and triggered off the ignition trigger pulse. 

3. Results and Discussion 

It was important to ensure that the igniter was able to ignite the propellant charge within a proper 

delay time. Several test runs were conducted with various weights of thermite powder and ball 

powder to determine the necessary igniter composition. It was concluded that a total weight of 

35 g (15 g of thermite powder and 20 g of ball powder) was sufficient. 

Figure 2 displays a series of images obtained from the high-speed camera showing a typical 

sequence of the flame development in open air ignition. The test series determined that the 

ignition delay ranged from 10 to 15 ms (it should be noted that the ignition delay was defined to 

be the time at which the first visible light was seen after application of the firing voltage). 

Within 4 ms of first light, the illuminated area had expanded widely and the light became very 

bright, demonstrating a very high temperature region. Numerous burning particles, ejected from 

the igniter, were seen. The illumination was sustained for more than 30 ms. 
4

Figure 2. Flame development of igniter in open air. 

4. Summary 

An igniter suitable for hot-metal fragment impact simulation on a large-caliber propellant bed 

contained in a shipping container was design, constructed, and tested. The combination of fast 

thermite and ball powder propellant zones in the igniter provided for fast ignition of the main 

propellant bed in similar fashion as a fast hot-metal fragment that entered the shipping container 

creating hot-metal particles and a propellant “rubble” zone. 

The igniter was designed for, and demonstrated, nearly symmetric ignition about its z-axis, thus 

overcoming prior art. The ignition delay was more than an order of magnitude shorter than prior 

art, thus reducing the potential for igniter-dependant effects. 
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