NATIONAL BUREAU OF STANDARDS REPORT

5268

THE OBSERVED NATURE OF IGNITION AND BURNING

OF

TWO SOLID PROPELLANTS AT PRESSURES BELOW ONE ATMOSPHERE

by

T. G. Lee

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1002-30-4873 May 2, 1957

NBS REPORT

5268

THE OBSERVED NATURE OF IGNITION AND BURNING

OF

TWO SOLID PROPELLANTS AT PRESSURES BELOW ONE ATMOSPHERE

by

T. G» Lee

for

Bureau of Ships

Department of the Navy

Code 538

Index Number NS-183-001

IMPORTANT NOTICE

NATIONAL BUREAU OF STAN

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production, or open-literature m is obtained in writing from

uch permission is not needed,

epared if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

THE OBSERVED NATURE OF IGNITION AND BURNING

OF

TWO SOLID PROPELLANTS AT PRESSURES BELOW ONE ATMOSPHERE

ABSTRACT

Experimental observations are reported on the burning

characteristics of a double base and a composite propellant under low ambient pressure conditions.

INTRODUCTION

The theory of the influence of pressure on burning

rate of solid propellants has been given considerable

attention (1). Generally, however, data are available

only for pressures normally found inside rocket motors and

ballistic chambers. If one extrapolates these pressureburning rate data to zero pressure, a finite burning rate

is found, although propellants cease to burn at higher

pressures. Thus, it was shown by Huggett (1) that such

extrapolation is not valid. Very little unclassified

data are available on propellant burning rates at reduced

pressure. The present work was undertaken to determine

experimentally a pressure below which self-sustaining

combustion of a small sample of a given propellant would

not be maintained in an ambient atmosphere at 75 °F. We

shall call that pressure the "maximum quenching pressure."

Two types of propellant, supplied by the Navy, were

investigated, Double Base Navy Mark-32 and a composite

propellant containing 82 percent KClOl*., NH4.CIO4., and

18 percent polyurethane. The pressure region investigated was between 10 mm and 760 mm Hg absolute. Some

information on the combustion behavior of the propellants

near the region of maximum quenching pressure and its

dependence on propellant composition was also obtained.

Ignition and combustion of propellants are governed

by energy balance relations (2). Ignition occurs when

a small volume of the propellant is raised to a temperature at which the rate of heat generation by exothermic
-2 -

reaction exceeds the rate of heat loss by conduction,

convection, and radiation. Quenching or extinction of a

burning propellant will occur if the reverse of the above

case is true. At reduced pressure (generally below atmospheric) high heat loss is caused by diffusion of hot

gaseous reaction products and reacting vapor away from

the fizz zone. This reduces the rate of decomposition

or melting in the subsurface zone and finally results in

quenching

.

The maximum quenching pressure appears to be influenced

by propellant composition, including stabilizer and

coolant, as well as by specimen configuration. For

composite propellants, the type of matrix (binder) and

the particle size of the filler are also important factors

(3).

EXPERIMENTAL PROCEDURES

The experiment was designed to observe the nature of

ignition, combustion, and quenching at reduced pressures

ranging from 10 mm to 760 mm Hg absolute and a ambient

temperature of 75°F for a Double Base Propellant-Navy

Mark-32 and a composite propellant consisting mainly of

potassium and ammonium perchlorate filler and polyurethane matrix.

Electrically heated 26 gauge Nichrome resis tance

wire, 3 cm long, was used as the ignition source. The

wire was inserted through a hole in the center along the

short axis of a specimen 2 mm thick, in the shape of an

equilateral triangle 7 mm on a side. To prevent subsequent sliding, the wire was slightly bent downward at

the middle where the specimen rested. The ends of the

wire were connected to two electrode clips suspended in

a 7 liter vacuum jar. The jar could be evacuated to any

desired pressure down to about 10 mm Hg absolute. The

power supplied to the ignition wire, about 4 watts, was

sufficient to make the wire red hot.

Depending on the pressure condition, the hot wire

would cause melting, decomposition, slow combustion or

ignition of the propellant at the surface of contact with

the wire. In the non-ignition cases, slow decomposition

or melting next to the hot wire would gradually increase

the diameter of the hole in the propellant. As a result

of the weight of the specimen, a slot would be formed in

the specimen by the hot wire, allowing it to drop from

the wire. Then all activity would cease. If the pre-ssure
-3-

in the jar were slightly higher than the maximum quenching

pressure, the specimen would continue its slow combustion

or decomposition after the drop, as evidenced by fuming

or generation of white or brown smoke. At a still higher

pressure, with double base propellant there was spark

burning but no visible flame. In this case small glowing

particles were ejected from the burning propellant.

Table 1 is a summary of the results obtained. It

is based on a limited number of runs, 30 runs were made

for the two types of propellant. The indicated pressure

ranges are only approximate, since only gradual transition

from one mechanism to the other was observed. For the

double base propellant, the pressure rise was less than

5 percent above the initial absolute pressure. The composite propellant produced somewhat higher pressures.

CONCLUSIONS

For the two propellants tested, there exist maximum

quenching pressures below which all specimens were

quenched. Such quenching pressures probably depend

primarily on the composition of the propellant, but

experimental conditions such as specimen configuration,

size, ignition -wire temperature and contact area may

influence the quenching pressure observed.

The quenching pressure range for the Double Base,

Mark-32 propellant was between 300 and 4-00 mm Hg absolute.

For the composite propellant of KClOq.-NH^ClO^-polyurathane

,

it was between 4-0 and 50 mm Hg absolute.

Additional work should be done to determine the

maximum quenching pressure for other propellants and

the effect of specimen size and configuration on quenching

pressure before any general conclusions can be drawn.
Table 1.

Observed

Nature

of

Ignition

and

Burning

of

Two

Propellants

at

Reduced

Pressures

—

CD ft d -p 0

ctf

O bfl o d

d

ft 0 d 1—1 d

d 0

-p -p -h

a 0 •H 0 a 0 d ft o -p a -p ft p OOP ft d ft ft o d o d ft 0 o o bO 0 0 P O 0 •H Oh rH -p p ft d ft P CO o 0 ft 0 •H « co ft

ft ft ft e J" bO 0 ft d • r—1 ° bO o d ft o O ft o •H Qh d d

rH -H 0 P o oid ft o O ft o a-Hd p 0 0 P •h d P ft o r^J a 0 ft -p p

ft 0 d

p P •h

d

a 0 r—1 H 0 P d ft i ° a a ^ 0 d 0 0 bO j- d M -H O ft o P ft ft ft o o o H ft o O ft 0 H •H 0 0 0 a 0 ° 0 0 ft o ft o ft d ft ft ftl ft M •H 0 0 ft bO 0 ft bO 0 0 0 d o 0 d a 0 d a •H *'' a j bO 0 P ® ft -H •H -p ft p ft 0 d

•H ft 0 0 •H r! o •h

d 0 0 a 0 0 P ft P d p 0 d p d a ^ d

-P

O P ft -H bO P ft bO

d o 3 i—i o

•H ft 0 0 13

M ft 0 1—1 ft o M ft o wo

ft0O o o o o 0 o CM o \D 0 ft UA i—i

rp o- P cd P o o O o 0 bO ft ft ft ft 0 ft 0 o o O o p a 1—1

lT\ CM o

ft

a ft fft

ft o ft •N o 0 0 0 ft • o « a a 0

ft ft 0 ft 0 d 0 a O bO O ft o p 0 h d 0 d p P p p o d ft 0

ft -H

a 0 ft

d ft ft o d

d ft o bO

® 0 0 o ft o OOP p d P p ft ft o o d ft 0 0 ft 0 -p 0 d bO 0 i—1 s O ft O ft bO 0 •h d

-p P ft •H 0 ft 0 ftda

p 0 0 ft 0 ft o ft 0 ft 0 •H *H ft a

ft ft 0 d

d

d o •H

bO 0 ft 0 ft

O bO

O bO

p 0 ~ o

C\J

d ft o O 0 o d o d

d ft

d 0

POH 0 P Jx{ •H •H ft CO

O ft i a -h dd 0 d ft .d ft d •H CO ft P ft •H 0 o 0 P 0 • ft p ft 0 d d d ft ft •H 0 a 0 0 ft bO 0 bOft >» o d • g ® a a > 0 d d d -p p bO bO d i—i *h O O ft O3 •H i ft •h d 0 o o ft P d d h 0 •H 0 •H » 0 0 ft p P -H a p 0 d

aj ft 0 ft o d ° d

p 0 0 -p

p

PQ •H 0 0 0 p ft 0 ft 0 H ft 0 d d o 0 ft o ft ft ft •H ft 0 bO 0 p » ft 0 M d 0 ft I 1 •H ft 0 0 0 ft P ft p 0 £ 0 ft

ft

p ft

p

a o 0 P 0 a

O ft

a 0 P O P ft -H CD i—1

ft

d ft o a 0 O S 0 0 [5 CO 0 co 0 CO g CO 0 H ft Q o o o o o o 0 o o o o o AO 0 ft C\J m ft- VA AO [>- P 0 P o o o o o o 0 bO ft -p ft ft ft ft 0 ft

** 0 o o o o o o P a 1—1 o o o o o

ft

a C\J rp J- UA AO
-5-

REFERENCES

(1) Lewis, B., Pease, R. N. , Taylor, H. S., Editors,

High Speed Aerodyanmics and Jet Propulsion, Vol. II,

Combustion Processes, Princeton University Press,

1956.

(2) Altman, David, and Grant, A. F. , Jr., Thermal Theory

of Solid Propellant Ignition by Hot Wire, Fourth

Symposium on Combustion, William and Wilkin Co»,

Baltimore, Maryland, 1953.

(3) Crawford, B. L., et al. Study on Propellants,

Office of Scientific Research and Development

Report 637^5 194-5*
I* ,
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

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