AU463597B2 - Pyrotechnic generator of gas under pressure - Google Patents

Description

48,3 80/72 The present invention relates to pyrotechnic

generators of gas under pressure. In certain

applications, especially in the field of safety

apparatus, such as extinguishers, inflatable lifeboats

and life-saving sledges, it is frequently necessary to

have availablo a generator apparatus of low weight

which can, in a relatively short time, produce a large

amount-of gas under pressure at a relatively moderate

temperature and with a practically constant flow rate. Pyrotechnic generators are already kznown. which

produce gases under pressure by combustion of a block

or charge of propellant fuel and cooling of the.

combustion gases by contact with a solid coolant charge

usually in particulate form and which is capable of

absorbing the heat of the said combustion gases whilst

it undergoes decomposition or sublimation.

However, those generators do not allow sufficient

cooling of the combustion gases to be achieved,

firstly because of the o:,trernely high temperatures of. 0 those gases which can reach 1,800 to 2,000 C and

wh ich it is necessary to bring back to a value of

about 100 0 C within a relatively short time and

secondly because of the coolant charge collapsing

under the influence of gravity during its

decomposition or sublimation, creating passages

through which the hot gases escape instead of passin g through the cooling charge. Furthermore, the generators no longer permit

satisfactory regulation of the gas flow, because of

463,597

48,380n2 the passages which are created. is provided a- According to the present invention there such generator pyrotechnic generator of gas under pressure, dividing the interior comprising an outer casing, a partition

of the casing into first and second chambers, a charge of first chamber and a charge propellant fuel being located in the second chamber, means of solid coolant being located in the cause said propellant for igniting the propellant charge to characterised in that it charge to give off combustion gases the combustion gases into also comprises means for directing helical flow to said said second chamber so as to impart a flow of said gases ombustion gases and to prevent direct

through said second chamber. According to a first embodiment of the pyrotechnic the means for directing generator according to the invention, two laterally directed the combustion gases comprises at least and oriented in outlet nozzles, mounted on said partitions of the gases through opposition so as to impart a helical flow of the particles of said the coolant charge, causing movement for directing the charge. In a modified embodiment the means member located in combustion gases includes a tapered helical obliquely directed cali- said second chamber and at least one in the same sense as brated orifice in said partition directed

the pitch of said helical member. directing the In a further embodiment the means for of calibrated orifices combustion gases comprises a plurality screw located in said in said partition and an Archimedes

463,597

48,3 80/72 I second chamber and defining with the walls of said chamber a helical compartment for spid solid coolant charge.

4 597

48,3 8 072 By varying the particle size of the coolant fluidized bed of charge it is possible to obtain a any preferred coolant charge particles which prevents contact. passage and ensures good gas-solids coolant The geometric arrangement of the solid that during the charge is directed towards ensuring the gases issuing period of operation of the generator at the from the second chamber are approximately charge. decomposition temperature of the coolant flow rate Under these conditions, the total gas fuel and gases (gases produced from the propellant proportional to produced from the coolant charge) is from the propellant the flow rate of the gases produced this flow fuel and it thus suffices only to regulate fuel rate of gases produced from the propellant rate) by (instead of regulating the total gas flow from the providing calibrated orifices at the outlet being placed combustion chamber, the coolant charge

downstream from the said orifices. varied, as The law controlling the flow rate is using solid in the case of a propelling mechanism of the block and propellant fuel, by varying the shape

the size of the calibrated orifices. should The arrangement of the coolant charge

conform to the following criteria: be large contact surface with the gases to

cooled throughout the period of operation; hot gases; suppression of preferred passages for not as little excess material (materia

463,597

48,3 800/72 decomposed at the end of the operation) as possible;

and

elimination of residuies which could block the

nozzles or interfere with the use (of the equipment).

The coolant charge can especially consist of salts which may or may not be hydrated and can be

docomposed by heat, such as ammonium carbonate and

ammonium bicarbonate, ammzonium carbamate, ammonium

chloride, calcium oxalate, amnmonium acetate, amnmonium,

oxalate, aminoguanidine nitrate, guanidine oxalate,

guanidine nitrate or urea, advantageously in the form

of granules or of pellets.

The most suitable propellant fuels are double-

base moulded propellant fuels of low potential (less

than or equal to about 500 cal/g) and of low speed of

combustion.

In order that the invention will more readily

be understood, the following description is given,

merely by way of example, reference being made to the

accompanying drawings, in which:-

Figure 1 is an elevation in cross-section of a

first embodiment of generator according to the

invention;

Figure 2 is a graph showing the variation in

pressure and temperature inside a chamber pressurized

by means of the generator of Figure 1;

Figure 3 is a view similar to Figure 1 of ,a

second embodiment;

Figure 4 is a graph showing the variation in the

6 d63597

48,3 8 0/72 pressure and the temperature inside the generator of

Figure 3; and

Figure 5, is a view similar to Figure 1 of further embodiment of generator according to the invention.

Referring to Figure 1 of the drawing, the generator according to the invention comprises a

substantially cylindrical tubular casing 1, for

example of aluminium alloy, closed at its two ends by

a front end cap 2 and a rear end cap 3, the latter

ending in a gas outlet nozzle 4.

The interior of the casing 1 is divided by a transverse partition 5 into two adjacent chambers isolated by diaphragms 5a which are destroyed at the time of firing. The first chamber is a combustion chamber 6 in which is housed a combustion propellant

fuel block or charge 7, for example a block of 300 g of Epictete powder, of potential 483 cal/g, burning

to produce a pressure of 170 bars and a temperature of 1,100°C, with its lighting device 8, for example two igniters in contact with a lighting coating based on powder of the "thermite" type. In the second chamber 9 is placed a coolant charge 10, for example 400 g of ammonium carbonate which can be sublimed from 58*C onwards and is used in pellets of size 9.5 mm diameter and 5 mm thickness.

The propellant fuel combustion gases issuing from the combustion chamber 6 are injected-into the second chamber 9 through two lateral outlet nozzles 11

7- 63.597

48,3 80 72 mounted on the dividing partition 5, near the

periphery of the latter and oriented in opposition so

as to impart a turbulent movement to the gases.

The maximum pressure in the second chamber 9 is

about 35 bars and the maximum temperature is 120"C at

filter-grid 12 mounted at the inlet of the nozzle 4,

between the casing 1 and the rear end cap 3.

The cooled gases under pressure which are

obtained are used to pressurize a chamber or

reservoir, for example of 180 litres. The temperature

in this reservoir always remains below

The variation in pressure and temperature

inside this reservoir is shown on the graph of Figure 2

which gives, as the ordinates, the absolute pressure

in bars and the temperature in OC, firstly at the

propellant fuel block (curves I and II respectively)

and secondly inside the reservoir (curves III and IV

respectively), as a function of the time in seconds,

given as the abscissa.

According to this graph, the pressure plateau

and a plateau in the temperature of the propellant fuel

block are reached between 1 and 5 seconds after

ignition (corresponding to a constant gas flow) and at

the end of the combustion of the propellant fuel (6

seconds after lighting) the pressure and the

temperature in the reservoir (maximum values) are

respectively 1.8 bars and

After 30 seconds, the temperature in the

reservoir is 50°C; after 60 seconds it is 41eC and

4 8,380/72 after 90 seconds it is 36"C.

Referring to Figure 3, this embodiment of

generator according to the invention comprises a

cylindrical tubular casing 12 extended upstream into

a very thick hollow cylinder 13 and closed downstream by

an end cap 14 ending in a gas outlet nozzle The assembly of the casing 12 and the cylinder 13

makes it possible to hold in position a transverse .partition 16 which defines two chambers isolated by

diaphragms 17 which are destroyed at the moment of

firing. An annular combustion propellant fuel block

18 is housed in the combustion chamber 19 and in the

central channel a flame tube 20 forms the ignition

device. The second chamber 21 for the coolant charge

is provided with a tapered helical member 22 and the

coolant charge 23 consists, for example, of pellets of

sublimable ammonium carbamate.

The propellant fuel combustion gases issuing from

the combustion chamber 19 are injected into the

chamber. 21 through two calibrated orifices 24 passing

obliquely and in opposition through the partition 16,

so that the gas flow is fed in the same direction as

the pitch of the helical member 22. The turbulent movement initiated by the calibrated orifices is

amplified by the first turn of the helical member

and the latter is tapered so as to increase the

filling coefficient of the second chamber.

The maximum pressure in the second chamber 21

is about 30 bars and at the filter grid 25 the maximum

9 46a597

48,380/72 temperature is 70°C. The temperature in the

combustion chamber 19 is 1,200^C and the temperature in

the second chamber in the vicinity of the orifices is

800"C. The variation in the pressure and temperature

inside the generator is shown on the graph on Figure 4,

with the ordinates indicating the absolute pressure in

bars and the temperature in 'C,.the abscissa

indicating the time in seconds.

The curve V shows the variations in temperature

at the filter grid 25. The curve VI indicates the

variations in pressure recorded at the filter grid

The curve VII shows the variations in pressure recorded

in the combustion chamber 19.

Because of the fact that an annular combustion

propellant fuel block is used, rising curves are

obtained on the graph and the maxima recorded are at

the end of the combustion period, say after about

seconds.

The use of calibrated orifices 24 and of a

calibrated outlet nozzle 15 makes it possible to

maintain a substantially constant ratio (equal to

about 2.7 for example) between the pressure in the

combustion chamber and the pressure at the filter

grid 25. The excess cooling charge can be reduced to

less than 5% of the initial weight of the ammonium

carbamate without changing the characteristics shown

on the graph.

In the embodiment shown in Figure 5, the

combustion chamber 6 is separated from the second

48,3 80/72

chamber 9 by a plate 26 with calibrated orifices 27

distributed around its periphery, whilst an Archimedes

screw with three or four turns 28 of diameter equal .to

its length occupies the entire length of the.second

chamber and defines, with the walls of this chamber, a

helical compartment containing the coolant charge 29.

The rear end cap 3 ends in an outlet nozzle 4.

The presence of the Archimedes screw forces the

combustion gases liberated in the combustion chamber 6

to pass through the helical compartment and to pass into

the coolant charge even if the latter is half consumed,

and regardless of the orientation of the generator.

11 463.597

Claims (2)

48,3 8 0/72 The claims defining the invention are as follows

1. A pyrotechnic generator of gas under pressure, such generator comprising an outer casing, a partition dividing the interior of the casing into first and second chambers, a charge of propellant fuel being located in the first chamber and a charge of solid coolant being located in the second

chamber, means for igniting the propellant charge to cause said propellant charge to give off combustion gases charac-

terised in that it also comprises means for directing the combustion gases into said second chamber so as to impart a

helical flo;- to said combustion gases and to prevent direct

flow of said gases through s aid second chamber.

2. A generator according to claim 1, wherein said means for directing the combustion gases comprises at least two later-

ally directed outlet nozzles, mounted on said partitions and orienbd in opposition so as to impart a helical flow of the

gases through the coolant charge, causing movement of the particles of said charge.

3. A generator as claimed in claim 1, wherein said means for directing the combustion gases includes a tapered helical'

member located in said second chamber and at least one

obliquely directed calibrated orifice in said partition

'directed in the same sense as the pitch of said helical member.

4. A generator as claimed in claim 1, wherein the means for directing the combustion gases comprises a plurality of cali-

brated orifices in said partition and an Archimedes screw

located in said second chamber and defining with the walls of said chamber a helical compartment for said solid coolant

c-arge.

463,597

48,3 8072 A generator according to any one of the preceding claims, iLerein the charge of solid coolant is a hydrated or anhydrous

thermo-decomnosable salt.

6. A generator according to claim 5, wherein said salt is

ammonium carbonate, ammonium bicarbonate, ammonium carbamate,

ammonium chloride, ammonium oxalate, ammonium acetate,

calcium oxalate, aminoguanidine nitrate, gaanidine oxalate,

guanidine nitrate or urea.

7. A generator according to claim,7 or 8, wherein said

solid charge is in the form of granules or pellets.

8. A generator according to any one of the. preceding

claims, wherein said propellant fuel is a moulded double base,

low combustion rate propellant having a potential at most

equal to 500 cal/g.

9. A pyrotechnic genaator of gas under pressure, such

generator being constructed and arranged substantially as

hereinbefore described with reference to Figure 1 of the

accompanying drawings. A pyrotechnic generator of gas under pressure, such

generator being constructed and arranged substantially as

hereinbefore described with reference to Figure 3 of the

accompanying drawings. 11. A pyrotechnic generator of gas under pressure, such

generator being constructed and arranged substantially as

hereinbefore described with reference to Figure 5 of the

accompanying drawings.

D A T E D this 8th day of July, 1975.

SOCIETE ATIO-TAI-E D:S 1OUDRES ET EXPLOSIFS

By its Patent Attorneys:

CALLINAIT AND AS0OCIATES.

46 597

48, 380/72

=fi

(Y) 1=1912

2 4 6 8, 12 74 76 le PO 2 R4 26 emps2 .econoes

463,597

48,380/72

't

P borsMe 7c

K

o 23456 78910 Temp.s secorc/oes 17- 463,59 7

48,3 8O/72

I'm 2

19, 1946a5 97