RU2066561C1 - Gas generator for powder-type fire extinguisher - Google Patents

Abstract

FIELD: fire-fighting equipment. SUBSTANCE: gas generator for powder-type fire extinguisher has combustion chamber with holes for gas discharge and gas generating charge located inside the chamber in a spaced relation to walls. Gas- generating charge has digressive combustion surface and made of composition capable of gas generation at normal pressure, and total area of holes for gas discharge is equal to (-.0013-0.05) of the charge total area. Gas- generating charge may be made in form of a set of tablet having no channels, and holes for air discharge are closed with material decomposing under the effect of temperature of burning of gas-generating composition or at pressure which does not exceed the supercritical pressure differential for generated gas. EFFECT: higher efficiency. 2 cl, 1 dwg

Description

 The proposed solution relates to fire fighting equipment, in particular, to means for creating working pressure in the bodies of powder fire extinguishers.

 Known gas generator for a powder fire extinguisher (Autosvid. USSR N 860773 1979). The gas generator is a series-connected chamber containing a gas-generating charge, a cooler made in the form of coaxial cylinders of heat-absorbing material and a gas duct.

 A known gas generator of a powder fire extinguisher (RF Patent N 1537279, 1990). The gas generator is a chamber with an initiator located inside it with a part of the gas-generating charge, coaxially to which a gas duct is installed, perforation is performed on a part of its side surface. Around the gas perforation is the main part of the gas-generating charge.

 A disadvantage of the known devices is the complexity and low-tech designs, as well as in some cases the inability to use fire-extinguishing powders on a fusible basis for displacing from the fire extinguisher body.

 The prototype of the proposed technical solution is a powder fire extinguisher gas generator (RF patent N 1637813, 1990), because It coincides with the proposed for the greatest number of signs.

 The gas generator comprises a combustion chamber with openings for gas outlet, a gas generating charge located inside the chamber, installed with a gap relative to the walls.

The disadvantage of the prototype is the insufficient breadth of operational capabilities. This drawback is due to the impossibility of using the known device for displacing fire extinguishing powders made on the basis of low-melting components, for example, ammonium phosphates. So, ammonium phosphates have a melting point of about 180 ^o C, and the temperature of the generator gases generated by the combustion of a gas generating charge is from 500 to 1500 ^o C. Therefore, when using the known device for displacing powders on a low melting point as a result of exposure to high temperature gases on the powder in it forms agglomerates that prevent the free flow of powder from the body of the fire extinguisher.

 The aim of the invention is to expand the operational capabilities of the gas generator.

 The essence of the proposed technical solution consists in the fact that in a gas generator for a powder fire extinguisher containing a combustion chamber with openings for gas outlet and a gas generating charge located inside the chamber, installed with a gap relative to the walls, the gas generating charge has a degrading combustion surface and is made of a composition capable of generating gas at normal pressure, and the total area of the gas outlet openings is (0.0013-0.05) the total initial surface area of the charge.

 In a preferred embodiment, the gas generator, the gas generating charge is made in the form of a set of channelless tablets.

 The invention consists in the following.

 As a result of experimental studies, it was found that high-temperature generator gases have a negative effect on powders made from a fusible base only in the presence of a supercritical pressure differential between the combustion chamber of the gas generator and the fire extinguisher body when there is a supersonic gas stream flowing out of the gas generator. Only in this case does the powder melt and form agglomerates in the powder, which prevent the free flow of the powder from the extinguisher body through the flow valve. At a subsonic speed of gas outflow from the gas generator to the powder, agglomerates are not formed in it and the high-temperature generator gas does not adversely affect low-melting powders.

 To ensure the subsonic velocity of gas outflow from the gas generator, it is necessary to use a charge from a composition capable of generating gas without the presence of excess pressure in the combustion chamber, i.e. capable of burning in a confined space at normal pressure, and the total area of the gas outlet openings should ensure the outflow of the resulting gas without the appearance of excessive pressure in the combustion chamber. In addition, the area of charge burning, which determines the gas intake, should not increase over time, but rather have a degressive surface, i.e. decreasing over time. In this case, the highest value of the velocity of the gas stream flowing out of the gas generator takes place at the initial time and will decrease over time, which guarantees that there is no negative effect on the powder of the generator gas over the entire life of the gas generator, even taking into account a small increase in the burning rate of the composition due to pressure increase in the body of the fire extinguisher and, accordingly, in the combustion chamber of the gas generator.

 In addition, the degressive shape of the surface of the charge charge provides a quick set of pressure in the fire extinguisher body at the beginning of the gas generator operation and its subsequent slight maintenance when the flow valve is opened (when powder is supplied to the fire) until the gas generator is completed.

плотность генераторного газа в начальный момент времени работы газогенератора, кг/м³;
Р_н начальное давление в корпусе огнетушителя в начальный момент времени работы газогенератора, н/м²
R газовая постоянная генераторного газа, Дж/кг К;
Т_гo температура генераторного газа в газогенераторе,К;
v_г скорость газового потока истекающего из камеры сгорания газогенератора, кг/с.The total area of the outlet openings in the gas generator, which ensures the outflow of the produced gas without the presence of a supercritical pressure difference between the combustion chamber of the gas generator and the fire extinguisher body, can be determined from the continuity equation (equality of the gas intake of the gas outlet):
v _g ρ _g S _a = S _g • v • ρ _t (1-κ) (1)
where S _{g the} initial surface area of the gas-generating charge, m ² ;
v burning rate of the gas generating composition, m / s;
κ relative amount of slag composition formed during combustion;
r _{t is the} density of the gas generating composition, kg / m ³ ;
S _{a the} total area of the gas outlet openings in the gas generator, m ² ;

the density of the generator gas at the initial time of the gas generator, kg / m ³ ;
P _{n the} initial pressure in the body of the fire extinguisher at the initial time of the gas generator, n / m ²
R gas constant of the generator gas, J / kg K;
T _{g the} temperature of the generator gas in the gas generator, K;
v _{g the} speed of the gas stream flowing from the combustion chamber of the gas generator, kg / s

где R газовая постоянная генераторного газа, Дж/кг К; Т_гo- температура генераторного газа в камере газогенератора, К; к коэффициент изоэнтропы генераторного газа. Преобразуя исходное выражение (1), получаем следующую зависимость для определения общей площади выходных отверстий газогенератора, обеспечивающих отсутствие сверхкритического перепада давлений:

Подставляя предельное значение характеристик газогенерирующих составов, применяемых в газогенераторах порошковых огнетушителей (v (0,5 - 5)•10^-3 м/с, ρ_т= (1,4-1,6)•10^-3 кг/м³, κ = (0-0,55), R (330-360) Дж/кг К, Т_го= (773-1773)К, к (1,15-1,27), получаем, что в зависимости от характеристик используемого газогенерирующего состава отношение общей площади выходных отверстий газогенератора к общей начальной поверхности заряда составляет:
S_a/S_г= (0,0013 0,05)
Выполнение газогенерирующего заряда в виде набора прессованных таблеток обеспечивает дегрессивную форму поверхности заряда, причем, бесканальная таблетка является наиболее технологичной формой заряда, что является весомым фактором при массовом выпуске порошковых огнетушителей.We accept that the gas flow rate is critical, above which it should not rise:

where R is the gas constant of the generator gas, J / kg K; T _g - the temperature of the generator gas in the chamber of the gas generator, K; to the coefficient of isentropes of the generator gas. Transforming the original expression (1), we obtain the following dependence for determining the total area of the outlet openings of the gas generator, ensuring the absence of supercritical pressure difference:

Substituting the limiting value of the characteristics of gas generating compositions used in gas generators of powder fire extinguishers (v (0.5 - 5) • 10 ^-3 m / s, ρ _t = (1.4-1.6) • 10 ^-3 kg / m ³ , κ = (0-0.55), R (330-360) J / kg K, T _go = (773-1773) K, k (1.15-1.27), we obtain that depending on the characteristics used gas-generating composition, the ratio of the total area of the outlet of the gas generator to the total initial surface of the charge is:
S _a / S _g = (0.0013 0.05)
The implementation of the gas-generating charge in the form of a set of pressed tablets provides a degressive shape of the surface of the charge, and a channel-free tablet is the most technologically advanced form of charge, which is a significant factor in the mass production of powder fire extinguishers.

 The essence of the proposed technical solution is illustrated by the drawing, which shows a General view of the gas generator in section. The gas generator has a shut-off and start-up head 1 with an igniter 2, a combustion chamber 3 with a gas-generating charge 4. installed inside it with a gap relative to the walls, made of a pressed pyrotechnic mixture capable of stably burning in the combustion chamber at normal pressure. In the walls of the decomposition chamber, holes 5 are made with a total area providing a subsonic regime for the outflow of gas jets from the gas generator.

 The gas generator operates as follows.

 Using the shut-off-start head 1, the igniter 2 is started. From which the gas-generating charge 4 is ignited. The generated generator gas leaves the openings 5 at a subsonic speed and creates operating pressure in the fire extinguisher body. The pressure in the combustion chamber monitors the pressure in the extinguisher body, i.e. with increasing pressure in the fire extinguisher body, the pressure in the combustion chamber also increases, however. for the entire duration of the gas generator operation, the pressure difference between the combustion chamber and the fire extinguisher body will retain a subcritical value.

 Using the proposed technical solution in comparison with known devices provides the ability to pressurize a powder fire extinguisher and displace from it not only powders on a refractory basis (for example, sodium bicarbonate), which are mainly used to extinguish fires of classes B, C, E, but also powders fusible basis (ammonium phosphates), which, in turn, are used to extinguish fires of classes A, B, C, E.

Claims (2)

 1. A gas generator for a powder fire extinguisher, containing a combustion chamber with gas outlet openings and a gas generating charge located inside the chamber, installed with a gap relative to the walls, characterized in that the gas generating charge has a degrading combustion surface and is made of a composition capable of generating gas at normal pressure, and the total area of the gas outlet openings is (0.0013 0.05) the total initial surface area of the charge.  2. The gas generator according to claim 1, characterized in that the gas-generating charge is made in the form of a set of channel-free tablets.