PROCEEDINGS
OF THE TOMSK ORDER OF THE OCTOBER REVOLUTION
AND ORDER OF THE RED BANNER OF LABOR
POLYTECHNIC INSTITUTE named after S. M. KIROV

Vol. 258 　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1976

APPARATUS FOR INVESTIGATING THE CONCENTRATION LIMITS OF FLAME PROPAGATION IN VAPOR–GAS MIXTURES UNDER VARIOUS CONDITIONS

L. K. PARFENOV, V. F. PANIN, A. V. BAIKOV, A. I. SENIN

(Presented by the scientific seminar of the Department of Radiation Chemistry)

In the practice of experimental investigation of the influence of various factors on the concentration limits (CL) of flame propagation in gases, various test devices are used—depending on the aims of the research and on the conditions under which the gas mixture is found [1, 2, etc.].

Important factors that may affect the CL are the initial temperature, ionizing radiations, gas flow, and the total pressure of the mixture.

In view of the great importance of studying the influence of these factors on the CL for safety engineering and for the theory of limiting phenomena, broad experimental investigations in this field are of considerable interest.

To investigate the influence of these factors on the CL of flame propagation in vapor–gas mixtures, an apparatus was constructed and tested, consisting of a combustion chamber, an ignition source, a system for creating a gas flow with a specified velocity, a system for thermostatting the constancy of the initial temperature of the mixture under investigation, and a system for ultraviolet irradiation of the space in the combustion chamber (Fig. 1).

The combustion chamber 4 is a thick-walled cylindrical tube. The lower end of the tube is closed by a quartz window 12, which is clamped in Teflon seals 13. The upper end of the tube is closed by a flange 14, into which two inlet fittings 15 are welded. The fittings serve for admission and discharge of the combustible mixture. One of the inlet fittings in the interior part of the chamber is connected to a tube 9 pressed against the chamber wall. The tube passes through the entire combustion chamber and is connected at the bottom to a flow distributor 10, which is in the form of a toroid with a large number of holes. The toroid provides a uniform flow of the gas mixture through the combustion chamber. In the upper part of the combustion chamber there is also installed a flow distributor 16, made of metal mesh. The combustion chamber is connected by flexible pipelines 7 to the pneumatic circuit of the apparatus. To create a gas flow in the chamber, a compressor 5 is connected to it in series. The valve head of the compressor is separated from the cylinder by a rubber gasket—to ensure tightness of the system at pressures differing from atmospheric pressure.

The maximum velocity of the gas flow that can be achieved when using piston compressors depends on the parameters

Fig. 1. Experimental schematic of the apparatus: 1 — mixer; 2 — RVN-20 vacuum pump; 3 — U-shaped mercury manometer; 4 — combustion chamber; 5 — piston compressor; 6 — flow “smoother”; 7 — supply pipelines; 8 — high-voltage ignition electrodes; 9 — connecting tube; 10 — flow distributor; 11 — thermocouple; 12 — quartz glass; 13 — rubber gaskets; 14 — upper flange; 15 — fittings; 16 — flow distributor (honeycomb); 17 — rotary device; 18 — heating furnace; \(K_1\)–\(K_7\), \(K_{\mathrm{reg}}\) — valves.

In-figure inscriptions: “supply of mixture components”; “supply of microimpurities”; “vacuum”; “to electronic potentiometer”; “~220”; “city gas.”

of the compressor used, from which the maximum flow velocities in any cross section of the pipelines along its path of motion can be calculated. The flow velocity is regulated by the regulating valve \(K_{\mathrm{reg}}\). To eliminate flow pulsations, “smoothers” 6 are provided in the pneumatic circuit of the apparatus.

In the case of low pressures and slow flows, the latter can be created with the aid of mixer 1. For this purpose valve \(K_6\) is closed, and with valve \(K_5\) open the required pressure is created by valve \(K_4\) (recorded by manometer 3). Valve \(K_7\) is then opened, and the pressure drop in the chamber is balanced (with the aid of valve \(K_4\)) by the excess pressure of the mixture in the mixer; a uniform flow is established in the chamber.

The thermostating system provides regulation of the initial temperature within the range from \(+20\) to \(+200^\circ\mathrm{C}\). Its main element is an electronic potentiometer. It receives a signal on the temperature value from thermocouple 11, installed inside the combustion chamber. Thermocouple 11 is also used to record flame propagation. By means of intermediate relay \(P_1\), the electronic potentiometer controls the power circuit of the thermostating system, maintaining the initial temperature in the combustion chamber at the required level.

The source of ultraviolet irradiation is a PRK-4 lamp, connected into a circuit with choke \(D_r\), capacitors \(C_1\), \(C_2\), \(C_3\), and start button \(K\) (Fig. 1). (The parameters of these elements are determined by the type of lamp used.)

For ignition of the gas mixture, electrodes of the discharge ignition gap are placed in the lower part of the chamber (above flow distributor 10). A high-voltage ignition pulse is supplied to electrodes 8 from the pulse source described in [3]. The rotary device, an element of which, 17, is shown in Fig. 1, makes it possible to study the effect on the CL of the angle between the direction of flame propagation and the acceleration of gravity.

With the apparatus described, it is possible to investigate the CL of flame propagation in the pressure interval \(10^1 \div 3\cdot10^3\) mm Hg, temperatures \(+20\)–\(200^\circ\mathrm{C}\), and flow velocities \(0 \div 5.0\) m/sec; the spark ignition source [3] makes it possible to study the influence of the duration of the ignition pulse and its energy content on flame propagation.

REFERENCES

1. B. Lewis, G. Elbe. Combustion and Explosions in Gases. “Mir,” 1968.
2. Fire Hazard of Substances and Materials (Handbook). Moscow, Stroiizdat, 1970.
3. V. F. Panin, L. K. Parfenov. PTÉ, 1970, No. 5, 106.