RU2169311C1 - Method of combustion control in chamber - Google Patents

Abstract

FIELD: combustion control methods for various pulsating and detonating combustion devices. SUBSTANCE: method consists in acting on degree of turbulence of combustion front by electrical discharge formed in chamber and matched with hydrodynamic structure of combustion front in such way that degree of turbulence is increased at stabilization of discharge in current and is decreased at stabilization of discharge in voltage. EFFECT: enhanced efficiency of combustion control through decelerating or accelerating motion of combustion front waves. 6 dwg

Description

 The invention relates to power engineering and can be used to control combustion processes in chambers, which is widely used in various pulsating and detonation combustion devices.

 Known methods of controlling combustion by changing the parameters of turbulence, for example, by superimposing external oscillations on the combustion region [1], using additional tubular and tape turbulators installed in the channels [2]. There is also known a method of controlling the instability of combustion by an arc discharge created by a current source with an output impedance that varies depending on the control task [3]. However, methods of controlling combustion processes by superimposing external oscillations on the combustion region and a method of controlling combustion by an arc discharge are ineffective in controlling processes occurring in a moving self-accelerating wave of the combustion front. The first of them is used only to change the turbulence parameters if the combustion front is localized in a limited area, for example, on a burner device. The second, since the arc discharge cannot move together with the combustion front due to its contraction into the plasma cord, is ineffective in controlling combustion in the chambers. The methods associated with the use of additional mechanical turbulators installed in the channels can only increase the degree of turbulization of the process, therefore, their capabilities are limited. In addition, due to the statistical properties of the turbulence of gas flows created by additional mechanical turbulators, the use of this control method gives a significant statistical spread of adjustable parameters.

 The closest by the mechanism of influence on the combustion zone to the proposed one is a method of controlling combustion by influencing the degree of turbulence [2] of the combustion front using additional turbulators. In this case, the effect is carried out both on the combustion front and on the entire medium in the chamber. This method has the above disadvantages.

 The claimed invention solves the problem of creating a method of controlling the combustion processes in the chamber, which allows depending on the control task to slow down or accelerate the movement of the wave of the combustion front.

 The technical result achieved by using the claimed invention is to provide an impact on the degree of turbulence of the combustion front with the possibility of both increasing and decreasing it, but it can affect the value of the acoustic pressure in the combustion chamber, accelerating or slowing down the movement of the wave of the combustion front. In addition, the inventive method extends the range of controls for combustion processes in the chamber.

 This technical result is achieved by the fact that when controlling the combustion process in the chamber by influencing the degree of turbulence of the combustion front, the effect is carried out by forming a diffuse electric discharge in the chamber, which is consistent with the structure of the combustion front so that when the discharge is stabilized, the degree of turbulence is increased, and when the discharge is stabilized, voltage reduces the degree of turbulization.

 A feature of the proposed method is that a diffuse electric discharge is excited in the combustion chamber, which, due to the consistency with the hydrodynamic structure of the combustion front, moves together with the combustion front. The mechanism of influence on the degree of turbulization of the combustion front is as follows: upon excitation of a current-stabilized diffusion discharge, the variable heat generation associated with the discharge lags behind the phase of the variable heat generation associated with combustion and the phase of the acoustic pressure supported by chemical processes is greater than π / 2. This leads to a decrease in the level of acoustic pressure in the channel and, accordingly, to a decrease in the degree of turbulization of the combustion zone. The propagation time of the wave of the combustion front is delayed. When a voltage-stabilized diffuse discharge is excited in the channel, the phase shift becomes less than π / 2, the acoustic pressure, on the contrary, increases, the degree of turbulence of the combustion front increases, and the propagation of the wave of the combustion front accelerates.

 The described method can be implemented using a device, a diagram of which is shown in FIG. 1.

 The device includes a chamber 1 closed at one end of the pipe in the form of a rectangular section. Two opposite walls are coarse made of metal and at the same time serve as electrodes 2, between which excite diffuse discharge 8 from the power source 7 with varying impedance. The other two walls of the rectangular pipe were made of non-conductive material, for example, organic glass. The combustible mixture is prepared dynamically. Propane, air and additional oxygen are fed into the chamber through the mixer 3. Ignition of the combustible mixture is carried out by a spark at the closed end of the 4 pipes. The pressure is recorded by a piezoceramic pressure sensor 5 through an amplifier at the closed end of the pipe. The flame propagation rate was fixed by two photomultipliers 6 through windows 1 mm wide. The signals from the output of the amplifier of the pressure sensor, photomultipliers, and the power source were fed through an analog-to-digital converter to the computer's memory, where they were further processed.

 The method is as follows. The combustible mixture is fed into the chamber 1 through the mixer 3, ignite the mixture with a spark at the closed end 4 of the pipe. At the same time, the turbine front of the flame is affected by current stabilized (to reduce the degree of turbulence) or voltage (to increase the degree of turbulence) diffuse discharge 8, which moves in the chamber along with the combustion front. The effect of a diffuse discharge (stabilized by current or voltage) is judged by the acoustic pressure waveforms obtained using the sensor 5, as well as the flame propagation velocity waveforms obtained using photomultipliers.

 Examples of a specific embodiment of the method are shown in FIG. 2-6.

The action of electric discharges stabilized by current or voltage on the combustion zone of propane-air and propane-oxygen mixtures in pipes occurs in different ways and substantially depends on the method of stabilization of the electric diffuse discharge and to some extent on the chemical composition of the mixture. In FIG. Figure 2 shows the pressure oscillograms recorded when a spark was ignited with propane-air mixtures of various compositions at the closed end of the pipe when a current-stabilized discharge was applied: a, b — C ₃ H ₈ content — 3.2%: c, d — 4.0%; a, b - without discharge; b, d - with discharge in accordance with the claimed invention. As can be seen from the given oscillograms, the effect of a current-stabilized discharge is most pronounced for stoichiometric mixtures. The pressure in this case is almost halved. More clearly, the effect of electric discharges as a result of the effect on the degree of turbulence of the combustion front is manifested when recording the propagation velocity of the combustion front, which was recorded as the average propagation velocity over the entire length of the coarse by the signals of two photomultipliers. The results show that the flame propagation rate of stoichiometric mixtures decreases by more than two times. The effect of delaying the acceleration time of the flame front is observed.

 The pre-knock length for propane-air mixtures is much greater than for propane-oxygen mixtures. Therefore, to elucidate the effect of discharges on characteristic pre-knock processes, the combustion process in the chamber was controlled for mixtures enriched with oxygen upon ignition at the closed end. In FIG. Figure 3 shows the oscillograms of pressure fluctuations for a stoichiometric propane-oxygen mixture diluted with 60% nitrogen: 3a - without discharge, 3b - with discharge. As can be seen from the oscillograms, the intensity of the pressure fluctuations in the case of applying a current-stabilized discharge to the combustion zone (Fig. 3b) decreases by 20%, but the rise time of the amplitude of the pressure fluctuations almost doubles compared to the rise time without discharge, i.e. High-energy mixtures also delay the pre-knock period. The latter is demonstrated by the dependences of the ratio of the propagation velocity of the accelerating flame front in stoichiometric propane-air oxygen mixtures with and without discharge, depending on the percentage of nitrogen in oxygen obtained by processing the signals of two photomultipliers (Fig. 4 is a graph of the relationship between the average flame propagation velocity and discharge to velocity without discharge) located at a distance of 200 mm from each other and spaced from the closed end at a distance of 700 mm.

 It is seen that for low-energy mixtures, the average propagation velocity of the accelerating flame front in an electric discharge is greater than without a discharge. With an increase in the percentage of oxygen, the relative velocity becomes less than unity, that is, the effect of delaying pre-knock processes also manifests itself.

 To confirm the interaction, stabilized by the discharge voltage, consistent with the moving combustion front, measurements were carried out to determine the flame propagation velocity along the pipe. The speeds were determined using two photomultipliers located at a fixed distance of 0.1 m from each other and which as a whole moved along the axis of the pipe. The velocity distribution graph is shown in FIG. 5 (dependence of the local flame propagation velocity on the position of the flame front in the pipe for a stoichiometric propane-oxygen mixture diluted by 72% with nitrogen: 1 — no discharge, 2 — current-stabilized discharge, 3 — voltage-stabilized). From FIG. Figure 5 shows that under the action of a voltage-stabilized discharge, an increase in the degree of turbulence of the flame front occurs, which means that an increase in the flame velocity at the exit is coarse by more than 30%. When approaching the propagation velocity of the combustion wave to the speed of sound, the superposition of discharges on the combustion zone stabilized by current or voltage at different points of the transition section can both increase and decrease the local propagation velocity. Moreover, the general tendency to reduce the turbulent burning rate (current-stabilized discharge) or increase (voltage-stabilized discharge) is maintained.

 The effect of discharges on the degree of turbulization of the combustion front is confirmed by studies on visualization of the combustion zone at the initial stage of the effect of a diffuse discharge. In FIG. 6 (fragments of a schlieren film of the propagation of a combustion wave in a rectangular channel: a - without discharge, b - with a discharge of I = 10 mA) it is shown that when a discharge is stabilized (Fig. 6b), the degree of turbulization of the combustion zone in the channel decreases compared with the case of flame propagation without discharge (Fig. 6a).

 The above examples show that with the help of diffuse discharges it is possible to control the combustion processes upon initiation of detonation in the channels, and the effect is carried out by controlling the degree of turbulization of the combustion front.

Sources of information
1. Copyright certificate SU 556281, cl. F 23 N 5/00, 1977.

 2. Copyright certificate SU 1244423, cl. F 23 C 11/04, F 23 R 7/00, 1986.

 3. Copyright certificate SU 270666, cl. B 061/20, 1987.

Claims (1)

 A method of controlling the combustion process in the chamber by influencing the degree of turbulence of the combustion front, characterized in that the action is carried out by forming a diffuse electric discharge in the chamber, consistent with the hydrodynamic structure of the combustion front, so that when the discharge is stabilized by the current, the degree of turbulence is increased, and when the discharge is stabilized in the direction reduce the degree of turbulization.

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