RU2774001C1 - Method for ignition and stabilization of combustion of fuel-air mixture by pulse optical quasi-stationary discharges and its implementation device - Google Patents

Abstract

FIELD: power engineering.

SUBSTANCE: invention relates to methods and devices for ignition of a fuel-air mixture and stabilization of combustion in power plants. The invention can be used in combustion chambers of power plants, in particular in systems of ignition of a fuel-air mixture and stabilization of combustion of air-jet engines. A method for ignition and stabilization of combustion of a fuel-air mixture by a pulse optical quasi-stationary discharge, and its implementation device are proposed.

EFFECT: increase in the reliability of ignition, and improvement of stabilization of combustion of hydrocarbon fuels due to pulse optical quasi-stationary discharges and plasma formations (plasmoids) formed as a result of these discharges in a combustion chamber of a power plant, in particular, during the operation at low static temperature and pressure, on poor and depleted mixtures, at high speeds of flows in air-jet engines.

8 cl, 1 dwg

Description

The invention relates to methods and devices for igniting a fuel-air mixture and stabilizing combustion in power plants. The invention can find application in the combustion chambers of power plants, in particular in systems for igniting the fuel-air mixture and stabilizing the combustion of jet engines used in various industries (aviation, energy, processing)

Known device for ignition and stabilization of supersonic combustion (utility model patent No. 192758 dated September 30, 2019). The device consists of a fragment of a direct-flow combustion chamber and two pylons protruding into the flow inside the combustion chamber. It can be used to ensure reliable ignition and stabilization of the combustion of hydrocarbon fuels in supersonic combustion chambers of ramjet engines. During the operation of the device, active chemical additives are injected into the combustion chamber, characterized by high ignition rates and heat release during combustion. These additives are injected into the combustion chamber from the source, together with the main fuel from the source, through the injectors installed in the pylon, in a ratio sufficient to form a stable flame, due to which a zone of increased pressure is also created in the channel. The rest of the fuel without chemical additives (due to which their consumption is reduced compared to the prototype) is supplied from the source through the injector installed in the pylon, in the flame-free region of the combustion chamber. In this case, a part of the fuel that is not activated by chemical additives is mixed with air and the resulting mixture ignites when interacting with flames of chemically activated fuels downstream. The formation of an increased pressure zone in the channel also contributes to easier ignition of the main fuel, that is, in addition to the fire mechanism, the gas-dynamic mechanism of influence on intra-chamber processes is also involved. Stabilization of the combustion of the main fuel is provided by the action of a more stable flame of chemically activated fuel. The plasma torch type device is activated for a short time at the start of a ramjet engine to ignite a flame with additional fuel by ejecting plasma into the fuel-air mixture through the plasma output channel. The disadvantage of this utility model is the presence of pylons inside the combustion chamber that can introduce constant flow resistance, as well as a non-permanent mode of operation - namely, only at the start of the engine.

Known supersonic plasma-chemical combustion stabilizer (patent for invention No. 2499193 dated 11/20/2013). A supersonic plasma-chemical combustion stabilizer for a direct-flow combustion chamber consists of two electrodes installed in the flow part of the combustion chamber, arranged in series along the flow, made in the form of streamlined pylons with symmetrical aerodynamic profiles, one of which is an anode, electrically isolated from the metal wall of the combustion chamber and equipped with a tube for fuel supply and injectors for fuel injection into the flow. The objective and technical result of the invention is the development of a supersonic plasma-chemical combustion stabilizer for a direct-flow combustion chamber, which ensures reliable ignition and stabilization of the combustion of hydrocarbon fuels in a direct-flow supersonic combustion chamber under conditions where traditional gas-dynamic methods do not allow this (low static temperatures and pressures, lean mixtures) , technologically compatible with the combustion chamber and providing a low level of aerodynamic losses. The solution of the problem and the technical result of the invention are achieved by the fact that a supersonic plasma-chemical combustion stabilizer for a direct-flow combustion chamber, consisting of two electrodes installed in the flow part of the combustion chamber, arranged in series along the flow, made in the form of streamlined pylons with symmetrical aerodynamic profiles, of which the first is the anode, electrically isolated from the metal wall of the combustion chamber and equipped with a tube for supplying fuel and injectors for injecting fuel into the flow, and the second electrode - the cathode is located in the wake of the first and is directly fixed on the wall of the combustion chamber. To form a gas-dynamic flow structure behind the anode, which ensures the stabilization of the position of the discharge channel and the intensification of plasma-chemical reactions, the anode design has a break in the leading and trailing edges so that the root part of the anode has a negative sweep relative to the flow direction, and the end part has a zero sweep, while in the streamlined surface The anode additionally has a built-in tube and injectors for injection into the flow simultaneously with the fuel of chemically active additives. The disadvantage of this technical is the presence of pylons inside the combustion chamber that can introduce significant flow resistance, as well as the need to supply auxiliary fuel (for example, propane, ethylene, synthesis gas) and chemically active additives to intensify the discharge and plasma-chemical processes.

Known invention CN102798149 "Plasma concave-cavity flame stabilizer for engine" dated 07/30/2014. The technical result of this invention is related to the solution of the problems of self-excited oscillations, the high resistance of the niche stabilizer and the narrow range of application of the niche flame stabilizer, as well as the proposal of a new type of niche flame stabilizer for engines. In the present invention, the plasma exciter is installed in a niche flame stabilizer. The plasma exciter generates a non-equilibrium plasma, creating a discharge in the air. The strength of the electric field generated by the non-equilibrium plasma and the heat generated affect the flow in the cavity, reducing the resistance of the cavity, reducing self-excited oscillations in the niche region, improving the mixing of fuel and air, and at the same time cause activation, dissociation, ionization and other activating effects on the injected fuel, further increasing combustion efficiency. The invention consists of a niche stabilizer, an unbalanced plasma exciter, a power supply system and a control system. Non-equilibrium plasma exciter refers to equipment that creates non-equilibrium plasma in air, including dielectric barrier discharge and partial arc discharge, which are smoothly installed on the front, front and bottom walls of the cavity, at the back wall, downstream and at the fuel nozzle. The excitation power supply system is a power supply system that provides the discharge energy for the non-equilibrium plasma exciter. Types of excitation power supplies include a high voltage AC power supply for a dielectric barrier discharge exciter, or a high voltage combined AC/DC power supply, or a high voltage repetitive nanosecond pulse power supply, or a high voltage repetitive nanosecond pulse power supply for a plasma arc discharge exciter. The control system is able to control and change in real time and accurately switch both the parameters of the power system in real time and the combustion conditions in the combustion chamber of the engine, adjusting the excitation to the flight conditions of the aircraft so that it is possible to create an unbalanced plasma. The system includes sensors, microprocessors and actuators. The disadvantage of this invention is the narrow focus of application, namely the presence of niche cavities of the stabilizer and the complexity of the design due to the introduction of dielectric surfaces in the combustion chamber.

The closest in technical essence is the invention "LASER CONTROLLED FLAME STABILIZATION", (patent US 6,302,682 B1 dated 10/16/2001), which is taken as a prototype by the maximum number of similar essential features. Flame stabilization method, including: focusing a high peak power pulsed beam from a laser through a focusing lens and a laser window to a focusing point in the fuel-air mixture at intervals necessary to prevent fuel combustion from ceasing, thereby resuming or maintaining fuel combustion. A device for stabilizing a flame, containing a laser, a nozzle, at least one source of fuel supply and at least one source of air supply, devices for regulating the pressure and amount of air and fuel, a feedback control system for determining the level of emission of flame light and reactivation specified laser. The control system consists of a light-collecting lens, a photodiode, a device for transmitting signals from said photodiode signal level discriminator to said laser. In this solution, the discharge spark provides the initiation and stabilization of the flame during the combustion of lean fuel-air mixtures in gas turbines. The method and apparatus can be used to stabilize and sustain the combustion of fuel in natural gas combustion energy sources such as gas turbine power plants. The disadvantage of this invention is the local ignition and insufficient stabilization of the combustion of the fuel-air mixture in the combustion chamber only by creating a point optical discharge and plasma formation. This method is inefficient for igniting and stabilizing the combustion of the fuel-air mixture in large power plants.

The technical problem to be solved is the difficulty of igniting the fuel-air mixture and insufficient stabilization of combustion in the combustion chambers of a power plant, in particular when operating at low static temperatures and pressures, on lean and lean mixtures, and at high flow rates in jet engines.

The technical result is to increase the reliability of ignition and improve the stabilization of the combustion of hydrocarbon fuels in the combustion chamber of a power plant, in particular, when operating at low static temperatures and at low pressure, on lean and lean mixtures, at high flow rates in jet engines.

The technical result of the method of igniting and stabilizing the combustion of the fuel-air mixture by pulsed optical quasi-stationary discharges and the device for its implementation is achieved by the fact that multiple quasi-stationary formations of low-temperature plasma (plasmoids) are created in the volume of the combustion chamber, which effectively and reliably ignite the fuel-air mixture and at the same time create a hydraulic resistance of the fuel-air mixture, and form zones of reverse currents in the flow of hot gases, which creates conditions for the stabilization of the combustion process, preventing the "breakdown" of the flame. An additional effect of combustion stabilization is due to the fact that the interaction of the counter directed fuel flow with the compressed air flow creates turbulence in the ignition zone, which leads to an increase in the efficiency of mixing and stabilization of the combustion of the fuel-air mixture.

Figure 1 shows a drawing of a device for igniting and stabilizing the combustion of the fuel-air mixture pulsed optical quasi-stationary discharges. A device for igniting and stabilizing the combustion of the fuel-air mixture by a pulsed optical quasi-stationary discharge is placed on the combustion chamber, contains an air supply device (1), fuel injectors (3) located at an acute angle α to the longitudinal axis of the combustion chamber, located on the combustion chamber housing (5 ) pulsed lasers (2), focusing lenses (4).

Consider the implementation of the method of ignition and stabilization of the combustion of the fuel-air mixture by a pulsed optical quasi-stationary discharge. Fuel is injected from injectors (3) into the combustion chamber against the flow of compressed air emanating from the air supply device (1), located at an acute angle α to the longitudinal axis of the combustion chamber, which leads to the formation of a swirling flow of the fuel-air mixture in the mixing zone air and fuel flow, multiple pulsed optical quasi-stationary discharges are carried out using laser beams emerging from the laser (2) and passing through the focusing lenses (4). Lasers are located on the body of the combustion chamber (5) in 2 or more rows, the discharges create multiple plasma formations (plasmoids), which ignite and slow down the flow of the mixture, thus stabilizing the combustion of the fuel-air mixture

The invention is carried out as follows.

Example 1 Kerosene is supplied from the fuel nozzles at a temperature of 550 K. Air is supplied from the air supply device with a temperature of 373 K and a pressure of 50,000 to 140,000 Pa, kerosene is injected through nozzles located at an angle to the longitudinal axis of 45 °, as a result of mixing air and fuel flows, fuel-air mixture with a speed of 30 to 70 m/s and an excess air ratio of 0.2 to 0.6. Two lasers are placed on the body of the combustion chamber, which form multiple pulsed optical discharges through a focusing lens, as a result of which quasi-stationary plasma formations are formed in the mixing zone, which ignite the fuel-air mixture. Laser parameters: laser pulse duration 10 ns, pulse energy 0.35 J, peak pulse power 50 MW, wavelength 1064 nm, frequency 20 Hz. During implementation, the fuel-air mixture is ignited with the help of plasma formations (plasmoids), the hydraulic resistance of the flow changes due to the appearance of plasma formations (plasmoids), reverse current zones are formed, the picture of the interaction of flows in the combustion chamber changes, turbulences are created, i.e. combustion stabilization is observed both in the case of counter-mixing of air and fuel flows, and in the formation of quasi-stationary plasma formations.

Claims (8)

1. A method for igniting and stabilizing the combustion of a fuel-air mixture by pulsed optical quasi-stationary discharges, including separate fuel injection through fuel injectors and supplying a compressed air stream to the combustion chamber, forming a fuel-air mixture, igniting and stabilizing combustion using a pulsed laser, characterized in that that fuel is injected towards the compressed air flow through fuel injectors located at an acute angle to the longitudinal axis of the combustion chamber, which leads to the formation of a swirling flow of the fuel-air mixture, in the mixing zone of air and fuel flows, multiple pulsed optical quasi-stationary discharges are carried out using lasers, located on the combustion chamber body in 2 or more rows, the discharges create multiple quasi-stationary plasma formations that ignite the fuel-air mixture, slow down the flow of the fuel-air mixture and thus stabilize the combustion of the fuel-in air mixture. 2. The method according to claim 1, operating under conditions of subsonic or supersonic combustion. 3. The method according to claim 1, in which fuel is injected against the flow of compressed air through fuel injectors located at an angle to the plane of the cross-section of the combustion chamber. 4. The method according to claim 1, operating at a laser frequency of 10 to 10,000 Hz. 5. The method of claim 1, wherein the pulses of said pulse beam have a peak power in the range of 10 kW to 10 GW. 6. The method of claim 1, wherein the pulses of said high peak power pulsed beam have a wavelength in the range of 200 nm to 12 µm. 7. A device for igniting and stabilizing the combustion of the fuel-air mixture by pulsed optical quasi-stationary discharges, consisting of an air supply device, fuel injectors, pulsed lasers, focusing lenses in the combustion chamber housing, characterized in that the fuel injectors are installed at an acute angle to the longitudinal axis of the combustion chamber towards the outgoing compressed air flow; 2 or more lasers are fixed on the outer side of the combustion chamber, located one after another with an interval between them, the lasers are located perpendicular to the longitudinal axis of the combustion chamber, so as to create multiple optical pulsed quasi-stationary discharges through the focusing lenses in the fuel-air mixture mixing zone. 8. The device according to claim 7, in which the fuel injectors are installed at an angle to the plane of the cross section of the combustion chamber towards the outgoing compressed air flow.

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