CN112197975B - Experimental device for fuel combustion and soot generation characteristics under microwave radiation - Google Patents

Abstract

The invention belongs to the technical field of energy conservation and emission reduction of engines and discloses an experimental device for fuel combustion and soot generation characteristics under microwave radiation. The experimental device comprises a high-voltage power supply, a signal generator, a magnetron, a tuner, a combustion chamber, an axial flow burner and a capillary, wherein the magnetron is used for generating microwaves, and the tuner is used for adjusting impedance in a circuit; the combustion chamber is a closed metal cavity; the axial flow combustor is used for generating axial flame in a combustor chamber; the capillary tube is arranged in the flame, is provided with a small hole, and the substance in the flame at the position of the capillary tube is sucked into the small hole under the action of negative pressure and then enters a gas analyzer, the composition of the substance in the flame is obtained under the analysis of the analyzer, and the position of the capillary tube in the flame is adjusted to realize the analysis of combustion products at different positions, so that the comprehensive detection of the combustion products is realized.

Description

An experimental device for fuel combustion and soot generation characteristics under microwave radiation

technical field

The invention belongs to the technical field of engines, and more particularly relates to an experimental device for the combustion and soot generation characteristics of microwave-assisted combustion.

Background technique

With the increase of engine ownership, engine has become one of the most important fossil energy consumption products, and the most important component of particulate matter in engine exhaust is soot particles, which has brought serious harm to the human environment. Therefore, how to improve the combustion efficiency of the engine while reducing the emission of harmful substances is particularly important for the further development of the engine.

On the one hand, common engine energy saving and emission reduction strategies include lean burn and exhaust gas recirculation technology, both of which essentially dilute the fuel-air mixture. However, when the dilution ratio is too large, it reduces the rate at which fuel is burned in the engine, detrimental to its power output. Therefore, solving the problem of too slow fuel combustion under extreme conditions is the key to the application of such energy-saving and emission-reduction strategies. On the other hand, the soot particles generated by engine combustion have a fractal accumulation structure, and the particles of each accumulation structure are composed of a considerable number of spherical primary particles. These particles form PM after being discharged from automobile exhaust, of which PM2.5 is due to It can enter the respiratory tract of the human body unobstructed and is extremely harmful; in order to reduce the generation of soot during the working process of the engine, researchers often use the method of reducing the fuel-air equivalence ratio. Especially in diesel engines, because the diesel engine injects fuel into the cylinder and then compresses and ignites, it takes a long time for the fuel to absorb heat from the liquid phase and evaporate to the gas phase to mix uniformly, resulting in a fuel-rich area in the mixture during the actual combustion process. Insufficient combustion, resulting in soot formation.

In recent years, researchers have tried to use an external electric field to improve the fuel combustion process, accelerate fuel oxidation, improve combustion efficiency and reduce soot generation. Since the flame is essentially a collection of a large number of charged particles, under the action of an external electric field, some of the particles will be accelerated to collide and stimulate to generate more active particles, which accelerates the combustion reaction. This method improves combustion efficiency and reduces soot generation to a certain extent. Since it is difficult to directly set an electric field in the engine, whether the method of applying an electric field to improve combustion efficiency and reduce soot generation is practical remains to be further studied. .

Since the engine cylinder is a closed metal wall space, the use of microwave radiation to create a strong electric field in the cylinder is a potential method to reduce engine soot emissions. Patent CN106762330B discloses an experimental device for visual research on microwave plasma-assisted ignition, which uses spark plugs to ignite to form initial plasma, and then radiates microwave energy into it to expand it, so as to achieve the effect of enhancing ignition. This document uses microwaves to enhance lean mixing. The ignition process of the gas can make the combustible mixture thinner, thereby improving the thermal efficiency of the engine, and achieving the effect of energy saving and emission reduction, but its main application background is gasoline engines, which are aimed at the ignition process and diesel engine scenarios where diffusion combustion is the main combustion mode. different. In addition, since the patent CN 106762330 B is aimed at the visualization of the ignition transient process, it is not conducive to the diagnosis of the fuel combustion and soot generation process; in the past, engineers usually used the form of a steady-state axial flow flame to carry out the fuel combustion soot generation process. The basic research work of this paper uses the probe to penetrate deep into the axial flow flame to make part of the soot condense on the probe. By changing the height of the probe, the soot generation at different positions can be obtained. The advantages of this method are that it is convenient, fast, and cheap. However, because the combustion reaction does not stop during the sampling process of the probe, it is difficult to collect the intermediate substances in the soot generation process, so it will bring certain problems to the subsequent analysis. With the development of laser diagnosis technology, researchers use laser-induced fluorescence technology, laser-induced incandescent light technology, etc. to diagnose axial flow flames. This method of diagnosis can more accurately detect intermediate substances in the process of soot formation. and its distribution, so it has received extensive attention, but the price of laser diagnostic devices is relatively high, and when studying the influence of electromagnetic fields on the soot generation process, the laser energy will bring additional effects to the electromagnetic field, which will affect the combustion analysis under the electromagnetic field. It brings interference, so it is currently only used for basic research on conventional axial flames.

To sum up, it is particularly important to invent an experimental device and method that is conducive to exploring the fuel combustion characteristics and soot generation characteristics under electromagnetic field-assisted combustion.

SUMMARY OF THE INVENTION

In view of the above defects or improvement needs of the prior art, the present invention provides an experimental device for fuel combustion and soot generation characteristics under microwave radiation. Microwave-assisted combustion promotes the combustion of fuel and reduces the generation of soot. On the other hand, it is convenient and quick to collect combustion products at different flames, providing a simple and convenient experimental detection device, which is energy-saving, environmentally friendly, safe and reliable.

In order to achieve the above purpose, an experimental device for fuel combustion and soot generation characteristics under microwave radiation is provided according to the present invention. The research device includes a high-voltage power supply, a signal generator, a magnetron, a tuner, a combustion chamber, an axial flow combustion devices and capillaries, including:

The high-voltage power supply is connected to the magnetron, and provides a high-voltage power supply for the magnetron. The magnetron is used to generate microwaves. A signal generator is also arranged between the magnetron and the high-voltage power supply. The generator is used to send out a waveform signal, so as to regulate the pulse time and frequency of the microwave generated by the magnetron; the tuner is connected to the magnetron to adjust the distance between the magnetron and the combustion chamber impedance in the line, thereby maximizing the transmission efficiency of microwaves into the combustion chamber;

The combustion chamber includes a metal casing and a metal mesh, and the metal mesh is arranged at the upper and lower ends of the metal casing to form a closed metal cavity; the axial flow burner is arranged below the combustion chamber, for generating an axial flame in the burner chamber under microwave radiation;

The capillary is arranged in the flame, and a small hole is opened on it. The material in the flame at the position of the capillary is sucked into the small hole under the action of negative pressure in the capillary, and then enters the gas connected with the capillary. In the analyzer, the composition of the substance in the flame is obtained under the analysis of the analyzer, that is, the analysis of the combustion product is realized, and the analysis of the combustion product at different positions is realized by adjusting the position of the capillary in the flame. Comprehensive detection of combustion products.

Further preferably, a circulator is also provided in the experimental device, and the circulator is arranged on the magnetron to be connected with the tuner, and one end of the circulator is also connected with a water load, and the circulator is used to convert the combustion chamber from the combustion chamber. Microwaves reflected back from the chamber are directed into the water load to be absorbed, preventing the reflected microwaves from entering the magnetron.

Further preferably, one end of the capillary is connected with a second slide rail for adjusting the height and position of the capillary in the flame.

Further preferably, one end of the metal mesh on the upper end of the combustion chamber is provided with a first sliding rail, which is used to adjust the height of the metal mesh, thereby adjusting the size of the combustion chamber.

Further preferably, one end of the capillary is connected with a high-pressure nitrogen cylinder, and on the one hand, nitrogen is used to flow through the capillary to form a negative pressure to absorb combustion products; , so as to better obtain the intermediate substances in the combustion process.

Further preferably, the axial flow burner is provided with staggered glass fibers for fully mixing the gas entering the axial flow burner.

Further preferably, the axial flow burner is further provided with a honeycomb core material, and the honeycomb core material is provided with a plurality of evenly distributed air holes, so that the airflow outputted through the axial flow burner is uniform and stable.

In general, compared with the prior art, the above technical solutions conceived by the present invention have the following beneficial effects:

1. In the present invention, the principle of microwave resonance is fully utilized in the combustion chamber. By adjusting the position of the metal mesh, the microwave is resonated in the flame zone, thereby strengthening the interaction between the flame and the microwave, and using the electromagnetic effect of the microwave to accelerate the flame zone. Charged particles, generating more active particles to speed up the reaction and reduce soot generation;

2. The combustion chamber of the present invention adopts a metal shell and a metal mesh to form a closed metal cavity. Since the natural frequency of the microwave used in the present invention is 2.45 GHz, the corresponding wavelength is basically in the order of centimeters, and only the metal mesh is required. The size of the grid is less than a quarter of the wavelength of the microwave, which can realize the electromagnetic shielding of the microwave in the combustion chamber, prevent the radiation damage to external operators caused by microwave leakage and the microwave energy loss caused by leakage, and adjust the upper metal mesh. The position of the whole combustion chamber is changed, and the spatial structure size of the entire combustion chamber is changed. The microwave is reflected on the walls of the combustion chamber and superimposed with other incident waves in space, which is conducive to the microwave resonance to generate a strong electric field;

3. In the present invention, a capillary invasive collection method is adopted, wherein the use of low-temperature inert nitrogen is used to stop the reaction on the one hand, thereby retaining the intermediate product, and on the other hand, the negative pressure state in the capillary is guaranteed, which is beneficial to the collection process;

4. The detection device for fuel combustion products under microwave radiation provided by the present invention couples microwaves to the flame of fuel combustion to achieve the purpose of collecting intermediate substances in the combustion process, with simple operation, energy saving, environmental protection, safety and reliability.

Description of drawings

1 is a schematic structural diagram of a detection device for fuel combustion products under microwave radiation provided by a preferred embodiment of the present invention;

FIG. 2 is a partial schematic view of the front and rear connecting sections of the capillary in FIG. 1 .

Throughout the drawings, the same reference numbers are used to refer to the same elements or structures, wherein:

1- high voltage power supply, 2- signal generator, 3- magnetron, 4- circulator, 5- tuner, 6- metal casing, 7- metal mesh, 8- first slide rail, 9- second slide rail , 10-flame, 11-capillary, 12-high pressure nitrogen cylinder, 13-honeycomb core material, 14-glass fiber, 15-axial flow burner, 16-gas analyzer, 17-water load, 18-insulated grid bipolar Type transistor, 19-small hole, 20-rubber hose.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

As shown in FIG. 1 , an experimental device for fuel combustion and soot generation characteristics under microwave radiation provided by a preferred embodiment of the present invention fully utilizes the principle of microwave resonance. Generate resonance to strengthen the interaction between flame and microwave; use the electromagnetic effect of microwave to accelerate charged particles in the flame area, generate more active particles to speed up the reaction and reduce soot generation; use nitrogen to flow through the capillary to form a negative pressure in the tube , the particles in a certain process of the reaction are sucked into the capillary tube, and then the low temperature and chemical inertness of nitrogen are used to make the local combustion reaction stop instantly, so as to better obtain the intermediate substances in the combustion process and achieve the purpose of basic research. In addition, the power of the microwave generated by the magnetron can be determined by the target waveform emitted by the signal generator in combination with the IGBT.

The detection device includes a high-voltage power supply 1, a signal generator 2, a magnetron 3, a circulator 4, a tuner 5, a metal casing 6, a metal mesh 7, a first slide rail 8, a second slide rail 9, a capillary 11, and high-pressure nitrogen. Bottle 12 , honeycomb core 13 , glass fiber 14 , axial flow burner 15 , gas analyzer 16 , water load 17 , insulated gate bipolar transistor (IGBT) 18 , small hole 19 and rubber hose 20 .

The high-voltage power supply 1 is connected to the magnetron 3, the high-voltage power supply 1 and the magnetron 3 are connected by an insulated gate bipolar transistor (IGBT) 18, the other end of the IGBT is connected to the signal generator 2, and the magnetron 3 is connected to the circulator 4 in turn. , the tuner 5 and the metal casing 6 are connected, the water load 17 is connected to the other end of the circulator 4, the axial flow burner 15 is located under the metal casing 6, and there are metal meshes 7 above and below the metal casing 6, which together form an electromagnetic shielding The closed cavity here is closed in a broad sense, which refers to the closure on the electromagnetic level, so that the microwave cannot be radiated from the combustion chamber. Since the exhaust gas after combustion in the combustion chamber can be discharged in time, the upper and lower layers need to be The flame 10 of the axial flow burner 15 is accommodated in the cavity, and the two ends of the capillary 11 are respectively connected with rubber hoses 20, which are then connected to the high-pressure gas cylinder 12 and the gas analyzer 16 respectively.

The high-voltage power supply 1 supplies power to the magnetron 3, and the signal generator 2 sends out a specific waveform signal, which is controlled on and off by the IGBT18, thereby controlling the output mode of the magnetron 3, and the circulator 4 guides the reflected microwave into the water load 17 to absorb it to avoid microwave reflection. The magnetron is damaged, the tuner 5 adjusts the transmission impedance, so that the microwave energy loss is minimized and the energy transmitted into the metal shell 6 is the largest, and the upper metal mesh 7 of the metal shell 6 is adjusted to make the microwave achieve the best resonance effect. The flame 10 interacts to reduce soot generation, the second slide rail 9 can adjust the relative position of the capillary 11 and the flame 10, the capillary 11 has a small hole 19, and the high-pressure nitrogen bottle 12 has a throttle valve to introduce low-temperature nitrogen into the capillary 11. A negative pressure is formed in the capillary 11, and the material in the flame 10 is sucked into the capillary 11 through the small hole 19, and finally flows into the gas analyzer 16 with nitrogen. The low-temperature nitrogen can quickly stop the combustion reaction and achieve the purpose of collecting intermediate substances in the combustion process. , the capillary 11 is connected to the high-pressure gas cylinder 12 and the gas analyzer 16 by a rubber hose 20, so that the capillary 11 can move up and down freely. Diffusion combustion and other modes of fuel combustion, and built-in 14 sections of glass fiber and 13 sections of honeycomb core material to make the gas mixing more evenly, the metal shell 6 has a quartz window on the wall, and is coated with ITO film, which not only shields microwaves, but also It is convenient to carry out optical observation from the outside, and obtain combustion characteristic parameters such as hydroxyl distribution, flame speed, etc., to analyze the combustion characteristics of fuel. The metal mesh 7 can be disassembled and moved, which can not only shield microwaves, but also allow the exhaust gas generated by the combustion of the flame 10 to be removed in time. In addition, when conducting experiments in the diffusion combustion mode, the metal mesh 7 can also allow outside air to enter, so that the combustion can be carried out.

A method of using an experimental device for fuel combustion and soot generation characteristics under microwave radiation, the using method comprising the following steps:

S1 fills the pre-ground fuel into the axial flow burner from different air inlets as required; remove the metal mesh under the metal casing, use the ignition device to ignite the fuel at the outlet of the axial flow burner, and adjust the position of the fine metal mesh so that the It is flush with the outlet of the axial flow burner or slightly lower than the outlet, and the upper fine metal mesh is adjusted to keep a reasonable distance from the flame tip;

S2 adjusts the output waveform of the signal generator to achieve the experimental purpose. Adjust the tuner to maximize microwave transmission efficiency;

S3 After the flame is stable, adjust the relative position of the capillary and the flame, open the high-pressure nitrogen bottle, and adjust the nitrogen flow rate to meet the experimental requirements;

S4 conducts optical observation through the quartz window on the wall of the metal casing; collects combustion substances at different heights of the axial flow flame, and diagnoses it by a gas analyzer.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (6)

1. An experimental device for fuel combustion and soot generation characteristics under microwave radiation, characterized in that, the experimental device comprises a high voltage power supply (1), a signal generator (2), a magnetron (3), a tuner (5), a combustion chamber, an axial flow burner (15) and a capillary tube (11), wherein:

the high-voltage power supply (1) is connected with the magnetron (3) and provides a high-voltage power supply for the magnetron (3), the magnetron (3) is used for generating microwaves, and a signal generator (2) is arranged between the magnetron and the high-voltage power supply and used for sending a waveform signal so as to regulate and control the pulse time and frequency of the microwaves generated by the magnetron; the tuner (5) is connected with the magnetron and used for adjusting the impedance in a circuit between the magnetron and the combustion chamber so as to maximize the transmission efficiency of the microwave transmitted into the combustion chamber;

the combustion chamber comprises a metal shell (6) and a metal net (7), wherein the metal net (7) is arranged at the upper end and the lower end of the metal shell (6) to form a closed metal cavity; the axial flow combustor (15) is arranged below the combustion chamber, the bottom of the axial flow combustor is provided with a plurality of air inlets, pre-ground fuel is filled into the axial flow combustor from different air inlets, and the axial flow combustor is used for generating axial flame in the combustion chamber under microwave radiation; one end of the metal net at the upper end of the combustion chamber is provided with a first sliding rail (8) for adjusting the height of the metal net and further adjusting the size of the combustion chamber;

the capillary tube (11) is arranged in the flame, a small hole (19) is formed in the capillary tube, substances in the flame at the position of the capillary tube are sucked into the small hole (19) under the action of negative pressure in the capillary tube and then enter a gas analyzer (16) connected with the capillary tube, the components of the substances in the flame are obtained under the analysis of the analyzer, namely, the analysis of combustion products is realized, and the analysis of the combustion products at different positions is realized by adjusting the position of the capillary tube in the flame, so that the comprehensive detection of the combustion products is realized.

2. The experimental device for the fuel combustion and soot generation characteristics under microwave radiation according to claim 1, characterized in that a circulator (4) is further provided in the experimental device, the circulator is arranged on the magnetron (3) and connected with a tuner (5), one end of the circulator is further connected with a water load, and the circulator is used for guiding the microwave reflected from the combustion chamber into the water load to be absorbed, so as to prevent the reflected microwave from entering the magnetron.

3. The experimental device for the fuel combustion and soot generation characteristics under microwave radiation as claimed in claim 1, wherein one end of the capillary (11) is connected with a second slide rail (9) with a scale for adjusting the height of the capillary in the flame.

4. The experimental device for the fuel combustion and soot generation characteristics under microwave radiation according to claim 1, characterized in that one end of the capillary (11) is connected with a high pressure nitrogen gas bottle (12), on one hand, nitrogen gas flows through the capillary to form negative pressure in the capillary, on the other hand, the low temperature and chemical inertness of the nitrogen gas are used to instantly terminate the local combustion reaction, thereby better obtaining the intermediate substances in the combustion process.

5. The experimental device for the fuel combustion and soot generation characteristics under microwave radiation as claimed in claim 1, wherein the axial flow burner (15) is provided with staggered distribution of glass fibers (14) for fully mixing the gas entering the axial flow burner.

6. The experimental device for the fuel combustion and soot generation characteristics under microwave radiation according to claim 1, wherein the axial flow burner (15) is further provided with a honeycomb core material (13) which is provided with a plurality of uniformly distributed air holes, so that the air flow output by the axial flow burner is uniform and stable.

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