CN107795993A - A kind of micro-combustor for possessing multilayer wall structure - Google Patents

Abstract

The present invention belongs to the related field of gas combustion equipment, and more specifically relates to a micro-combustor with a multi-layer wall structure, which includes a gas inlet and an exhaust gas outlet connected to each other, and a combustion chamber between the two, wherein The entire wall of the burner used to enclose the gas inlet, exhaust gas outlet and combustion chamber is composed of a double-layer structure from the inside to the outside, wherein the thermal conductivity of the first wall on the inside is designed to be higher than that of the second wall on the outside Thermal conductivity; In addition, the combustion chamber is also processed with a plurality of concave cavities adjacent to the gas inlet, and these concave cavities are symmetrically arranged on the first wall surface. Through the present invention, compared with the existing equipment, the combustion efficiency and stable combustion range can be further improved, and at the same time, it has the advantages of compact structure, convenient manufacture and use, and wide application.

Description

A micro burner with multi-layer wall structure

technical field

The invention belongs to the related field of gas combustion equipment, and more specifically relates to a micro burner with a multi-layer wall structure, which is suitable for providing heat sources or high-temperature gas sources for various micro power devices in the form of gas combustion, and at the same time It has the characteristics of compact structure, wide stable combustion range and high combustion efficiency.

Background technique

With the rapid development of micro-processing technology, various portable micro-electro-mechanical systems (such as micro-robots and mobile phones, etc.) and micro-aircraft (such as micro-satellites, micro-drones) are emerging. Traditional electrochemical batteries have shortcomings such as large volume and weight, low energy density, and long charging time, and are increasingly unsuitable for use in these fields. In comparison, the energy density (energy contained per kilogram of energy) of hydrogen and hydrocarbon fuels is tens to hundreds of times higher than that of chemical batteries. For example, the energy density of liquid octane is about 45MJ/kg, while the energy density of the most advanced lithium battery is about 1.2MJ/kg, the former is 37.5 times that of the latter. Therefore, combustion-based micro-power systems have received extensive attention.

At present, researchers have produced micro-thermal photovoltaic power generation systems, micro-thermoelectric systems, micro-gas turbines, micro-rotor engines, micro-propulsion systems, and so on. In all these systems, the micro burner is the core component. However, on the one hand, as the size of the burner shrinks, the ratio of its surface area to volume increases sharply (about two to three orders of magnitude larger than conventional scales), so that a large part of the heat released by the combustion process passes through On the other hand, due to the extremely short residence time of the gas mixture in the micro-combustor, the fuel and the oxidant often do not have enough time to fully react, and the heat is too late to be completely released. The above factors cause the micro burner to face great challenges such as poor flame stability and reduced combustion efficiency.

For the above challenges, some solutions have been proposed in the prior art. For example, Sitzki L et al. proposed a burner with a "Swiss-Roll" structure (Combustion in microscale heat-recirculating burners. Proceedings of the Third Asia-Pacific Conference on Combustion. Seoul, Korea, June 24-27, 2001), wherein the thermal cycle principle is used to stabilize the flame; CN200910241592.5 proposes a countercurrent heat exchange catalytic burner without an ignition device, which discloses that the gas channel with a spiral structure can be used to increase the specific surface area of the catalyst. As another example, the inventor of the present application proposed a micro burner in CN201110057146.6 earlier, which disclosed that the combustion efficiency and stable combustion range were improved by adding multiple preheating channels and blunt bodies. In addition, CN200810123660.3 discloses a high-efficiency porous media burner for micro-thermophotoelectric systems, and points out that the flame can be stabilized and the combustion efficiency can be improved by thermal circulation of the porous media solid skeleton.

However, further studies have shown that the above-mentioned existing solutions still have the following defects or deficiencies: first, the structure of this type of burner is still relatively complicated, which leads to problems such as processing or assembly difficulties, high manufacturing costs and inconvenient operation; secondly, this In the actual test of this type of equipment, it often happens that the catalyst is easy to melt and agglomerate at high temperature, or loses its activity due to CO in the flue gas; finally, this type of equipment does not fully consider the heat cycle and heat dissipation in actual use. The problem of coordination between losses leads to certain limitations in the improvement of combustion efficiency and stable combustion range. Correspondingly, further research and improvement are urgently needed in this field in order to better meet the higher requirements in modern production.

Contents of the invention

Aiming at the above deficiencies and improvement needs of the prior art, the present invention provides a micro-combustor with a multi-layer wall structure, in which by combining the application characteristics of the micro-power device itself, and fully considering the thermal cycle and heat dissipation In order to solve the problem of coordination between losses, the wall structure of the miniature gas burner is designed as a multi-layer heterogeneous structure with different thermal conductivity. Improvements can be made to further improve combustion efficiency and stable combustion range compared with existing equipment. At the same time, it has the advantages of compact structure, easy manufacture and use, and wide application, so it is especially suitable for micro-electromechanical systems or micro-aircrafts. Combustion energy supply occasions.

In order to achieve the above object, according to the present invention, there is provided a micro-combustor with a multi-layer wall structure, the micro-combustor is a flat or cylindrical structure, and includes a gas inlet and an exhaust gas outlet that communicate with each other, and is located at The combustion chamber between the two is characterized by:

The burner is used to surround the entire wall forming the gas inlet, exhaust gas outlet and combustion chamber from the inside to the outside by a double-layer structure, wherein the thermal conductivity of the first wall on the inside is designed to be higher than that of the second wall on the outside. The thermal conductivity of the wall surface, and the thickness of the first wall surface is designed to be greater than the thickness of the second wall surface;

In addition, the combustion chamber is further processed with a plurality of concave cavities adjacent to the gas inlet, and the concave cavities are symmetrically arranged on the first wall surface.

Through the above ideas, since the wall of the entire burner is divided into a double-layer structure and its key structural parameters are specifically limited, correspondingly in the entire gas combustion process, the inner wall of a material with a higher thermal conductivity can be significantly improved. The amount of heat circulation from the high-temperature combustion gas to the upstream wall fully strengthens the preheating effect on the unburned mixture; at the same time, the outer wall made of materials with lower thermal conductivity further reduces the heat loss from the burner to the external environment The actual test shows that the flame stability can be further improved, and high combustion efficiency can be obtained even at a high intake velocity; on the other hand, by adding a plurality of concave cavities that are symmetrically distributed on the inner wall surface, It can also provide a gas residence area to make the flame more stable, prolong the residence time of the gas in the burner, and further improve the combustion efficiency and stable combustion range in a way that is easy to control and facilitates processing and maintenance.

As a further preference, the thermal conductivity of the first wall is preferably designed to be in the range of ≥10W/(mK), and is preferably made of heat-resistant stainless steel, silicon carbide, silicon nitride or other similar materials; the second The thermal conductivity of the wall is preferably designed in the range of ≤1.0W/(mK), and is preferably made of quartz or other similar materials.

As a further preference, the thickness of the first wall is preferably designed to be more than 2 times the thickness of the second wall, more preferably 2.5 to 3.0 times.

As a further preference, the number of the concave cavities is preferably designed to be 2, and the distance between these concave cavities and the gas inlet is preferably designed to be 1/4 to 1/2 of the total length of the entire burner.

As further preferably, for each of the concave cavities, it is preferably designed to have a right-angled trapezoidal cross-sectional structure, and wherein the relatively short waist is located on the side adjacent to the gas inlet, and the relatively long waist is far away from the gas inlet. the other side of the gas inlet.

As a further preference, the application object of the micro-combustor is preferably a portable micro-electro-mechanical system or a micro-aircraft.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:

1. By combining the application characteristics of the miniature power plant itself, the key improvement of the present invention is to design the wall surface of the integral burner as a double-layer structure, so that on the one hand, the inner wall surface can be fully utilized to improve the flow rate from the high-temperature gas after combustion to the upstream. The amount of heat circulation on the wall surface strengthens the preheating effect on the unburned mixture. On the other hand, the outer wall surface is used simultaneously to reduce the heat dissipation loss of the burner to the external environment, and it is beneficial to improve the flame stability. Therefore, the present invention can be more Solve the coordination problem between thermal cycle and heat dissipation loss of micro burner well;

2. In the present invention, concave cavities are symmetrically arranged on the above-mentioned inner wall surface, and at the same time, further research is given on its specific structure and key parameters. The recirculation zone and low-velocity zone are generated inside, which can better stabilize the flame root, and can effectively prolong the residence time of the mixed gas in the entire burner, thereby further improving the combustion efficiency;

3. According to the micro burner of the present invention, the overall structure is compact, easy to manufacture and use, wide application, low cost, and it is suitable for hydrogen, also suitable for other all gaseous hydrocarbons such as methane, so it is especially suitable for such as Combustion energy supply occasions such as micro-electromechanical systems or micro-aircrafts.

Description of drawings

Fig. 1 is the overall structure schematic diagram of the built miniature combustor according to the preferred embodiment of the present invention;

Fig. 2 is the curve schematic diagram that carries out combustion efficiency comparison with a plurality of single-layer wall surface burners according to the embodiment of the present invention;

Fig. 3 is the curve schematic diagram that compares the amount of heat loss with a plurality of single-layer wall surface burners according to an embodiment of the present invention;

Fig. 4 is the curve schematic diagram that compares the amount of thermal cycle with a plurality of single-layer wall surface burners according to the embodiment of the present invention;

Throughout the drawings, the same reference numerals are used to designate the same elements or structures, wherein:

1-gas inlet 2-exhaust gas outlet 3-cavity 4-first wall 5-second wall

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, 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 constitute a conflict with each other.

Fig. 1 is a schematic diagram of the overall structure of a micro burner constructed according to a preferred embodiment of the present invention. As shown in FIG. 1 , the miniature burner is, for example, a flat or cylindrical structure, mainly including a gas inlet 1 and an exhaust gas outlet 2 communicating with each other, and basic components such as a combustion chamber between the two. A detailed explanation of its improvements will be given below.

Referring to Fig. 1, the burner is used to surround the entire wall forming the gas inlet, exhaust gas outlet and combustion chamber from the inside to the outside by a double-layer structure, wherein the thermal conductivity of the first wall 4 on the inside is designed to be higher than The thermal conductivity of the second wall 5 on the outside, and the thickness of the first wall 4 is designed to be greater than the thickness of the second wall 5;

In addition, the combustion chamber is further processed with a plurality of concave cavities 3 adjacent to the gas inlet 1 , and the concave cavities 3 are arranged symmetrically on the first wall surface 4 .

More specifically, the following is a specific embodiment according to the present invention.

The burner is, for example, a flat plate, and the equivalent ratio of hydrogen/air mixed gas is φ=0.4. The distance between the upper and lower walls of the burner is W ₁ = 1mm, the total length of the burner is L ₀ = 10mm, the depth of the cavity is W ₂ = 1mm, the length of the cavity is L ₂ = 3mm, the inclination angle of the rear wall of the cavity is θ = 45°, the cavity The distance of the cavity from the burner inlet is L ₁ =3mm. In addition, the inner wall of the burner is made of silicon carbide and the outer wall is made of quartz, both of which can withstand high temperatures above 1700K. Among them, the thermal conductivity of silicon carbide is 32.8W/(mK), and the thermal conductivity of quartz is 1.05W/(mK).

By utilizing the general-purpose CFD calculation software Fluent, and adopting the detailed chemical reaction mechanism (comprising 19 reversible reactions and 13 kinds of components) of hydrogen and oxygen reaction, the combustion process in the present invention has been numerically simulated, and adopts single-layer carbonization respectively Silicon and single-layer quartz wall burners were compared.

First of all, the combustion efficiency of the three burners varies with the intake velocity as shown in Figure 2. It can be seen from Fig. 2 that as the intake velocity increases, the combustion efficiency of the present invention is higher than that of the other two single-layer flat-plate burners. For example, when the intake velocity is 28m/s, the efficiencies of the other two single-layer wall burners are all below 90%, while the combustion effect of the present invention can still be maintained above 92%. This is mainly due to the design of the double wall surface, on the one hand, the amount of heat dissipation is appropriately reduced (see Figure 3), and at the same time, the amount of heat circulation is increased to a certain extent (see Figure 4). Calculations also show that the blowout limit of the present invention can reach above 40m/s. These prove that the burner of the present invention has the advantages of high efficiency and stable combustion.

In summary, because the wall of the burner according to the present invention is divided into a double-layer structure and its key structural parameters are specifically limited, correspondingly in the entire gas combustion process, the inner wall of a material with a higher thermal conductivity can be significantly improved. Increase the amount of thermal circulation from the burning high-temperature gas to the upstream wall, and fully strengthen the preheating effect on the unburned mixture; at the same time, the outer wall of the material with lower thermal conductivity further reduces the heat dissipation of the burner to the external environment The actual test shows that the flame stability can be further improved, and high combustion efficiency can be obtained even at a high air intake velocity; on the other hand, by adding multiple concave cavities that maintain symmetrical distribution on the inner wall surface , it can also provide a gas residence area to make its flame more stable, and at the same time, it can prolong the residence time of the gas mixture in the burner, so that the combustion efficiency and stable combustion range can be further improved in a way that is easy to control and facilitates processing and maintenance. .

It is easy for those skilled in the art to understand that the above descriptions 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, All should be included within the protection scope of the present invention.

Claims (5)

1. A micro-combustor with a multi-layer wall structure, the micro-combustor is a flat or cylindrical structure, and includes a gas inlet (1) and an exhaust gas outlet (2) communicated with each other, and a The combustion chamber between is characterized by: The burner is used to surround the entire wall forming the gas inlet, exhaust gas outlet and combustion chamber from the inside to the outside by a double-layer structure, wherein the thermal conductivity of the first wall (4) on the inside is designed to be higher than that on the outside The thermal conductivity of the second wall (5), and the thickness of the first wall (4) is designed to be greater than the thickness of the second wall (5); In addition, the combustion chamber is further processed with a plurality of concave cavities (3) adjacent to the gas inlet (1), and the concave cavities (3) are arranged symmetrically on the first wall surface (4). 2. The miniature burner as claimed in claim 1, characterized in that, the thermal conductivity of the first wall (4) is preferably designed to be in the range of ≥10W/(mK), and is preferably made of heat-resistant stainless steel, carbonized Made of silicon, silicon nitride or other similar materials; the thermal conductivity of the second wall (5) is preferably designed to be in the range of ≤1.0W/(mK), and is preferably made of quartz or other similar materials. 3. The miniature burner according to claim 1 or 2, characterized in that, the thickness of the first wall (4) is preferably designed to be more than 2 times the thickness of the second wall, more preferably 2.5 times to 3.0 times. 4. The miniature burner according to any one of claims 1-3, characterized in that, the number of the concave cavities (3) is preferably designed to be 2, and these concave cavities are far from the gas inlet (1) The distance is preferably designed to be 1/4 to 1/2 of the total length of the entire burner. 5. The miniature burner according to claim 4, characterized in that, for each of the concave cavities (3), it is preferably designed to have a right-angled trapezoidal cross-sectional structure, and wherein the relatively short waist is located adjacent to One side of the gas inlet (1), while the relatively longer waist is away from the other side of the gas inlet (1).