Micro non-premixed combustor based on concave-convex wall structure

Abstract

The application provides a micro non-premixed combustor based on a concave-convex wall structure and relates to the technical field of micro-scale thermal-optical-electric power conversion, which comprises a combustor outer wall, the inner side of the combustor outer wall is provided with a porous medium, two groups of concave-convex walls are installed on the inner side of the combustor outer wall in a stacked manner, the two groups of concave-convex walls divide the inner side of the combustor outer wall into a first air inlet channel, a second air inlet channel and an air outlet channel, the first air inlet channel and the second air inlet channel are symmetrically arranged on the two sides of the air outlet channel, the first air inlet channel and the second air inlet channel are both communicated with the porous medium, the porous medium is communicated with the air outlet channel, and the air outlet channel comprises a combustion chamber, a blunt body and an air outlet which are communicated in sequence; the combustor outer wall can improve the combustion efficiency of the combustor, enhance the combustion stability, reduce heat loss, maintain a high-temperature environment and uniform temperature distribution.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro-scale heat-optical power conversion, and particularly relates to a micro non-premixed combustor based on a concave-convex wall structure. BACKGROUND

[0002] With the development of MEMS (Micro-Electro-Mechanic Systems) technology, a large number of micro-scale and meso-scale devices have appeared in the past decade. Micro power systems based on combustion (i.e. micro combustors) can provide a promising alternative to traditional batteries due to the higher energy density of hydrocarbon fuels, which can overcome the problems of short service life, low energy density and long charging time of traditional batteries. In addition, compared with batteries, micro combustors can be considered more environmentally friendly because they eliminate the risk of environmental impact from battery disposal. Compared with other hydrocarbon fuels, micro combustors fueled by hydrogen have extremely high combustion speed, so their flames can be better maintained in micro combustors.

[0003] Compared with conventional combustors, micro combustors have a large specific surface area, strong heat dissipation, short fuel residence time, and large pressure drop caused by friction due to the reduction in volume, which directly leads to low combustion efficiency, narrow operating range and difficulty in stable combustion of micro combustors. The overall combustion efficiency of a micro combustor mainly depends on the structural design of the micro combustor, and the micro combustor relies on its own effective organization of combustion to not only reduce heat loss but also broaden the stable combustion range of the micro combustor. Therefore, designing an optimized and reasonable micro combustor structure to achieve high-efficiency combustion is of great significance to the application and rapid development of micro energy power systems.

[0004] There are designs of parallel plate combustors in the prior art, but the parallel plate combustor still has deficiencies, for example: (1) Most of the prior art works adopt a premixed combustion mode, which has a risk of backfire under low-speed and high-equivalence-ratio operating conditions;

[0005] (2) The prior art achieves uniform distribution of the outer wall temperature by setting a single abrupt expansion or cavity, but this setting has limited improvement effect on the system, and setting multiple structures will complicate the internal structure and processing technology of the combustor, and also cause device failure due to uneven thermal stress between components;

[0006] (3) The prior art does not utilize the preheating of fuel combustion, and the flame stability in the micro combustor is limited, accordingly, there is an urgent need in the art to make further research and improvement in this regard in order to better meet the higher requirements of micro combustors in modern production.

[0007] (4) The residence time of the fuel is short, the short residence time of the fuel is due to the reduction of the characteristic length scale of the burner and the increase of the flow velocity, the reduction of the characteristic length scale and the high flow velocity result in the shortening of the residence time of the fuel, especially when the residence time of the component is close to the characteristic combustion time, the incomplete combustion of the fuel results in the reduction of the heat release and the increase of the heat loss, this phenomenon hinders the self-ignition of the flame and even can cause the flame to be extinguished.

[0008] Therefore, the present application proposes a micro non-premixed combustor based on a concave-convex wall structure to solve the problems in the prior art. SUMMARY

[0009] In view of the above problems, the present application aims to provide a micro non-premixed combustor based on a concave-convex wall structure, which has the advantage of improving the combustion efficiency of the combustor and solves the problems in the prior art.

[0010] To achieve the purpose of the present application, the present application realizes the following technical scheme: a micro non-premixed combustor based on a concave-convex wall structure, comprising a combustor outer wall, the inner side of the combustor outer wall is provided with a porous medium, the inner side of the combustor outer wall is provided with two groups of concave-convex walls arranged in a stack, the two groups of concave-convex walls divide the inside of the combustor outer wall into a first air inlet channel, a second air inlet channel and an air outlet channel, the first air inlet channel and the second air inlet channel are symmetrically arranged on the two sides of the air outlet channel, and the first air inlet channel and the second air inlet channel are both in communication with the porous medium, the porous medium is in communication with the air outlet channel, and the air outlet channel comprises a combustion chamber, a bluff body and an air outlet which are sequentially connected.

[0011] Further improvement lies in that the outer side of the combustor outer wall is provided with a mounting seat, both sides of the mounting seat are provided with an extension, and the extension is provided with a socket, both sides of the combustor outer wall are provided with a locking part, and the cross section of the locking part is arranged in an L shape, one end of the locking part penetrates through the extension and is connected with the extension through a fastener.

[0012] Further improvement lies in that the inner side of the mounting seat is provided with a metal elastic sheet, and the metal elastic sheet is in contact with the combustor outer wall.

[0013] Further improvement lies in that the first air inlet channel, the second air inlet channel and the air outlet channel are arranged in parallel.

[0014] Further improvement lies in that the bluff body is in a cylindrical shape, and the concave-convex walls are symmetrically arranged around the axis of the bluff body.

[0015] Further improvement lies in that the porous medium is made of Si3N4 material.

[0016] Further improvement lies in that the pore shape of the porous medium is one of hexagon, triangle and circle.

[0017] Further improvement lies in that the pore size of the porous medium is 0.08-0.12 mm.

[0018] Further improvement lies in that the size of the blunt body is 0.5-0.8 mm.

[0019] Further improvement lies in that the inner wall of the combustion chamber is provided with a catalyst.

[0020] The present application has the advantages that: the present application is designed based on the concave-convex wall structure, so that the hydrogen gas and the combustion-supporting gas entering from the first and second air inlet channels are mixed and combusted after being fully disturbed by the porous medium, the catalyst on the wall surface of the combustion chamber reduces the activation of the fuel, reduces the energy required for ignition, shortens the ignition delay time, makes the fuel more easily ignite, the blunt body connected to the combustion chamber anchors the flame, increases the residence time of the flame in the combustion chamber, improves the ignition and extinction limit, widens the air inlet speed of the air inlet channel, thereby improving the combustion efficiency of the burner, enhancing the combustion stability, reducing the heat loss, maintaining the high-temperature environment and uniform temperature distribution. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a structural schematic diagram of the present application.

[0022] Figure 2 is a lateral structural schematic diagram of the present application.

[0023] Figure 3 is a schematic diagram of the recirculation zone and low-speed zone formed behind the cylindrical blunt body in the present application.

[0024] Figure 4 is an outer wall temperature nephogram of the present application.

[0025] Figure 5 is an outer wall temperature nephogram of the flat plate type micro-burner.

[0026] Figure 6 is a temperature distribution curve diagram of the influence of the air inlet speed of the air inlet channel of the present application on the outer wall temperature of the burner.

[0027] Figure 7 is an outer wall temperature distribution curve diagram of the present application and the flat plate type micro-burner.

[0028] Figure 8 is a top view structural schematic diagram of the connection between the outer wall of the burner of the present application and the mounting seat.

[0029] Figure 9 is a top view schematic diagram of the connection between the outer wall of the burner of the present application and the mounting seat.

[0030] 1, first air inlet channel; 2, second air inlet channel; 3, air outlet channel; 4, outer wall of combustor; 5, porous medium; 6, concave-convex wall; 7, combustion chamber; 8, bluff body; 9, air outlet; 11, catalyst; 12, mounting seat; 13, extension; 14, locking part; 15, fastener; 16, metal elastic sheet. DETAILED DESCRIPTION

[0031] In order to deepen the understanding of the present application, the present application will be further described below in conjunction with examples, which are only used to explain the present application and do not constitute a limitation on the scope of protection of the present application.

[0032] According to Figures 1-9 As shown in the figure, the present embodiment proposes a micro non-premixed combustor based on concave-convex wall structure, which comprises an outer wall 4 of combustor, the inner side of the outer wall 4 of combustor is provided with a porous medium 5, two groups of concave-convex walls 6 are mounted on the inner side of the outer wall 4 of combustor, the two groups of concave-convex walls 6 divide the inner side of the outer wall 4 of combustor into a first air inlet channel 1, a second air inlet channel 2 and an air outlet channel 3, the first air inlet channel 1 and the second air inlet channel 2 are symmetrically arranged on both sides of the air outlet channel 3, and the first air inlet channel 1 and the second air inlet channel 2 are both in communication with the porous medium 5, the porous medium 5 is in communication with the air outlet channel 3, and the air outlet channel 3 comprises a combustion chamber 7, a bluff body 8 and an air outlet 9 which are sequentially communicated.

[0033] The first air inlet channel 1, the second air inlet channel 2 and the air outlet channel 3 are arranged in parallel, and the first air inlet channel 1 and the second air inlet channel 2 are respectively used for fuel gas or combustion-supporting gas to enter the outer wall 4 of combustor; when the first air inlet channel 1 is used for fuel gas to enter the outer wall 4 of combustor, the second air inlet channel 2 is used for combustion-supporting gas to enter the outer wall 4 of combustor; when the first air inlet channel 1 is used for combustion-supporting gas to enter the outer wall 4 of combustor, the second air inlet channel 2 is used for fuel gas to enter the outer wall 4 of combustor.

[0034] In operation, hydrogen fuel and combustion-supporting gas enter the outer wall 4 of combustor through the first air inlet channel 1 or the second air inlet channel 2 respectively; the hydrogen fuel and the combustion-supporting gas are preheated in the first air inlet channel 1 or the second air inlet channel 2 respectively; the preheated hydrogen fuel and combustion-supporting gas are fully disturbed by the porous medium 5, a large amount of heat generated by combustion is transmitted to the upstream through the heat conduction and heat radiation of the solid matrix of the porous medium 5, and fresh unburned mixed gas is preheated and ignited and burned in the porous medium 5 or the combustion chamber 7; the flame is stably burned under the catalysis of the catalyst 11 on the wall surface of the combustion chamber 7 and the anchoring effect of the cylindrical bluff body 8; the high-temperature gas generated by combustion is discharged through the air outlet.

[0035] By symmetrically arranging the first air inlet channel 1 and the second air inlet channel 2 on both sides of the air outlet channel 3 and arranging the combustion chamber 7 in the air outlet channel 3, the heat loss of the outer wall surface is effectively reduced, the combustion efficiency is improved, and the stability of the combustion process is enhanced.

[0036] Preferably, the fuel gas is hydrogen fuel; and the combustion-supporting gas is air or oxygen.

[0037] The bluff body 8 is cylindrical, and has a size of 0.5-0.8 mm, and in this embodiment, 0.8 mm.

[0038] In order to increase the stability of combustion and improve the combustion characteristics in the combustion chamber, a cylindrical bluff body 8 is designed, which forms a recirculation zone and a low-speed zone behind the bluff body 8, as shown in FIG. 2. The recirculation zone and the low-speed zone can prolong the residence time of the chemical reaction components, which is helpful for the complete combustion of the hydrogen fuel and the stable flame. The cylindrical bluff body 8 can change the flow pattern of the gas flow to occur around the flow, promote the full mixing of the hydrogen fuel and the combustion-supporting gas, improve the combustion efficiency, and prolong the combustion time, so that the hydrogen fuel has more time to burn. Figure 3

[0039] In this embodiment, the shape of the bluff body 8 and the size of the bluff body 8 on the temperature of the outer wall 4 of the burner are studied. As shown in Table 1, triangular bluff bodies and circular bluff bodies are selected, and the size of the bluff body 8 is 0.5 mm, 0.8 mm and 1 mm, respectively. The influence of different shapes of the bluff body 8 and different sizes of the bluff body 8 on the average temperature of the outer wall 4 of the burner is measured.

[0040] Table 1 Influence of the shape and size of the bluff body on the temperature of the outer wall of the burner

[0041]

[0042] As shown in Table 1, when the size of the bluff body 8 is in the range of 0.5-0.8 mm, the average temperature of the outer wall 4 of the burner provided with the triangular bluff body 8 and the circular bluff body 8 increases with the increase of the size of the bluff body 8; when the size of the bluff body 8 is in the range of 0.8-1 mm, the average temperature of the outer wall 4 of the burner provided with the triangular bluff body 8 and the circular bluff body 8 decreases with the increase of the size of the bluff body 8; when the size of the bluff body 8 is 0.8 mm, the average temperature of the outer wall 4 of the burner provided with the triangular bluff body 8 and the circular bluff body 8 is the highest; and when the size of the circular bluff body 8 is 0.8 mm, the average temperature of the outer wall 4 of the burner is the highest, reaching 1061 K.

[0043] In this embodiment, the temperature of the flat plate type micro-burner is compared with the temperature of the burner, as shown in FIG. 3 and FIG. 4. The temperature of the outer wall 4 of the burner in this embodiment is 400 K higher than that of the flat plate type micro-burner, as shown in FIG. 5. Figure 4 Figure 5 Figure 4 ​​​It can be seen that in the embodiment, the temperature of the outer wall 4 of the burner is high from the mixing and combustion of hydrogen fuel and combustion-supporting gas to the outer wall of the gas outlet, the flame is anchored around the cylindrical bluff body 8 by the cylindrical bluff body 8, the time for the flame to be blown out is delayed, the residence time of the flame is prolonged, the ignition and flameout limit is improved, and the inlet velocity of the inlet passage (the first inlet passage 1 and the second inlet passage 2) is widened.

[0044] Further, the anchoring of the cylindrical bluff body 8 to the flame means that the bluff body 8 can form a certain blockage to the mixed gas, so that part of the high-temperature combustion products after combustion generates a backflow movement (that is, opposite to the direction of the incoming flow), as a sustained ignition source with automatic compensation capability, to constantly ignite fresh unburned combustible mixture, so as to achieve the purpose of stabilizing the flame.

[0045] The influence of the inlet velocity of the first inlet passage 1 and the second inlet passage 2 on the temperature of the outer wall 4 of the burner is studied, as shown in Figure 6 , in the speed range of 8-20 m / s, as the speed increases, the average temperature of the outer wall also increases; the peak value of the outer wall temperature moves to the outlet direction as the speed increases, and the reason is that as the speed increases, the hydrogen and air entering the combustion chamber per unit time also increases, so the temperature also increases.

[0046] The concave-convex wall 6 is symmetrically arranged around the axis of the bluff body 8, and in the embodiment, the concave-convex wall 6 is made of stainless steel. Due to the expansion effect of the concave-convex wall 6, the recirculation effect of the low-speed backflow of the fuel at the step is achieved, and the mixing and heat transfer of hydrogen and air are optimized; the heat generated in the combustion chamber 7 is transferred to the reaction initial substance in the inlet passage through the heat conductivity of the concave-convex wall 6, the initial reaction temperature is improved, super-enthalpy combustion is realized, and better mixing and heat transfer are achieved.

[0047] In the embodiment, the heat generated in the combustion chamber 7 can be transferred to the reaction initial substance in the inlet passage by the heat conductivity of the concave-convex wall 6, the fresh gas is preheated, the initial reaction temperature is improved, the ignition point is reduced, and super-enthalpy combustion is realized. On the other hand, the inlet passage is arranged outside the outlet passage 3, and the combustion chamber 7 is arranged on the outer wall surface of the outlet passage 3, and because the inlet temperature is low, the heat dissipation is greatly reduced.

[0048] The outer wall temperature of the flat plate type micro-burner is compared and studied, as shown in Figure 7 , taking the present application as the invention group and the flat plate type micro-burner as the control group, under the same conditions, the temperature of the outer wall 4 of the burner is monitored from the combustion chamber 7 to the gas outlet 9, and it can be seen from Figure 7It can be seen that the temperature of the flat plate micro-combustor in the combustion chamber has a slight rise, and then slowly decreases along the direction of the gas outlet; the temperature of the outer wall of the invention group first continues to rise, reaches the highest temperature of 1221K near the bluff body 8, and then rapidly decreases to 1026K along the gas outlet 9. Therefore, the combustor of the invention group releases more heat than the flat plate combustor of the comparison group, and the average temperature of the outer wall is higher; compared with the flat plate micro-combustor, due to the increase in the longitudinal length of the invention and the increase in the relative flow distance, the longitudinal heat conduction of the concave-convex wall 6 and the thermal balance of the whole combustor are strengthened. Therefore, for a small fuel photovoltaic power generation device, the invention is the best choice.

[0049] The porous medium 5 is made of Si3N4 material, and the pore size of the porous medium is 0.08-0.12mm. In this embodiment, the pore size is 0.08mm. The pore shape of the porous medium 5 is one of hexagonal, triangular and circular, and preferably the pore shape of the porous medium 5 is hexagonal. The gas mixing is realized through the Si3N4 porous medium, and the fuel gas and the combustion-supporting gas do not need to be premixed in advance, thereby reducing heat loss, improving combustion efficiency, maintaining a high-temperature environment and uniform temperature distribution.

[0050] In view of the insufficient mixing of hydrogen and air leading to insufficient combustion, the invention designs a porous medium 5 made of Si3N4 material in the combustor. The porous medium 5 can pre-mix fresh gas, and the gas is hindered by the porous medium 5, continuously splits and converges among the pores of the porous medium 5, and is subjected to severe disturbance to generate vortex. In the combustion process, part of the heat generated by combustion is absorbed and transmitted to the porous medium 5, and hydrogen and air are mixed and burned in these pores. The porous medium 5 re-radiates these heat to the combustion chamber, improving the temperature of the flame. The Si3N4 material has good heat insulation and heat preservation performance, can reduce heat loss in the combustion process, improve combustion efficiency, and can help maintain a high-temperature environment inside the combustion chamber 7 and make the outer wall 4 of the combustor reach a more uniform temperature.

[0051] The invention studies the influence of the pore shape and size of the porous medium 5 on the temperature of the outer wall 4 of the combustor. As shown in Table 2, hexagonal, triangular and circular pore shapes are selected, and the influence of different pore shapes and sizes on the temperature of the outer wall 4 of the combustor is measured under the conditions of pore sizes of 0.08mm, 0.1mm and 0.12mm.

[0052] Table 2 Influence of pore shape and size of porous medium on temperature of outer wall of combustor

[0053]

[0054] As shown in Table 2, the average temperature of the outer wall 4 of the burner decreases with the increase of the pore size, and the average temperature of the outer wall 4 of the burner is the highest when the pore size is 0.8mm; the average temperature of the outer wall 4 of the burner is the highest when the pore size is 0.08mm, and the average temperature of the outer wall 4 of the burner reaches 1385K.

[0055] The inner wall (wall surface) of the combustion chamber 7 is provided with a catalyst 11, and the loading amount of the catalyst 11 is 0.1-0.5g·mol / cm 2 , preferably, the loading amount of the catalyst 11 is 0.3g·mol / cm 2 , further, the catalyst 11 is a metal catalyst or silicon nitride, and in the embodiment, the catalyst 11 is silicon nitride.

[0056] The hydrogen fuel and the combustion-supporting gas are not easy to burn in the combustion chamber 7 and have a long time of sufficient combustion, which is easy to make the hydrogen fuel not completely burned and be blown out; the catalytic combustion can realize the high-efficiency reaction of the lean fuel at a lower temperature, and the catalyst 11 can greatly reduce the activation energy of the fuel reaction, thereby reducing the energy required for ignition; therefore, the catalyst 11 is arranged on the wall surface of the combustion chamber 7, which can make the fuel more fully burned, effectively reduce the heat loss, expand the ignition limit range, and improve the combustion stability.

[0057] In the embodiment, the influence of the type of the catalyst 11 and the thickness of the catalyst 11 on the temperature of the combustion chamber is studied, as shown in Table 3, three kinds of catalyst 11 materials, platinum, stainless steel and silicon nitride, are selected, and the thicknesses of 0.1mm, 0.3mm and 0.5mm are arranged respectively, and the influence of different catalysts 11 at different thicknesses on the temperature of the combustion chamber is measured.

[0058] Table 3 Influence of the type of the catalyst and the thickness of the catalyst on the temperature of the combustion chamber

[0059]

[0060] As shown in Table 3, under the condition of the thickness of 0.3mm, the average temperature of the combustion chamber is the highest for different catalysts 11; among the three kinds of catalysts 11, the average temperature of the combustion chamber is the highest for the silicon nitride catalyst with the thickness of 0.3mm, and the average temperature of the combustion chamber reaches 2332K.

[0061] Further, the outer side of the outer wall 4 of the burner is sleeved with a mounting seat 12, the mounting seat 12 is connected with the external equipment, the device is connected with the mounting seat 12, which is convenient for disassembly and installation, and the mounting seat 12 can provide protection for the outer wall 4 of the burner.

[0062] The two sides (front and back) of the mounting base 12 are provided with extension parts 13, and the extension parts 13 are provided with sockets. The two sides of the outer wall 4 of the burner are provided with locking parts 14, the locking parts 14 are in contact with the extension parts 13, and the cross section of the locking parts 14 is in L shape. As shown in Figure 8 the locking part 14 passes through the extension part 13 and is connected with the extension part 13 through a fastener 15. The fastener 15 passes through the extension part 13 and the locking part 14 and is connected with the mounting base 12 through screw thread, which plays a limiting role.

[0063] Further, the inner side of the mounting base 12 is provided with a metal elastic sheet 16, which is in contact with the outer wall 4 of the burner. The metal elastic sheet 16 has elasticity and is in a state of shrinkage deformation after the outer wall 4 of the burner is installed, thereby providing a certain resistance and improving the stability of the outer wall 4 of the burner after installation.

[0064] The above shows and describes the basic principles, main features and advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples. The above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the framework and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A micro non-premixed combustor based on a concave-convex wall structure, characterized by: The burner comprises an outer wall (4), the inner side of which is provided with a porous medium (5), and two groups of concave-convex walls (6) are installed on the inner side of the outer wall (4) in a stacked manner, which divides the inner side of the outer wall (4) into a first air inlet channel (1), a second air inlet channel (2) and an air outlet channel (3), the first air inlet channel (1) and the second air inlet channel (2) are symmetrically arranged on the two sides of the air outlet channel (3), and the first air inlet channel (1) and the second air inlet channel (2) are both in communication with the porous medium (5), the porous medium (5) is in communication with the air outlet channel (3), the air outlet channel (3) comprises a combustion chamber (7), a blunt body (8) and an air outlet (9) which are sequentially communicated, the outer side of the outer wall (4) is sleeved with a mounting seat (12), the mounting seat (12) is provided with an extension part (13) on each side, and the extension part (13) is provided with a socket, the outer wall (4) is provided with a locking part (14) on each side, the cross section of the locking part (14) is in L shape, one end of the locking part (14) penetrates through the extension part (13) and is connected with the extension part (13) through a fastener (15), and the inner side of the mounting seat (12) is provided with a metal elastic sheet (16), and the metal elastic sheet (16) is in contact with the outer wall (4).

2. The micro-combustor based on the concave-convex wall structure according to claim 1, characterized in that: The first air inlet channel (1), the second air inlet channel (2) and the air outlet channel (3) are arranged in parallel.

3. The micro-combustor based on the concave-convex wall structure according to claim 1, characterized in that: The blunt body (8) is in cylindrical shape, and the concave-convex walls (6) are symmetrically arranged around the axis of the blunt body (8).

4. The micro-combustor based on the concave-convex wall structure according to claim 1, characterized in that: The porous medium (5) is made of Si3N4 material.

5. The micro-combustor based on the concave-convex wall structure according to claim 1, characterized in that: The shape of the pores of the porous medium (5) is one of hexagon, triangle and circle.

6. The micro-combustor based on the concave-convex wall structure according to claim 1, characterized in that: The size of the pores of the porous medium (5) is 0.08-0.12mm.

7. The micro-combustor based on the concave-convex wall structure according to claim 1, characterized in that: The size of the blunt body (8) is 0.5-0.8mm.

8. The micro-combustor based on the concave-convex wall structure according to claim 1, characterized in that: The inner wall of the combustion chamber (7) is provided with a catalyst (11).

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