JP2005226920A - Liquid fuel combustion equipment using porous element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize combustion when reducing the area of a porous element and to miniaturize an air supply apparatus. <P>SOLUTION: Ceramic fibers 22 are formed bonded through a heat resistant binder 23 to obtain the porous element 20. Because of using the ceramic fibers, higher porosity than the case of using sintered porous metal can be achieved, and at the same time, heat dissipation is suppressed to assure fuel evaporation on a downstream surface at a high level. Liquid fuel fed in with air from the upstream side passes through clearances of the ceramic fibers and is rapidly and uniformly diffused on the downstream surface to form a desirable fuel phase. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid fuel combustion apparatus for producing a homogeneous mixed phase of liquid fuel and combustion air with a porous element, and more particularly to a structure of a porous element for miniaturizing the apparatus and reducing manufacturing costs and running costs. .

  As a technique for forming a thin film-like liquid phase on the surface of the porous element and continuously burning it, there is a conventional technique such as JP-A-05-203117. The principle of this apparatus is that air and liquid fuel are sent from the upstream side of the porous element to form a foamed thin film fuel phase on the surface of the porous element, which is continuously burned.

  This type of combustion apparatus has the advantage that the specific surface area of the fuel can be dramatically increased, and the problem of poor response in general evaporative combustion and high air ratio in spray combustion can be solved.

  However, an apparatus such as Japanese Patent Laid-Open No. 05-203117 showing the basic principle has a problem that it is difficult to inject liquid fuel uniformly over the entire range of the porous element 1 in terms of nozzle control.

  As a proposal for solving this problem, for example, a device in which porous elements are provided in series in two stages in the front and rear (a device described in Japanese Patent Laid-Open No. 05-203116) has been known. However, since the liquid fuel is fed into the gap between the two porous elements, the combustion surface is limited to the upward direction, and there is a disadvantage that the combustion surface cannot be used sideways. This is because the liquid fuel sinks due to gravity.

In order to solve this, the present applicant has proposed a technique of joining two porous elements and sandwiching a sheet for diffusing liquid fuel between them (Japanese Patent Laid-Open No. 2002-147715). By using a liquid fuel diffusion sheet, the liquid fuel does not settle due to gravity, and a thin film fuel phase can be formed uniformly on the surface of the porous element. However, the use of two porous elements has the disadvantage that the ventilation resistance of the combustion air is increased, the blower supplying the air is enlarged, and the cost is increased.
Japanese Patent Laid-Open No. 05-203117 JP 2002-147715 A

  The problem is that with a conventional porous element such as sintered metal, it is difficult to reduce the size of the apparatus, and there is a limit to cost reduction. The reason is as follows.

  The combustion device using the porous element has an advantage that the specific surface area of the fuel can be surely increased. On the other hand, when the porous element is downsized, it is difficult to ensure the stability of combustion.

  The reason for this is that the porous element has a relatively large thermal conductivity, such as sintered metal, and a material with a low emissivity reduces the amount of heat transferred from the flame to the porous element, and from the porous element to the porous element. The amount of heat transfer to the support member increases, and an increase in the heat dissipation rate due to downsizing can be mentioned. In other words, the smaller the porous element, the greater the rate of heat escape to the metal member that supports the outer periphery of the porous element, the lower the surface temperature of the porous element, and the lower the amount of fuel evaporation. In addition, the balance of fuel evaporation necessary for stable combustion is lost. In this case, the surface flame is partially shortened or lengthened and is not leveled, and the combustion state cannot be stabilized.

  In order to improve combustion instability with the conventional structure, in principle, it is necessary to increase the pressure of liquid fuel and air fed from the upstream side. However, if this method is followed, the apparatus for sending in air becomes larger, which is against the problem of downsizing the entire apparatus, and the cost of the apparatus increases on the contrary.

  Accordingly, an object of the present invention is to simplify the mechanism of a fuel system for feeding liquid fuel and air while stably improving combustion even when the porous element is downsized.

  In order to achieve the above object, a combustion apparatus for liquid fuel using a porous element according to the present invention forms the porous element by bonding a large number of ceramic fibers via a heat-resistant binder (claim). Item 1).

  The porous element may have a porosity of 60 to 95% (Claim 2) and a bulk density of 0.2 to 0.7 g / cm 3 (Claim 3). In some cases, the porous element includes a net material formed of ceramic fibers therein.

  Ceramic fibers may have an average fiber diameter of 2.5 to 50 μm (Claim 5) and an average fiber length of 0.01 to 50 mm (Claim 6).

  Since the combustion apparatus according to claim 1 uses ceramic fibers as the porous element, it can achieve a higher porosity than the case of using porous sintered metal, and at the same time, suppresses heat dissipation and increases the evaporation of fuel on the downstream surface. Can be guaranteed in dimension. The liquid fuel fed together with air from the upstream side diffuses quickly and uniformly on the downstream surface through the gap between the ceramic fibers to form a preferable fuel phase. Since the atomized liquid fuel fed together with air moves through the microscopic voids between the ceramic fibers by an action similar to capillary action, a homogeneous mixed phase of fuel and air is formed on the downstream surface of the porous element. Therefore, even if the combustion surface is directed upward, downward, or sideways, the combustion is stabilized, and the use environment of the apparatus can be liberalized. In the present invention, upstream / downstream is based on the flow of liquid fuel and combustion air.

  According to the present invention, the fuel phase can be homogenized due to the high porosity, that is, the combustion stability can be ensured even if the area of the porous element is reduced, and at the same time, the air supply device can be simplified. .

  FIG. 1 illustrates one embodiment of a combustion apparatus according to the present invention. Since the configuration of the apparatus may be the same as that of the conventional apparatus, for example, the porous element 20 formed of ceramic fibers is mounted at an appropriate position via the holder 11, while the fuel injection nozzle 14 and the rectifying plate 15 are installed upstream thereof. The fuel phase shown by the symbol F is formed on the downstream surface of the porous element 20 by feeding the atomized liquid fuel. Reference numeral 17 denotes a case body that wraps around the outer periphery of the combustion portion, 18 denotes a surface ring of the holder 11, and 19 denotes a fixing bracket (for example, a screw) for fixing the surface ring 18. A sealing material 16 is disposed on the outer peripheral portion of the porous element 20 to seal between the holder 11 and the porous element 20 to prevent fuel leakage.

  2 and 3 exemplify the porous element 20 in cross section. The porous element 20 is formed by dispersing ceramic fibers and an inorganic binder in water, adding a polymer flocculant to form an aggregate, and then forming a paper sheet. Then, the agglomerate is suction filtered on the mesh to be deposited. After forming, drying and high-temperature firing, the inorganic binder sinters the contact points between the ceramic fibers to bond the ceramic fibers to a certain strength. By changing the average fiber diameter and the average fiber length of the ceramic fibers, the porous element can be controlled to have a target density (porosity) and openings (pore diameter), and necessary air permeability can be ensured.

  For example, alumina (aluminum oxide; Al 2 O 3) is used as the ceramic fiber 22 so as to be applied to the combustion apparatus and ensure heat resistance. Alumina alone has a heat resistance of about 1400 ° C. Silica (silicon dioxide; SiO2) can be used for the binder 23. When silica (SiO2) is used alone, the heat-resistant temperature may be lower than 1000 ° C, but when used with alumina (Al2O3). It has the ability to withstand high temperatures of about 1200 ° C. The binder 23 is 1 to 20% per weight of the ceramic fiber.

  In a combustion apparatus of a type in which atomized liquid fuel is fed together with air to form a fuel phase on the downstream surface of the porous element 20, it can be practically used if heat resistance of 1000 to 1200 ° C. can be guaranteed. Therefore, a panel structure using ceramic fibers 22 instead of the sintered metal can be used.

  When the heat-resistant ceramic fibers 22 such as alumina (Al2O3) are bonded through a binder mainly composed of silica (SiO2), for example, a large amount of voids can be formed inside the panel material, and the voids The rate can also be changed freely. In the case of the combustion apparatus according to the present invention, it is preferable that the porosity (porosity) is as high as possible. For example, when alumina having a porosity of 60 to 95% is used, the bulk density in this case is about 0.2 to 0.7 g / cm 3.

  As described above, since the porous element 20 according to the present invention can increase the porosity of the panel, the flow resistance of the air fed from the upstream side is reduced, and the downstream of the porous element 20 even with a lower air pressure. A homogeneous fuel phase can be formed on the surface. As a result, there is no need to increase the air pressure and forcibly blow air, and stable combustion can be realized even with a small air supply device such as a fan. If the porosity is uniform, a homogeneous fuel phase is formed in the central portion and the outer peripheral portion of the porous element 20, and at the same time, instability factors due to variations in the state of the fuel phase are eliminated.

  Further, since the porous element 20 is formed by the ceramic fiber 22 and the ceramic binder 23 having a low thermal conductivity, the heat dissipation on the combustion surface can be suppressed as compared with the conventional sintered metal. This is because the amount of heat transfer to the holder 11 and the surface ring 18 that support the outer peripheral portion is small. For this reason, a large amount of heat is retained on the combustion surface, the fuel vaporization rate of the fuel phase is stably improved, and a continuously stable combustion phenomenon can be continued. Further, since the ceramic fiber 22 and the ceramic binder 23 are used, the weight of the porous element 20 can be reduced.

  The ceramic fiber 22 used for the porous element 20 according to the present invention is not limited to alumina. A ceramic fiber other than alumina may be used as long as it has a heat resistance of at least 800 ° C. or more, preferably 1000 ° C. or more. For example, it is a ceramic fiber (trade name Isowool; Isolite Kogyo Co., Ltd.) in which 40 to 60% alumina is mixed with 60 to 40% silica (silicon dioxide). This ceramic fiber has a heat resistance of 1200 ° C. The average fiber diameter is 2.5-3 μm.

  Further, a silicon carbide (SiC) composite material (SiC-SiC composite material) may be used as a fiber. Among the silicon carbide composite materials, the most excellent material for heat resistance and strength retention is, for example, a silicon polymer (SiC reinforced fiber obtained by two-dimensionally knitting a fiber bundle of silicon oxide (for example, 15 μm in diameter, 500 pieces / bundle), and a silicon polymer ( For example, polycarbosilane PCS, polyvinylsilane PVS, SiC fine powder, etc. are melt-filled in a vacuum, the silicon polymer is fixed based on the electron beam irradiation insolubilization method, and then heated to a high temperature (for example, 1200 ° C. in an inert gas). About) it can be fired to convert the silicon polymer into ceramics. The ceramic fibers thus obtained are less likely to lose strength even in a high temperature environment. The silicon carbide composite material is in the form of a woven fabric at the time of molding, but can be used as the ceramic fiber according to the present invention by finely cutting. At this time, the ceramic fibers appear in a bundle, but by adjusting the porosity, the ceramic fibers serve exactly the same function as the individual fibers as the constituent material of the porous element 20 of the combustion apparatus. Further, the net-like silicon carbide composite material obtained in this way can be improved in strength of the porous element 20 by being sandwiched between the porous elements 20. When silicon carbide composite woven fabric (net) is used, not only one sheet but also multiple sheets may be sandwiched, and the silicon carbide composite woven fabric with two-dimensional expansion is divided into small pieces and ceramic fibers 23 may be solidified with a binder (23). This is because the strength can be reliably increased.

  Ceramic fibers excellent in heat resistance and strength are not limited to products formed into individual yarns, but are also two-dimensionally knitted like silicon carbide composites, both of which are porous according to the present invention It can be used as a ceramic fiber constituting the ceramic 20. In the case of the present invention, the preferable fiber diameter (2.5 to 50 μm) for each one is only a guide. Even if ceramic fibers are bundled and the apparent fiber diameter becomes large, if the porosity and void structure that allows the atomized liquid fuel to be uniformly led to the downstream surface are realized and have sufficient heat resistance and strength, They can be settled through a preferable heat-resistant binder to form a porous element (20). Moreover, the preferable length (0.01-50 mm) of ceramic fiber is also a temporary standard. For example, when a woven fabric of silicon carbide is cut into ceramic fibers, the length of the fiber bundle may be 2 cm or less, or may be 5 cm or more. The same applies to the case of using ceramic fibers formed as a single fiber.

  In the combustion device that makes the atomized liquid fuel appear as a fuel phase on the downstream surface of the porous element (20), it is important to be able to form a uniform fuel phase with less air pressure, so the fiber diameter and fiber length are large. It is preferable to determine the relationship with the sheath porosity. The porous element (20) according to the present invention is designed for the purpose of uniform combustion stability and miniaturization of the apparatus. Of course, the porous element (20) may be applied to a large apparatus having a large combustion area.

It is a figure which shows the structural example of the combustion apparatus which concerns on this invention from the side. It is sectional drawing which illustrates the porous element which concerns on this invention. It is a figure which expands and illustrates a part of fiber shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Holder 14 Fuel injection nozzle 15 Current plate 16 Seal material 17 Case body 18 Surface ring 19 Fixing metal fitting 20 Porous element 22 Ceramic fiber 23 Binder F Fuel phase

Claims (6)

In a combustion apparatus that sends liquid fuel and combustion air atomized from the upstream side of the porous element, forms a thin film of liquid fuel on the upstream surface of the porous element, and burns the mixed phase of liquid fuel and air,
The porous element is formed by bonding ceramic fibers through a heat-resistant binder and molding the liquid fuel using the porous element.   2. The liquid fuel combustion apparatus using a porous element according to claim 1, wherein the porous element has a porosity of 60 to 95%.   3. The liquid fuel combustion apparatus using the porous element according to claim 1, wherein the porous element has a bulk density of 0.2 to 0.7 g / cm <3>.   4. A combustion apparatus for liquid fuel using a porous element according to claim 1, wherein the porous element includes a net material formed of ceramic fibers therein.   5. The liquid fuel combustion apparatus using a porous element according to claim 1, wherein the ceramic fiber has an average fiber diameter of 2.5 to 50 μm.   6. The liquid fuel combustion apparatus using a porous element according to claim 1, wherein the ceramic fibers have an average length in a range of 0.01 to 50 mm.

Images