JP4871844B2 - Waste heat recovery device - Google Patents

Description

  The present invention relates to an apparatus for recovering waste heat from exhaust gas generated from an internal combustion engine of a vehicle.

  In automobiles, in order to further improve fuel efficiency, a technique for recovering heat in exhaust gas from an engine and converting it into electric energy or the like has been studied. And the thermoelectric power generator which collect | recovers the thermal energy of the waste gas discharged | emitted from the engine of a motor vehicle as an electrical energy is known (for example, patent documents 1-3).

  In patent documents 1-3, the waste heat of the exhaust gas which flows through an exhaust pipe is collect | recovered with a heat exchange fin, and the heat is conducted to a thermoelectric conversion module (thermoelectric conversion element). And electric power generation is performed by the thermoelectric effect by the temperature difference in a thermoelectric conversion module. In order to efficiently transfer heat to the thermoelectric conversion module, heat transfer members such as heat exchange fins that recover the heat of exhaust gas have been improved.

  In addition, a Rankine cycle that includes an evaporator that generates steam by heat in exhaust gas from an engine and converts the thermal energy of the steam into electric power has been studied (Non-Patent Document 1).

JP 2006-207428 A JP 2005-295725 A Japanese Patent Application Laid-Open No. 2006-21780

"Study on in-vehicle waste heat regenerative system using Rankine cycle" Preprints of Academic Lecture No.92-06 15-20

  However, the heat exchange fin is formed of a metal having a high thermal conductivity such as Cu. However, the heat exchange fin is likely to deteriorate when used in a high temperature exhaust gas for a long time and has a short life. Further, SUS can be used in an exhaust gas environment, but has a limited thermoelectric conversion efficiency due to low thermal conductivity and low waste heat recovery performance. Some thermally conductive ceramics that can be used in an exhaust gas environment have higher thermal conductivity than SUS or the like. However, it is difficult to form a complicated heat exchange fin shape with ceramics, and the manufacturing cost is high.

  The Rankine cycle evaporator as described in Non-Patent Document 1 requires a metal pipe and fins, but has a complicated structure. For this reason, there are restrictions on the same materials as described above, and the manufacturing cost is high.

  An object of the present invention is to provide a waste heat recovery device for exhaust gas of a vehicle internal combustion engine that can be used for a long time in the exhaust gas of an internal combustion engine, has high efficiency of waste heat recovery, and can reduce manufacturing costs. It is.

The present invention is a waste heat recovery device installed in an exhaust pipe of an internal combustion engine of a vehicle,
Piping for flowing exhaust gas of an internal combustion engine, a tubular porous ceramic member through which exhaust gas permeates , a sealing material installed on the inlet side of the porous ceramic member, and a porous ceramic member A ring-shaped sealing material installed on the outlet side, and a thermoelectric conversion element installed on the outside of the pipe for recovering radiant heat from the porous ceramic member , and exhaust gas from the outer peripheral surface of the porous ceramic member and the pipe The porous ceramic member permeates through the space between the inner peripheral surface of the porous ceramic member and flows into the inner space of the porous ceramic member, and the radiant heat from the outer peripheral surface of the porous ceramic member is recovered by the thermoelectric conversion element through the pipe. Features.

  According to the present invention, the porous ceramic member is installed in the pipe for flowing the exhaust gas of the internal combustion engine, and the porous ceramic member is designed so that the exhaust gas permeates. Then, a heat recovery member is installed, and waste heat of the exhaust gas is recovered by radiant heat from the porous ceramic member.

  According to such an apparatus, the porous ceramic member can be used for a long time in the exhaust gas of the internal combustion engine, and the manufacturing cost can be reduced as compared with the case where the heat radiation fin having a complicated shape is formed of ceramics. Furthermore, since the pore surface area of the porous ceramics can be increased, the efficiency of recovering waste heat in the exhaust gas is high, and the efficiency of recovery of waste heat by the heat recovery member can also be increased.

1 and 2 are cross-sectional views schematically showing a waste heat recovery apparatus according to an embodiment of the present invention. Figure 3 is a cross-sectional view showing the cross section of the waste heat recovery system of FIG. 2 schematically.

  The piping 2 is connected to a predetermined internal combustion engine exhaust gas piping system (not shown). Inside the pipe 2, a cylindrical porous ceramic member 9 is installed. A sealing material 7 is installed at the inlet-side end of the porous ceramic member 9 and hermetically closes the inlet of the porous ceramic member 9. A ring-shaped sealing material 8 is installed on the outlet side of the porous ceramic member 9, and the opening 8 a of the sealing material 8 communicates with the inner space 5 of the porous ceramic member 9.

  Exhaust gas flows from the inlet 2a of the pipe 2 as shown by an arrow A, is dammed by the sealing material 7, and flows toward the peripheral edge of the pipe as shown by an arrow B in the inlet-side space 3. Next, the porous ceramic member flows through the space 4 between the inner peripheral surface of the pipe 2 and the outer peripheral surface 9a of the porous ceramic member 9 and moves toward the inner space 5 of the porous ceramic member 9 as indicated by an arrow C. Transparent. Next, it passes through the outlet side space 6 as indicated by an arrow D, and is discharged from the outlet 2b to the piping system.

  A heat recovery apparatus 10 is installed outside the pipe 2. Here, the heat recovery apparatus may be attached to the pipe so as to contact the outer wall surface of the pipe 2. Alternatively, the heat recovery apparatus 10 may be fixed at a position away from the pipe 2.

  While the exhaust gas passes through the porous ceramic member 9 as indicated by the arrow C, heat accumulates inside the member 9 due to the contact between the exhaust gas and the pores. Then, heat is radiated from the outer peripheral surface of the porous ceramic member 9 as indicated by an arrow E. The heat recovery member 10 receives this heat radiation and uses it as another form of energy.

  When a space 4 extending in the longitudinal direction of the porous ceramic member 9 is formed between the outer surface of the cylindrical porous ceramic member 9 and the inner surface of the pipe, the exhaust gas is as indicated by an arrow C. It is easy to permeate toward the inner space 5 over a large area. Therefore, it is effective in reducing the pressure loss when passing through the porous ceramic member.

As shown in the waste heat recovery apparatus 1 </ b> A of FIG. 2, a thermoelectric conversion element 11 is installed on the outer wall surface of the pipe 2 as a heat recovery apparatus . Then, heat radiation is performed as indicated by an arrow E from the porous ceramic member 9 toward the inner peripheral surface of the thermoelectric conversion element 11. A predetermined refrigerant is brought into contact with the outside of the thermoelectric conversion element 11.

  As described above, by implementing the present invention, the thermal energy of high-temperature exhaust gas can be efficiently recovered with a small member. When heat is recovered by a fin or the like, heat is obtained from heat transfer from the gas on the fin surface, heat is transferred by heat conduction of the fin member, and heat is transferred to the thermoelectric element on the outer periphery of the exhaust pipe. On the other hand, since the geometric surface area in the pores of the porous ceramic is larger than the surface area of the fin and the efficiency of heat transfer is high, the member may be small. Further, radiation from the solid has higher heat transfer efficiency than conduction in the solid due to heat conduction of the fin member. In particular, the higher the temperature, the higher the heat transfer efficiency by radiation. In this case, the material used is limited to a high heat-resistant material such as ceramics. That is, a heat recovery member having excellent durability is provided.

In the present invention, the form of the piping is not particularly limited, and may be, for example, cylindrical (cylindrical, polygonal cylindrical, etc.). The form of the porous ceramic member may be , for example, a cylindrical shape or a polygonal cylindrical shape. However, when both the pipe and the porous ceramic member are cylindrical, it is particularly preferable that they are coaxial. Moreover, when piping or a porous ceramic member is cylindrical, the outer diameter and inner diameter may be changing toward the longitudinal direction. For example, it is possible to make the upstream side of the gas narrower and thicken the downstream side of the gas among the piping and the porous ceramic member.

  The material of the pipe is not particularly limited, but the material of at least the part that receives radiant heat in the pipe is transparent to heat radiation, or is a black body or a material having radiation / absorption characteristics close to that of a black body. preferable. Examples of such materials include quartz glass, ceramics such as silicon nitride, alumina, and cordierite, stainless steel whose surface is black-treated, and heat-resistant metals such as nickel.

  Inside the piping, it is preferable to block the path other than the porous ceramic member with a sealing material so that the exhaust gas permeates the porous ceramic member. For example, in the above example, 7 and 8 correspond to the sealing material. Such a sealing material preferably has a low thermal conductivity, preferably a dense material, and preferably has high durability in an exhaust gas environment.

  The material of the sealing member is preferably a dense material with low thermal conductivity, and may be integrally joined to the porous ceramic member. As a bonding method, diffusion bonding, brazing bonding, glass bonding, or the like is applied. Examples of this material include refractory metals (SUS, Ni alloy), ceramics (alumina, zirconia, mullite, spinel, silicon nitride, cordierite).

  The porous ceramic member preferably has a high porosity so that the pressure loss does not increase when the exhaust gas permeates. From this viewpoint, the porosity of the porous ceramic member is preferably 50% or more, and more preferably 60% or more. In addition, if the porosity of the porous ceramic member is too high, it is difficult to handle. From this viewpoint, 90% or less is preferable.

  The material of the porous ceramic member is preferably highly durable in an exhaust gas environment and has a high thermal emissivity. As a result, the porous ceramics deprived of heat of the exhaust gas has high energy conversion efficiency to radiant heat.

  Specifically, the form of the porous ceramic member is preferably a uniform foamed ceramic foam. Alternatively, a honeycomb structure as described later (the honeycomb cell wall has a high porosity) is also preferable. Examples of the material of the porous ceramic member include alumina, cordierite, zirconia, silicon nitride, and silicon carbide.

  The “ceramic foam” can be produced by impregnating a urethane foam with a ceramic slurry and then sintering. Alternatively, the ceramic raw material sol may be foamed and gelled at the end of the foaming to obtain a foam, which may be sintered to form a ceramic foam.

In the present invention , the heat recovery member is a thermoelectric conversion element. The thermoelectric conversion element converts heat energy into electric energy, and generates an electromotive force due to the Seebeck effect due to a temperature difference generated between the inner surface on the high temperature side and the outer surface on the low temperature side. A plurality of thermoelectric elements can be discretely arranged side by side in the circumferential direction on the outer surface of the exhaust gas pipe. By arranging in this way, more thermoelectric elements can be arranged, and heat energy can be efficiently supplied. Can be converted into energy. An electrode (not shown) is formed on the thermoelectric element. An air cooling or water cooling mechanism (not shown) can be arranged on the outer side which is the low temperature side.

  An exhaust gas purifying catalyst may be supported in the pores of the porous ceramic member. Thereby, it can be installed directly under the engine, and at the same time as purifying the exhaust gas, the heat of the high-temperature exhaust gas can be recovered. Not only that, it is also possible to recover the heat of purification reaction of the exhaust gas. Here, the exhaust gas purifying catalyst is, for example, a three-way catalyst supported on an alumina coat containing noble metals such as Pt, Rh, and Pd and CeO2 as an oxygen storage component.

  A large temperature gradient is generated in the porous ceramic member in the direction of permeation of the exhaust gas. From the viewpoint of preventing breakage due to thermal stress due to this, for example, the stress can be thermally dispersed by dividing the porous ceramic member into a plurality of parts.

For example, in the apparatus 1D of FIG. 4 , the porous ceramic member 19 includes an inner porous ceramic member 20 and an outer porous ceramic member 21. Each porous ceramic member is coaxial. The porous ceramic members 20 and 21 may be in close contact with each other, or a gap may be provided. The exhaust gas flows from the outer space 4 to the inner space 5 as indicated by an arrow C, and at this time, the waste heat is recovered by the porous ceramic member. Radiation is generated from the outer peripheral surface 19 a of the porous ceramic member 21 as indicated by an arrow E.

Moreover, in the apparatus 1E of FIG. 5 , the honeycomb structure 22 is used as a porous ceramic member. In this example, the exhaust gas flows from the outer space 4 to the inner space 5 as indicated by an arrow C, and at this time, waste heat is recovered by the porous ceramic member. Radiation is generated from the outer peripheral surface 22 a of the porous ceramic member 22 as indicated by an arrow E, and this is recovered by the heat recovery device 10. In this example, the cell walls of the honeycomb structure 22 are made of porous ceramics, and the exhaust gas flows through the cell walls.

  As described above, when a cylindrical porous ceramic member is installed in a pipe, gas flows in a direction perpendicular to the flow direction in the pipe even when the shape of the pipe is straight. It is easy to radiate waste heat in a direction perpendicular to the flow direction.

It is sectional drawing which shows typically the waste heat recovery apparatus 1 which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the waste heat recovery apparatus 1A which concerns on one Embodiment of this invention. It is a cross-sectional view which shows typically the waste heat recovery apparatus which concerns on embodiment of this invention. It is sectional drawing which shows typically the waste heat recovery apparatus 1D which concerns on other embodiment of this invention. It is sectional drawing which shows typically the waste heat recovery apparatus 1E which concerns on other embodiment of this invention.

Claims (5)

A waste heat recovery device installed in an exhaust pipe of an internal combustion engine of a vehicle,
A pipe for flowing the exhaust gas of the internal combustion engine, a cylindrical porous ceramic member that is installed in the pipe and through which the exhaust gas permeates , a sealing material that is installed on the inlet side of the porous ceramic member, porous ceramic rings installed on the outlet side of the member shape seal member, and the placed on the outside of the pipe, provided with a thermoelectric conversion element to collect radiant heat from the porous ceramic member, the exhaust gas, the The outer peripheral surface of the porous ceramic member that flows through the porous ceramic member from the space between the outer peripheral surface of the porous ceramic member and the inner peripheral surface of the pipe and flows into the inner space of the porous ceramic member. A waste heat recovery device for an internal combustion engine of a vehicle , wherein the radiant heat from the vehicle is recovered by the thermoelectric conversion element through the pipe . The waste heat recovery apparatus according to claim 1, wherein a plurality of the thermoelectric conversion elements are arranged in a circumferential direction on an outer surface of the pipe. The waste heat recovery apparatus according to claim 1 or 2 , wherein the porous ceramic member includes a plurality of porous ceramic layers. The waste heat recovery apparatus according to any one of claims 1 to 3 , wherein the porous ceramic member has a honeycomb structure including a porous wall. The waste heat recovery apparatus according to any one of claims 1 to 4 , wherein an exhaust gas purifying catalyst is supported on the porous ceramic member.

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