JP5533446B2 - Internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine, and more particularly to an internal combustion engine having a heat insulating film on a combustion chamber wall.

  In order to reduce the heat loss of the internal combustion engine, a heat insulating film is provided on the combustion chamber wall. For example, Patent Document 1 includes a large number of granular heat insulating materials as a heat insulating film formed on a wall surface facing the combustion chamber of an internal combustion engine and a heat insulating material formed in a film shape. The material has a thermal conductivity equal to or lower than the thermal conductivity of the combustion chamber base material, and the granular heat insulating material has a thermal conductivity lower than the thermal conductivity of the combustion chamber base material and per unit volume of the base material. A structure having a heat capacity per unit volume lower than the heat capacity, a heat conductivity lower than the heat conductivity of the film-like heat insulating material, and a heat capacity per unit volume lower than the heat capacity per unit volume of the film-like heat insulating material Is disclosed.

  Although not directly related to the present invention, Patent Document 2 discloses, as an intake / exhaust passage structure of an internal combustion engine, a rough surface that rectifies the flow of fluid and reduces frictional resistance on the inner wall surfaces of the intake passage and the exhaust passage. Is disclosed. As this rough surface, it is described that a minute uneven shape having a height extending along the flow direction of about 200 μm or a shark-scale uneven shape is used.

As a technique related to the present invention, a dimensionless distance y ⁺ = (ρUτY / μ) = [ρ {τ _W / ρ} ^1/2 Y for a turbulent boundary layer when there is a flow along a solid wall. / Μ] is used to classify into a viscous bottom layer, a buffer region, and a turbulent region. Here, ρ is the density of the fluid, Uτ is the friction velocity, and τ _W is expressed as Uτ = {τ _W / ρ} ^1/2 where τ _W is the wall shear stress, Y is the distance from the wall surface, μ is the molecule Viscosity coefficient. In Non-Patent Document 1, it is stated that unevenness of about y ⁺ = 10 is optimal for reducing the frictional resistance near the wall surface.

JP 2009-243352 A JP 2000-18091 A

Sakate et. Al., Turbulence control with a wall-adjacent thin-layer spanwise velocity fluctuations, Int. J. Heat Fluid Flow, 17 (1996), p343

  As described above, in the internal combustion engine, when a heat insulating film or a heat shielding film is formed on the combustion chamber wall surface, the surface temperature of the heat insulating film follows the temperature of the combustion gas that becomes high during combustion, It becomes possible to reduce heat loss. This effect is larger as the heat flux flowing into the combustion chamber wall surface is larger. Therefore, the effect is greater when the internal combustion engine is at a high load than when the load is low. Therefore, it is desired to further reduce heat loss even when the internal combustion engine has a low load.

  By the way, active turbulent heat transfer occurs in the flow of the combustion gas or the like in the combustion chamber of the internal combustion engine. This turbulent heat transfer is one of the causes of heat loss.

  An object of the present invention is to provide an internal combustion engine that can suppress turbulent heat transfer in a combustion chamber.

The internal combustion engine according to the present invention is formed on a wall surface of the combustion chamber base material facing the combustion chamber, with each element constituting the combustion chamber of the internal combustion engine as a combustion chamber base material, and more than the thermal conductivity of the combustion chamber base material. A heat insulating film having a low thermal conductivity and a heat capacity per unit volume lower than the heat capacity per unit volume of the combustion chamber base material is provided, and the heat insulating film is a piston of the wall surface facing the combustion chamber of the combustion chamber base material. The upper surface or the lower surface of the cylinder head portion facing the upper surface of the piston has a predetermined uneven height and is formed radially from the position directly below the ignition plug on the upper surface of the piston, or the ignition of the lower surface of the head portion. look including an uneven shape formed radially from the plug position, uneven shape, the density of the fluid flowing through the combustion chamber and [rho, the molecular viscosity coefficient and mu, as the wall shear stress _{τ W, U τ = {τ} W / [rho} friction velocity U _tau represented by ^1/2 , Dimensionless distance calculated by the distance Y from the wall ^{_{y + = (ρU τ Y /}} μ) = [ρ {τ W / ρ} 1/2 Y / μ] using a dimensionless distance y ⁺ = 10 It has the uneven | corrugated height corresponding to .

  In the internal combustion engine according to the present invention, it is preferable that the heat insulating film includes a large number of hollow particle heat insulating materials formed in a granular form and a binder heat insulating material. In the internal combustion engine according to the present invention, the heat insulating film is preferably composed of an anodized film having a porous structure.

  Further, in the internal combustion engine according to the present invention, the piston or the head portion as the combustion chamber base material before the heat insulating film is formed includes an uneven shape having an upper surface having a predetermined uneven height in the case of the piston, In this case, it is preferable that the lower surface includes an uneven shape having a predetermined uneven height.

In the internal combustion engine according to the present invention, the heat insulating film has an uneven height corresponding to a dimensionless distance y ⁺ = 10, and the heat insulating film has an uneven shape having an uneven height of 0.1 mm to 0.2 mm. It is preferable to include.

  With the above configuration, in the internal combustion engine, the heat insulating film having a thermal conductivity lower than that of the combustion chamber base material and a heat capacity per unit volume lower than that of the combustion chamber base material faces the combustion chamber. Formed on the wall. And as for a heat insulation film, an unevenness | corrugation is radially formed from the position directly under the ignition plug of the upper surface of a piston. Or the uneven | corrugated shape is radially formed from the ignition plug position of the lower surface of a head part. Thereby, the flow of the gas in the combustion chamber is rectified, turbulent heat transfer can be suppressed, and heat loss can be reduced.

  Further, in the internal combustion engine, the upper surface of the piston is formed in an uneven shape in advance, and a heat insulating film is provided thereon. Or the lower surface of a head part is previously formed in uneven | corrugated shape, and a heat insulation film | membrane is provided on it. Thereby, an uneven | corrugated shape can be formed easily.

In an internal combustion engine, a dimensionless distance y ⁺ = (ρUτY / μ) = [ρ {τ _W / ρ} ^1/2 Y / calculated using the physical properties of the fluid flowing in the combustion chamber and the distance from the wall surface. [mu]] is used to include a concavo-convex shape having a concavo-convex height corresponding to the dimensionless distance y ⁺ = 10, so that the frictional resistance in the vicinity of the wall surface can be effectively reduced.

In the internal combustion engine, the heat insulating film has an uneven height of 0.1 mm or more and 0.2 mm or less. This uneven height is a value corresponding to the uneven height corresponding to the dimensionless distance y ⁺ = 10 under the operating conditions of a general internal combustion engine. Further, the height of the irregularities is preferably a height that does not allow the gas flow in the combustion chamber to enter the indentation, and if the height is too high, the irregular surface area increases, which may increase heat loss. is there. From these viewpoints, it is preferable that the height of the projections and depressions be set as described above when the operating condition is a general internal combustion engine.

It is a figure explaining the composition of the internal-combustion engine of an embodiment concerning the present invention. It is a figure explaining an example of composition of a heat insulation film in an embodiment concerning the present invention. It is an enlarged view of the A section of FIG. It is sectional drawing of the uneven | corrugated shaped part in embodiment which concerns on this invention.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. In the following, a spark ignition type gasoline engine will be described as an internal combustion engine. This is because, in a spark ignition type internal combustion engine such as a gasoline engine, rectification of the gas flow in the combustion chamber is more effective in suppressing heat loss. It is an illustration for being considered, and of course, a diesel engine may be used. In a compression ignition type internal combustion engine such as a diesel engine, the flow of gas in a combustion chamber is different from that of a gasoline engine, but turbulent heat transfer is also generated in the combustion chamber. Note that the internal combustion engine includes those with various specifications such as the number of cylinders and the arrangement form of the cylinders.

  In the following, a cylinder, a piston, an intake valve, an exhaust valve, and a spark plug will be described as the configuration of the combustion chamber. However, this is a major element related to the wall surface of the combustion chamber. Contains elements other than. For example, a fuel injection valve, a throttle valve, a flow meter, EGR, etc. are included, but these descriptions are merely omitted.

  Further, the following shape of the combustion chamber, arrangement of the components of the combustion chamber, and the like are examples for explanation, and can be appropriately changed according to the specifications of the internal combustion engine.

  Below, the same code | symbol is attached | subjected to the same element in all the drawings, and the overlapping description is abbreviate | omitted. In the description in the text, the symbols described before are used as necessary.

  FIG. 1 is a view for explaining the periphery of the combustion chamber 26 in the internal combustion engine 10. The internal combustion engine 10 is a spark ignition type gasoline engine, and FIG. 1 shows a cross-sectional view of one cylinder thereof.

  Here, a piston 12 and a cylinder 14 on which the piston 12 slides are shown. The piston 12 has a cylindrical outer shape, and the upper surface 30 has a recess called a cavity at the center. The cylinder 14 includes a cylindrical inner wall that guides the sliding of the piston 12 and an upper member that forms a cylindrical ceiling portion. The cylindrical portion is called a liner portion, and the upper member constituting the ceiling portion is called a head portion. A space surrounded by the upper surface 30 of the piston 12 and the lower surface 32 of the head portion of the cylinder 14 is a combustion chamber 26.

  An intake valve 16, an intake passage 18, an exhaust valve 20, an exhaust passage 22, a spark plug 24, and the like are provided in the head portion of the cylinder 14. Therefore, the elements constituting the inner wall of the combustion chamber 26 include the upper surface 30 of the piston 12, the lower surface 32 of the head portion of the cylinder 14, the tip portion of the intake valve 16 disposed on this lower surface, the tip portion of the exhaust valve 20, and ignition. The tip of the plug 24 and the like are included. These elements are collectively referred to as elements constituting the combustion chamber, and are referred to as a combustion chamber base material. Since the piston 12 and the cylinder 14 are made of an aluminum alloy, the material of the combustion chamber base material may be considered to be an aluminum alloy except for a part thereof.

  The heat insulating films 40 and 42 are formed on the wall surface where the combustion chamber base material faces the combustion chamber 26, and insulate the temperature of the combustion gas in the combustion chamber 26 so as not to escape to the combustion chamber base material to maintain a high temperature. It is a thermal barrier film. The heat insulating films 40 and 42 have a thermal conductivity lower than the thermal conductivity of the combustion chamber base material and a heat capacity per unit volume lower than the heat capacity per unit volume of the combustion chamber base material. The heat insulating film 40 is provided not only on the upper surface 30 of the piston 12 and the lower surface 32 of the head portion of the cylinder 14 but also on the lower surfaces of the intake valve 16 and the exhaust valve 20 disposed there. Moreover, it is good also as what provides a heat insulating film also in the liner part which is a cylindrical part of the cylinder 14. FIG.

  As such heat insulation films | membranes 40 and 42, what is comprised including many hollow particle heat insulating materials formed in granule and a binder heat insulating material can be used. The binder heat insulating material may be a film. An anodized film having a porous structure can be used. Below, the case where an anodized film is used is demonstrated. FIG. 2 is a cross-sectional view illustrating the configuration of the heat insulating film 42 as an anodized heat insulating film. The heat insulating film 42 is an alumina film 44 having a large number of holes 46 by anodizing aluminum which is a material of the piston 12 which is a combustion chamber base material by a known anodizing method. The thickness of the heat insulating films 40 and 42 can be adjusted by the conditions of the anodizing treatment. Considering the heat insulating effect, the thickness of the heat insulating films 40 and 42 can be set to, for example, about 50 μm to 150 μm.

  As shown in FIG. 2, the numerous holes 46 are formed in the alumina film 44 as elongated holes connected toward the combustion chamber 26 side. The diameter of the hole 46 is about several tens of nm. Since the air holes 46 are air, the heat conductivity is lower and the heat capacity per unit volume is smaller than that of the piston 12 made of aluminum.

  As the heat insulating films 40 and 42, if they have a thermal conductivity lower than the thermal conductivity of the combustion chamber base material and a heat capacity per unit volume lower than the thermal capacity per unit volume of the combustion chamber base material, It may be a known heat insulating film. For example, what combined many heat insulating materials formed in the granular form currently disclosed by patent document 1 and the heat insulating material formed in the film form can be used. Alternatively, a mixed film of appropriate hollow particles and a binder may be used.

  Returning to FIG. 1 again, the state of the upper surface 30 of the piston 12 is shown here. The uneven shape 50 provided on the upper surface 30 of the piston 12 is a minute unevenness that acts as a guide groove for rectifying the gas flow in the combustion chamber 26. As shown in FIG. 1, a plurality of uneven shapes 50 are provided radially from the central portion of the upper surface 30 of the piston 12 toward the peripheral portion.

  FIG. 3 is an enlarged view of a portion A in FIG. The uneven shape 50 has a shape called a triangular protrusion shape or a mountain shape. Since this radial shape extends from the central portion of the upper surface 30 of the piston 12 to the peripheral portion, the gas 60 ignited by the spark plug 24 at the center of the combustion chamber of the gasoline engine flows into the peripheral portion, It can be rectified radially.

  As a result, the flow of the gas 60 is neatly guided from the central portion to the peripheral portion, so that the turbulent flow of the gas 60 can be suppressed, turbulent heat transfer can be prevented, and the action of the heat insulating films 40 and 42 can be prevented. The heat loss of the engine 10 can be further reduced.

  A similar uneven shape can be provided on the lower surface 32 of the head portion of the cylinder 14. Also in this case, uneven shapes are formed radially from the center of the lower surface 32 of the head portion. The uneven shape is preferably provided on both the upper surface 30 of the piston 12 and the lower surface 32 of the head portion. Of course, as described above, it may be provided only on the upper surface 30 of the piston 12, or may be provided only on the lower surface 32 of the head portion. Also, the concave and convex shapes may be provided on the lower surfaces of the intake valve 16 and the exhaust valve 20 so as to be aligned with the concave and convex shapes 50 on the lower surface 32 of the head portion.

  FIG. 4 is an enlarged cross-sectional view of the concavo-convex shape 50. The concavo-convex shape 50 is such that the upper surface of the piston 12 that is the combustion chamber base material is previously formed into a concavo-convex shape, and anodization is performed in this state, resulting in the concavo-convex shape 50 of the heat insulating film 42. That is, the upper surface 30 of the piston 12 as the combustion chamber base material before the heat insulating film 42 is formed is molded in advance so as to have a predetermined uneven height h.

  The unevenness height h is preferably set such that the vortex in the combustion chamber 26 does not enter the unevenness, that is, into the groove. By doing so, it becomes easy to maintain the temperature of the gas 60 in the combustion chamber 26 at a high temperature. In FIG. 4, the groove width is substantially the same as the uneven height h because it is shown by the unevenness of the right triangle cross section.

From the analysis of the fluid flow, as described in Non-Patent Document 1, it is considered optimal for the flow in the vicinity of the wall surface to consider the dimensionless distance y ⁺ as about 10. As described above, the dimensionless distance y ⁺ = (ρUτY / μ) = [ρ {τ _W / ρ} ^1/2 Y / μ], where ρ is the density of the fluid and Uτ is the friction velocity. In this case, Uτ = {τ _W / ρ} ^1/2 where τ _W is a wall shear stress, Y is a distance from the wall surface, and μ is a molecular viscosity coefficient.

When Y is set to h and the maximum pressure at this time is set to 2 MPa to 3 MPa in a combustion period when a general gasoline engine is operated at 50% load, h corresponding to y ⁺ = 10 is obtained on the upper surface of the piston 12. H = 0.1 mm to 0.2 mm. Therefore, the uneven height h adapted to the flow along the wall surface of the gas 60 in the combustion chamber 26 is preferably about 0.1 mm to 0.2 mm. From another point of view, if the height is too high, the surface area of the concavo-convex shape 50 increases, and heat loss cannot be reduced.

  The internal combustion engine according to the present invention can be used for gasoline engines and diesel engines.

  DESCRIPTION OF SYMBOLS 10 Internal combustion engine, 12 Piston, 14 Cylinder, 16 Intake valve, 18 Intake path, 20 Exhaust valve, 22 Exhaust path, 24 Spark plug, 26 Combustion chamber, 30 Upper surface, 32 Lower surface, 40,42 Thermal insulation film, 44 Alumina film, 46 holes, 50 irregularities, 60 gas.

Claims (5)

Each element constituting the combustion chamber of the internal combustion engine is formed on the wall surface of the combustion chamber base material facing the combustion chamber, and has a thermal conductivity lower than that of the combustion chamber base material, and the combustion chamber A heat insulating film having a heat capacity per unit volume lower than the heat capacity per unit volume of the base material,
The heat insulating film has a predetermined uneven height on the upper surface of the piston or the lower surface of the head portion of the cylinder facing the upper surface of the piston among the wall surfaces of the combustion chamber base material facing the combustion chamber. the formed radially from the spark plug position directly below the upper surface, or viewing including an uneven shape formed radially from the spark plug position of the lower surface of the head portion,
The uneven shape is
The density of the fluid flowing through the combustion chamber and [rho, the molecular viscosity coefficient and mu, as the wall shear stress tau _W, and friction velocity U _tau represented by _{U τ = {τ W / ρ} } 1/2, from the wall surface Using dimensionless distance y ⁺ = (ρU _τ Y / μ) = [ρ {τ _W / ρ} ^1/2 Y / μ] calculated by distance Y, irregularities corresponding to dimensionless distance y ⁺ = 10 An internal combustion engine having a height . The internal combustion engine according to claim 1,
An internal combustion engine, wherein the heat insulating film includes a large number of hollow particle heat insulating materials formed in a granular form and a binder heat insulating material. The internal combustion engine according to claim 1,
An internal combustion engine, wherein the heat insulating film is composed of an anodized film having a porous structure. The internal combustion engine according to claim 1,
The piston or head portion as the combustion chamber base material before the heat insulation film is formed includes a concavo-convex shape whose upper surface has a predetermined concavo-convex height in the case of a piston, and in the case of a head portion, the lower surface thereof has a predetermined concavo-convex shape. An internal combustion engine comprising an uneven shape having a height. The internal combustion engine according to any one of claims 1 to 4 ,
The internal combustion engine, wherein the heat insulating film includes a concavo-convex shape having a concavo-convex height of 0.1 mm to 0.2 mm as a concavo-convex height corresponding to the dimensionless distance y ⁺ = 10.

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