JP2011052630A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal combustion engine including a constructional member having an improved heat insulation property. <P>SOLUTION: Heat insulation material 26 is arranged adjacently to the inner wall of an exhaust passage 22. High-temperature working gas (exhaust gas) flows along a flow passage formed of the heat insulation material 26. In the heat insulation material 26, particles of MSS (Mesoporous-Silica-Sphere) particles 26a of a mean diameter of 0.1-3 μm are layered through joint material 26b so that the particles are compacted. A great number of mesopores 26c of a mean pore diameter of 1-10 nm are formed in the MSS particles 26a. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an internal combustion engine, and more particularly, to an internal combustion engine that employs a heat insulating material as part of a structural member that constitutes a combustion chamber or the like.

  Conventionally, when a heat insulating material is used for a structural member of an internal combustion engine, it is known that a cooling loss due to the structural member is reduced and thermal efficiency is increased. For example, Patent Literature 1 discloses a cylinder in which a liner portion of a cylinder block is formed of a porous ceramic material. Since this ceramic material is a porous material, it is considered that the heat insulating performance is high. Therefore, if this conventional cylinder is used, the thermal efficiency of the internal combustion engine can be increased, so that an improvement in output and fuel consumption can be expected.

JP-A-6-10757

  By the way, further improvement of the heat insulation performance is required for the structural members of the internal combustion engine. One means for this is to increase the porosity of the heat insulating portion of the structural member. Increasing the porosity of the heat insulating part means that the internal space of the heat insulating part is increased. Since the thermal conductivity of air is relatively small, increasing the internal space improves the heat insulation performance. However, when the internal space is increased, the strength per volume of the heat insulating material decreases. In addition, when the internal space is increased, it is difficult to uniformly configure the distribution of the space constituting the heat insulating material. For this reason, in an environment where strength is required for the heat insulating material, a large amount of the internal space of the heat insulating material cannot be taken, and uniform high heat insulating properties cannot be obtained.

  The present invention has been made in order to solve the above-described problems, and an object thereof is to provide an internal combustion engine including a structural member with improved heat insulation.

In order to achieve the above object, a first invention is an internal combustion engine,
A heat insulating material composed of an aggregate of spherical porous materials having pores with an average pore diameter of 1 to 10 nm and an average particle diameter of 0.1 to 3 μm, and disposed adjacent to the heat insulating material And a structural member having a base material.

The second invention is the first invention, wherein
The pores are configured to be radially formed from the central portion to the surface portion of the spherical porous material, and the heat insulating material configures at least a part of the inner wall of the flow path of the gas sucked into the internal combustion engine It is characterized by doing.

The third invention is the second invention, wherein
The gas contact surface in the heat insulating material and the heat insulating material adjacent surface in the base material communicate with each other through the gaps between the spherical porous material grains and the pores, and the thickness of the heat insulating material is 0.5 mm. It is characterized by the following.

The fourth invention is the invention according to any one of the first to third inventions,
The spherical porous material is spherical mesoporous silica.

According to the first invention, since the spherical porous material has an average particle diameter in the range of 0.1 to 3 μm, and the heat insulating material is an aggregate of the spherical porous materials having a uniform particle diameter, It becomes relatively homogeneous. In addition to high strength, the spherical porous material itself gathers together a set of grains, so that the heat insulating material has high strength.
In addition, when used in a combustion chamber of an internal combustion engine, a high-pressure field is formed in the combustion chamber, the thermal conductivity of gas molecules existing there is increased, and the amount of heat transferred by the gas molecules in the pores is increased. It cannot be ignored. In addition, in the high-pressure field, the mean free path of the gas itself becomes small, so the pores need to be made sufficiently small.
According to the first invention, since the pore diameter of the spherical porous material is 1 to 10 nm and is sufficiently smaller than the mean free path of the gas in the high-pressure field, it is possible to suppress the movement of heat due to the gas molecules in the pores. In addition, since the gap between grains becomes small, a part of such effects can be used. Therefore, the heat insulation performance can be improved rather than simply securing a space and performing heat insulation.

According to the second invention, the spherical porous material having radial pores can effectively disperse the stress applied to the particles. In addition, the heat insulating material that is the aggregate can have a high rigidity because these particles having a uniform particle diameter can be arranged at high density.
According to the third invention, the gas contact surface and the heat insulating material contact surface of the base material can be communicated with each other through the gaps between the particles of the spherical porous material and the pores. Therefore, it can be set as the structural member which has the thin heat insulating material of 0.5 mm or less which can adapt also to the environment where the gas pressure inhaled by the internal combustion engine changes.

  According to the fourth invention, it is possible to provide an internal combustion engine including a structural member whose heat insulating performance is improved by spherical mesoporous silica.

It is a figure for demonstrating the internal combustion engine of embodiment. It is the figure which expanded a part of exhaust path of FIG. It is a figure which shows the relationship between the size of the space in 1000 degreeC and 1 Mpa, and thermal conductivity.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

  FIG. 1 is a diagram for explaining a configuration of an internal combustion engine according to an embodiment of the present invention. Among the constituent members of the internal combustion engine 10 are a cylinder 12 and a cylinder head 14. A piston 16 is inserted into the inner diameter of the cylinder 12 so as to be slidable in the vertical direction. A combustion chamber 18 is formed by a portion surrounded by the inner peripheral surface of the cylinder 12, the lower surface of the cylinder head 14, and the top surface of the piston 16.

  The cylinder head 14 is connected to an intake passage 20 for introducing gas sucked from outside into the combustion chamber 18. The cylinder head 14 is connected to an exhaust passage 22 for discharging the gas discharged from the combustion chamber 18 to the outside. In the middle of the exhaust passage 22, a reflux passage 24 for returning a part of the gas flowing through the exhaust passage 22 to the intake passage 20 is connected.

  Further, as indicated by a thick line in FIG. 1, a heat insulating material 26 is provided on the inner wall of the combustion chamber 18. It is also effective to provide the heat insulating material 26 on a part of the inner wall of the exhaust passage 22 and the inner wall of the reflux passage 24. The heat insulating material 26 is provided with a thickness of 0.2 to 0.5 mm on each inner wall.

(Insulation 26)
FIG. 2 shows a part (enlarged) of a cross section of the exhaust passage 22 shown in FIG. As shown in FIG. 2, a heat insulating material 26 is disposed adjacent to the inner wall of the exhaust passage 22. The high temperature working gas (exhaust gas) flows along the flow path formed by the heat insulating material 26. The heat insulating material 26 is laminated in a state where each particle of MSS (Mesoporous-Silica-Sphere; spherical mesoporous silica) particles 26a is closely packed through a bonding material 26b. The bonding material 26b is disposed so as to connect the MSS particles 26a with a contact.

Thus, since the particle diameters of the MSS particles 26a are uniform, the particles can be arranged uniformly while reducing the gaps between the particles. In general, when the gas pressure fluctuates, the gas enters the gap between the particles due to the pressure drop, but since the particles are arranged uniformly with a small gap, the gas on the side that should hold the heat is directly Very little heat is transferred to the surface of the substrate, thus ensuring thermal insulation.
Here, “the particle size is uniform” means that the monodispersity is 10% or less when a plurality of particles (preferably 20 particles or more) manufactured under the same conditions are observed with a microscope. Shall mean. This monodispersity is expressed by dividing the standard deviation of the particle size by the average particle size. The particle size is determined by analysis of an observation image using a scanning electron microscope (SEM).

(MSS particle 26a)
As the name indicates, the MSS particles 26a constituting the heat insulating material 26 are spherical silica particles having mesopores 26c. In addition to the spherical particles, the particle diameter is extremely uniform, so that the particles can be densely stacked without gaps, and the exhaust passage 22 having rigidity can be formed. Here, “spherical” means that when a plurality of (preferably 20 or more) particles produced under the same conditions are observed with a microscope, the average value of sphericity of each particle is 13% or less. That means. The “sphericity” is an index representing the degree of deviation of the outer shape of each particle from the perfect circle, and the circumscribed circle and the particle with respect to the radius (r ₀ ) of the smallest circumscribed circle in contact with the particle surface. This is a value represented by the ratio (= Δr _max × 100 / r ₀ (%)) of the maximum value (Δr _max ) of the distance in the radial direction from each point on the surface.

  The MSS particles 26a have innumerable mesopores 26c formed from the center to the surface. By having innumerable mesopores 26c, a high porosity of 70% or more can be realized when formed into a molded body. Therefore, it is possible to configure the exhaust passage 22 having high heat insulation. Further, the innumerable mesopores 26c are formed from the central portion toward the surface portion, that is, the mesopores 26c are formed in a radial shape, thereby ensuring the uniformity of the heat insulating performance even at the individual particle level. can do. In addition, since the meso holes 26c are formed in a radial shape, an external force is received in the length direction of the hole with respect to deformation from any direction, and the rigidity of each particle is high. Therefore, it is possible to compensate for a decrease in strength per volume caused by increasing the porosity.

  By the way, in the combustion chamber of the internal combustion engine, the pressure fluctuates due to the vertical movement of the piston or the rapid combustion of the fuel mixture. Among these, especially in the case of high pressure, the mean free path itself of gas molecules existing in these engines is shortened.

  FIG. 3 is a diagram showing the relationship between the space size of air at 1000 ° C. and 1 MPa, for example, and the thermal conductivity. The horizontal axis represents the space size (nm), and the vertical axis represents the thermal conductivity (W / mK). As shown in FIG. 3, when the size of the space is reduced, the thermal conductivity of air is reduced. If the space size is made equal to or less than the mean free path (28 nm) of air, the heat conduction of air can be made sufficiently small.

  In this embodiment, the gas component in the combustion chamber is almost the same as air, and the diameter of the mesopores 26c in the MSS of the present invention is small enough to obtain the effect of reducing the thermal conductivity of the gas molecules. is there. Specifically, the mesopores 26c have a hole diameter of 1 to 10 nm (average), which is sufficiently below the mean free path, and heat conduction by gas molecules existing in the internal space of the heat insulating material even in a high pressure environment such as a combustion chamber Can be suppressed. The pore diameter is determined by a method of calculating from a pore distribution curve by a nitrogen gas adsorption method.

  Moreover, as described above, each particle of the MSS particle 26a has the mesopores 26c formed in a radial shape, and in addition to the high heat insulating property of the particle itself, each particle is connected at the contact point by the bonding material 26b. Therefore, the heat insulation as a structure is extremely high. Therefore, even if the heat insulating material is thin, sufficient heat insulating properties can be secured. Since the thickness can be reduced, the burden caused by the inflow and outflow of gas into the interparticle gap of the heat insulating material in the pressure fluctuation field in the combustion chamber is reduced, and fatigue damage of the heat insulating material due to gas flow can be avoided.

(Joint material 26b)
The bonding material 26b constituting the heat insulating material 26 is made of silica. However, the bonding material 26b may be an oxide of a transition metal element or a typical metal element such as alumina, titania, magnesia, or zirconia. Further, the bonding material 26b may be a mixture using two or more kinds of silica and oxides of these metal elements.

  Since the bonding material 26b connects each particle of the MSS particles 26a with a contact point, the shape thereof is not particularly limited. However, in order to connect each particle with a contact point, the surface area is desirably smaller than the surface area of the MSS particle 26a. In order for the heat insulating material 26 to exhibit low thermal conductivity and high rigidity, the ratio of the surface area of the bonding material 26b to the surface area of the MSS particles 26a is preferably 1/4 or less, and 1/10 or less. Is more desirable.

  There are various methods for joining the heat insulating material 26 to the piston 16. For example, there is a method of joining the heat insulating material after processing the piston. The manufacturing method includes (1) a base material forming step, (2) a base material cutting step, (3) a heat insulating material manufacturing step, and (4) a joining step.

  (1) In the base material forming step, a mold corresponding to a predetermined shape of the piston base material is prepared, and molten metal such as an aluminum alloy is injected into the mold. And it cools for a predetermined time in this state, and a piston base material is obtained by demolding.

  Subsequently, in the (2) base material cutting step, a predetermined cutting process is performed on the piston base material obtained in the (1) base material forming step.

  On the other hand, the heat insulating material 26 is produced separately from (1) the base material forming step and (2) the base material cutting step ((3) heat insulating material producing step). This step includes (3-1) a mixing step, (3-2) a molding step, (3-3) a reaction step, and (3-4) a removal step.

(3-1) In the mixing step, a small amount of the reactive binder and the third component are mixed in the MSS in which the masking substance is filled in the pores. Here, as the masking substance, a surfactant and a diameter expanding agent used in the production of MSS (described later) are used as they are. However, these surfactants and the like may be removed and used separately.
As the masking substance, octadecyltrimethylammonium chloride (C ₁₈ TMACl) and trimethylbenzene (TMB) are used, but this C ₁₈ TMACl may be used alone or another organic substance such as furfuryl alcohol may be used. That is, the masking substance is not particularly limited as long as it is a substance that can be decomposed and removed.
Further, tetraethoxysilane (TEOS) is used as the reactive binder, but silica raw materials such as tetramethoxysilane (TMOS), titanium tetraisopropoxide (((CH ₃ ) ₂ CHO) ₄ Ti), and the like are used. A compound that has a functional group capable of binding to a silanol group on the silica surface, such as an alkoxide containing the above metal element, and can be polymerized by an external stimulus such as heat or light to form a metal oxide may be used.
The reactive binder is mixed in a liquid state or a solution containing the reactive binder. By carrying out like this, a reactive binder can be unevenly distributed between MSS, and each particle | grain of MSS can be combined with a contact.
In mixing, it is desirable to adjust the amount of the reactive binder so that the bonding material 26b is 20 parts by weight or less with respect to 100 parts by weight of MSS.
Further, polytetrafluoroethylene (PTFE) is used as the third component. This PTFE is used as a binder for temporarily bonding the MSS particles until the MSS particles are firmly connected with the reactive binder. Note that the optimum amount of the third component can be selected.

  In the (3-2) molding step, the mixture obtained in the (3-1) mixing step is poured into a mold having a predetermined shape and compression molded. The pressure at the time of compression is 20 MPa, but may be 60 MPa, for example, and can be performed under optimum conditions in consideration of the composition of the material, the shape of the mold, the molding method, and the like.

  In the (3-3) reaction step, the reactive binder that is unevenly distributed among the MSS particles is reacted by applying external stimuli such as heat and light to the molded body obtained in the (3-2) molding step. It is a process to make. Specifically, TEOS is polymerized by applying heat to the obtained molded body to bind the MSS particles.

  The (3-4) removal step is a step of removing the masking substance from the MSS particles by firing the molded body obtained in the (3-3) reaction step. By passing through this process, the heat insulating material 26 in which the bonding material for connecting the MSS particles with the contacts is arranged can be produced. This step is performed by firing the molded body in air at 550 ° C. for 6 hours, and can be performed by selecting an optimum firing temperature, time, firing atmosphere and the like according to the type of the masking substance.

  In the steps (3-1) to (3-4), by optimizing various manufacturing conditions, it is possible to produce a heat insulating material in which MSS particles having a uniform particle size are stacked in a dense state. Thus, the produced heat insulating material has the outstanding heat insulation performance whose heat conductivity is 0.1 W / mK or less.

  (4) In the joining step, (2) the piston base material obtained in the base material cutting step and (3) the heat insulating material 26 obtained in the heat insulating material producing step are joined. For joining, for example, the heat insulating material 26 may be attached to the piston base material using an appropriate adhesive. Through this step, the piston 16 provided with the heat insulating material 26 on the surface can be manufactured.

  Next, a method for manufacturing MSS will be described. In MSS, (1) a raw material containing a silica raw material and a surfactant is mixed in a solvent and reacted under a predetermined temperature condition. During the reaction, the surfactant forms rod micelles by self-organization, and the rod micelles are oriented radially while maintaining hexagonal symmetry. This is a template for forming silica. Next, (2) a diameter expanding agent is added to the precursor particles containing the surfactant, and the pore diameter of the precursor is expanded under a predetermined temperature condition, and (3) the surfactant particles are converted into the surfactant. And the sizing agent is removed. By optimizing the production conditions (1) to (3) above, MSS having pores having an average pore diameter of 1 to 10 nm formed radially and having an average particle diameter of 0.1 to 3.0 μm. Particles can be produced.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 14 Cylinder head 16 Piston 22 Exhaust passage 24 Recirculation passage 26 Heat insulation material 26a Particle | grain 26b Joining material 26c Meso hole

Claims (4)

  A heat insulating material composed of an aggregate of spherical porous materials having pores with an average pore diameter of 1 to 10 nm and an average particle diameter of 0.1 to 3 μm, and disposed adjacent to the heat insulating material An internal combustion engine comprising a structural member having a base material.   The pores are configured to be radially formed from the central portion to the surface portion of the spherical porous material, and the heat insulating material configures at least a part of the inner wall of the flow path of the gas sucked into the internal combustion engine The internal combustion engine according to claim 1.   The gas contact surface in the heat insulating material and the heat insulating material adjacent surface in the base material communicate with each other through the gaps between the spherical porous material grains and the pores, and the thickness of the heat insulating material is 0.5 mm or less. The internal combustion engine according to claim 2, wherein   The internal combustion engine according to any one of claims 1 to 3, wherein the spherical porous material is spherical mesoporous silica.

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