JP2015081527A - Heat insulation layer provided on member surface facing engine combustion chamber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat insulation layer that has high heat insulation performance, can prevent fuel penetration, can maintain high heat insulation performance for a long term, and can improve heat efficiency of an engine.SOLUTION: A heat insulation layer 21 provided on the surface of a member 19 facing an engine combustion chamber contains hollow particles 23 mainly composed of an inorganic oxide, and a non-powder type dense binder material 25 connecting between the hollow particles 23 and between the hollow particle 23 and the member 19. The hollow particles 23 are contained in the heat insulation layer 21 at a volume ratio of 60 vol.% or more and 75 vol.% or less. The heat conductivity of the heat insulation layer 21 is in the range of 0.10 W/m K or more and 0.16 W/m K or less. The volume specific heat of the heat insulation layer 21 is in the range of 350 kJ/mK or more and 720 kJ/mK or less.

Description

  The present invention relates to a heat insulating layer provided on a member surface facing an engine combustion chamber.

In the 1980s, as a way to increase the thermal efficiency of the engine, it is proposed to provide a heat-insulating layer in a portion facing the engine combustion chamber, then, heat-insulating layer made of ceramic sintered body, or low thermal conductivity of zirconia having a (ZrO ₂ ) A heat insulating layer composed of a sprayed layer containing particles has been proposed.

  In recent years, a heat insulating layer using a hollow material as a heat insulating material is known. For example, Patent Document 1 discloses a first heat insulating material that is a hollow material having a thermal conductivity lower than that of a base material provided with a heat insulating layer and a heat capacity per unit volume lower than that of the base material. An insulation layer for an internal combustion engine is presented that has a thermal conductivity and includes a second insulation for protecting the first insulation from combustion gases in the combustion chamber. In the heat insulating layer of Patent Document 1, the first heat insulating material has a heat capacity per unit volume lower than that of the second heat insulating material. As the first heat insulating material, hollow ceramic beads, glass beads, Examples thereof include a heat insulating material having a fine porous structure mainly composed of silica or silica aerosol. Further, as the second heat insulating material, solid ceramics such as zirconia, silicon, titanium or zirconium, organic silicon compounds containing carbon, oxygen, silicon, etc., or high strength and high heat resistance ceramic fibers, etc. Illustrated.

In Patent Document 1, as one of the indexes indicating the performance of the heat insulation layer, a change in the combustion chamber wall surface temperature (swing width: ΔT) during one combustion cycle of the diesel engine provided with the heat insulation layer is described. It is suggested that the swing width ΔT is related to heat loss. The concept is well-known, but is based on the formula for obtaining the heat loss Q, Q = A × h × (Tg−Twall). In this equation, A is the surface area (m ² ) in the cylinder, h is the heat transfer coefficient (W / m ² · K) due to the pressure and gas flow in the cylinder, and Tg is in the cylinder. Gas temperature (K), and Twall is the temperature (K) of the wall surface facing the cylinder (in contact with the combustion gas in the cylinder). As can be seen from the above equation, when the Twall rises so as to approach the temperature of Tg during combustion of the combustion gas, the value of the heat loss Q decreases. In other words, when the swing width ΔT is large, the value of the heat loss Q decreases. Therefore, the swing width ΔT is used as the index.

Republished patent WO2009 / 020206

  In Patent Document 1, a material having a thermal conductivity equivalent to zirconia is used as the second heat insulating material for the analysis of the swing width ΔT. When this is specifically zirconia, the heat insulating layer is considered to be coated with zirconia particles. In such a heat insulating layer, the fuel is infiltrated between the zirconia particles, or the infiltrated fuel is carbonized, so that the thermal conductivity is gradually increased. For this reason, not only the desired heat loss reduction effect is not obtained, but also the soaked fuel hardly contributes to combustion, so that the thermal efficiency is substantially lowered. Further, not only the zirconia particles but also the thermal spray layer or a heat insulating material such as ceramic, it is considered that the particles (powder) are bonded to each other to form a layer. This causes the same problem as above.

  The present invention has been made in view of the above-mentioned problems, and its purpose is to have high heat insulation properties, prevent the infiltration of fuel, maintain high heat insulation properties over a long period of time, and thereby improve the thermal efficiency of the engine. The purpose is to obtain a heat insulating layer that can be improved.

  In order to achieve the above-described object, the present invention provides a non-powder-like material that combines hollow particles, the hollow particles, and the hollow particles and a substrate as a material for the heat insulating layer of the engine combustion chamber wall surface. A dense binder material was used.

Specifically, the heat insulating layer provided on the surface of the member facing the engine combustion chamber according to the present invention includes a plurality of hollow particles mainly composed of an inorganic oxide, the hollow particles, and the hollow particles and the member. And a non-powder dense binder material that binds to each other, the hollow particles are contained in the heat insulating layer in a volume ratio of 60 vol% or more and 75 vol% or less, and the heat conductivity of the heat insulating layer is 0. It is 10 W / m · K or more and 0.16 W / m · K or less, and the heat capacity of the heat insulating layer is 350 kJ / m ³ · K or more and 720 kJ / m ³ · K or less.

According to the heat insulating layer provided on the surface of the member facing the engine combustion chamber according to the present invention, the volume ratio of the hollow particles is as large as 60 vol% or more as a component of the heat insulating layer, and a large amount of air layer can be contained in the heat insulating layer. The heat conductivity of a heat insulation layer can be reduced and the heat insulation performance of a heat insulation layer can be improved. Specifically, the heat insulating layer according to the present invention has a thermal conductivity of 0.10 W / m · K to 0.16 W / m · K, and 350 kJ / m ³ · K to 720 kJ / m ³ · Since it has a volumetric specific heat of K or less, the heat loss suppression effect in the combustion chamber can be increased. Note that the heat insulating layer having a low volume specific heat can solve the problem that the heat insulating layer temperature is lowered by intake air in the intake stroke of the engine, so that the intake charge amount is reduced, and the thermal efficiency can be improved. In addition, by setting the volume ratio of the hollow particles in the heat insulating layer to 75 vol% or less, a sufficient amount of the vitreous material for bonding the hollow particles can be secured, and a durable film is formed. Is possible. Further, the dense binder material is in a non-powder state, and unlike the porous sprayed layer or the ceramic layer such as zirconia, the dense binder material itself is dense, so that the fuel injected into the engine combustion chamber is contained in the heat insulating layer. Can be prevented from entering. As a result, the generation of carbon deposits due to the soaked fuel can be prevented and the heat insulation performance can be prevented from being lowered, so that the thermal efficiency of the engine can be improved.

  The heat insulation layer provided on the surface of the member facing the engine combustion chamber according to the present invention preferably has a thickness of 50 μm or more and 100 μm or less.

  When the thickness of the heat insulating layer is less than 50 μm, it is difficult to obtain sufficient heat insulating performance because the thickness is thin. On the other hand, even if the thickness of the heat insulating layer is larger than 100 μm, the heat insulating performance is not improved and only the cost is increased. For this reason, it is preferable that the thickness of a heat insulation layer shall be 50 micrometers or more and 100 micrometers or less.

  The heat insulating layer provided on the surface of the member facing the engine combustion chamber according to the present invention preferably has a temperature fluctuation range of 250 ° C. or more during one combustion cycle in HCCI combustion of the engine.

  If it does in this way, since the surface temperature which contacts the combustion gas of a heat insulation layer closely approximates combustion gas temperature, a heat loss can be made small.

  In the heat insulating layer provided on the surface of the member facing the engine combustion chamber according to the present invention, the engine is preferably switchable so that HCCI combustion is performed at a low load and SI combustion is performed at a high load.

HCCI combustion is also referred to as premixed compression auto-ignition (Homogeneous Charge Compression Ignition) combustion, and is a combustion mode different from normal Spark Ignition (SI) combustion. Accordingly, it is known as a combustion system in which gasoline in a combustion chamber is compressed and ignited in a lean atmosphere for combustion. HCCI combustion is the combustion in a relatively low temperature, and makes it possible the improvement of reducing the thermal efficiency of the NO _x emissions. For such an engine that performs HCCI combustion, the thermal efficiency can be further improved by using the heat insulating layer. Further, the heat insulating layer provided on the surface of the member facing the engine combustion chamber according to the present invention may have a temperature fluctuation range of 530 ° C. or less when the engine is performing SI combustion when the load is high. The engine may be capable of HCCI combustion in the entire region from a low load to a high load.

  According to the heat insulating layer on the surface of the member facing the engine combustion chamber according to the present invention, the thermal conductivity and volume specific heat are low, good heat insulating characteristics can be obtained, and further, the penetration of fuel can be prevented, and it is high over a long period of time. Thermal insulation can be maintained, and the thermal efficiency of the engine can be improved.

It is sectional drawing which shows the engine structure which concerns on embodiment of this invention. It is sectional drawing which shows the heat insulation layer provided in the member surface which faces the engine combustion chamber which concerns on this invention. It is an expanded sectional view showing the heat insulation layer provided in the member surface which faces the engine combustion chamber concerning the present invention. It is a graph which shows the relationship between the content rate of the hollow particle in a heat insulation layer, the heat conductivity of a heat insulation layer, and volume specific heat. It is a graph which shows the result of having analyzed swing width | variety (DELTA) T of the heat insulation layer surface which concerns on this invention.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its method of application, or its application.

  In this embodiment, a heat insulating layer on the surface of a member facing the engine combustion chamber is employed in the engine shown in FIG.

<Engine features>
In the direct injection engine E shown in FIG. 1, reference numeral 1 is a piston, reference numeral 3 is a cylinder block, reference numeral 5 is a cylinder head, reference numeral 7 is an intake valve for opening and closing the intake port 9 of the cylinder head 5, and reference numeral 11 is an exhaust port 13. An exhaust valve that opens and closes, reference numeral 15 denotes a fuel injection valve. The combustion chamber of the engine is formed by the top surface of the piston 1, the cylinder block 3, the cylinder head 5, and the valve head surfaces of the intake and exhaust valves 7 and 11 (surfaces facing the combustion chamber). A cavity 17 is formed on the top surface of the piston 1. In FIG. 1, illustration of the spark plug and the cylinder liner is omitted.

  The engine used in the present embodiment is not limited to an engine that performs only spark ignition (SI) combustion in which fuel is burned with the assistance of a normal spark plug. In addition to this, for example, the low load side of the engine is set as an operation region by premixed compression compression ignition (HCCI) combustion, and the high load side is spark ignition (Spark Ignition: SI) An engine that switches a combustion mode as an operation region by combustion may be used, or an engine that performs HCCI combustion in the entire region from a low load to a high load.

  By the way, it is known that the thermal efficiency of an engine increases as the geometric compression ratio increases theoretically and the excess air ratio of the working gas increases (increases the specific heat ratio). However, in practice, as the compression ratio is increased and the excess air ratio is increased, the cooling loss increases. Therefore, the improvement of the thermal efficiency due to the increase in the compression ratio and the excess air ratio reaches its peak.

  That is, the cooling loss depends on the heat transfer rate from the working gas to the engine combustion chamber wall, the heat transfer area, and the temperature difference between the gas temperature and the wall temperature. For this reason, in the engine combustion chamber, a heat insulating layer made of a material having a lower thermal conductivity than the metal base material of the engine component is formed on the surface of the metal base material.

<Configuration of heat insulation layer>
Next, the structure of the heat insulation layer formed on the surface of the member facing the engine combustion chamber will be described with reference to FIGS. In the present embodiment, the heat insulating layer formed on the top surface of the piston as the member surface facing the engine combustion chamber will be described, but the heat insulating layer formed on the member surface facing the other engine combustion chamber such as a cylinder block is also described. It can be set as the same structure.

  As shown in FIG. 2, a heat insulating layer 21 is formed on a top surface 19a (a member surface facing the engine combustion chamber) of a piston main body 19 as an engine member. A concave portion corresponding to the cavity 17 is formed at the center of the top surface 19a of the piston body 19, and the heat insulating layer 21 is formed with a uniform thickness so as to follow the shape of the top surface 19a. The piston main body 19 of this embodiment is made of an aluminum alloy that has been subjected to T6 treatment. Further, the top surface 19a of the piston body 19 on which the heat insulating layer 21 is formed may be subjected to a roughening treatment such as a blast treatment and an anodic oxidation treatment (alumite treatment). By performing the roughening treatment, irregularities are formed on the top surface 19a of the piston main body 19, and the adhesion between the piston main body 19 and the heat insulating layer 21 can be improved. As a result, the heat insulating layer 21 is peeled off from the piston main body 19. Can be prevented.

  As shown in FIG. 3, the heat insulating layer 21 of the present embodiment includes hollow particles 23 mainly composed of inorganic oxides and a dense binder material 25. In the heat insulating layer 21, the dense binder material 25 covers the hollow particles 23, the hollow particles 23 are bonded to each other, and the hollow particles 23 and the piston main body 19 are bonded to each other on the top surface 19 a of the piston main body 19. It has a layered structure. The dense binder material 25 combines them so as to fill the gaps between the hollow particles 23, and the dense binder material 25 is non-powdered and is itself densely configured. Yes. For this reason, there is no gap through which the fuel can pass between the hollow particles 23 or in the dense binder material 25 itself, and as a result, the fuel injected into the engine combustion chamber can be prevented from entering the heat insulating layer 21. .

  In the present embodiment, the dense binder material 25 is non-powdered as described above, and the material is not particularly limited as long as the dense binder material 25 itself is densely configured. For example, a silicone resin can be used. . As the silicone resin, for example, a silicone resin composed of a three-dimensional polymer having a high degree of branching represented by methyl silicone resin and methylphenyl silicone resin can be suitably used. As a specific example, for example, polyalkylphenylsiloxane can be used. Can be mentioned.

In the present embodiment, the hollow particles 23 mainly composed of an inorganic oxide include Si-based oxide components (for example, silica (SiO ₂ )) such as fly ash balloon, shirasu balloon, silica balloon, airgel balloon, or Al-based. It is preferable to employ ceramic hollow particles containing an oxide component (for example, alumina (Al ₂ O ₃ )). Each material and particle size are as shown in Table 1. The hollow particles 23 preferably have a median diameter of 5 μm or more and 30 μm or less, and hollow heavy particles having a median diameter of less than 5 μm may be further added.

For example, the chemical composition of the fly ash _{balloons, SiO 2; 40.1~74.4%, Al} 2 O 3; 15.7~35.2%, Fe 2 O 3; 1.4~17.5%, MgO; 0.2 to 7.4%, CaO; 0.3 to 10.1% (the above is mass%). The chemical composition of the Shirasu _{balloon, SiO 2; 75~77%, Al} 2 O 3; 12~14%, Fe 2 O 3; 1~2%, Na 2 O; 3~4%, K 2 O; 2~ 4%, IgLoss; 2 to 5% (the above is mass%).

  The heat insulating layer 21 contains such hollow particles 23 at a volume ratio of 60 vol% or more and 75 vol% or less. Since the content of the hollow particles 23 as a component of the heat insulating layer 21 is as large as 60 vol% or more by volume ratio, a large amount of air layer can be contained in the heat insulating layer 21. For this reason, the thermal conductivity and volume specific heat of the heat insulation layer 21 can be reduced, and the heat insulation performance of the heat insulation layer 21 can be improved. Moreover, since the volume ratio of the hollow particles 23 in the heat insulating layer 21 is 75 vol% or less, a sufficient amount of the dense binder material 25 for bonding the hollow particles 23 to each other can be secured to form a durable film. It becomes possible to do. The volume ratio of the hollow particles 23 to be contained is calculated from the apparent density of the particles and the density of the dense binder material 25, and then calculated from the mass of the hollow particles 23 added to the dense binder material 25. can do.

  Moreover, it is preferable that the heat insulation layer 21 is 50 micrometers or more and 100 micrometers or less in thickness. The reason for this is that when the thickness of the heat insulating layer is less than 50 μm, it is difficult to obtain sufficient heat insulating performance because the thickness is thin, while the heat insulating performance is large even if the thickness of the heat insulating layer is larger than 100 μm. This is because there is no change and the cost increases.

  In the present embodiment, a filler material may be included in the heat insulating layer 21 in order to improve the strength or hardness of the heat insulating layer 21.

<Performance test of heat insulation layer>
Below, the result of having examined the relationship between the hollow particle content ratio in the heat insulating layer on the surface of the member facing the engine combustion chamber according to the present embodiment, the thermal conductivity of the heat insulating layer, and the volume specific heat will be described. Here, different heat insulating layers are produced in the range of the content ratio of the hollow particles in the heat insulating layer from 0 vol% to 75 vol%, and the respective heat conductivity and volume specific heat of the heat insulating layers having different content ratios of the hollow particles. Were measured and compared. Specifically, as the heat insulating layer, four types of heat insulating layers each containing hollow particles at a volume ratio of 0 vol%, 55 vol%, 60 vol%, or 75 vol% were prepared.

  As a material for producing the heat insulating layer, the above Shirasu balloon was used for the hollow particles, a silicone resin was used as the dense binder material, and polyalkylphenylsiloxane was specifically used. A heat insulating layer containing these materials was formed on an aluminum alloy substrate. For the formation of the heat insulating layer, first, hollow particles were added to the silicone-based resin in the above volume ratio and mixed, and the mixture was applied onto an aluminum alloy substrate. Then, the heat insulation layer was formed on the said base material by drying and baking the apply | coated mixture.

The thermal diffusivity (m ² / s), density (kg / m ³ ) and weight specific heat (kJ / kg · K) were measured for each of the heat insulating layers having different volume ratios of the obtained hollow particles. Each of these measurement methods uses a conventional method, specifically, the thermal diffusivity is measured using the laser flash method, the density is measured using the Archimedes method, and the specific heat by weight is the differential scanning calorimetry (DSC method). And measured. In addition, the measurement was performed on 25 degreeC conditions. Based on these measurement results, the volume specific heat and thermal conductivity are expressed as follows: volume specific heat (kJ / m ³ · K) = density × thermal diffusivity, thermal conductivity (W / m · K) = thermal diffusivity × density × Each was calculated from the formula of weight specific heat. The result is shown in FIG.

As shown in FIG. 4, the heat conductivity and volume specific heat of the heat insulation layer decreased as the content ratio of the hollow particles in the heat insulation layer increased. Specifically, when the heat insulating layer does not contain hollow particles (0 vol%), the thermal conductivity was about 0.25 W / m · K and the volume specific heat was about 1800 kJ / m ³ · K. When the content ratio of the hollow particles is increased to 60 vol%, the thermal conductivity is about 0.16 W / m · K, the volume specific heat is reduced to about 720 kJ / m ³ · K, Both the thermal conductivity and the volume specific heat were low, and good values were obtained for use as a heat insulating layer. Furthermore, when the content ratio of the hollow particles in the heat insulating layer is increased to 75 vol%, the thermal conductivity is about 0.10 W / m · K, and the volume specific heat is reduced to about 350 kJ / m ³ · K. Even better values were obtained for use as a thermal insulation layer.

  From the above results, in the heat insulating layer, by including hollow particles at a high content ratio, specifically 60 vol% or more and 75 vol% or less, both the thermal conductivity and the volume specific heat are low, the heat insulating performance is high, and It was suggested that a heat-insulating layer having high durability can be obtained.

<Swing width analysis of heat insulation layer>
Next, the change in the combustion chamber wall surface temperature in one combustion cycle when the heat insulation layer according to the present invention was provided on the combustion chamber wall surface of the gasoline engine as described above was calculated using CAE. Here, a model of the combustion gas in the combustion chamber and the aluminum alloy base material of the member facing the combustion chamber is prepared, and in the combustion gas, the average temperature and pressure of the gas based on the gas equation of state from the amount of heat generated for one cycle below. On the other hand, for the aluminum alloy base material, the wall temperature of the surface of the heat insulating layer was calculated based on the calculated gas temperature and the thermal conductivity of the following heat insulating layer using a one-dimensional heat conduction equation. In this calculation, the thickness of the heat insulating layer provided on the combustion chamber wall surface is 75 μm, the heat conductivity of the heat insulating layer is 0.155 W / m · K, and the volume specific heat of the heat insulating layer is 708.4 kJ / m ³ K. did. The displacement of one cylinder of the engine was 500 cc, and the compression ratio was 18.4. Further, in this test, assuming that an engine that performs HCCI combustion at a low load and performs SI combustion at a high load, two types of tests, a case of performing HCCI combustion and a case of performing SI combustion, were performed. Specifically, in the case of assuming HCCI combustion, the engine rotation speed was set to 1000 rpm, the illustrated average effective pressure was set to 300 kPa, the load was low, and the generated heat amount for one cycle was set to 360 J. On the other hand, in the case of assuming SI combustion, the engine rotation speed was set to 6000 rpm, the illustrated average effective pressure was set to 1540 kPa, and the load was high, and the heat generation amount for one cycle was set to 1760 J. FIG. 5 shows the calculation result of the surface temperature of the heat insulating layer in one combustion cycle when the conditions are set in this way.

  As shown in FIG. 5, under a low load condition assuming HCCI combustion, the combustion stroke after the compression stroke in which the piston rose to the top dead center (crank angle (CA) = 360 ° in FIG. 5) It was found that the combustion chamber wall temperature rose from about 370 ° C. to about 670 ° C. That is, the swing width ΔT was about 300 ° C. Even in the case of HCCI combustion, which is combustion at a relatively low temperature, the swing width ΔT is preferably a value of 250 ° C. or more in order to obtain good heat insulation.

  On the other hand, in the case of high load conditions assuming SI combustion having a higher combustion temperature than HCCI combustion, the combustion chamber wall surface temperature rose from about 510 ° C. to about 1040 ° C. in the combustion stroke. That is, the heat insulation layer according to the present embodiment can increase the swing width ΔT to about 530 ° C. under high load conditions. For this reason, since the said wall surface temperature can also be raised largely following the temperature rise of combustion gas, a heat loss can be reduced more. Therefore, it was suggested that the said heat insulation layer shows a favorable heat insulation characteristic.

  As described above, the heat insulating layer provided on the surface of the member facing the engine combustion chamber according to the present embodiment has a low thermal conductivity and a low volume specific heat, and exhibits a high swing width ΔT as described above. Therefore, the thermal efficiency of the engine can be improved.

DESCRIPTION OF SYMBOLS 1 Piston 3 Cylinder block 5 Cylinder head 7 Intake valve 11 Exhaust valve 19 Piston main body 19a Top surface 21 Heat insulation layer 23 Hollow particle 25 Dense binder material

Claims (6)

A heat insulating layer provided on the surface of the member facing the engine combustion chamber,
A plurality of hollow particles mainly composed of inorganic oxide;
The hollow particles, and a non-powder dense binder material that bonds the hollow particles and the member,
The hollow particles are contained in the heat insulating layer in a volume ratio of 60 vol% or more and 75 vol% or less,
An engine combustion chamber having a thermal conductivity of 0.10 W / m · K to 0.16 W / m · K and a volume specific heat of 350 kJ / m ³ · K to 720 kJ / m ³ · K A heat insulating layer provided on the surface of the member facing the surface.   The heat insulating layer provided on the surface of the member facing the engine combustion chamber according to claim 1, wherein the thickness is 50 μm or more and 100 μm or less.   3. The heat insulating layer provided on the surface of the member facing the engine combustion chamber according to claim 1, having a temperature fluctuation range of 250 ° C. or more during one combustion cycle in HCCI combustion of the engine.   The heat insulation layer provided on the surface of the member facing the engine combustion chamber according to claim 3, wherein the engine is switchable so that HCCI combustion occurs at a low load and SI combustion occurs at a high load.   5. The heat insulating layer provided on the surface of the member facing the engine combustion chamber according to claim 4, wherein when the engine is performing SI combustion at a high load, the temperature fluctuation range is 530 ° C. or less.   The heat insulation layer provided on the surface of the member facing the engine combustion chamber according to claim 3, wherein the engine is capable of HCCI combustion in the entire region from a low load to a high load.

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