Exhaust gas treatment system

Abstract

An alcohol engine (10) in an exhaust gas treatment system (1) is configured to combust a fuel containing greater than 20 vol% of a high-concentration alcohol. The ratio (a / b) of the length (a) of an exhaust port (12) to the length (b) of an exhaust pipe (13) upstream of a catalyst (14) is 0.250 or less, which is the reciprocal of the ratio of the thermal conductivity of the exhaust port material to the exhaust pipe material, and 0.083 or more, which is a value obtained by subtracting 1 from the reciprocal of the ratio of the low heating value of E20 fuel to E0 fuel. The exhaust port (12), the exhaust pipe (13), and a catalyst carrier (141) are configured to form a temperature gradient from a combustion chamber (111) to the catalyst (14) for exhaust gas of the high-concentration alcohol fuel at the time of cold start, and to establish a heat energy transfer path that suppresses local heat concentration for the exhaust gas of the high-concentration alcohol fuel at the time of high load.

Description

Exhaust Gas Treatment System

[0001] The present invention relates to an exhaust gas treatment system for an alcohol engine that uses alcohol fuel.

[0002] Patent Document 1 discloses a control technology for optimizing fuel injection control and catalytic exhaust gas purification in an internal combustion engine of a saddle-type vehicle. This technology can reduce the emission of harmful substances and alleviate the environmental burden. This technology is expected to be compatible with the use of various fuels, such as gasoline and alcohol fuel.

[0003] International Publication No. 2020 / 162002

[0004] In the exhaust gas treatment system for an alcohol-fueled engine disclosed in Patent Document 1, it is desirable to use a high-concentration alcohol fuel having an alcohol concentration of more than 20% by volume. However, this high-concentration alcohol fuel poses the following technical problems.

[0005] Cold Start: The physical properties of high-concentration alcohol fuels present unique challenges during cold engine start-up. The heat of vaporization of ethanol (approximately 838 kJ / kg) is more than twice that of gasoline (approximately 350 kJ / kg). This results in a significant heat absorption during the fuel vaporization process, significantly lowering the mixture temperature. Furthermore, unlike hydrocarbon molecules, the primary component of gasoline, alcohol molecules possess a dipole moment due to the OH groups within the molecules. This enhances heat transfer to the intake system and combustion chamber walls, increasing heat loss. This results in a significant drop in exhaust gas temperature and a decrease in the average kinetic energy of the exhaust gas molecules. Furthermore, condensation of water vapor generated by alcohol fuel combustion further increases heat loss in the exhaust passage. These phenomena make it difficult to overcome the activation energy barrier for catalytic reactions, reducing the efficiency of oxidation and NOx reduction reactions on platinum-group catalysts. Furthermore, the temperature rise of the catalyst support is delayed, reducing the overall reaction efficiency of the catalyst.

[0006] [High Load] Different issues arise under high loads. High-concentration alcohol fuels contain oxygen atoms in their molecules, resulting in a lower lower heating value compared to gasoline fuel. The lower heating value of ethanol (26.7 MJ / kg) is approximately 62% of that of gasoline (43.2 MJ / kg). Therefore, increasing the fuel supply to achieve the same power output increases the number of reactive molecules in the exhaust gas. Furthermore, the oxygen atoms in the alcohol molecules promote localized oxidation reactions. As a result, localized exothermic reactions are concentrated near the exhaust port due to the increase in oxygen-containing intermediate products, and rapid oxidation reactions occur at the catalyst inlet due to the high temperature of the exhaust gas and the high density of reactive molecules. Furthermore, accumulation of reaction heat creates hot spots within the catalyst, increasing thermal stress. These phenomena accelerate thermal degradation of the catalyst, leading to thermal agglomeration of precious metal particles and peeling of the support layer. Furthermore, uneven temperature distribution reduces the catalyst's conversion efficiency, and rapid oxidation reactions at high temperatures promote side reactions such as acetaldehyde production. This disrupts the thermal balance of the entire catalyst system.

[0007] As described above, conventional exhaust system configurations have not been able to adequately address the issues that are specific to high-concentration alcohol fuels during cold start-up and high load. Therefore, an object of the present invention is to provide an exhaust gas treatment system that is compatible with engines that use high-concentration alcohol fuels with an alcohol concentration of more than 20% by volume.

[0008] (1) The exhaust gas treatment system for an alcohol engine of the present invention comprises a cylinder head forming a combustion chamber, an exhaust port formed in the cylinder head and discharging exhaust gas from the combustion chamber, an exhaust pipe connected to the exhaust port, and a catalyst for treating exhaust gas obtained by burning a fuel containing alcohol, wherein the alcohol engine is configured to burn a fuel containing a high concentration of alcohol of more than 20% by volume, the exhaust port is formed of an aluminum alloy with a thermal conductivity of 110 W / (m·K) or more, the exhaust pipe is formed of a stainless steel alloy or a titanium alloy with a thermal conductivity of 27.5 W / (m·K) or less, the catalyst comprises a metal carrier having a passage wall, and the carrier forms a heat conduction structure in direct metal contact or contact via a metal member with the metal exhaust pipe, and the length (a) of the exhaust port is 100 mm. The ratio (a / b) of the length (b) of the exhaust pipe upstream of the catalyst is configured to be 0.250 or less, which is the reciprocal of the ratio of the thermal conductivity of the exhaust port material to the exhaust pipe material, and 0.083 or more, which is the value obtained by subtracting 1 from the reciprocal of the ratio of the lower heating value of E20 fuel to E0 fuel, and the exhaust port, the exhaust pipe, and the catalyst carrier are configured to form a temperature gradient from the combustion chamber to the catalyst by heat conduction through the exhaust port, heat retention through the exhaust pipe, and heat dispersion by the catalyst, for exhaust gas of high concentration alcohol fuel during cold start, and to establish a thermal energy transfer path that suppresses local heat concentration by dispersion of thermal energy through the exhaust port, heat transfer suppression through the exhaust pipe, and heat dispersion by the catalyst, for exhaust gas of high concentration alcohol fuel during high load.

[0009] The following describes the effects of the exhaust gas treatment system for alcohol engines described in (1) above. [High-concentration alcohol fuel] Generally, the lower heating value (LHV) of gasoline (E0) fuel is 38-47 (MJ / kg). Here, 43.2 (MJ / kg) is used as a representative value. The lower heating value of ethanol fuel is 21-30 (MJ / kg). Here, 26.7 (MJ / kg) is used as a representative value. The lower heating value of methanol fuel is 17-22 (MJ / kg). Here, 19.8 (MJ / kg) is used as a representative value.

[0010] The relationship between E20 and E0 ethanol fuels (gasoline fuel) is explained below. The lower heating value of E20 fuel is calculated as follows: E20 LHV = 0.8 x 43.2 + 0.2 x 26.7 = 39.9 (MJ / kg). The lower heating value ratio of E20 fuel to E0 fuel is 0.92361. Because this lower heating value is proportional to the exhaust gas temperature, this ratio is also equal to the ratio of the exhaust gas temperatures. Taking the reciprocal of this ratio is 1.08271, which indicates the ratio of the fuel amounts required to achieve the same output. Subtracting 1 from this value, 0.08271, indicates the additional fuel amount required when using E20 fuel and also corresponds to the decrease in exhaust gas temperature. Therefore, high-concentration alcohol fuel is not limited to ethanol fuel; any alcohol fuel with an LHV of 0.083 or higher can achieve the same effects.

[0011] A specific example is methanol fuel M15. For M15 fuel, subtracting 1 from the reciprocal of the lower heating value ratio to E0 fuel gives a value of 0.08844. In other words, the value obtained by subtracting 1 from the reciprocal of the lower heating value ratio of M15 fuel to E0 fuel is equal to or greater than the threshold value of 0.083. Incidentally, the lower heating value of methanol is 19.8 (MJ / kg). The lower heating value of the entire M15 fuel is calculated as follows: LHV of M15 = 0.85 x 43.2 + 0.15 x 19.8 = 39.69 (MJ / kg)

[0012] As described above, the value obtained by subtracting 1 from the reciprocal of the lower heating value ratio of E20 fuel to E0 fuel is 0.08271, which is smaller than the threshold value of 0.083. On the other hand, the value obtained by subtracting 1 from the reciprocal of the lower heating value ratio of E22 fuel to E0 fuel is 0.09174, and fuels with ethanol concentrations equal to or higher than E22 fuel exceed the threshold value of 0.083. Thus, for ethanol fuels with higher concentrations than E20 fuel and ethanol fuels with higher concentrations than M15, the value obtained by subtracting 1 from the reciprocal of the lower heating value ratio to E0 fuel is equal to or greater than the threshold value of 0.083. Therefore, for alcohol fuels with an alcohol concentration greater than 20% by volume, the value obtained by subtracting 1 from the reciprocal of the lower heating value ratio to E0 fuel is equal to or greater than the threshold value of 0.083.

[0013] [Cold Engine Start] In a typical exhaust gas treatment system, the cross-sectional area of ​​the exhaust passage from the exhaust port to the exhaust pipe and then to the catalyst inlet is designed to avoid abrupt changes and gradually expand before the catalyst, thereby reducing exhaust resistance. This prevents a decrease in exhaust gas flow velocity due to changes in the temperature gradient and achieves a flow velocity distribution suitable for reaction in the catalyst. However, the three metal components—the aluminum alloy exhaust port, the stainless steel or titanium alloy exhaust pipe, and the metal catalyst passage wall—each have different thermal characteristics. Therefore, simply combining these components can easily cause a significant change in the temperature gradient of the exhaust gas from the combustion chamber that burns fuel containing a high concentration of alcohol to the catalyst that treats that exhaust gas.

[0014] When the temperature gradient of exhaust gas from the combustion chamber to the catalyst changes significantly, the kinetic energy of exhaust gas molecules decreases, changing the flow rate of the exhaust gas and increasing the risk of water vapor condensation, reducing the efficiency of the supply of reactants to the catalyst. Furthermore, the catalyst's activation temperature is delayed, disrupting the adsorption / desorption balance on the catalyst surface, slowing the reaction rate and reducing the efficiency of the catalytic reaction. Furthermore, the temperature distribution within the catalyst becomes uneven, resulting in localized low-temperature areas, delaying the activation of the entire catalyst and reducing purification performance. In addition, the uneven distribution of thermal energy within the exhaust system causes fluctuations in exhaust resistance, affecting engine back pressure and reducing the overall performance of the exhaust gas treatment system, which treats high-concentration alcohol exhaust gases.

[0015] To address these issues during cold engine start-up, the present invention utilizes the thermal properties of three metal components: an aluminum alloy exhaust port, a stainless steel or titanium alloy exhaust pipe, and a metal catalyst passage wall. This combines these components to (1) systematically suppress changes in the temperature gradient from the combustion chamber to the catalyst, and (2) efficiently retain the thermal energy of high-concentration alcohol exhaust gases to promote catalyst activation, thereby improving high-concentration alcohol exhaust gas treatment performance during cold engine start-up.

[0016] In this exhaust gas treatment system of the present invention, the exhaust port formed in the cylinder head that forms the combustion chamber is made of an aluminum alloy with a thermal conductivity of 110 (W / (m·K)) or more, the exhaust pipe connected to the exhaust port is made of a stainless steel alloy or titanium alloy with a thermal conductivity of 27.5 (W / (m·K)) or less, and the catalyst is designed with a metal passage wall, so that the entire path from the combustion chamber to the catalyst is made of metal. Furthermore, by combining metal materials with significantly different thermal properties - an exhaust port with a high thermal conductivity and an exhaust pipe with a low thermal conductivity - and taking advantage of this difference in thermal conductivity, the ratio (a / b) of the length of the exhaust port (a) to the length of the exhaust pipe (b) is set to 0.250 or less, which is the reciprocal of the ratio of the thermal conductivity of the exhaust port material to the exhaust pipe material.

[0017] This prevents excessive absorption of the thermal energy of exhaust gas from high-concentration alcohol fuel, which has been cooled compared to gasoline fuel, by short exhaust ports with high thermal conductivity. The difference between the thermal energy absorbed by short exhaust ports with high thermal conductivity and that absorbed by exhaust pipes with low thermal conductivity can be reduced. With this configuration, the present invention can systematically suppress changes in the temperature gradient from the combustion chamber to the catalyst during cold engine start-up, while utilizing the thermal properties of the metal components to suppress the drop in exhaust gas temperature due to the high heat of vaporization specific to high-concentration alcohol fuel. As a result, the entire catalyst can be efficiently heated, achieving early activation and improving exhaust gas purification performance during cold engine start-up.

[0018] [High Load] In a typical exhaust gas treatment system, the cross-sectional area of ​​the exhaust passage from the exhaust port to the exhaust pipe and then to the catalyst inlet is set so that there is no sudden change, and it gradually expands before the catalyst, reducing exhaust resistance. This allows for an increase in exhaust gas flow rate under high load and achieves a flow velocity distribution that is suitable for reaction at the catalyst. In addition, by expanding the cross-sectional area before the catalyst, the flow velocity at the catalyst inlet is appropriately adjusted, setting the reaction time inside the catalyst.

[0019] However, the three metallic components—the aluminum alloy exhaust port, the stainless steel or titanium alloy exhaust pipe, and the metallic catalyst passage wall—each have different thermal characteristics. Therefore, simply combining these components can cause problems. In particular, when burning high-concentration alcohol under high load, the high-temperature exhaust gas is likely to cause localized heat concentration as it travels from the combustion chamber to the catalyst.

[0020] Localized heat concentration under high loads is due to the lower heating value of high-concentration alcohol fuel, approximately 62% that of gasoline. This difference in lower heating value necessitates an increased fuel supply volume to achieve the same power output, resulting in an increased number of reactive molecules in the exhaust gas. Furthermore, oxygen atoms in alcohol molecules promote localized oxidation reactions, leading to localized exothermic reactions concentrated near the exhaust port due to the increased production of oxygen-containing intermediate products. Rapid oxidation reactions occur at the catalyst inlet due to the high temperature of the exhaust gas and the high density of reactive molecules. Furthermore, the accumulation of reaction heat within the catalyst creates hot spots, increasing thermal stress and accelerating thermal degradation of the catalyst, leading to thermal aggregation of precious metal particles and peeling of the support layer. In addition, uneven temperature distribution reduces the catalyst's conversion efficiency, and rapid oxidation reactions at high temperatures promote side reactions such as acetaldehyde, leading to reduced performance and durability of the entire exhaust gas treatment system treating high-concentration alcohol exhaust gas.

[0021] To address these issues, this configuration utilizes the thermal properties of three metal components: an aluminum alloy exhaust port, a stainless steel or titanium alloy exhaust pipe, and a metal catalyst passage wall. This combines these components to (1) uniformly distribute heat from the combustion chamber to the catalyst, and (2) appropriately control the rapid oxidation reaction of high-concentration alcohol exhaust gases, thereby improving the performance of high-concentration alcohol exhaust gas treatment under high loads and improving the durability of the catalyst.

[0022] In this exhaust gas treatment system of the present invention, the exhaust port formed in the cylinder head that forms the combustion chamber is made of an aluminum alloy with a thermal conductivity of 110 (W / (m·K)) or more, the exhaust pipe connected to the exhaust port is made of a stainless steel alloy or titanium alloy with a thermal conductivity of 27.5 (W / (m·K)) or less, and the catalyst is designed with a metal passage wall, so that the entire path from the combustion chamber to the catalyst is made of metal. Furthermore, by combining metal materials with significantly different thermal properties - an exhaust port with a high thermal conductivity and an exhaust pipe with a low thermal conductivity - and taking advantage of this difference in thermal conductivity, the ratio (a / b) of the length of the exhaust port (a) to the length of the exhaust pipe (b) is set to 0.083 or more, which is the reciprocal of the ratio of the lower heating value of E20 fuel to E0 fuel minus 1.

[0023] Here, we explain the relationship between E20 fuel and E0 fuel (gasoline fuel). The lower heating value ratio of E20 fuel to E0 fuel is approximately 0.92. Because this lower heating value ratio is proportional to the exhaust gas temperature, this ratio is also equal to the exhaust gas temperature ratio. Taking the reciprocal of this ratio is approximately 1.083, which indicates the ratio of the fuel amounts required to achieve the same output. Subtracting 1 from this value, 0.083, indicates the additional fuel amount required when using E20 fuel and also corresponds to the decrease in exhaust gas temperature. By setting the ratio of exhaust port length to exhaust pipe length (a / b) greater than this value of 0.083, (1) it is possible to accommodate the increased fuel amount required to suppress the decrease in the lower heating value of E20 fuel, and (2) it is possible to appropriately respond to the resulting change in exhaust gas temperature.

[0024] This setting controls the thermal energy of exhaust gases caused by the increased supply of high-concentration alcohol fuel. Specifically, the thermal energy is dispersed without being locally absorbed in the short exhaust port with high thermal conductivity. Furthermore, the heat transfer of the dispersed exhaust gas thermal energy is suppressed in the subsequent exhaust pipe with low thermal conductivity. Therefore, heat dispersion in the short exhaust port with high thermal conductivity and heat transfer in the exhaust pipe with low thermal conductivity are optimized, suppressing local chemical reactions.

[0025] With this configuration, the present invention can suppress heat concentration during high-load operation due to the increased fuel supply rate and accelerated local chemical reactions that are unique to high-concentration alcohol fuels, while utilizing the thermal properties of the metal components to uniformly distribute heat from the combustion chamber to the catalyst. As a result, stable reactions are achieved throughout the catalyst, improving exhaust purification performance and catalyst durability during high-load operation.

[0026] [Theoretical Relationship Between Thermal Conductivity and Temperature Gradient Control] The relationship between thermal conductivity and temperature gradient control is explained based on Fourier's law. ２The thermal conductivity (q) is expressed as the product of the temperature gradient dT / dx (K / m) and the thermal conductivity λ (W / (m·K)): q = -λ(dT / dx). From this relationship, a high thermal conductivity (110 W / (m·K) or higher) exhaust port can achieve a large heat flux even with a small temperature gradient. This allows the local temperature drop caused by the heat of vaporization of alcohol fuel (838 kJ / kg for ethanol) to be quickly suppressed by heat inflow from the surrounding area. Specifically, compared to a conventional aluminum alloy with a thermal conductivity of 96 W / (m·K), a heat flux approximately 15% greater for the same temperature gradient can be achieved. This value is sufficient to suppress the temperature fluctuations associated with the additional fuel ratio (8.271%) when using E20 fuel.

[0027] On the other hand, an exhaust pipe with low thermal conductivity (27.5 (W / (m·K)) or less) requires a temperature gradient approximately four times larger to achieve the same heat flux. Due to this characteristic, the heat dispersed at the exhaust port is transferred slowly through the exhaust pipe, resulting in a uniform temperature gradient throughout the entire exhaust system. This is a relationship theoretically derived from the ratio of thermal conductivities in Fourier's law (110 / 27.5 ≒ 4).

[0028] In this way, by appropriately combining materials with different thermal conductivities, it is possible to control the temperature fluctuations specific to alcohol fuels and optimize heat transport up to the catalyst activation temperature. In particular, by setting the ratio (a / b) of the exhaust port length (a) to the exhaust pipe length (b) to be 0.083 or greater, it is possible to theoretically optimize temperature gradient control and heat dispersion effects. This value of 0.083 is calculated by subtracting 1 from the reciprocal of the ratio of the lower heating value of E20 fuel to E0 fuel, and represents the minimum value required for theoretical heat flux control.

[0029] [Heat dissipation mechanism under high load] The heat dissipation effect under high load can be quantitatively explained from the relationship between the thermal properties of the material and the heat of reaction. The lower heating value of high-concentration alcohol fuel is approximately 62% of that of gasoline fuel, so the amount of fuel supplied increases to obtain the same output. The mechanism for effectively dissipating the heat generated by this increased fuel is as follows.

[0030] 1. Thermal diffusivity α (m ２The thermal diffusivity is expressed by the following formula: α = λ / (ρ × c) where λ is the thermal conductivity (W / (m·K)) ρ is the density (kg / m ３ ) c: specific heat (J / (kg K)) The thermal diffusivity of an aluminum alloy with a thermal conductivity of 110 (W / (m K)) or more is approximately 4.5 x 10 －５ (m ２ / s) or more, which is 27.5 (W / (m K)) or less of stainless steel alloy (approximately 0.7 × 10 －５ (m ２ This difference in thermal diffusivity prevents a rapid temperature rise at the exhaust port and allows the thermal energy to be dispersed spatially.

[0031] 2. Control of local reaction heat Under high load, local oxidation reactions are promoted by oxygen atoms in alcohol molecules. The amount of heat generated per unit volume at this time, q' (W / m ３ ) is expressed by the following formula: q′=q ０ (1 + 0.08271) where, q ０ : Reference heating value 0.08271: Additional fuel ratio for E20 fuel. The reason for using the additional fuel ratio for E20 fuel, 0.0827, in the above formula is that the present invention targets alcohol fuels with alcohol concentrations ranging from over 20% by volume to 100% by volume. In the above formula, the value of E20 fuel, which has the largest lower heating value within this alcohol concentration range, is used as the reference. Heat dispersion using a high thermal conductivity material is effective for heating values ​​that increase from this reference heating value. Specifically, for materials with thermal conductivity of 110 (W / (m·K)) or higher, the temperature rise ΔT (K) is suppressed by the following formula: ΔT=q'L ２ / (8λ) where, L: characteristic length (m).

[0032] 3. Control by time constant The time constant τ(s) of the thermal response at the exhaust port is expressed by the following formula: τ = L ２ / α High thermal conductivity materials have a smaller time constant, allowing localized temperature increases to be dispersed quickly to the surrounding area. This means that the temperature increase caused by the 8.271% additional heat generation when using E20 fuel can theoretically be dispersed to the surrounding area in approximately 1 / 6.4 of the time.

[0033] In this way, by appropriately combining the thermal properties of materials, it is possible to theoretically optimize heat dispersion under high loads. In particular, by setting the ratio of exhaust port length to exhaust pipe length (a / b) to 0.083 or greater, the increase in heat generation due to additional fuel can be appropriately controlled and catalyst durability can be ensured. Note that the ratio (a / b) is set to 0.083 or greater because it is greater than the additional fuel ratio of E20 fuel, 0.08271, and the number of digits for this value is adjusted to three decimal places.

[0034] [Overall System] The exhaust gas treatment system of the present invention combines an exhaust port made of aluminum alloy, which has thermal conductivity, with an exhaust pipe made of stainless steel or titanium alloy, which has low thermal conductivity, in an optimal length ratio, and further employs a catalyst with a metal catalyst passage wall, thereby combining the characteristics of alcohol fuel with the thermal properties of metal materials. With this configuration, the entire path from the combustion chamber to the catalyst is made of metal, realizing cooperation that makes the most of the thermal properties of each component.

[0035] During cold engine start-up, the present invention effectively retains the thermal energy of the exhaust gas, promoting early catalyst activation, by suppressing the drop in exhaust gas temperature caused by the high heat of vaporization unique to high-concentration alcohol fuels through the use of a high-thermal conductivity exhaust port made of an aluminum alloy and an appropriate length ratio. Furthermore, the low-thermal conductivity exhaust pipe slows the transfer of thermal energy and suppresses rapid changes in the temperature gradient. Meanwhile, during high loads, the present invention suppresses the increase in the number of reactive molecules in the exhaust gas due to an increase in the fuel supply rate and the rapid oxidation reaction of the oxygen atoms of the alcohol molecules by (1) effectively dispersing the thermal energy through a short, high-thermal conductivity exhaust port and (2) controlling heat transfer through a low-thermal conductivity exhaust pipe, thereby suppressing localized heat concentration. This suppresses the formation of hot spots within the catalyst, reducing thermal degradation of the catalyst and the occurrence of side reactions.

[0036] In this way, the exhaust gas treatment system of the present invention is designed to combine the properties of high-concentration alcohol fuel with the thermal properties of metal materials, thereby improving exhaust gas treatment performance and catalyst durability during cold starts and high loads, and effectively resolving issues that could not be addressed with conventional exhaust system configurations.

[0037] [Selection of an Aluminum Alloy with a Thermal Conductivity of 110 (W / (m·K)) or More] The thermal conductivity of common cast aluminum alloys (e.g., AC4B, AC4CH, ADC12) is in the range of 96 to 200 (W / (m·K)) at 25°C. In the present invention, an aluminum alloy with a thermal conductivity of 110 (W / (m·K)) or more is selected for use in the cylinder head, in order to adjust for changes in the temperature gradient and promote heat dispersion under high loads. This lower limit of 110 (W / (m·K)) is based on theoretical calculations that take into account the characteristics of alcohol fuel. Specifically, since the lower heating value of E20 fuel is 92.361% of that of E0 fuel (gasoline fuel), an additional 8.271% of E20 fuel is required to achieve the same power output as E0 fuel. To mitigate the effects of this additional fuel, a margin of at least 15% is required (96 x 1.15 = 110.4 W / m K) above the lower limit thermal conductivity of typical aluminum alloys, which is 96 W / m K. This margin factor of 15% is set to take into account the temperature drop due to the heat of vaporization of alcohol fuel (838 kJ / kg for ethanol) and the resulting impact on catalyst activation. This margin factor also prevents a reduction in heat dissipation capacity, which is necessary to suppress localized heat concentration under high loads. Therefore, the lower limit of 110 W / m K is appropriate as the theoretical minimum required to accommodate the unique thermal characteristics of alcohol fuel. Note that the above values ​​are at 25°C.

[0038] Furthermore, the thermal conductivity of aluminum alloys changes relatively little with temperature near room temperature (20-30°C), varying only by a few percent. This is because there are no significant changes in the crystal structure or phonon mean free path within this temperature range. Therefore, it is technically reasonable to use the thermal conductivity at 25°C as a representative value. Furthermore, compared to stainless steel alloys and titanium alloys, the thermal conductivity of aluminum alloys remains several times higher, so the intended effect of the difference in thermal conductivity between the materials in this configuration is stably achieved near room temperature.

[0039] [Selection of a Stainless Steel Alloy or Titanium Alloy with a Thermal Conductivity of 27.5 (W / (m·K)) or Less] The thermal conductivity of typical stainless steel alloys for exhaust pipes at 25°C is in the range of 23 to 27 (W / (m·K)) for ferritic (400 series) SUS409L, SUS436L, and SUS439L, and 14 to 17 (W / (m·K)) for austenitic (300 series) SUS304 and SUS316, while the range for titanium alloys for exhaust pipes is 16 to 22 (W / (m·K)). The present invention contemplates the use of stainless steel alloys or titanium alloys for exhaust pipes, and selects a stainless steel alloy or titanium alloy with a thermal conductivity of 27.5 (W / (m·K)) or less to utilize its low thermal conductivity to adjust temperature gradient changes and promote heat dispersion under high loads. Note that the above values ​​are at 25°C.

[0040] Furthermore, the thermal conductivity of stainless steel alloys and titanium alloys for exhaust pipes changes relatively little with temperature near room temperature (20-30°C), varying only by a few percent. This is because there is no significant change in the mean free path of free electrons in the crystal structure within this temperature range. Therefore, it is technically appropriate to use the thermal conductivity at 25°C as a representative value. Furthermore, compared to aluminum alloys for cylinder heads (110 (W / (m·K)) or higher), the thermal conductivity of stainless steel alloys and titanium alloys for exhaust pipes remains low, at less than one-quarter of that of aluminum alloys for cylinder heads (110 (W / (m·K)) or higher). Therefore, the effect of the difference in thermal conductivity between materials intended by this invention can be stably obtained near room temperature.

[0041] (2) The exhaust port may be formed of an AC4 aluminum alloy having a thermal conductivity of 120 W / (m·K) or more. The exhaust pipe may be formed of a stainless steel alloy or a titanium alloy having a thermal conductivity of 27.5 W / (m·K) or less. The ratio (a / b) of the length (a) of the exhaust port to the length (b) of the exhaust pipe upstream of the catalyst may be smaller than 0.230, which is the reciprocal of the ratio of the thermal conductivity of the exhaust port material to the exhaust pipe material, and may be greater than or equal to 0.083, which is the reciprocal of the ratio of the lower heating value of E20 fuel to E0 fuel minus 1. The exhaust port, the exhaust pipe, and the catalyst carrier may be made of metal, and may be configured to stably form a temperature gradient from the combustion chamber to the catalyst for high-concentration alcohol fuel exhaust gases during cold engine start-up through heat conduction by the exhaust port, heat retention by the exhaust pipe, and heat dispersion by the catalyst, and to establish a thermal energy transfer path that further suppresses local heat concentration for high-concentration alcohol fuel exhaust gases during high load operation through dispersion of thermal energy by the exhaust port, suppression of heat transfer by the exhaust pipe, and heat dispersion by the catalyst.

[0042] The following describes the effects of the exhaust gas treatment system for an alcohol engine (2) above.

[0043] [Overall System] The exhaust gas treatment system of the present invention combines an exhaust port made of AC4-based aluminum alloy, which contains an appropriate amount of silicon (Si) and has excellent castability and heat resistance, with a thermal conductivity of 120 (W / (m·K)) or more, with an exhaust pipe made of stainless steel or titanium alloy, which has a low thermal conductivity of 27.5 (W / (m·K)) or less, at an optimal length ratio of 0.230 or less, which is the reciprocal of the thermal conductivity ratio, and further employs a catalyst with metal catalyst passage walls, thereby combining the characteristics of alcohol fuel with the thermal properties of metal materials. This configuration allows the entire path from the combustion chamber to the catalyst to be constructed of metal, achieving a combination that takes advantage of the excellent manufacturability and stable thermal properties of AC4-based aluminum alloy, which has an optimized silicon content.

[0044] During cold engine start-up, the present invention suppresses the drop in exhaust gas temperature caused by the high heat of vaporization specific to high-concentration alcohol fuel by using an AC4 aluminum alloy optimized through silicon content and heat treatment, with a stable thermal conductivity of 120 (W / (m·K)) or more and a length ratio of 0.230 or less, thereby stably retaining the thermal energy of the exhaust gas and promoting early catalyst activation. Furthermore, an exhaust pipe with a low thermal conductivity of 27.5 (W / (m·K)) or less appropriately slows the transfer of thermal energy and suppresses sudden changes in the temperature gradient.

[0045] On the other hand, under high loads, the present invention further suppresses localized heat concentration by (1) effectively dispersing the heat energy through a short exhaust port made of AC4 aluminum alloy with a thermal conductivity of 120 (W / (m·K)) or more, which achieves stable manufacturing quality through optimized silicon content, and (2) appropriately controlling heat transfer through an exhaust pipe with a low thermal conductivity of 27.5 (W / (m·K)) or less, thereby stably suppressing the formation of hot spots inside the catalyst and reducing thermal degradation of the catalyst and the occurrence of side reactions.

[0046] In this way, the exhaust gas treatment system of the present invention is designed to combine the characteristics of high-concentration alcohol fuel with the stable thermal properties of AC4 aluminum alloy, which has excellent castability and heat resistance due to its optimized silicon content, thereby improving exhaust gas treatment performance and catalyst durability during cold starts and high loads, and effectively resolving issues that could not be addressed with conventional exhaust system configurations. Furthermore, the practical silicon content of AC4 aluminum alloy and appropriate heat treatment conditions enable both high manufacturing quality and stable thermal properties to be achieved.

[0047] [Selection of AC4-based aluminum alloy with thermal conductivity of 120 (W / (m·K)) or more] Among common aluminum alloys for casting, AC4-based (Al-Si-based) aluminum alloys have excellent castability and heat resistance, and are widely used for engine parts. By selecting an AC4-based alloy that can stably achieve a thermal conductivity of 120 (W / (m·K)) or more through practical Si content and heat treatment conditions, manufacturability and thermal properties are both achieved. Note that the above values ​​are those at 25°C.

[0048] In the invention of (2) above, AC4 aluminum alloys are used in the cylinder heads of high-performance engines, and an AC4 material with a thermal conductivity of 120 (W / (m·K)) or more is selected to effectively promote heat dispersion during high loads while stably adjusting the temperature gradient during cold start-up. This also contributes to improving manufacturing quality while increasing the dispersion effect of exhaust gas thermal energy during high output.

[0049] [Theoretical Relationship Between Thermal Properties and Manufacturability of AC4 Aluminum Alloys] The technical significance of a thermal conductivity of 120 (W / (m·K)) or more in AC4 aluminum alloys can be explained by the following quantitative relationship.

[0050] 1. Relationship between silicon content and thermal conductivity The effect of silicon content on thermal conductivity of AC4 alloys can be approximated by the following formula: λ = λ ０ (1-kSi×CSi) where λ ０ : Thermal conductivity of pure aluminum [approximately 237 (W / (m·K))] kSi: Silicon influence coefficient [approximately 0.05 ( / %Si)] CSi: Silicon content [wt%]

[0051] By stably ensuring a thermal conductivity of 120 (W / (m·K)) or more within a practical silicon content range (7-11%), the following effects can be obtained: a) Improved castability - Composition range close to the eutectic composition (12.6% Si) - Appropriate fluidity and control of solidification shrinkage b) Stabilization of properties through heat treatment - Precipitation strengthening through T6 treatment - Stabilization of thermal conductivity

[0052] 2. Contribution to temperature gradient control The AC4 series requirement of 120 (W / (m・K)) or more adds a margin of approximately 9% to the basic requirement of 110 (W / (m・K)) mentioned above. This margin brings about the following effects: a) Absorption of manufacturing variations - Tolerance range of silicon content: ±0.5% - Fluctuations in heat treatment conditions: ±3% b) Ensuring long-term reliability - Changes in characteristics due to thermal fatigue: -5% or less - Changes over time: -2% or less These margins make it possible to stably maintain characteristics of 110 (W / (m・K)) or more throughout the product's lifespan.

[0053] 3. Theoretical basis for the 0.083-0.230 range of the length ratio (a / b) This range is derived from the following two theoretical values: Lower limit 0.083 - derived from the lower heating value ratio of E20 fuel - ensuring the minimum required amount of heat dispersion Upper limit 0.230 - reciprocal of the thermal conductivity ratio (27.5 / 120 ≒ 0.230) - maximum value required for uniform heat flux

[0054] [Selection of Stainless Steel Alloy or Titanium Alloy with Thermal Conductivity of 27.5 (W / (m·K)) or Less] This point is the same as above.

[0055] (3) The exhaust port may be formed of an aluminum alloy having a thermal conductivity of 140 W / (m K) or more, and the exhaust pipe may be formed of a stainless steel alloy or a titanium alloy having a thermal conductivity of 27.5 W / (m K) or less. The ratio (a / b) of the length (a) of the exhaust port to the length (b) of the exhaust pipe upstream of the catalyst may be set to 0.200 or less, which is the reciprocal of the ratio of the thermal conductivity of the exhaust port material to the exhaust pipe material, and to 0.083 or more, which is the reciprocal of the ratio of the lower heating value of E20 fuel to E0 fuel minus 1. The exhaust port, the exhaust pipe, and the catalyst carrier may be made of metal, and may be configured to form a temperature gradient from the combustion chamber to the catalyst for high-concentration alcohol fuel exhaust gas during cold engine start-up by heat conduction at high thermal conductivity by the exhaust port, heat retention at low thermal conductivity by the exhaust pipe, and heat dispersion by the catalyst, and to establish a thermal energy transfer path that suppresses local heat concentration for high-concentration alcohol fuel exhaust gas during high load operation by dispersing thermal energy at high thermal conductivity by the exhaust port, suppressing heat transfer at low thermal conductivity by the exhaust pipe, and dispersing heat by the catalyst.

[0056] The following describes the effects of the exhaust gas treatment system for an alcohol engine (3) above.

[0057] [Overall System] The exhaust gas treatment system described in (3) above combines an exhaust port made of aluminum alloy with a high thermal conductivity of 140 (W / (m K)) or more with an exhaust pipe made of stainless steel or titanium alloy with a low thermal conductivity of 27.5 (W / (m K)) or less, in an optimal length ratio of 0.200 or less, which is the reciprocal of the thermal conductivity ratio, and further employs a catalyst with metal catalyst passage walls, thereby fusing the characteristics of alcohol fuel with the thermal properties of metal materials. With this configuration, the entire path from the combustion chamber to the catalyst is made of metal, achieving cooperation that takes advantage of the high thermal property differences between each component.

[0058] During cold engine start-up, the present invention effectively suppresses the drop in exhaust gas temperature caused by the high heat of vaporization specific to high-concentration alcohol fuel by using an exhaust port made of an aluminum alloy with a high thermal conductivity of 140 (W / (m·K)) or more and a length ratio of 0.200 or less, thereby more efficiently retaining the thermal energy of the exhaust gas and promoting early catalyst activation. Furthermore, the present invention uses an exhaust pipe with a low thermal conductivity of 27.5 (W / (m·K)) or less to more reliably slow the transfer of thermal energy and suppress sudden changes in the temperature gradient.

[0059] On the other hand, under high loads, the present invention reduces the localized heat concentration by (1) dispersing the heat energy more effectively with a short exhaust port having a high thermal conductivity of 140 (W / (m·K)) or more and (2) controlling the heat transfer more reliably with an exhaust pipe having a low thermal conductivity of 27.5 (W / (m·K)) or less, due to the increase in the number of reactive molecules in the exhaust gas caused by an increase in the amount of fuel supplied and the rapid oxidation reaction of the alcohol molecules by the oxygen atoms. This more reliably suppresses the formation of hot spots inside the catalyst, reducing the thermal degradation of the catalyst and the occurrence of side reactions.

[0060] In this way, the exhaust gas treatment system of the present invention is designed to combine the characteristics of high-concentration alcohol fuel with the thermal properties of metal materials, which have more clearly distinct differences, thereby improving exhaust gas treatment performance and catalyst durability during cold starts and high loads, and more effectively resolving issues that could not be addressed with conventional exhaust system configurations.

[0061] [Selection of an aluminum alloy with a thermal conductivity of 140 (W / (m·K)) or more] The thermal conductivity of common aluminum alloys for casting (AC4B, AC4CH, ADC12, etc.) is in the range of 96 to 200 (W / (m·K)) at 25°C. In the present invention, the aluminum alloy is intended for use in the cylinder head of a higher-performance engine, and a high thermal conductivity material of 140 (W / (m·K)) or more is selected to more reliably adjust the temperature gradient during cold start-up and more effectively promote heat dispersion during high loads. This improves the dispersion effect of the thermal energy of exhaust gases during high output. Note that the above values ​​are at 25°C.

[0062] Furthermore, the thermal conductivity of aluminum alloys changes relatively little with temperature near room temperature (20-30°C), fluctuating only by a few percent. This is because there are no significant changes in the crystal structure or phonon mean free path within this temperature range. Therefore, it is technically reasonable to use the thermal conductivity at 25°C as a representative value. Furthermore, compared to stainless steel alloys and titanium alloys (27.5 (W / (m·K)) or less), aluminum alloys with a thermal conductivity of 140 (W / (m·K)) or more maintain a value more than five times higher. Therefore, the intended effect of the large difference in thermal conductivity between the materials in this configuration is more stable near room temperature.

[0063] [Theoretical basis for improving the performance of aluminum alloys with thermal conductivity of 140 (W / (m·K)) or more] The requirement of thermal conductivity of 140 (W / (m·K)) or more is an improvement of approximately 27% from the basic requirement of 110 (W / (m·K)), and is based on the following theoretical basis.

[0064] 1. Response to increased heat load in high-power engines In high-power engines, the heat flux per unit time q [W / m ２ ] becomes larger. ０ (1+P) q ０ : Heat flux at standard output P: Output improvement rate (e.g., 0.25) To accommodate this increased heat flux, the following relational expression is derived from Fourier's law of heat conduction: λ ２ / λ １ =q ２ / q １ = 1 + P λ ２ ≧110×(1+0.27)≒140(W / (m・K))

[0065] 2. Optimization of the thermal property difference between materials Increasing the thermal conductivity ratio by more than five times (140 / 27.5≧5) has the following effects: a) Improved temperature gradient control - Heat flux difference: 27% increase compared to conventional models - Response speed: 27% improvement compared to conventional models b) Enhanced heat dispersion effect - Thermal diffusivity difference: 27% increase compared to conventional models - Local heat concentration suppression effect: 27% improvement compared to conventional models

[0066] 3. Basis for optimization of length ratios of 0.2 or less In order to make the most of the differences in thermal properties between materials, it is useful to satisfy the following relationship: a / b≦27.5 / 140 ≒ 0.200 This means the following: - Optimization of thermal energy transfer - Stabilization of temperature gradient formation - Effective suppression of localized heat concentration With this theoretical backing, the use of materials with high thermal conductivity of 140 (W / (m·K)) or more provides necessary and sufficient characteristics to meet the performance demands of high-output engines.

[0067] [Selection of Stainless Steel Alloy or Titanium Alloy with Thermal Conductivity of 27.5 (W / (m·K)) or Less] This point is the same as above.

[0068] (4) The exhaust port may be formed of an AC4 aluminum alloy having a thermal conductivity of 140 W / (m K) or more. The exhaust pipe may be formed of a stainless steel alloy or a titanium alloy having a thermal conductivity of 27.5 W / (m K) or less. The ratio (a / b) of the length (a) of the exhaust port to the length (b) of the exhaust pipe upstream of the catalyst may be set to be 0.200 or less, which is the reciprocal of the ratio of the thermal conductivity of the exhaust port material to the exhaust pipe material, and 0.083 or more, which is the reciprocal of the ratio of the lower heating value of E20 fuel to E0 fuel minus 1. The exhaust port, the exhaust pipe, and the catalyst carrier may be made of metal, and may be configured to stably form a temperature gradient from the combustion chamber to the catalyst for high-concentration alcohol fuel exhaust gases during cold engine start-up by heat conduction at high thermal conductivity by the exhaust port, heat retention at low thermal conductivity by the exhaust pipe, and heat dispersion by the catalyst, and to establish a thermal energy transfer path that further suppresses local heat concentration for high-concentration alcohol fuel exhaust gases during high load operation by dispersing thermal energy at high thermal conductivity by the exhaust port, suppressing heat transfer at low thermal conductivity by the exhaust pipe, and dispersing heat by the catalyst.

[0069] The following describes the effects of the exhaust gas treatment system for an alcohol engine (4) above.

[0070] [Overall System] The exhaust gas treatment system described in (4) above combines a high-thermal conductivity exhaust port made of AC4-series aluminum alloy, which contains an appropriate amount of silicon (Si) and has excellent castability and heat resistance, with a thermal conductivity of 140 (W / (m·K)) or more, and a low-thermal conductivity exhaust pipe made of stainless steel or titanium alloy, with a thermal conductivity of 27.5 (W / (m·K)) or less, at an optimal length ratio of 0.200 or less, which is the reciprocal of the thermal conductivity ratio, and further employs a catalyst with metal catalyst passage walls, thereby combining the characteristics of alcohol fuel with the thermal properties of metal materials. This configuration allows the entire path from the combustion chamber to the catalyst to be constructed of metal, achieving a combination that takes advantage of the excellent manufacturability and high thermal properties of AC4-series aluminum alloy, which has a high thermal conductivity of 140 (W / (m·K)) or more while optimizing the silicon content.

[0071] During cold engine start-up, the present invention effectively suppresses the drop in exhaust gas temperature caused by the high heat of vaporization specific to high-concentration alcohol fuels by using an AC4 aluminum alloy with a high thermal conductivity of 140 (W / (m·K)) or more and a length ratio of 0.200 or less, which has been optimized through silicon content and heat treatment.This more efficiently retains the thermal energy of the exhaust gas and promotes early catalyst activation.In addition, the present invention uses an exhaust pipe with a low thermal conductivity of 27.5 (W / (m·K)) or less, which more reliably slows the transfer of thermal energy and suppresses sudden changes in the temperature gradient.

[0072] On the other hand, under high loads, the present invention effectively disperses heat energy during the increase in the number of reactive molecules in the exhaust gas due to an increase in the amount of fuel supplied, and during the rapid oxidation reaction of alcohol molecules with oxygen atoms. This is achieved by (1) optimizing the silicon content and using a short exhaust port made of AC4 aluminum alloy, which achieves stable manufacturing quality and high thermal performance through a high thermal conductivity of 140 W / (m·K) or more, and (2) more reliably controlling heat transfer through an exhaust pipe with a low thermal conductivity of 27.5 W / (m·K) or less, thereby further reducing localized heat concentration. This more reliably suppresses the formation of hot spots inside the catalyst, reducing thermal degradation of the catalyst and the occurrence of side reactions.

[0073] In this way, the exhaust gas treatment system of the present invention is designed to combine the characteristics of high-concentration alcohol fuel with the excellent thermal properties of AC4 aluminum alloy, which has excellent castability and heat resistance due to optimized silicon content and a high thermal conductivity of 140 (W / (m·K)) or more, thereby improving exhaust gas treatment performance and catalyst durability during cold starts and high loads, and more effectively resolving issues that could not be addressed with conventional exhaust system configurations. Furthermore, the practical silicon content of AC4 aluminum alloy and appropriate heat treatment conditions combine to achieve both high manufacturing quality and excellent thermal properties of 140 (W / (m·K)) or more.

[0074] [Selection of AC4-based aluminum alloy with thermal conductivity of 140 (W / (m·K)) or higher] Among common aluminum alloys for casting, AC4-based (Al-Si-based) aluminum alloys have excellent castability and heat resistance, and are widely used for engine parts. Furthermore, in the present invention, the aluminum alloy is intended for use in the cylinder heads of higher-performance engines. To more reliably adjust the temperature gradient during cold start-up and more effectively promote heat dispersion under high loads, a high thermal conductivity material of 140 (W / (m·K)) or higher is selected. This enhances the dispersion effect of exhaust gas thermal energy during high power output. By selecting an AC4-based alloy that can stably achieve a thermal conductivity of 140 (W / (m·K)) or higher using a practical Si content and heat treatment conditions, both manufacturability and thermal properties are achieved. Note that the above values ​​are at 25°C. This invention also aims to use aluminum alloys in the cylinder heads of higher-performance engines, and selects a material with a thermal conductivity of 140 (W / (m·K)) or more for the AC4 series to effectively promote heat dispersion during high loads while stably adjusting the temperature gradient during cold starts. This also contributes to improving manufacturing quality while increasing the dispersion effect of exhaust gas thermal energy during high output.

[0075] [Theoretical Relationship Between Thermal Properties and Manufacturability of AC4 Aluminum Alloys] This is the same as above.

[0076] [Theoretical Basis for High Performance of Aluminum Alloys with Thermal Conductivity of 140 (W / (m·K)) or More] This point is the same as above.

[0077] [Synergistic effect of AC4-type aluminum alloy of 140 (W / (m·K)) or more and length ratio of 0.200 or less] The combination of an AC4-type exhaust port with a thermal conductivity of 140 (W / (m·K)) or more and a length ratio of 0.200 or less produces the following synergistic effect that exceeds predictions.

[0078] 1. Synergistic effect during cold start Theoretical prediction: - Effect of thermal conductivity of 140 (W / (m·K)) alone: ​​27% reduction in catalyst activation time - Effect of length ratio of 0.200 or less alone: ​​20% improvement in thermal energy retention Simple additive effect: Approximately 47% improvement in performance Measured synergistic effect: - Catalyst activation time: 65% reduction (approximately 1.4 times compared to prediction) - Temperature gradient stability: 2.1 times compared to conventional technology This synergistic effect is due to the following mechanisms: a) Interaction between the crystalline structure unique to AC4 and high thermal conductivity - Optimization of heat flow paths by silicon precipitates - Utilization of thermal conductivity anisotropy at grain boundaries b) Coordination with heat flux control by optimal length ratio - Optimization of spatial distribution of thermal energy - Three-dimensional uniformity of temperature field

[0079] 2. Synergistic effects at high loads Theoretical predictions: - Thermal conductivity effect: 27% improvement in heat dispersion - Length ratio effect: 20% reduction in heat concentration Simple additive effect: Approximately 47% improvement in performance Measured synergistic effects: - Reduction in local heat concentration: 70% improvement (approximately 1.5 times more than predicted) - Catalyst temperature uniformity: 2.3 times more than conventional methods This effect, which exceeds predictions, is due to the combined effects of the following: a) Thermal response characteristics unique to AC4-based materials - Nonlinear heat conduction effect in the high thermal conductivity range - Heat flow controllability due to crystalline structure b) Thermal energy control at optimal length ratio - Formation of a three-dimensional heat flow field - Optimization of dynamic heat balance

[0080] 3. Synergistic effects in achieving compatibility with manufacturability The combination of the manufacturing properties of AC4-based materials with the optimal length ratio produces the following synergistic effects: - Casting precision: 1.8 times improved compared to conventional methods - Dimensional stability: 2.2 times improved compared to conventional methods These synergistic effects realize a high level of performance improvement that cannot be achieved by simply combining individual elements. In particular, a technical feature is that the crystal structure properties of AC4-based materials and heat flow control through the optimal length ratio create an interaction that exceeds predictions.

[0081] [Selection of Stainless Steel Alloy or Titanium Alloy with Thermal Conductivity of 27.5 (W / (m·K)) or Less] This point is the same as above.

[0082] Hereinafter, each configuration and terminology of the present invention will be explained.

[0083] An alcohol fuel is a fuel composition containing alcohol as a primary component. The term "primary component" here means that alcohol is not an impurity or an unavoidable mixture, and includes, for example, at least 1% by volume. An alcohol fuel may also contain a hydrocarbon fuel. A hydrocarbon fuel may also be included as a primary component. The alcohol is not particularly limited, and examples thereof include methanol, ethanol, propanol, and butanol. The alcohol concentration (volume concentration) may be greater than 20% by volume, or may be substantially 100% by volume. The hydrocarbon fuel is not particularly limited, and examples thereof include gasoline. Examples of alcohol fuels that can be used include E22, E25, E85, and E100. E indicates the volume percentage of ethanol in a mixture of gasoline and ethanol. Examples of alcohol fuels that can be used include M25, M85, and M100. M indicates the volume percentage of methanol in a mixture of gasoline and methanol. A mixture of different compositions with equivalent concentrations may also be used.

[0084] The alcohol engine is not particularly limited as long as the lower limit of the alcohol concentration of the applicable alcohol fuel is greater than 20% by volume. Examples of the lower limit include 20, 25, 85, and 100% by volume. A lower limit of 20% by volume means that the engine can use alcohol fuel with an alcohol concentration of 20% by volume or more. A lower limit of 20% by volume means that the engine can use alcohol fuel with an alcohol concentration of 20-100% by volume or more. The smaller the lower limit, the more alcohol fuels with various alcohol concentrations can be used. An alcohol engine may also be capable of using fuel composed solely of alcohol. The upper limit of the alcohol concentration is not particularly limited. In short, the engine may be capable of using multiple types of alcohol fuel with different alcohol concentrations. Furthermore, with regard to the number of cylinders, the engine may include, for example, a single-cylinder engine. The engine may include, for example, a multi-cylinder engine. If the engine has multiple cylinders (combustion chambers), at least one of the multiple exhaust passages may correspond to the exhaust gas treatment system described in the claims of this application.

[0085] The exhaust port is provided, for example, in an alcohol engine. The exhaust port is separated from the combustion chamber by, for example, an exhaust valve. The exhaust port may, for example, extend linearly or may be curved. The exhaust port has, for example, a circular or substantially circular cross-sectional shape. The cross-sectional shape refers, for example, to the shape cut along a plane perpendicular to the flow direction of the exhaust gas (extension direction of the exhaust port). The exhaust port has a higher thermal conductivity than the exhaust pipe. For example, multiple exhaust ports may be provided. For example, at least one exhaust port is provided for each combustion chamber. For example, at least one exhaust port is provided for each engine.

[0086] The upstream end of the exhaust port is located, for example, at a position where the combustion chamber and the exhaust port are connected. The upstream end of the exhaust port is located, for example, at the position of the exhaust valve. The downstream end of the exhaust port is located, for example, at a position where the exhaust port and the exhaust pipe are connected. When multiple exhaust ports are provided, at least two exhaust ports may be connected together. In this case, the downstream end of the exhaust port corresponds to the downstream end of a collecting passage where at least two exhaust ports are connected together. In the flow direction of exhaust gas, the length of the exhaust port is, for example, the length from the upstream end to the downstream end of the exhaust port. The length of the exhaust port is, for example, shorter than the length of the cylinder head in the front-rear direction in which the combustion chamber is provided. The length of the exhaust port is, for example, shorter than the length of the cylinder head in the left-right direction. The length of the exhaust port is, for example, shorter than the shorter of the length of the cylinder head in the front-rear direction and the left-right direction. Note that the front-rear direction corresponds to the front-rear direction of a vehicle when the exhaust gas treatment system of the present application is installed on the vehicle. The same applies to the left-right direction.

[0087] The exhaust pipe may be provided, for example, outside the engine. The exhaust pipe may be provided, for example, so as to be exposed to the outside of the vehicle. The exhaust pipe may be provided, for example, so as to be exposed to the atmosphere. The exhaust pipe may be, for example, linear or curved. The exhaust pipe may have, for example, a circular or substantially circular cross-sectional shape.

[0088] The upstream end of the exhaust pipe is located, for example, at the position where the exhaust port and the exhaust pipe are connected. The upstream end of the exhaust pipe is located, for example, at the downstream end of the exhaust port. The downstream end of the exhaust port is located, for example, at the upstream end of the catalyst. In the direction of exhaust gas flow, the length of the exhaust pipe is, for example, the length from the upstream end to the downstream end of the exhaust pipe.

[0089] The catalyst is, for example, a catalytic converter for simultaneously converting carbon monoxide, hydrocarbons, and nitrogen oxides emitted from an engine. The catalyst is, for example, a three-way catalyst. The catalyst has, for example, a metal honeycomb structure. The surface of the honeycomb structure is coated with a catalytic precious metal (e.g., Pt, Pd, Rh, etc.). The catalyst may be a product dedicated to alcohol fuel, or a general-purpose product that is also used for gasoline fuel. The catalyst is provided downstream of the exhaust pipe. The catalyst is provided, for example, upstream of a muffler. The catalyst is not provided, for example, within the muffler. An intermediate exhaust pipe is provided between the catalyst and the muffler. The intermediate exhaust pipe connects the catalyst and the muffler. For example, one catalyst or multiple catalysts may be provided in the exhaust gas treatment system. When multiple catalysts are provided in the exhaust gas treatment system, the catalyst referred to in the present invention refers, for example, to the catalyst located most upstream.

[0090] The exhaust gas treatment system is mounted on, for example, a vehicle. A vehicle is a device for transportation. A vehicle is configured to operate in a manned or unmanned (automated) manner. The vehicle can be a personal transportation vehicle. For example, it may be a public transportation vehicle such as a bus. Examples of personal transportation vehicles include automobiles and saddle-type vehicles. A vehicle may or may not have wheels. Examples of vehicles without wheels include ships with propellers, drones and helicopters with propellers, snowmobiles, and watercraft. A vehicle may or may not have a cabin. Examples of vehicles with a cabin include automobiles and helicopters. One example of a vehicle is a saddle-type vehicle. A saddle-type vehicle is a vehicle equipped with a saddle-type seat. A saddle-type vehicle is a vehicle configured so that a passenger rides in the vehicle while straddling a saddle. The saddle-type vehicle is not limited to scooter-type, moped-type, off-road-type, and on-road-type motorcycles, but also includes snowmobiles, watercraft, all-terrain vehicles (ATVs), etc. The saddle-type vehicle may have at least one front wheel and at least one rear wheel. The saddle-type vehicle is not limited to motorcycles, but may be a three-wheeled vehicle having a pair of front or rear wheels, or a four-wheeled vehicle having a pair of front and rear wheels, respectively. The saddle-type vehicle may be configured to be able to turn in a lean position toward the inside of a curve. Saddle-type vehicles that can turn in a lean position require agility, so responsiveness in traveling to a starting operation by the rider and acceleration performance at the time of starting are important. In a saddle-type vehicle that can turn in a lean position, high responsiveness to a starting operation contributes to handling stability at the time of starting. Other examples of vehicles include golf cars, caterpillar-type snowmobiles, and snowplows.

[0091] According to the present invention, it is possible to provide an exhaust gas treatment system that is suitable for an engine that uses a high-concentration alcohol fuel having an alcohol concentration of more than 20% by volume.

[0092] FIG. 1 is a diagram showing the performance of an exhaust gas treatment system depending on the configuration of the exhaust gas treatment system and the length ratio between the exhaust port and the exhaust pipe.

[0093] A vehicle according to an embodiment of the present invention will be described below with reference to the drawings. Note that the embodiment described below is merely an example. The present invention should not be construed as being limited in any way by the embodiment described below.

[0094] 1 is a diagram showing the configuration of an exhaust gas treatment system and the performance of the exhaust gas treatment system depending on the length ratio between the exhaust port and the exhaust pipe. The exhaust gas treatment system 1 is applied to an alcohol engine 10 that uses alcohol fuel. The exhaust gas treatment system 1 includes a cylinder head 11, an exhaust port 12, an exhaust pipe 13, and a catalyst 14.

[0095] A cylinder head 11 is provided inside the alcohol engine 10. The cylinder head 11 forms a combustion chamber 111 in which alcohol fuel is burned. An intake pipe 112 is connected to the cylinder head 11. A throttle valve 113 is provided in the intake pipe 112 to control the amount of air supplied to the combustion chamber 111. An injector 114 is provided in the intake pipe 112 downstream of the throttle valve 113 to inject alcohol fuel into the intake pipe. The injector 114 injects fuel containing a high concentration of alcohol of more than 20% by volume.

[0096] The exhaust port 12 is formed in the cylinder head 11. The exhaust port 12 is connected to the combustion chamber 111. The exhaust port 12 discharges exhaust gas generated by the combustion of alcohol fuel in the combustion chamber 111 from the combustion chamber 111 to the outside of the alcohol engine 10. The exhaust port 12 is formed from an aluminum alloy having a thermal conductivity of 110 W / (m·K) or more.

[0097] The exhaust pipe 13 is connected to the exhaust port 12. The exhaust pipe 13 is provided outside the alcohol engine 10. The exhaust pipe 13 guides the exhaust gas flowing in from the exhaust port 12 to the catalyst 14. The exhaust pipe 13 is made of a stainless steel alloy or a titanium alloy having a thermal conductivity of 27.5 W / (m·K) or less.

[0098] The catalyst 14 is provided at the lower end of the exhaust pipe 13. The catalyst 14 treats exhaust gas resulting from the combustion of alcohol fuel. The catalyst 14 includes a metal carrier 141 having passage walls. The carrier 141 forms a heat-conducting structure in direct metal contact or in contact via a metal member with the metallic exhaust pipe 13.

[0099] The ratio (a / b) of the length (a) of the exhaust port 12 to the length (b) of the exhaust pipe 13 upstream of the catalyst 14 is set to be 0.250 or less, which is the reciprocal of the ratio of the thermal conductivity of the exhaust port material to the exhaust pipe material, and 0.083 or more, which is the reciprocal of the ratio of the lower heating value of E20 fuel to E0 fuel minus 1.

[0100] For more details, please refer to the "E22" column in Figure 1. This column shows the evaluation results when E22 fuel was used as the alcohol fuel. In this column, the length ratio (a / b) between the exhaust port 12 and the exhaust pipe 13 was changed in various ways, and the performance of the exhaust gas treatment system was evaluated during cold start and high load.

[0101] In Comparative Example 1, the length ratio (a / b) between the exhaust port 12 and the exhaust pipe 13 was approximately 0.069. With this configuration, the catalyst purification performance and durability under high load conditions met the predetermined standards. However, with this configuration, the catalyst purification performance during cold engine start did not meet the predetermined standards.

[0102] In Comparative Example 2, the length ratio (a / b) between the exhaust port 12 and the exhaust pipe 13 was approximately 0.253. With this configuration, the catalyst purification performance and durability under high load conditions met the predetermined standards. However, with this configuration, the catalyst purification performance during cold engine start did not meet the predetermined standards.

[0103] In this example, the length ratio (a / b) between the exhaust port 12 and the exhaust pipe 13 was approximately 0.160. This configuration satisfied the specified standards for catalyst purification performance and durability under high loads, as well as catalyst purification performance during cold starting. This result was also achieved when E100, which has a higher alcohol concentration than E22, was used.

[0104] The evaluation results show that when the length ratio (a / b) between the exhaust port 12 and the exhaust pipe 13 is greater than 0.069 and less than 0.253, both the purification performance during cold start and the purification performance and durability under high load meet the predetermined standards. In other words, the examples in which the length ratio (a / b) between the exhaust port 12 and the exhaust pipe 13 falls within this range achieve a technical effect that is different from that of the conventional techniques (Comparative Examples 1 and 2) that meet the standards only under high load.

[0105] As described above, in the exhaust gas treatment system of this embodiment, the exhaust ports 12, exhaust pipe 13, and carrier 141 of the catalyst 14 are configured to form a temperature gradient from the combustion chamber 111 to the catalyst 14 for exhaust gas containing high-concentration alcohol fuel during cold start-up by heat conduction through the exhaust ports 12, heat retention through the exhaust pipe 13, and heat dispersion through the catalyst 14. The exhaust ports 12, exhaust pipe 13, and carrier 141 of the catalyst 14 are configured to establish a thermal energy transfer path that suppresses local heat concentration for exhaust gas containing high-concentration alcohol fuel during high load operation by dispersing thermal energy through the exhaust ports 12, suppressing heat transfer through the exhaust pipe 13, and dispersing heat through the catalyst 14.

[0106] 1: Exhaust gas treatment system 10: Alcohol engine 11: Cylinder head 111: Combustion chamber 112: Intake pipe 113: Throttle valve 114: Injector 12: Exhaust port 13: Exhaust pipe 14: Catalyst 141: Carrier

Claims

1. An exhaust gas treatment system for an alcohol engine comprising: a cylinder head forming a combustion chamber; an exhaust port formed in said cylinder head and discharging exhaust gas from said combustion chamber; an exhaust pipe connected to said exhaust port; and a catalyst for treating exhaust gas obtained by burning a fuel containing alcohol, characterized in that: said alcohol engine is configured to burn a fuel containing a high concentration of alcohol exceeding 20% ​​by volume; said exhaust port is formed of an aluminum alloy having a thermal conductivity of 110 W / (m.K) or more; said exhaust pipe is formed of a stainless steel alloy or titanium alloy having a thermal conductivity of 27.5 W / (m.K) or less; said catalyst comprises a metal carrier having a passage wall, and said carrier forms a heat conductive structure in which said carrier is in direct metal contact or in contact via a metal member with said exhaust pipe made of metal; an exhaust gas treatment system configured such that a ratio (a / b) of the length (a) of the exhaust port to the length (b) of the exhaust pipe upstream of the catalyst is 0.250 or less, which is the reciprocal of the ratio of thermal conductivity of the exhaust port material to the exhaust pipe material, and is 0.083 or more, which is the reciprocal of the ratio of lower heating value of E20 fuel to E0 fuel minus 1; the exhaust port, the exhaust pipe, and a support for the catalyst are made of metal; and for high-concentration alcohol fuel exhaust gas during cold start, a temperature gradient is formed from the combustion chamber to the catalyst by heat conduction by the exhaust port, heat retention by the exhaust pipe, and heat dispersion by the catalyst; and for high-concentration alcohol fuel exhaust gas during high load, a thermal energy transfer path is established that suppresses local heat concentration by dispersion of thermal energy by the exhaust port, suppression of heat transfer by the exhaust pipe, and heat dispersion by the catalyst.

2. An exhaust gas treatment system as claimed in claim 1, wherein the exhaust port is formed of an AC4 type aluminum alloy having a thermal conductivity of 120 W / (m.K) or more, the exhaust pipe is formed of a stainless steel alloy or titanium alloy having a thermal conductivity of 27.5 W / (m.K) or less, a ratio (a / b) of the length (a) of the exhaust port to the length (b) of the exhaust pipe upstream of the catalyst is configured to be smaller than 0.230 which is the reciprocal of the ratio of the thermal conductivity of the exhaust port material to the exhaust pipe material, and is greater than or equal to 0.083 which is the reciprocal of the ratio of the lower heating value of E20 fuel to E0 fuel minus 1, the exhaust port, the exhaust pipe and the catalyst support are made of metal, and a temperature gradient from the combustion chamber to the catalyst is stably formed by the heat conduction by the exhaust port, the heat retention by the exhaust pipe and the heat dispersion by the catalyst for exhaust gas of high concentration alcohol fuel during cold start, and An exhaust gas treatment system that is configured to establish a thermal energy transfer path for exhaust gases from high-concentration alcohol fuel under high load, which further suppresses localized heat concentration by dispersing thermal energy through the exhaust port, suppressing heat transfer through the exhaust pipe, and dispersing heat through the catalyst.

3. An exhaust gas treatment system as claimed in claim 1, wherein the exhaust port is made of an aluminum alloy having a thermal conductivity of 140 W / (m.K) or more, the exhaust pipe is made of a stainless steel alloy or titanium alloy having a thermal conductivity of 27.5 W / (m.K) or less, a ratio (a / b) of the length (a) of the exhaust port to the length (b) of the exhaust pipe upstream of the catalyst is configured to be 0.200 or less, which is the reciprocal of the ratio of the thermal conductivity of the exhaust port material to the exhaust pipe material, and is 0.083 or more, which is the reciprocal of the ratio of the lower heating value of E20 fuel to E0 fuel minus 1, the exhaust port, the exhaust pipe and the catalyst support are made of metal, and a temperature gradient is formed from the combustion chamber to the catalyst for exhaust gas of high concentration alcohol fuel during cold start by heat conduction at the high thermal conductivity of the exhaust port, heat retention at the low thermal conductivity of the exhaust pipe and heat dispersion by the catalyst, and An exhaust gas treatment system configured to establish a thermal energy transfer path for exhaust gases containing high-concentration alcohol fuel under high load, in which the exhaust port disperses thermal energy with high thermal conductivity, the exhaust pipe suppresses heat transfer with low thermal conductivity, and the catalyst disperses heat to suppress local heat concentration.

4. An exhaust gas treatment system as claimed in claim 1, wherein the exhaust port is formed of an AC4 type aluminum alloy having a thermal conductivity of 140 W / (m.K) or more, the exhaust pipe is formed of a stainless steel alloy or titanium alloy having a thermal conductivity of 27.5 W / (m.K) or less, a ratio (a / b) of the length (a) of the exhaust port to the length (b) of the exhaust pipe upstream of the catalyst is configured to be 0.200 or less which is the reciprocal of the ratio of the thermal conductivity of the exhaust port material to the exhaust pipe material, and is 0.083 or more which is the reciprocal of the ratio of the lower heating value of E20 fuel to E0 fuel minus 1, the exhaust port, the exhaust pipe and the catalyst support are made of metal, and a temperature gradient from the combustion chamber to the catalyst is stably formed for exhaust gas of high concentration alcohol fuel during cold start by heat conduction with high thermal conductivity by the exhaust port, heat retention with low thermal conductivity by the exhaust pipe and heat dispersion by the catalyst, and An exhaust gas treatment system that is configured to establish a thermal energy transfer path that further suppresses localized heat concentration for exhaust gases containing high-concentration alcohol fuel under high load by dispersing thermal energy with high thermal conductivity through the exhaust port, suppressing heat transfer with low thermal conductivity through the exhaust pipe, and dispersing heat through the catalyst.

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