WO2023070077A1

WO2023070077A1 - Engine piston having crevice catalyst

Info

Publication number: WO2023070077A1
Application number: PCT/US2022/078493
Authority: WO
Inventors: Thomas Miller Harris; Warran Boyd Lineton; Greg Salenbien
Original assignee: Tenneco Inc
Current assignee: Tenneco Inc
Priority date: 2021-10-22
Filing date: 2022-10-21
Publication date: 2023-04-27
Anticipated expiration: 2024-04-22

Abstract

An internal combustion engine and a piston for placement in a cylinder of the internal combustion engine are provided. The engine and piston are designed to reduce hydrocarbon emissions caused by unburnt fuel which remains in a crevice located between a top land of the piston and cylinder during or after a combustion event. A catalyst is disposed on a top land of the piston or an inner surface of the cylinder along the crevice. The catalyst is in the form of a coating including a base layer and a catalyst layer. The base layer is formed of nickel, nickel alloy, or nickel-based superalloy, and the catalyst layer being formed of precious metal, alloy containing precious metal, ceramic, or ceramic impregnated with precious metal. A transition layer can be disposed between the base layer and the catalyst layer, preferably when the catalyst layer is formed of the ceramic.

Description

ENGINE PISTON HAVING CREVICE CATALYST

[0001] This international (PCT) patent application claims priority to U.S. provisional patent application no. 63/270,715, filed October 22, 2021, the entire contents of which is incorporated by reference.

BACKGROUND

1. Technical Field

[0002] This invention relates generally to combustion engines and more particularly to management of the emissions from fuel introduced to a combustion chamber of an engine, and more particularly to reductions in hydrocarbon emissions from such chambers.

2. Related Art

[0003] Hydrocarbon emissions in combustion engines, such as Diesel engines, are strongly affected by an annular “crevice” that exists in the space that extends radially between the top land region of the piston and the cylinder, and axially between the top ring and top surface of the piston. A fuel/air mixture is introduced to a region above the piston in the cylinder for combustion, and a combustion event occurs when the mixture of fuel and air is ignited in the cylinder above the piston. A certain amount of unbumed fuel is forced radially outward and is caused to enter the “crevice” during the combustion event. The unbumt fuel accumulates and dwells in the crevice, protected from combustion, until the piston begins to retract in the cylinder at which time the unbumed fuel is expelled from the crevice into the exhaust stream Such discharge of unspent fuel contributes to undesirable hyrdrocarbon emissions.

[0004] Eliminating the crevice is not feasible since a certain amount of clearance is required to enable the piston to reciprocate in the cylinder.

[0005] While attention has been given to other parts of the piston to improve the quality and efficiency of combustion, such as shaping the combustion bowl, controlling the shape and dispersion of the air/fuel mixture or plume, and applying specialized coatings to cool or insulate the piston or to enhance the combustion reaction with the fuel mixture which occurs at the top surface of the piston; the events that take place in the crevice are not known to be addressed, particularly addressing the hydrocarbon emissions that stem from the accumulation of unbumt fuel in the crevice. SUMMARY

[0006] According to one aspect, a piston for a combustion engine has a top land portion treated with a catalyst reactive with unbumed fuel entering the crevice between the top land and cylinder wall during operation of the engine. The catalyst is effective to cause some or all of the unbumt fuel in the crevice to bum and reduce the level of hydrocarbons in the exhaust stream of the engine otherwise attributable to such unbumt crevice fuel.

[0007] According to another aspect, a combustion engine is provided having at least one piston having a top land, at least one top ring carried on the piston below the top land, and at least one cylinder in which the piston and ring are supported for reciprocation and which together define an annular crevice into which unbumt fuel is forced during a combustion event of the engine; and wherein at least one, some or all of the surfaces of the top land, the surface of the ring and the inner surface of the cylinder in the region of the crevice are treated with a catalyst effective to cause some or all of the unbumt fuel in the crevice to bum and reduce the level of hydrocarbons in the exhaust stream of the engine otherwise attributable to such unbumt crevice fuel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] These and other features and aspects will be better understood when considered in connection with the following detailed description and drawings, in which:

[0009] Figure 1 is a schematic fragmentary section view of a portion of a combustion engine;

[0010] Figure 2 is an enlarged portion of Figure 1 illustrating unbumt fuel entering a crevice;

[0011] Figure 3 is a view like Figure 2 but showing catalyzed surfaces of the crevice;

[0012] Figure 4 is an enlarged cross-sectional view of a portion of a catalyst according to a first example embodiment; and

[0013] Figure 5 is an enlarged cross-sectional view of a portion of a catalyst according to a first example embodiment.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0014] One aspect of the invention provides an internal combustion engine 10 containing a piston 12 which is designed to effectively bum at least some unbumt fuel which remains in the engine 10 after a combustion event. Reducing the amount of unbumt fuel reduces the level of hydrocarbons in an exhaust stream of the engine 10 otherwise attributable to such unbumt fuel. [0015] Figure 1 schematically illustrates a portion of the combustion engine 10 including the piston 12 having at least a top piston ring 14 carried in a top ring groove 16 of the piston 12.

[0016] The piston 12 and ring 14 are generally cylindrical and the ring 14 may be split for installation in the groove 14 in known manner.

[0017] The piston 12 is received in a cylinder 18 of an engine block 20. The cylinder 18 may be a bore of the block or may be a sleeve or liner installed in the bore. The cylinder 18 has an inner cylindrical surface 22 that is dimensioned to be relatively larger in diameter than an outer diameter of the piston 12 to provide radial clearance between the piston 12 and the cylinder 18 during reciprocation of the piston 12 within the cylinder 18 during operation of the engine.

[0018] The piston 12 has a top surface 24 that faces a cylinder head 26 of the engine 10. All or part of the top surface 24 is designed to support combustion of an air fuel mixture introduced into a combustion chamber 28 defined between the top surface 24 of the piston 10 and the opposing cylinder head 26. The top surface 24 may include features such as a top rim 24a and a combustion bowl 24b surrounded by the rim 24a, or have other features designed to manage the flow of the air/fuel mixture. During the upstroke cycle of the piston 12, the fuel air mixture is dynamically moved and compressed in the combustion chamber 28 to create conditions that lead to combustion (burning) of the mixture. Ideally, 100% of the fuel would be combusted, but in reality not all of the fuel is spent. During the upward movement of the piston 12 toward the stationary cylinder head 26, at least some of the fuel is caused to be pushed or displaced radially outwardly where it settles and accumulates in an outer annular crevice 30. The crevice 30 results from the radial clearance between the piston 12 and cylinder 18 needed to enable reciprocation of the piston 12 within the cylinder 18. The crevice 30 is a three- dimensional annular space that sits outward of and below the top surface 24 of the piston 12. It forms, in effect, a ditch into which a certain amount of unbumed fuel accumulates and, without intervention, never gets burned during the cycle of the engine 10. The annular crevice 30 is bounded on the inside by a top land portion 32 of the piston 12. This is the outer surface of the piston 12 that is above the top ring 14 and extends from the associated top groove 16 to the edge where the top surface begins. The crevice 30 is defined on its outer boundary by the inner surface 22 of the cylinder 18, and more particularly an uppermost portion opposite the top land 32 when the piston 12 is in position to combust the fuel in the chamber 28. The bottom of the crevice 30 is defined by the upper surface of the top ring 14. [0019] Normally, the unspent fuel that accumulates in the crevice 30 is expelled from the engine 10 as part of the exhaust stream when the piston 12 approaches top dead center and the waste gases are pushed through the exhaust valves. The presence of the unbumt fuel contributes to undesirable hydrocarbons in the exhaust stream.

[0020] A catalyst 34 is provided to one or more surfaces that make up the volume of the crevice 30 to cause some or all of the unspent fuel to bum. While this is not expected to contribute to the combustion efficiency of the engine 10 or otherwise improve performance since the burning does not take place above the piston crown, it nonetheless is beneficial as it reacts with the unspent fuel unspent fuel trapped in the crevice 30 and oxidizes it (bums it) before it gets released into the exhaust stream. This, in turn, lowers the hydrocarbon level in the exhaust stream and decreases dependence on downstream systems for the removal of hydrocarbon issuing from the cylinder 18. The strategic usage of the catalyst 34 in the area around the crevice 30 thus has the benefit of reducing the cost and dependence of other hydrocarbon removal systems (such as downstream catalytic converters and particulate filters) and decreasing the chances of them being emitted to the atmosphere. The presence of the catalyst 34 in the area around the crevice 30 also allows burning of unspent fuel to take place at the elevated temperature of the engine 10 and thus does not require reheating the fuel stream downstream of the engine 10. The use of the catalytic treatment in the crevice 30 is relatively inexpensive and may reduce the size and cost of any downstream hydrocarbon treatment system.

[0021] The surfaces of the crevice 30 that may be treated with the catalyst 34 include the top land 32, as illustrated in Figure 3. The inner surface 22 of the cylinder 18 opposite the top land 32 may also be treated with the catalyst at 34. An upper side surface (side flank) of the top ring 14 and/or an upper side surface of the ring groove 16 may also be treated with the catalyst at 34. When the catalyst 34 is located on the upper side surface of the top ring 14 and/or the ring groove 16, is it preferably located on a portion of the upper side surface of the top 14 that is outside the ring groove 16 and thus not in contact with the ring groove 16. Typically, the catalyst 34 is only applied to areas along the crevice 30, specifically the top land 32 of the piston 10, the inner surface 22 of the cylinder 18 opposite the top land 32, the upper side surface (side flank) of the top ring 14 and/or an upper side surface of the ring groove 16. However, the catalyst 34 could be disposed on the top surface 24 of the piston 10 in addition to along the crevice 30.

[0022] The catalyst 34 is an oxidation catalyst. This facilitates the reaction of the unbumed hydrocarbons trapped in the crevice volume 30 even as the gas temperature drops as the piston 12 retracts. The catalyst 34 may comprise a coating and may be a single layer or multiple layers. Candidate materials for the catalyst 34 include a base layer 36, also referred to as a bond layer in some embodiments, of nickel, nickel alloy, or nickel-based superalloy; a catalyst layer 38 formed of precious metal or alloy containing precious metal, such as platinum and/or rhodium, or a ceramic, such as a ceria stabilized zirconia; and in some embodiments, a transition layer 40 formed of a mixture of the base layer 36 and the catalyst layer 38. The transition layer 40 is typically used when the catalyst layer 38 is formed of the ceramic. The base layer 36 is typically 30-70 microns, preferably 50 microns, in thickness. The catalyst layer 38 is typically 70-130 microns, preferably 100 microns, in thickness. The transition layer 40 is typically 30-70 microns, preferably 50 microns, in thickness.

[0023] Figures 4 and 5 illustrate examples of the catalyst 34 disposed on the top land 32 of the piston 12 according to example embodiments. According a first example embodiment, shown in Figure 4, the catalyst 34 includes the base layer 36 formed of nickel and the catalyst layer 38 formed of the precious metal, specifically platinum and/or rhodium, disposed on the base layer 36. According to a second example embodiment, shown in Figure 5, the catalyst 34 includes the base layer 36 formed of a nickel-based superalloy, the catalyst layer 38 formed of the ceria stabilized zirconia, and the transition layer 40 formed of a mixture of the base layer 36 and the catalyst layer 38. Preferably, the catalyst layer 38 has a surface roughness of 5 microns Ra or less, preferably 3 microns Ra or less. The surface roughness can be measured by a contact profilometer or white light interferometry.

[0024] According to another embodiment, the catalyst 34 includes the coating described in US Patent 10,018,146 assigned to the assignee of the present invention, the contents of which are incorporated herein by reference. The example coating taught by the ‘146 patent includes the base layer 36 which is athermal barrier layer, such as ceramic. The coating also includes the transition layer 40 which is a sealant including metal. The coating also includes the catalyst layer 38 which includes at least one of platinum, ruthenium, rhodium, palladium, osmium, and iridium. According to one embodiment, the example coating taught by the ‘146 patent includes a bond layer disposed beneath the base layer 36. The bond layer can include at least one of nickel chromium aluminum yttrium (NiCrAlY) and cobalt nickel chromium aluminum yttrium (CoNiCrAlY). In this case, the base layer 36 is disposed on the bond layer and includes ceria stabilized zirconia (CSZ). The transition layer 40 is disposed on the base layer 36 and includes at least one of nickel chromium aluminum yttrium (NiCrAlY) and cobalt nickel chromium aluminum yttrium (CoNiCrAlY). The coating also includes the catalyst layer 38 which includes at least one of platinum, ruthenium, rhodium, palladium, osmium, and iridium.

[0025] According to another example embodiment, the catalyst layer 38 includes a ceramic material, for example ceria stabilized zirconia, impregnated with a precious metal, such as platinum. The catalyst layer 38 is disposed on the transition layer 40, and the transition lay er 40 is disposed on the base layer 38. The total thickness of the catalyst 34, which would include three layers 36, 38, 40, is about 0.2 mm. According to this example embodiment, the catalyst 34 is formed by plasma spraying the layers 36, 38, 40 and then applying chloroplatinic acid to the surface of the catalyst layer 38. The catalyst 34 is then dried and reduced by oven or flame treatment above 400°C. Catalytic activity is expected from both the ceramic and the platinum of this catalyst 34.

[0026] An important distinction between the prior usage of catalysts on piston crowns (the top) and the present usage in the crevice 30 is that the effect or goal of the prior usage was to change or alter combustion to increase engine efficiency. Here, the objective is to reduce hydrocarbon emissions by burning unspent fuel trapped in the crevice 30 so it does not get released in the unspent state as a hydrocarbon. The catalyst 34 does not alter combustion or otherwise contribute to increased engine efficiency, but simply oxidizes the trapped fuel in the crevice 30. The piston 10 including the catalyst 34, as described herein, can be used in engines operating with gasoline, diesel, or alternative fuel, such as ethanol, dimethyl ether, and natural gas.

[0027] Another aspect of the invention provides a method of manufacturing the piston 12. Various different methods can be used to manufacturing the piston 12 with the catalyst 34 described above.

[0028] According to one embodiment, the method includes applying the catalyst 34 in the form of a coating to the top land 32 of the piston 12. The piston 12 is formed of steel. Any manganese phosphate present on the top land 32 of the piston 12 should be removed, and the top land 32 of the piston 12 should be uncoated. The manganese phosphate can be removed by turning of the piston 12 in a lathe or with a suitable abrasive. The top land 32 is then prepared for the base layer 36. According to this embodiment, the base layer 36 is formed of nickel, referred to as a nickel strike layer. This base layer 36 is used because the catalyst layer 38 should not be disposed directly on the steel of the piston 12. The thickness of the nickel base layer 36 is a few microns. The base layer 36 is applied by placing a felt covered graphite anode in contact with the top land 32. Electrical contact is made to the piston 12 and the piston 12 becomes the cathode. A nickel solution is dripped onto the felt and runs into the felt filled gap between the top land 32 and griphite anode. When a potential of 8-12 volts of potential is applied, the nickel deposits on the top land 32 to form the base layer 36. To achieve a uniform base layer 36, the piston 12 and the anode are moved relative to one another, for example by the lathe. The method next includes rinsing the top land 32 and applying the catalyst layer 38 formed of the precious metal, for example platinum or rhodium A solution containing the precious metal is applied in the same manner as the nickel. A new felt electrode should be used for the catalyst layer 38 to avoid cross contamination of the metal solutions. The method next includes rinsing the piston 12, drying the piston 12, applying rust prevention to the piston 12, and packaging the piston. Smoothing of the catalyst 34 is not usually needed.

[0029] According to another embodiment, the catalyst layer 38 includes the ceramic, and tire method includes forming the catalyst 34 in the form of a coating that is about 0.2mm in thickness. The method begins by removing any material from the top land 32 to allow for the thickness of the coating and maintain clearance between the piston 12 and inner surface 22 of the cylinder 18. Any material can be removed with a lathe, or alternatively the piston print will show a reduced dimension in which space is allowed for the catalyst 34 during manufacture. The piston 12 is then masked so only the top land 32 is exposed. Next, the method includes grit blasting and washing the top land 32, placing the washed piston 12 in a fixture, and rotating the piston 12 at 700 RPM. The catalyst 34 is applied by plasma spray and includes the base layer 36 formed of the nickel based superalloy having a thickness of 50 microns, the transition layer 40 having a thickness of 50 microns, and then the catalyst layer 38 formed of the ceria stabilized zirconia and having a thickness of 100 microns. Next, the coating is smoothed to provide a surface roughness of 3 Ra microns. The smoothing can be conducted by spinning and contacting the piston 12 with an abrasive having an increased grit number. The method further includes providing rust prevention and packing the piston 12.

[0030] Another aspect of tire invention provides a method of manufacturing the engine

10. According to one embodiment, the catalyst 34 is applied to the piston 12, as described above, and the piston 12 is disposed in the engine 10. According to another example embodiment, the catalyst 34 is applied to the inner surface 22 of the cylinder 18, and the piston 12 is disposed in the engine 10.

[0031] Obviously, many modifications and variations of the present invention are possible in light of tire above teachings. It is, therefore, to be understood that the invention may be practiced otherwise than as specifically described while still being within the scope of the invention.

Claims

1. A piston, comprising: a body including a top land disposed between a combustion surface and a ring groove; a catalyst disposed on the top land of the body, the catalyst being in the form of a coating; the coating including a base layer and a catalyst layer disposed over the base layer; the base layer being formed of nickel, nickel alloy, or nickel-based superalloy; and the catalyst layer being formed of at least one of precious metal, alloy containing precious metal, or ceramic.

2. The piston according to claim 1, wherein the catalyst is disposed only on the top land on the piston and not disposed on other sections of the piston.

3. The piston according to claim 1, wherein the catalyst layer is disposed directly on the base layer, the base layer is formed of the nickel, the catalyst layer is formed of the precious metal, and the precious metal is at least one of platinum and rhodium.

4. The piston according to claim 1, wherein a transition layer is disposed between the base layer and the catalyst layer.

5. The piston according to claim 4, wherein the base layer is formed of the nickel-based superalloy, the catalyst layer is formed of the ceramic, the ceramic is ceria stabilized zirconia or ceramic impregnated with platinum, and the transition layer is formed of a mixture of the nickel-based supper alloy and the ceria stabilized zirconia.

6. The piston according to claim 5, wherein the base layer has a thickness of 30 to 70 microns, the catalyst layer has a thickness of 70-130 microns, and the transition layer has a thickness of 30-70 microns.

7. The piston according to claim 5, wherein the catalyst layer has a surface roughness of not greater than 5 microns Ra.

8. The piston according to claim 1, wherein the body is formed of steel.

9. An internal combustion engine, comprising: a cylinder including an inner surface; a piston disposed in the cylinder; the piston including a top land located between a combustion surface and a ring groove; the top land of the piston and the inner surface of the cylinder presenting a crevice therebetween; a catalyst disposed on the top land of the piston or the inner surface of the cylinder; the catalyst being disposed along the crevice; the catalyst being in the form of a coating; the coating including a base layer and a catalyst layer disposed over the base layer; the base layer being formed of nickel, nickel alloy, or nickel-based superalloy; and the catalyst layer being formed of at least one of precious metal, alloy containing precious metal, and ceramic.

10. The internal combustion engine according to claim 9, wherein the catalyst is disposed along a portion of the inner surface of the cylinder.

11. The internal combustion engine according to claim 10, wherein the portion of the inner surface is located adjacent the top ring land of the piston during a combustion engine, combustion engine a catalyst disposed on the top land of the piston or the inner surface of the cylinder;

12. The internal combustion engine according to claim 9, wherein the catalyst is disposed only on the top land on the piston and not disposed on other sections of the piston.

13. The internal combustion engine according to claim 9, wherein the catalyst layer is disposed directly on the base layer, the base layer is formed of the nickel, the catalyst layer is formed of the precious metal, and the precious metal is at least one of platinum and rhodium

14. The internal combustion engine according to claim 9, wherein a transition layer is disposed between the base layer and the catalyst layer.

15. The internal combustion engine according to claim 14, wherein the base layer is formed of the nickel-based superalloy, the catalyst layer is formed of the ceramic, the ceramic is ceria stabilized zirconia or ceramic impregnated with platinum, and the transition layer is formed of a mixture of the nickel-based supper alloy and the ceria stabilized zirconia.

16. The internal combustion engine according to claim 14, wherein the base layer has a thickness of 30 to 70 microns, the catalyst layer has a thickness of 70-130 microns, and the transition layer has a thickness of 30-70 microns.

17. The internal combustion engine according to claim 14, wherein the catalyst layer has a surface roughness of not greater than 5 microns Ra.

18. The internal combustion engine according to claim 9, wherein the piston is formed of steel.

19. A method of reducing hydrocarbon emissions, comprising: disposing a piston in a cylinder of an internal combustion engine; the piston including a top land disposed between a combustion surface and a ring groove; a catalyst disposed on the top land of the piston or an inner surface of the cylinder; the catalyst being disposed along the crevice; the catalyst being in the form of a coating; the coating including a base layer and a catalyst layer disposed over the base layer; the base layer being formed of nickel, nickel alloy, or nickel-based superalloy; and the catalyst layer being formed of precious metal, alloy containing precious metal, or ceramic. the piston according to claim 1 in an internal combustion engine, and operating the engine with the piston.

20. The method of claim 19 including operating the engine with the piston, and wherein the catalyst is disposed along the crevice during a combustion event.