Background Art Air pollution caused by automobile engines, as well as other internal combustion engines, continues to raise serious health and environmental concerns. The pollution is a result of the combustion of fuel in internal combustion engines that produces noxious emissions including unburned hydrocarbons, carbon monoxide, nitrous oxides, and particulates. The particulates, which make up most of the visible portion of the vehicle exhaust, are created during the combustion process when lubricants, i. e., oils, and other fuel impurities are heated and form the agglomeration and dehydrogenation of hydrocarbon fuels, both of these problems often being attributed to poor engine maintenance and aging of engine components and being of particular concern for diesel engines. The resulting particulates are generally smaller than 10 microns and comprise volatile compounds surrounding a carbonaceous core. The particulates are typically lofted by diesel and gasoline engines high into the air where they become an inhalation hazard to people, even at significant distances from the emission source.

In an attempt to control automobile pollution, governments worldwide have enacted increasingly stringent automotive exhaust emission standards to limit the release of noxious combustion products from the automobile exhaust. For example, the United States government requires that new internal combustion vehicle designs comply with the Environmental Protection Agency (EPA) Federal Test Procedure which contains relatively low acceptance limits, in grams per mile, for the emission of hydrocarbons, carbon monoxide, and nitrous oxides from the vehicle exhaust system. However, this procedure does not express a limit for particulate emissions and neither do local tailpipe concentration tests that often only test for hydrocarbons and carbon monoxide.

The enacted emission standards have promoted the widespread use of catalytic after- treatment to control automotive exhaust emissions. In this regard, a catalytic converter is usuallv installed in proximity to the engine's exhaust manifold and comprises a ceramic catalyst enclosed in a temperature resistant housing that guides the exhaust gases through the catalyst prior to discharge from the tailpipe. In the case of an oxidation catalyst. the function is to cause the carbon monoxide (CO) and hydrocarbons (HC), which result from incomplete combustion of fuel, to be converted to carbon dioxide (CO) and water. In the case of a three-way catalyst, the oxidation reactions (HC and CO) are combined with reduction reactions of nitrogen oxides (NO,) to create harmless nitrogen (N.) and oxygen (0 ;). Catalytic converters provide these conversion or catalysis functions by including one or more noble metals on a ceramic substrate (e. g., platinum, palladium, or rhodium dispersed on an alumina substrate). A preferred noble metal for high temperature hydrocarbon reduction is palladium. while rhodium is effective for improving nitrous oxide and carbon monoxide emissions. The operating, or"light-off."temperature range for noble metal catalysts is from about 600 to 800 °F (about 315 to 425 °C). At light-off temperatures, catalytic converters are very effective at reducing the emission of carbon monoxide, hydrocarbons, and nitrogen oxides.

However, catalytic converters have generally been designed to meet the EPA Federal Test Procedure limits and have not been designed specifically to address the problem of releasing harmful particulates. As discussed above, the particulates comprise small carbon cores with outer layers of volatile compounds. It is known that these particulates may be ignited by causing the particulates to remain for a period of time on catalyzed surfaces of 350 °C or higher, as exists in most catalytic converters operating at light-off temperature, or on uncatalyzed surfaces that are approaching 600 °C. Additionally, the particles may be reduced in size and/or made more dense by oxidation during sufficiently long exposures to elevated temperatures. i. e., at least about 200 °C. in the presence of oxygen. An existing problem is the well-established inverse relationship between removal of nitrogen oxides and creation and/or removal of particulates. In other words, as the effectiveness of nitrogen oxide conversion increases, the combustion of particulates decreases in effectiveness. For example. diesel engines can be manufactured. tuned, and operated to only produce low levels of nitrogen oxide, but this results in a high output of particulates. Further, current state of the art catalytic converters have not been effective in significant reducing the emission of particulates at least in part

because the particulates fail to remain on hot surfaces or be exposed to elevated temperatures for long enough periods of time to ignite before passing through the catalvtic converter. In fact. many converters are specifically designed with high-flow, honeycomb catalysts to achieve faster exhaust flow because unburned fuel and particulates that enter the converter may combust and overheat the converter, causing damage to the catalyst's substrate. Therefore, particulate emission remains a concern even though converters may have light-off temperatures above the combustion temperatures of many particulates.

Another recognized problem with current catalytic converter designs is that in a cold start of an internal combustion engine. 60-80% of the hydrocarbon and carbon monoxide pollutants that the vehicle produces are released in the first 200 seconds of operation before the catalytic converter reaches light-off temperature and the catalyst then becomes active. For example, J. C. Summers et al., in their paper"Use of Light-Off Catalysts to Meet the California LEV/ULEV Standards," Catalysts and Emission Technology, Society of Automotive Engineers Special Publication No. 968, Warrendale, Pa., 1993, reported that roughly 60-80% of the tailpipe hydrocarbon emissions occur during the initial cold start phase. In addition to the high release of hydrocarbons and carbon monoxide, particulates are also exhausted at a higher rate during cold start up, with the smoky emissions caused by particulates being more noticeable at startup of internal combustion engines.

Further, particulate emissions are also released during ongoing operation of a diesel or gasoline engine because idling or low throttle operations of the engine typically allow the catalyst to cool well below the light-off temperature.

To address the cold start up and the low throttle problems, several efforts have been made to reach light-off temperature more quickly or to maintain a higher idle or nonoperating temperature within the catalytic converter, generally by retaining exhaust heat as much as possible in the catalytic converter. However, while an insulation jacket around the catalytic converter can help to retain heat. the temperature of a catalytic converter during extended operation can rise very rapidly from the exothermic heat of the catalytic reactions with the exhaust gases after the light-off temperature is reached. If the heat generated during extended operation or from fuel-rich gases reacted in the catalytic converter cannot be dissipated efficiently, the heat can build up to a point that accelerated

aging of the catalyst, or even permanent damage to the catalytic converter or to adjacent components. can result.

U. S. Patent No. 5. 163. 289. issued to D. Bainbndge. discloses an insulation jacket around a catalytic converter wherein the insulation is a refractory fiber that conducts heat quickly at higher temperatures, releasing heat at temperatures above the light-off temperature and more slowly at lower temperatures to retain heat during non-operating or idling periods. In U. S. Patent No.

5. 477.676 issued to Benson et al., further improvements are shown in maintaining heat above light- off temperature for longer periods of time during non-operation periods. The Benson et al. patent uses a combination of vacuum insulation and phase-change thermal storage materials to retain the heat created during the exothermic reactions in the catalyst structures or honeycombs during short idle periods and during extended non-operating period. such as overnight. The Benson et al. heat management system also dissipates heat in high-temperature operation periods with a combination of variable conductance insulation and/or metal-to-metal thermal shunt mechanisms. The Benson et al. heat management system is helpful in storing heat and maintaining light-off temperatures longer and in reducing cold start emissions by increasing the initial start up temperature, such as after short stops of several hours or even for several days.

However, neither the Bainbridge device nor the Benson et al. heat management system addresses the need for reducing particulate emissions. Each system only incidently reduces particulate emission to normal operating emission levels by operating the catalytic converter at or near light-off temperatures during cold start up phases. Therefore, while the Bainbridge and Benson et al. patents and other developments represent significant advancements in cold start emissions control with catalytic converters, controlling particulate emissions continues to be a problem.

An existing method of controlling particulate emission is the use of particulate traps or filters that are positioned downstream of the catalytic converter to collect, and sometimes further combust. particulates discharged from the catalytic converter. However, particulate traps generally require periodic cleaning and/or replacement, and particulate filters or traps often only collect 60% to 90% of the particulates. Particulate traps and other devices may be complex and expensive to fabricate and install. Further. collected particulates progressively block the flow passage passage increase increase pressures, thus causing reduced engine output power and fuel economy.

In contrast to particulate traps, U. S. Patent No. 5.618.500. issued to WanE. discloses a device installable in the exhaust manifold of an engine that attempts to control emissions. including particulates. by improving the efficiency of combustion of the noxious emissions in the engine exhaust stream. The disclosed Wang device generally comprises a cylindrical, metal casing enclosing a reaction zone into which the engine exhaust is directed. The reaction zone is surrounded bv ceramic foam cells and contains a centrally-located. tubularly-shaped ceramic foam cell. The Wang device further includes an outer insulating layer (i. e.. vacuum form ceramic fibers, ceramic fiber blankets, or refractory fibers) to retain heat in the engine exhaust gases and heat created by exothermic oxidation reactions within the exhaust gases. When the engine is running, particulate-laden exhaust enters the device and contacts the porous ceramic foam cells (on the walls and in the center of the reactor device). Particulates may be deposited on the porous ceramic foam surfaces, transferring some heat to the surfaces. The deposited particulates are heated by conduction from the porous ceramic foam, by convection and radiation of heat trapped in the reaction zone by the outer insulating layer, and by the heat generated from combustion of any unburned hydrocarbons. If the temperatures are high enough, the carbon particulates residing on the ceramic surfaces are oxidized and burned in the presence of oxygen in the exhaust to form carbon monoxide. A portion of the carbon monoxide is in turn oxidized into carbon dioxide in the reactor. The oxidation and combustion of the carbon particulates deposited on the ceramic surfaces may also release heat helping to maintain or to raise the reactor device temperature.

While taking a step in a helpful direction, the disclosed Wang device fails to efficiently reduce particulate emissions and presents several operational problems that must be overcome. The Wang device utilizes conventional refractory insulation to retain exhaust gas and exothermic reaction heat.

Unfortunately, these insulation materials are relatively ineffective for extended time periods and therefore. would produce high heat losses, making it difficult to obtain and maintain temperatures for combustion of particulates and noxious gases. If high temperatures are achieved, the Wang device provides no protection against overheating that could easily damage the materials within the Wang device and components positioned nearby within the engine. In addition, the insulation method described bv Wan2 would result in loss of most. if not all. of the heat during long periods of engine shutdowns. e. Ei., 12 to 36-hour cold soak time specified in the EPA Federal Test Procedure. As

discussed above in relation to the Benson et al. patent, it is desirable to avoid or reduce cold start up problems of high emissions by maintaining heat in the catalytic converter, or, as in Want,, in the reaction zone. Further, the Wang device may be expensive to manufacture due to its complexity and may create undesirable exhaust gas pressure drops that may lower engine power and fuel efficiency.

In U. S. Patent No. 5,193,341, issued to Sibbertsen, a vortex tube device is shown for combusting soot particles in an exhaust line of a diesel engine. As disclosed in this patent, exhaust gases are adiabatically expanded by a diaphragm to raise the temperatures of the gases approximately 100 °C to cause further combustion of the soot particles. However, the vortex tube device assumes an inlet temperature of 500 °C. which would not be applicable for most internal combustion engines that operate over a wide range and cause tremendous temperature swings in the engine exhaust. Additionally, the disclosed vortex tube device would not be helpful in reducing emissions during cold start up, i. e.. the period in which 65% to 80% of the emissions occur in most engines, and during much of the normal operations. Further, a vortex tube device also may result in unacceptably high back pressures.

Consequently, while catalytic converters, alone and in combination with heat management systems. have been most helpful in reducing air pollution by controlling noxious emissions, especially emissions of hydrocarbons, carbon monoxide, and nitrogen oxides, an apparatus or system for more effectively controlling particulate emissions from internal combustion engines is still needed.

Disclosure of Invention Accordingly, it is a general object of the present invention to reduce air pollution caused by internal combustion engines, specifically reducing the volume of particulate emissions, in a cost- effective manner for new and retrofit applications.

A more specific object of the present invention is to reduce emissions of particulates from internal combustion engines during cold start up. low throttle, and idling operations.

Another specific object of the present invention is to improve the particulate reduction efficiency of exhaust systems which include a catalytic converter and a heat management system for reducing the time to reach light-off temperatures in the catalytic converter.

Additional objects, advantages. and novel features of the invention are set forth in part in the description that follows and will become apparent to those skilled in the art upon examination of the

following description and figures or may be learned by practicing the invention. Further, the objects and the advantages of the invention mav be realized and attained by means of the instrumentalities and in combinations particularly pointed out in the appended claims.

To achieve the foregoing and other objects and in accordance with the purposes of the present invention, as embodied and broadly described herein, a particulate reduction apparatus is provided comprising variable and controllable insulation around a housing that contains a catalytic converter and a particulate combustion chamber. The particulate combustion chamber has a sidewall defining an extended-length. particulate flow path upon which airborne particulates are exposed to radiant heat from the internal surface of the sidewall and from the combustion of nearby particulates. The particulate reduction apparatus is installed in an exhaust system of an internal combustion engine, such as a diesel engine, where it is useful in treating exhaust gases by using the catalytic converter to oxidize noxious pollutants. More important, the particulate combustion chamber is operated to ignite, or at least partially oxidize, combustible particulates in the exhaust gases, thereby minimizing lofting of the particulates by combusting a portion of the particulates and by densifying another portion of the particulates causing them to drop quickly out of the air after being emitted in the exhaust gases. Both of these sets of reactions are exothermic, and, in this regard, the variable and controllable insulation can be turned on to maintain or trap inside the housing the heat created in these reactions and the heat of the exhaust gases flowing through the housing. For example, the insulation may be turned on when no exhaust gases are flowing through the housing and when a desired combustion temperature has not been reached in the particulate combustion chamber and light-off temperature has not been reached in the catalytic converter. In this manner, higher temperatures may be more quickly achieved upon initially starting the engine, may be more effectively controlled during engine operations. and may be effectively maintained during extended periods of non-operation of the engine to minimize cold-start pollution problems. such as high emission of carbonaceous particulates due to limited. or no, exposure to temperatures high enough to cause oxidation or combustion.

To further achieve the foregoing and other objects, the variable and controllable insulation can be turned off when the temperature of the particulate combustion chamber is above a desired combustion temperature or at a predetermined point in an acceptable temperature range and the

catalytic converter temperature is above light-off. Further, the insulation preferably can be maintained in a variety of states between on and off to moderate temperatures inside the housing containing the catalytic converter and the particulate combustion chamber. The variable and controllable insulation can be a vacuum insulation with gas or solid conduction control capability for selectively enabling or disabling the insulation.

Additionally. the housing may include a heat storage and transfer element contacting both the particulate combustion chamber and the catalytic converter to store heat generated by the exothermic oxidation reactions and particulate ignitions and to transfer heat between the catalytic converter and the particulate combustion chamber. The heat storage and transfer element is useful in effectively using internally generated heat and in better controlling temperatures in these structures. and, to accomplish these functions, may comprise a phase change material.

Brief Description of Drawings The accompanying drawings, which are incorporated in and form a part of the specification. illustrate the preferred embodiments of the present invention, and together with the descriptions serve to explain the principles of the invention.

Figure 1 is a schematic representation of a particulate reduction apparatus of the present invention including a catalytic converter heat management system ; Figure 2 is a cross-sectional view of a catalytic converter housing structured to provide particle combustion according to the present invention; and Figure 3 is a cross-sectional view of an alternate embodiment in which a phase change material is positioned in the inner housing surrounding the catalyst substrate and in which a ceramic honeycomb is positioned within the particulate ignition chamber.

Best Mode for Carrying Out the Invention A particulate reduction apparatus 10 constructed with a heat management system according to this invention is shown in Figure 1 mounted in an exhaust pipe P that is connected to the exhaust manifold M of an internal combustion engine E of a motor vehicle (not shown). The present invention beneficial for use with all types of internal combustion engines E but is especially useful in combination with diesel engines for which carbonaceous particulate emission is a serious concern.

Utilization of the present invention results in a low-emission diesel engine because the engine can be

manufactured. tuned, and operated in a manner that produces low levels of nitrogen oxides and larger amounts of particulates that can be effectively controlled. as will be discussed in detail below.

While a number of heat management systems and controls may be used in practicing the present invention. a particularly effective heat management system, that will be described in detail in the following description, is the exhaust heat management system illustrated and described in our U. S.

Pat. No. 5. 477, 676. issued December 26. 1995. which is incorporated herein by reference.

Referring again to Figure 1. the exhaust pipe P carries exhaust gases from the engine E to the particulate reduction apparatus 10, which mav contain a catalytic converter portion 11 (Figure 2) with conventional 3-way catalysts for reacting noncombusted fuel in the exhaust gases reducing emissions of hydrocarbons, carbon monoxide. and nitrous oxides in the exhaust gases. The particulate combustion apparatus 10 may further contain a particulate combustion chamber 25 (Figure 2) with walls or surfaces 27 that radiate heat for igniting carbonaceous particulates in the exhaust gases. The reacted exhaust gases are then discharged through a tailpipe T. usually at the rear-end of the motor vehicle (not shown).

Referring now to Figure 2. the particulate reduction apparatus 10 according to this invention comprises an internal catalyst housing 12, preferably fabricated of metal or other material that is impermeable to gases, for containing one or more catalyst substrates 14 (only one being shown to clarify the description) which can be ceramic materials coated with 3-way catalyst material. such as platinum, palladium, and/or rhodium, although it is contemplated that materials other than ceramics or the enumerated coatings may be readily utilized. Exhaust gases from the engine E (Figure 1) flow through the particulate reduction apparatus 10. as indicated by the arrows 20 in Figure 2. including through the numerous small, catalyst-coated pores or channels 22 that are formed in the ceramic substrate 14 to increase the exposed surface area of the catalyst material. As the exhaust gases pass through the channels 22, at least a portion of the noncombusted fuel in the exhaust gases reacts and a significant portion of the hydrocarbons, carbon monoxide, and nitrous oxides in the exhaust gases undergo reducing reactions induced by the hot catalyst surfaces. which are preferably maintained at or above light-off temperatures.

While the catalytic converter portion 11 is effective in reacting these gaseous, noxious pollutants, it is only partially effective in reducing the number or volume of particulates (not shown) in

the exhaust gas flow 20. and is especially inefficient in particulate reduction during start up and low throttle periods when the catalyst surfaces are below light-off temperatures. The particulates are small. carbon-cored spheres, generally less than 10 microns, with volatile organic material outer lavers. The particulates result from incomplete or inefficient combustion processes within the engine E and make up the visible portion of the exhaust gas emitted from the tailpipe T. The particulates can be ignited while contacting or resting on a catalyzed surface of 350 °C or higher. or may be ignited while airborne when exposed to temperatures between 350 °C and 600 °C for a sufficient period of time. Additionally, exposure to temperatures above 250 °C for a sufficient period of time mav have a shrinking and densifying effect on a number of the airborne particulates due to partial oxidation. Airborne ignition offers a number of advantages over surface ignition including, but not limited to, eliminating the residue or ash build up on surfaces and reducing damage or wear to surfaces due to surface ignition. Airborne ignition also rapidly converts relatively large. low-density particulates into smaller volume (often less the 1/100 of the original volume) and denser carbonaceous material that falls more quickly from the air after being emitted from the tailpipe T, thereby reducing the dangers associated with inhalation resulting from lofting of low-density particulates into the air.

According to an important aspect of the present invention, to improve and facilitate airborne combustion of particulates in the exhaust gases 20, the particulate reduction apparatus 10 further includes a particulate combustion chamber 25configured to ignite airborne particulates that flow therethrough. The particulate combustion chamber 25 comprises a cylindrical sidewall 26, preferably fabricated of metal or other material that is impermeable to gases and that transfers heat through radiation and conduction. The cylindrical sidewall 26 of the particulate combustion chamber 25 and the internal catalyst housing 12 may be fabricated separately and later sealably joined or may be fabricated readily as a single unit or piece, as shown in Figure 2. The sidewall 26 has an inner surface 27 that defines the flow path 20 of the exhaust gases and included particulates within the particulate combustion chamber 25.

Significantly, the flow path defined by the inner surface 27 is such that the particulates are exposed to heat for a period of time sufficient to result in airborne combustion of a significant portion or number of the particulates. Of course, the period of time required for combustion will vary with

the temperatures maintained within the particulate combustion chamber 25 (discussed below).

Therefore, while the inner surface 27 shown defines a hollow cylindrical flow path with a specific length. the length and shape may be varied to suit anticipated temperatures. It should be understood that the inventor recognizes that a large number of other flow paths (not shown) may be utilized to successfully practice the present invention by matching a flow path (e. g.. straight. curved such as that in the retarder material 138. circuitous. cyclonic) and length to anticipated flow rates and inner surface 27 temperatures. Radiant fins or other devices (not shown) may also be placed on or be incorporated in the inner surface 27 to increase surface area to improve radiant heat transfer to particulates in the exhaust flow path 20. Preferably. any added fins or devices will not have undue edges or sharp comers that may act as traps for these particulates. thereby leading to clogging of the particulate combustion chamber 25 and reduced efficiency of airborne combustion of the particulates. Fins or other devices may also be utilized to direct flow of the exhaust gases toward the inner surface 27 to reduce the distance the heat 36 must travel to limit dissipation prior to being absorbed by a particulate. In this regard, a flow director device (not shown) may be added to the entrance of the particulate exhaust chamber 25 to direct flow toward the inner surface 27 establishing a zone of higher airborne combustion nearer the inner surface 27. Preferably, though, the temperature of the inner surface 27 will be maintained well above temperatures necessary for airborne combustion of particulates even in the center portion of the flow path defined by the inner surface 27. Also, to control heat 36 radiation, the inner surface 27 may comprise a material that differs from the sidewall 26, such as a coating that better facilitates heat transfer through radiation, but may comprise a wide variety of metals and other materials that radiate heat 36 inward when they are at elevated temperatures.

As discussed above, airborne ignition of the particles may be achieved at temperatures between 350 °C and 600 °C with partial reduction in volume occurring with extended exposure to temperatures over 250 °C. Therefore, the particulate combustion chamber 25. and particularly, the inner surface 27, is maintained at temperatures at least above 250 suc. and preferably above 350 °C with airborne combustion occurring more readily at temperatures approaching 600 °C. These temperatures are initially achieved from the combined heat in the exhaust gas flow 20. from heat released during the exothermic reactions in the adjacent catalyst substrate 14 that is radiated into the

particulate combustion chamber 25 and conducted from the internal catalyst housing 12 to the cylindrical sidewall 26. and from exothermic reactions in the particulate combustion chamber 25 itself. Once the desired elevated temperatures, or combustion temperatures, are reached. the inner surface 27 of the cylindrical sidewall 26 radiates heat 36 inward. thereby functioning as a radiant wall extension of the catalytic converter portion 11. This radiant wall extension feature increases the likelihood of particulate ignition and improves the completeness of combustion. As the particulates ignite (i. e., airborne combustion), they release heat that may be absorbed by nearby particulates to further increase the efficiency of the particulate combustion chamber 25. This released heat may also be absorbed by the inner surface 27 and transferred by conduction to other components of the particulate reduction apparatus 10 (discussed in more detail below) and/or may be absorbed by the catalyst substrate 14 to facilitate maintenance of light-off temperatures.

Once the desired combustion and light-off temperatures have been achieved, the particulate reduction apparatus 10 is operable to maintain these temperatures during engine E operations and even during extended periods without exhaust flow 20. Referring to Figure 2, the internal catalyst housing 12 and the cylindrical sidewall 26 are enclosed within an outer housing 24 that is positioned at a distance spaced radially outward from the internal catalyst housing 12 and the cylindrical sidewall 26. The outer housing 24 is preferably fabricated of metal or other material that is impervious to gas, even in a hot and high-order vacuum environment. The annular chamber 30 enclosed between the internal catalyst housing 12 and cylindrical sidewall 26 and the outer housing 24 is evacuated. The insulating performance of chamber 30 is preferably variable in a controllable manner, as will be described in more detail below. Suffice it to say at this point that the thermal insulating effect of chamber 30 can be enabled to inhibit transfer of heat from the particulate combustion chamber 25 and from the catalyst substrate 14 to the outer housing 24 to prevent it from dissipating to the surrounding environment, or it can be disabled to allow such heat transfer, thereby "dumpino heat from airborne combustion of particulates and the catalyst reaction of exhaust gases into the surrounding environment. Preferably, it can also be enabled or disabled to varying degrees between fully enabled and fully disabled. depending on the heat conductance or insulative capacity needed at any time. Therefore. the insulating chamber 30 can be enabled to retain heat in the particulate combustion chamber 25 and in the catalyst substrate 14. for example upon starting the

engine. to shorten the time required for the inner surface 27 to reach combustion temperatures and for the catalyst to reach light-off or optimum operating temperature. It can then be disabled when the inner surface 27 and the catalyst reaches an optimum operating temperature (s) to prevent excessive heat build up and high temperatures that could damage the substrate 14 or shorten the useful life of the catalyst material coated on the substrate 14. Perhaps more importantly. however, the insulation chamber 30 can be enabled when the engine is turned off to hold the heat in the particulate combustion chamber 25 and in the catalyst substrate 14 for as long as possible in order to keep the temperature above the combustion temperature and above the light-off temperature of the catalyst until the next time the engine E is started, or at least to keep the inner surface 27 and the substrate 14 above ambient temperature to minimize the time it takes to raise the inner surface 27 to the combustion temperature and the catalyst to light-off temperature the next time the engine E is started.

Such variable conductance insulation and methods and apparatus for controlling the thermal transfer capabilities are illustrated and described in detail in our U. S. patent application Ser. No.

07/960, 885, which is incorporated herein by reference. Essentially, the vacuum chamber 30 is sealed from the inside of internal catalyst housing 12 and cylindrical sidewall 26 where the exhaust gases flow through the catalyst substrate 14 and the particulate combustion chamber 25. The vacuum chamber 30 also is sealed from the environment exterior to the outer housing 24. Exactly how such sealing is accomplished is not necessarily limited to any particular technique. However, for a long-lasting seal, it is preferred that the seal be made by metal-to-metal welds.

For example, as illustrated in Figure 2, inner end plate 32 may be welded to internal catalyst housing 12 and inner end plate 34 may be welded to the cylindrical sidewall 26. The outer housing 24 similarly comprises outer end plates 38 and 40 welded to opposite ends of the outer cylindrical sidewall 42. The outer cylindrical wall 42 is held apart from the internal catalyst housing 12 and the inner cylindrical wall 26 by a plurality of spacers 50. preferably made of a low heat conducting material. such as ceramic, shaped with curved or pointed surfaces that form thermal resistance nodes that minimize the areas of surface contacts through which heat can be conducted from the internal catalyst housing 12 and from the cylindrical sidewall 26 to the outer housing 24. For example, as shown in Figure'the spacers 50 can comprise spherical ceramic beads 44 positioned between two

curved ceramic liners 46 and 48. thereby forming a series of four"near point."i. e.. very small, ceramic to ceramic surface contact areas or thermal resistance nodes between the internal catalyst housing 12 and cylindrical sidewall 26 and the outer housing 24. Two of the thermal resistance nodes are located where the curved outer surfaces of the liners 46. 48 contact respective internal catalyst housing 12, cylindrical sidewall 26. and outer sidewall 42. Two more of the thermal resistance nodes are where the diametrically opposite sides of the spherical beads 44 contact the inside surfaces of the respective liners 46 and 48. Of course, the curved liners 46 and 48 are not required, but they increase the resistance to heat flow through the spherical beads 44. Also. the beads 44 could be elongated strands wrapped around the inner catalyst housing 12 and the cylindrical sidewall 26, but that configuration would provide a greater contact surface area.

Ceramic spacers 50 are preferred to glass. porcelain, or other materials because ceramic can be fabricated of materials having higher melting temperatures, which may be necessary to preserve structural integrity in the high temperature environments generated by the catalytic reactions.

The exhaust gas paths between the inner end plates 32,34 and the outer end plates 38,40 may be enclosed by gas-impermeable. but thin, metal foil ducts 52 and 54 welded to the respective metal end plates 32,38, and 34,40 to maintain the vacuum-tight seal of the insulating chamber 30 between the internal catalyst housing 12 and cylindrical sidewall and outer housing 24. The ducts 52, 54 may be folded or corrugated like bellows to increase the effective distance that heat would have to travel in conduction from the internal catalyst housing 12 and cylindrical sidewall 26. through the ducts 52.54, to the outer housing 24. A plurality of thin, reflective metal foil radiation shields 56 which could be separated by spacers 58. preferably made of ceramic, but not a significant outgassing material, can be placed in chamber 30 to inhibit radiative transfer between the inner catalyst housing 12 and cylindrical sidewall 26 and the outer housing 24.

The chamber 30 is evacuated to a high vacuum, preferably in the range of 10-'to 10-6 torr for a highly effective vacuum insulating effect. However, a vacuum insulating disabling system, such as the gas control system 60 illustrated in Figure 2, can be included to selectivity enable or disable the insulation effect of vacuum chamber 30. This gas control system 60. as described in our U. S. patent application Ser. No. 07/960.885. can comprise a hydrogen gas source 62, such as a metal hydride, and a hydrogen window or gate 64. such as palladium, enclosed in respective metal

containers 66. 68. and connected via a conduit 70 to the vacuum chamber 30. When the metal hydride 62 is heated, for example by an electric heating element 72. it releases hydrogen gas that flows into chamber 30 and conducts heat across chamber 30. therebv effectively disabling or turning off the insulation effect of chamber 30. When the metal hydride 62 is cooled, it recaptures the hydrogen gas and creates a low pressure gradient in the container 66 that pulls the hydrogen gas back from chamber 30. thereby reenabling or turning on the insulation effect of chamber 30. The palladium gate 64 allows the hydrogen gas to pass through when the gate 64 is heated by the heating element 74. but the gate 64 is impervious to the hydrogen gas when the gate 64 is not heated.

Therefore, the hydrogen gas. once introduced into chamber 30 by heating both the metal hydride 62 and palladium gate 64, can be retained in the chamber 30 even when the electric power to the heating element 72 is turned off, by also turning off the electric power to heating element 74 and allowing the palladium gate 64 to cool. In fact, the palladium gate 64 would normally be allowed to cool first before cooling the metal hydride 62, to insure that substantially all the hydrogen is trapped in chamber 30 for maximum insulation disablement by the gas control system 60. When the insulation is to be turned back on again, only the palladium gate 64 must be heated momentarily to allow the hydrogen gas to be pulled out of chamber 30 through the palladium gate 64 and back into the metal hydride 62. Of course, the respective heating and cooling of the metal hydride 62 and palladium gate 64 can be controlled and timed to only partially enable or disable the gas conductance of heat across chamber 30 to any desired extent, thereby varying or controlling the rate of heat transfer between full on and full off.

Electric power for operating the gas control system 60 as described herein can be obtained from battery power, as indicated at 88. However, thermoelectric or thermovoltaic energy devices using heat generated by the particulate reduction apparatus 10 would also be appropriate. In fact, output of sufficient heat from the catalytic converter to start producing some threshold level of electricity in such thermoelectric or thermovoltaic device could start and sustain the heat conductance of the insulation chamber 30.

The heating elements 72. 74 can be turned on and off by any suitable electrical control svstem, such as respective relay switches 82.84 which are controlled by a suitable electronic control unit 86. such as a microprocessor or other logic circuit. as individuals skilled in designing and

fabricating electric control circuits may appreciate. For example, the control unit 86 could include a timing capability connected to the motor vehicle ignition switch 76 or other circuit that indicates when the engine E (Figure 1) is started and then actuate the relay switches 82. 84 to turn off the insulation chamber 30 after an appropriate time interval. The time interval may be set to allow the catalyst substrates 14 and inner surface 27 of the particulate combustion chamber 25 to reach the optimum operating temperatures, i. e., light-off and combustion temperature, respectively. The control unit 86 then can be programmed to turn the insulation chamber 30 on again when the engine E is turned off in order to retain the heat in the catalyst substrate 14 and the inner surface 27 as long as possible during the time that the engine E is not operating. rather than allowing it to cool quicky to ambient temperature. When controlled in that manner, the inner surface 27 of the particulate combustion chamber 25 and the catalyst substrate 14 can be maintained at temperatures above combustion temperature and light-off temperature for extended periods of time until the engine E is started again.

This temperature maintenance provides the benefit of facilitating the catalytic reactions on the exhaust gases and airborne combustion of the particulates almost immediately to reduce harmful exhaust emissions, rather than suffering the delay required to reach light-off temperature and combustion temperature again from ambient temperature.

Referring again to Figure 2. while the control unit 86 can be set up to turn the insulation chamber 30 off at some predetermined time after engine start-up, which is preferably a sufficient time for the catalyst to reach light-off temperature and the particulate combustion chamber 25 to reach desired combustion temperatures, other inputs and controls can also be used, as would be within the capabilities of persons skilled in this art once the principles of this invention are known. For example, an input from a temperature probe 78 in contact with the cylindrical sidewall 26 could be used to actuate the gas control 60. such as to shut off the insulation chamber 30, when the temperature of the cylindrical sidewall 26 reaches a certain desired operating temperature. Of course, such a temperature probe 78 may be positioned in various locations within the particulate reduction apparatus 10 and additional probes may be installed to monitor combustion temperatures to better control airborne combustion of particulates in the exhaust gases of the engine E andlor to monitor the light-off temperature within the catalyst substrate 14.

Further, it should be understood that, while the catalyst substrate 14 and the particulate combustion chamber 25 mav be maintained at different operating temperatures. in practice. the temperatures in each of these areas will be maintained within a temperature range above light-off and. also. above combustion temperature for the particulates. For example. but not as a design limitation, a temperature range of 350 °C to 400 °C or higher may be utilized for efficient operation of the particulate combustion chamber 25 and the catalvtic converter portion 11. The temperature probe 78 would have to be well insulated from the environment and from the outer housing 24 to avoid heat conduction therethrough when the insulation chamber 30 is turned on. It would also have to be sealed against leakage where it emerges through the outer housing 24. such as with ceramic sealing connectors similar to those described in our U. S. patent application Ser. Iso. 07/960, 885.

An alternative or additional temperature probe 79 in the downstream exhaust outlet 130 to measure the temperature of the exhaust gases emerging from the particulate reduction apparatus 10 could also be indicative of the temperature level of the catalyst substrate 14 and the particulate combustion chamber 25 and thus, be utilized for actuating the gas control 60. Such an alternative temperature probe 79 in the outlet 130 would not have to be insulated to avoid heat transfer or sealed to hold a vacuum, as would be required for the probe 78 extending through the insulation chamber 30.

Other inputs, such as a temperature sensor 80 positioned adjacent the outer housing 24. could be used to turn on or off the insulation chamber 30. For example, if other components or structures (not shown) near the particulate reduction apparatus 10 can withstand temperatures only so high. the temperature sensor 80 could cause the control unit 86 to actuate gas control 60 to turn on the insulation chamber 30 if the temperature of heat 81 radiating from the outer housing 24 rises above a preset level.

On the other hand, in other applications, it might be more important to"dump"heat from the catalyst substrate 14 and particulate combustion chamber 25 faster than the turned off insulation chamber 30 can process. Therefore, metal-to-metal contacts to function as thermal shunts between the internal catalyst housing 12 and cylindrical sidewall 26 of the particulate combustion chamber 25 and the outer housing 24 can be provided. For example, as shown in Figure 2. one or more bimetallic dimples or actuators 132. similar to those described in our U. S. patent application Ser.

No. 07/960, 885, can be provided in the cylindrical sidewall 26 and designed to actuate from a normally concave configuration to an alternate convex configuration, as indicated by broken lines 132', when the cylindrical sidewall 26 reaches a predetermined maximum temperature. Thermal shunt posts 134, preferably made of a good heat conducting metal, extend from the outer wall 42 of outer housing 24 into close enough proximity to the respective bimetallic actuators 132 such that when the bimetallic actuators snap to their convex configurations 132', they will make metal-to-metal contact with the posts 134. When such metal-to-metal contact is made, the posts 134 conduct heat very rapidly from the particulate combustion chamber 25 and the internal catalyst housing 12 to the outer housing 24, where it can dissipate to the surrounding environment.

It may also be desirable in some circumstances or applications to enhance conduction of heat from the catalyst substrate 14 to the internal catalyst housing 12 and into the insulation chamber 30, such as when the substrate 14 is made of ceramic materials that are poor conductors of heat. Such enhanced heat conduction can be provided by one or more elongated spikes 136, having one end extending into the substrate 14 and the other end extending through internal catalyst housing 12 and into the insulation chamber 30. If these spikes are not long enough to contact the outer wall 42 so that there is no metal-to-metal heat conduction through them to the outer housing 24. they will still conduct heat to the hydrogen gas in the insulation chamber 30 when the insulation chamber 30 is turned off by gas control 60, as described above. Similar elongated spikes (not shown) may readily be installed in the particulate combustion chamber 25 to increase conductive heat transfer, especially if ceramic materials or inserts are positioned within the inner surface 27, as discussed below.

It may also be preferable, but not necessary, to provide additional radiation and convection heat control by providing a heat absorber or retarder material 138, as shown in Figure 2. in the exhaust gas path 20 to inhibit direct axial radiation of heat from the particulate combustion chamber 25 out of the cylindrical sidewall 26, as well as to break up convection flows of hot exhaust gases in that area. While the heat absorber or retarder material 138 is shown as a solid maze structure in Figure 2. it could be a bulky material, such as ceramic wool fibers that are opaque to infrared radiation, thereby forcing multiple reradiations between fibers and retarding heat escape by axial radiation. Ceramic wool fibers or other materials also act to reduce the size of the convection cell, thereby retarding heat escape by convection. While the retarder material 138 is shown only

downstream of the particulate combustion chamber 25. a similar retarder could also be placed in the space immediately upstream of the substrate 14.

Heat generated by the airborne ignition of particulates and by the exothermic catalytic reactions within exhaust gases mav be put to beneficial use. stored, or dissipated. as appropriate for a variety of reasons. For example, the particulate reduction apparatus 10, 140 produces heat and heats up much more quickly than a cold engine E after start up, and a cold engine E not only does not run as efficiently as a warm engine E. but also produces more harmful exhaust emissions. such as carbonaceous particulates with volatile organic outer layers, and causes more wear on engine parts.

Further, passenger compartments of most vehicles are heated with hot engine coolant, so there is no heat for passenger comfort or windshield defrosting until the engine E heats up not only itself, but also the coolant in the water jacket of the engine E.

Therefore, referring to Figure 1, heat generated by the particulate reduction apparatus 10, 140, instead of being wasted by dissipation to the atmosphere, can be gathered in a manifold 142 and directed to the water jacket of the engine E, as indicated schematically by the broken line 144.

Alternatively or additionally, the heat generated by the particulate reduction apparatus 10,140 can be directed to the passenger compartment, as indicated schematically by broken line 148. to heat seats S or other components such as windshields, steering wheels. and space heaters. Since the temperature in and immediately around an operating particulate reduction apparatus 10, 140 are apt to be too high for standard engine coolant/antifreeze solutions, it is preferred to use a heat transfer and storage fluid (not shown) for heat exchange with the particulate reduction apparatus 10, 140 that has a higher boiling point and is more stable than engine coolant/antifreeze solutions at higher temperatures. Consequently, another heat exchanger interface 153 (Figure 1) is provided to transfer more moderate heat and temperature levels to the engine coolant/antifreeze solution that is used in the vehicle engine E.

When additional heat is not needed, such as during normal extended operation of the motor vehicle when the particulate reduction apparatus 10.140. engine E via a connection 144. and other components are already up to their normal operating temperatures. the heat generated in the particulate reduction apparatus 140 can be directed to a heat storage sink 150. to a heat dissipater 152. or to the engine E via connection 144 from where it can be dissipated along with heat from the

engine E into the atmosphere by the conventional vehicle radiator R. The actual plumbing. valves. controls. and the like for the various heat uses and components described above are not shown in detail because they are well within the capabilities of persons skilled in this art. once the principles of this invention are understood. Suffice it to say that if liquid engine coolant or other liquid medium is used to transfer heat, such a circulating circuit would comprise one conduit to send the liquid. another conduit to return the liquid, a pump. various valves, and valve controls that could be either manually or automatically operated by electricity, vacuum, air pressure. Also. the heat storage sink 150 can be used to store heat for later use in warming a start-up engine E or a cold passenger compartment, or the stored heat might also be used to help maintain an elevated temperature in the particulate reduction apparatus 10. 140 itself over more extended periods of time. It can be. for example. a heat storage device such as that described in the article entitled,"Latent Heat Storage." published in the February 1992 issue of Automotive Engineering. Vol. 100, No. 2, pp. 58-61. Heat pipes, while not specifically shown in the drawings, could also be used in place of a heat transfer fluid to transfer heat to and from the particulate reduction apparatus 10.140.

The thermal capacity of the particulate reduction apparatus 10. 140, can be increased further, particularly for storing sufficient heat for extended periods of time to heat the inner surface 27 to combustion temperatures and the substrate 14 to light-off temperature before starting the engine E. To accomplish this increased thermal capacity, a quantity of phase change material (PCM). such as metals. metal salt hydrates, or a hydride of trimethylol ethane (TME) or other polyhydric alcohols. described in U. S. Pat. Nos. 4,572.864 and 4,702,853. both of which are incorporated herein by reference. can be contained around or in thermal flow relation to the particulate combustion chamber 25 and to the substrate 14. For example, referring to Figure 3 which shows an alternate particulate reduction apparatus 140, a chamber 157 within the particulate reduction apparatus 140 could be filled instead with a PCM 158. As heat is created by the airborne combustion of particulates and the catalytic reaction, the thermal conductance of the insulation chamber 30 is actuated (insulative effect disabled), as described above, to transfer the heat into the solid PCM 158 where it serves as heat of fusion to melt the PCM 158. and is stored in that manner in the liquid PCM 158. Thereafter. if the PCM 158 is supercoolable or tnggerable. as the hydrates or hydndes referenced above, when the engine E is turned off and the particulate combustion chamber'5 and the substrate 14 consequently

cool off. the heat of fusion in the liquid PCM 158 is retained even as the PCM 158 super cools below its me) ting temperature, as described in the U. S. Pat. No. 4.860,729 which is incorporated herein by reference. Later, when the operator decides to start the engine E. a signal from the ignition switch 76 (Figure 2) can actuate a phase change tngger. such as that described in U. S. Pat. No.

4, 860, 729. which is also incorporated herein by reference. Such a phase change trigger. as indicated at 154 in Figure 1, could be connected to fittings (not shown) interconnected with the PCM 15S. When actuated, the phase change tngger 154 initiates nucleation of crystallization of the PCM 158 thereby causing it to give up its heat of fusion. With the conductance of the insulation chamber 30 also actuated (insulative effect disabled). the heat of fusion from the PCM 158 is conducted back into the particulate combustion chamber 25 and into the substrate 14 to help them reach particulate combustion temperature and light-off temperature, respectively.

There are. of course, numerous other ways to use a PCM for these purposes. For example, the heat sink 150 or another similar device could contain a PCM. The heat could also be transferred to and from an external PCM container with a liquid heat exchanger fluid (not shown). Still further, another chamber (not shown) could be positioned radially outward from a liquid heat exchanger chamber (not shown) that is wrapped-around the catalytic converter portion 11 and the particulate combustion chamber 25 to enable use of both a PCM and the thermal transfer fluid surrounding either or both the internal catalyst housing 12 and the cylindrical sidewall 26.

The implementation of a PCM as part of the present invention can be best understood by reference to the particulate reduction apparatus 140 illustrated in Figure 3. As shown, a ceramic container 156 with an annular chamber 157 is positioned inside the internal catalyst housing 12 and cylindrical sidewall 26 and in surrounding relation to the particulate combustion chamber 25 and the catalyst substrate 14. A porous insert 160 is included and illustrated as part of the particulate combustion chamber 25. The porous insert 160 may be fabricated from a porous ceramic or other porous material to define a circuitous flow path for the particulates in the exhaust flow 20. The porous insert 160 increases surface area for radiation of heat and reduces the distance heat must be radiated prior to being absorbed by particulates. A phase change material 158. such as aluminum or aluminum alloy almost. but not quite. fills the annular chamber 157. As the catalyst substrate 14 and the porous insert 160 heat up during operation of the engine E. thev also heat up the container 156

and phase change material 158. However. since ceramic is a poor heat conductor, this container 156 and phase change material 158 does not take up heat fast enough to increase the time required to heat the substrate 14 to light-off temperature and to heat the porous insert 160 to combustion temperatures. Over time. however, during operation of the engine E. the material 158 in chamber 157 will get hot enough to melt and heat up substantially to the optimum operating temperature of the particulate reduction apparatus 140. as controlled according to the features of this invention discussed above. The slight underfill leaves sufficient space in the chamber 157 to accommodate expansion of the material 158 as it heats up. Then. when the engine E is turned off. the phase change material 158 will help to hold heat on the porous insert 160 and the substrate 14. When the temperature cools down to the freezing point of the material 158, the temperature will stay relatively constant for an extended period of time as the material 158 gives up its heat of fusion.

Consequently, where the composition of the material 158 has a freezing/melting temperature above the combustion temperature of the particulates and the light-off temperature of the catalyst, the material 158 helps to maintain the porous insert 160 and the substrate 14 above preferred operating temperatures for extended periods of time.

The foregoing description is considered as illustrative only of the principles of the invention. and while the description and exemplary application of this invention has been directed primarily to vehicles with internal combustion engines and, particularly, diesel engines, it is not restricted to that application. Other applications include, for example, use in the chemical, petrochemical. and other industries for controlling particulate emissions. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and process shown and described above. Accordingly, resort may be made to all suitable modifications and equivalents that fall within the scope of the invention as defined by the claims which follow. The words"comprise.""comprises,"'comprising."''include,""includi ng."and "includes''when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components. or steps, but they do not preclude the presence or addition of one or more other features, integers. components. steps, or groups thereof.