Abstract:
The present invention relates to a method and apparatus for removing hydrocarbons from the exhaust stream of a diesel engine prior to cooling the exhaust for recycling through the intake manifold. A filter is used to remove hydrocarbon combustion products, including particulate matter, from the exhaust at a point after the exhaust gasses leave the exhaust manifold and before the exhaust gasses enter an exhaust gas cooler. Reduction of the hydrocarbon levels in the exhaust gasses slows or prevents buildup of hydrocarbon residue downstream of the filter, such as in the exhaust gas cooler, reducing the frequency of the requirement for cleaning or replacing the filter and effectively extending the life of the exhaust system.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to internal combustion engines and, more particularly, to a system for the removal of hydrocarbons from engine exhaust gasses and a reduction of hydrocarbon deposits in the engine interior. 
     BACKGROUND OF THE INVENTION 
     Internal combustion engines do not burn fuel very efficiently, and as a result produce exhaust gasses containing by-products of incomplete combustion, such as carbon monoxide, nitrous oxides, and a variety of hydrocarbons. Even diesel engines, which use a higher air-to-fuel ratio than do gasoline (Otto cycle) engines, produce excessive nitrous oxides along with carbon monoxide and some hydrocarbons. These combustion by-products are undesirable because they are both harmful to the environment and wasteful. 
     Carbon monoxide is a known greenhouse gas and is also toxic in large quantities, since it is preferentially absorbed over oxygen in red blood cells. Some nitrous oxides are also toxic, and contribute to acid rain. And among the plethora of hydrocarbons produced by inefficient combustion are carcinogenic benzpyrene and nitroaromates. Inefficient combustion is also wasteful insofar as the carbon monoxides, nitrous oxides, and hydrocarbons may yet be further oxidized to release potential chemical energy stored within. 
     One method of removing inefficient combustion by-products known in the art is to pass the exhaust stream through an afterburner to fully oxidize the by-products therein. While this technique is effective in removing the combustion by-products from the environment, it is inefficient in that afterburning is an endothermic process, actually taking more energy to perform and so further reducing the engine&#39;s efficiency. 
     Another method of removing inefficient combustion by-products known in the art is by using a trap to remove the by-products form the exhaust stream prior to its emission into the environment. Traps are most effective in removing hydrocarbons (soot) from the exhaust stream, and less effective at removing carbon monoxide and/or nitrous oxides. Further, traps must frequently be purged of the entrapped hydrocarbons so as not to become choked and block the engine exhaust stream, thus increasing ram pressure and decreasing engine power and efficiency. Purging may be accomplished by physically removing and cleaning the trap or through the application of heat to the trap sufficient to oxidize the entrapped hydrocarbons. In either event, purging the trap is time and/or energy consuming. 
     Another method known in the art of removing inefficient combustion by-products from engine exhaust is by routing some of the engine exhaust back into the air intake, such that the partially oxidized combustion by-products may be completely oxidized by the engine. This is known as exhaust gas recycling. While this method is efficient in reducing the level of inefficient combustion by-products (especially nitrous oxides and carbon monoxide) ultimately emitted by the engine, the exhaust gasses must first be cooled before being reintroduced into the engine in order to control the combustion process. Cooling is accomplished by routing the hot exhaust gasses through a cooling chamber. During cooling, hydrocarbons in the exhaust gas stream tend to condense or otherwise accumulate in the cooling chamber, eventually clogging it and necessitating a purge procedure similar to the one described above for the trap. 
     There is therefore a need for a way of preventing the accumulation of hydrocarbon residue from accumulating in the cooling chamber of an exhaust gas recycling system. The present invention addresses this need. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a method and apparatus for at least partially removing hydrocarbons from the exhaust stream of an internal combustion engine as or shortly after the exhaust gasses leave the exhaust manifold and prior to cooling the exhaust for recycling through the intake manifold. In a preferred embodiment, a filter is placed in the exhaust gas stream substantially adjacent the exhaust manifold, allowing the removal of hydrocarbon combustion by-products from the exhaust gasses at a point before the exhaust gasses can travel downstream of the exhaust manifold and deposit hydrocarbon residue within the exhaust gas recycling system (i.e., the exhaust gas transfer pipes or conduits and other exhaust gas processing devices). This is especially important in engine systems employing exhaust gas recirculation technology, since the exhaust gas recirculation conduits and exhaust gas recirculation cooler generally comprise a closed-loop system that requires expensive time and labor to clean or replace and is susceptible to clogging from residual hydrocarbon condensation and deposition from the cooling exhaust gasses circulating therethrough. 
     The filter may include a catalyst material to facilitate the removal of combustion by-products at the temperatures typical of engine exhaust gasses. Alternately, the filter may instead include means to heat the exhaust gasses passing therethrough sufficiently to ensure more efficient removal of the combustion by-products. Still alternately, the filter may feature a combination of both a catalyst and heating means. The filter removes hydrocarbons from the exhaust gasses as they leave the exhaust manifold, reducing the hydrocarbon levels in the exhaust gasses so as to slow or prevent buildup of hydrocarbon residue further downstream. The filter may operate to oxidize the hydrocarbons and other combustion by-products as the exhaust gasses pass therethrough, it may trap the hydrocarbons for periodic thermal purging in which the hydrocarbon build-up in the filter is bulk oxidized, or it may do both. 
     One object of the present invention is to provide an improved internal combustion engine exhaust system. Related objects and advantages of the present invention will be apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a first embodiment exhaust gas filtration system of the present invention. 
     FIG. 2A is a partial sectional plan view of a first filter used in the embodiment of FIG.  1 . 
     FIG. 2B is a partial sectional plan view of a second filter used in the embodiment of FIG.  1 . 
     FIG. 3A is a partial sectional perspective view of the filter of FIG.  2 A. 
     FIG. 3B is a perspective view of the filter element of FIG.  3 A. 
     FIG. 3C is a sectional schematic view of the pore structure of the filter element of FIG. 3A illustrating exhaust gas flow therethrough. 
     FIG. 3D is sectional view of the filter element of FIG. 3A illustrating the metal coating on the pores. 
     FIG. 4 is a partial sectional perspective view of the filter element of FIG.  2 B. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     FIG. 1 schematically illustrates a first embodiment of the present invention, a filter system  10  for removing volatile combustion by-products, such as hydrocarbons, carbon monoxide, nitrous and nitric oxides (Nox) from exhaust gasses produced by incomplete combustion of petroleum-based fuel oils. The filter system  10  includes a filter  20  fluidically connected to the exhaust manifold  22  of an internal combustion engine  24 . In this embodiment, the internal combustion engine is a diesel engine, but in other embodiments the filter system  10  may be adapted to work with any convenient internal combustion engine  24 . The diesel engine  24  receives air through an air intake  26  manifold fluidically connected thereto. The filter  20  is positioned adjacent or partially within the exhaust manifold  22 , such that while the engine  24  is running the filter  20  is heated by the exhaust manifold  22  and is maintained at a temperature of at least about 350° F., and, more preferably, in excess of about 450° F. The filter  22  is also fluidically connected to an exhaust gas recirculation (EGR) cooler  28 , which is in turn fluidically connected to the air intake manifold  26 . An EGR valve  30  is connected in fluid communication with the filter  20  and the EGR cooler  28 , such that the fluid flow from the filter  20  to the EGR cooler  28  may be independently regulated or interrupted. The EGR valve  30  is preferentially fluidically connected between the filter  20  and the EGR cooler  28 , although the EGR valve  30  may be positioned anywhere in the system  10  convenient to the regulation of fluid flow through the filter  20 . 
     In operation, the filter  20  receives at least some of the exhaust gasses emitted from the exhaust manifold  22 . The filter  20  acts to remove volatile combustion by-products from the exhaust gasses that would otherwise become trapped as residual buildup in the EGR cooler  28 . The EGR cooler  28  operates to cool exhaust gasses for reintroduction into the engine  24  through the air intake manifold  26 . If the EGR cooler  28  becomes clogged or blocked (for example, by hydrocarbon buildup), more energy is required to force the exhaust gasses therethrough (overcoming mounting backpressure), and the efficiency of the EGR cooler  28  and the engine  24  is accordingly reduced. Further, if hydrocarbons or other combustion by-product particles are carried from the EGR cooler  28  to the air intake manifold  26  to deposit within the engine  24 , additional engine wear may result. 
     FIGS. 2A and 2B illustrate the filter  20  in greater detail. FIGS.  2 A and  3 A-D illustrate a first embodiment filter  20 A, which operates to remove hydrocarbons from exhaust gasses by catalytically oxidizing them. Filter  20 A includes a filter body  32 A adapted to receive fluids through an inlet  34 A and expel them through an outlet  36 A. The filter body  32 A (see FIG. 3A) contains a porous refractory filter element  40 A (see FIG. 3B) having a catalytic precious metal  42 A coating at least some of the pores  44 A, such that exhaust gasses flowing therethrough are forced into contact with the catalyst metal  42 A as they transition through the filter  20 A (see FIGS.  3 C-D). The refractory body  40 A may be made of any convenient ceramic or other refractory material capable of withstanding the temperatures and temperature differentials experienced in or near the engine exhaust manifold  26 . One preferred refractory material is cordierite, although any porous refractory material having sufficient chemical stability may be used. The pores may be inherent in the refractory body  40 A, or they may be formed later through any convenient machining process. 
     The catalyst metal  42 A is preferably cerium, palladium, platinum, and/or rhodium, as these are materials metals known to readily catalyze the oxidation of hydrocarbons. The catalyst metal  42 A is more preferably a combination of cerium with palladium, platinum, and/or rhodium. The catalyst metal  42 A catalyzes oxidation of hydrocarbons in the exhaust gasses at temperatures as low as about 400° F., thereby allowing the hydrocarbons in the exhaust gasses to be broken down into water and carbon dioxide (or at least carbon monoxide) oxidation products. Cerium will begin to catalyze the oxidation of hydrocarbons at temperatures as low as about 350° F., while palladium, platinum and rhodium begin to catalyze oxidation of hydrocarbons at about 800-900° F. While Pa, Pt, and Rh have the advantage of being extremely stable at elevated temperatures and under a wide variety of chemical and pH environments, they have the disadvantages of being expensive and of having a high hydrocarbon catalysis threshold temperature (relative to the temperature of typical engine exhaust gasses). Since oxidation is an exothermic reaction, a catalyst metal  42 A including a combination of Ce with Pa, Pt, and/or Rh can therefore begin to catalyze oxidation of carbonaceous materials in the exhaust gas stream with the Ce portion of the catalyst metal  42 A at the lower temperature of about 400° F. (typical of engine exhaust gasses) until the heat produced by the oxidation reaction raises the temperature of the catalyst metal  42 A sufficiently for the Pa, Pt, and/or Rh portions of the catalyst metal  42 A to participate in the catalysis process. It is desirable to oxidize the carbonaceous materials in the exhaust gas stream at as high a temperature as possible, since high temperatures are more efficient for complete oxidation of the heavier carbonaceous materials (for example, long chain hydrocarbon molecules) as well as for any other, non-carbonaceous volatile combustion by-products (such as, for example, NOx). The oxidation products are then expelled through the outlet  36 A to be carried along with the rest of the exhaust gasses into the EGR cooler  28  for return to the engine  24  through the exhaust manifold  26 . 
     FIG. 2B illustrates a second embodiment of the filter  20 B of the present invention, operative to remove volatile combustion by-products from the exhaust gasses flowing therethrough. Filter  20 B includes a filter body  32 B having a filter inlet  34 B for receiving fluids and a filter outlet  36 B for expelling fluids. Filter  20 B further includes a filter element  40 B containing microwave-absorbing fibers  50 B (see FIG.  4 ). The microwave-absorbing fibers  50 B are preferably incased in a refractory paper matrix  52 B, and are more preferably formed from silicon carbide. 
     The filter  20 B further includes a microwave generator  54 B (such as a magnetron) operationally connected to a waveguide  56 B. The waveguide  56 B is positioned to direct microwaves generated by the microwave generator  54 B at the filter element  40 B. In operation, hydrocarbons from the exhaust gasses passing through the filter  20 B collect on the filter element  40 B. The filter element  40 B is then routinely purged by a microwave-induced heat treatment. Microwaves from the microwave source  54 B are directed through the waveguide  56 B to the filter element  40 B, where they are exothermically absorbed by the microwave-absorbing fibers  50 B. The heat generated by the absorption of the microwaves raises the temperature of the filter element  40 B sufficiently to oxidize the hydrocarbon residue collected thereon. The resulting water vapor, carbon dioxide and/or carbon monoxide is expelled through the outlet  36 B, cooled in the EGR cooler  28 , and reintroduced into the engine  24  through the intake manifold  26 . The microwave source  54 B may be adapted to automatically activate or may be activated by an electronic controller  60 B operationally coupled thereto. 
     In operation, the filter system  10  of the present invention operates to remove hydrocarbons and other volatile combustion by-products from the exhaust stream of an internal combustion engine  24  while the engine  24  is running by providing an exhaust gas filter  20  positioned downstream from the exhaust manifold  22  and adapted to receive at least some of the exhaust gasses emitted therefrom. The filter  20  is preferably positioned as close as possible to the exhaust gas manufold  22 . The hot exhaust gasses from the exhaust manifold  22  are circulated through the filter  20 , wherein at least some of the hydrocarbon content of the exhaust gasses is removed. Preferably, the filter temperature is maintained high enough that at least some of the hydrocarbons and other engine volatile combustion by-products are at least partially oxidized while in the filter  20 . More preferably, the amount of volatile combustion by-products of all kinds is substantially reduced as the exhaust gasses passes through the filter  20 . The exhaust gasses may then circulated from the filter  20  to the atmosphere. Alternately, the exhaust gasses may be circulated from the filter  20  to the engine&#39;s air intake manifold  26 . Preferably, the exhaust gasses are cooled before being introduced into the air intake manifold  26 . Cooling of the filtered exhaust gasses is preferably accomplished by circulating them through an EGR cooler  28  prior to circulating them into the air intake manifold  26 . 
     One preferred method of removing the hydrocarbons from engine exhaust gasses is to deposit the hydrocarbons within the filter  20 , and then occasionally heat the filter  20  sufficiently to oxidize the trapped hydrocarbons. Another preferred method of filtering the hydrocarbons from the exhaust gasses is to catalyze the oxidation of the exhaust gasses within the filter  20 , making use of the proximity of the filter  20  to the exhaust manifold to maintain the filter  20  at a temperature sufficient to support catalytic oxidation of the hydrocarbons. Preferred catalysts include Ce and/or refractory elements from column VIIIA, rows  5  and  6  of the periodic table (such as Pt, Pd, and Rh), although any convenient element, alloy, or compound having the desired thermal stability and catalytic properties may be used. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are to be desired to be protected.