Abstract:
A reactor that can be attached to the exhaust manifold of an internal combustion engine to oxidize and burn carbon soot particles, carbon monoxide, and unburned hydrocarbons, and to dissociate nitrogen and sulfur oxides. The reactor has a reaction zone that contains porous heat-retaining foam cells and that is bounded by a porous heat-retaining zone, which in turn is surrounded by ceramic insulation materials to minimize energy losses. Engine exhaust at elevated temperatures and containing some oxygen (air) enters the reaction chamber. By means of impinging heat transfer, thermal radiation enhancement, energy trapping and combustion of engine emissions, temperatures sufficient to oxidize carbon soot particles, carbon monoxide, and unburned hydrocarbons are attained. Steam or atomized water droplets are introduced to improve the efficiency of the reactor through gasification, regasification, water shift reactions, methanation, and hydrocracking reactions. Harmless product of the oxidation reactions, H 2  O and CO 2 , are released from the reactor.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is a reactor that burns toxic or undesired gaseous and particulate (including smoke and smog) emissions from vehicle internal combustion engine exhaust. The final product released to the atmosphere from the reactor contains only water vapor, carbon dioxide, and clean exhaust gases. It accomplishes this by recovering the exhaust heat from internal combustion engines; utilizing the exhaust emissions as fuels to generate additional combustion energy; applying thermal radiation enhancement, impinging heat transfer and energy trapping to achieve a high temperature environment of up to 800° C., or above; and using state-of-the-art insulation materials to minimize energy losses to the surroundings. 
     The present invention includes improvements over the reactor disclosed in U.S. Pat. No. 5,618,500. The improvements include injection of atomized water droplets or steam at the inlet to the reactor which improves the efficiency of the reactor. 
     Health and environmental concerns with automobile emissions have resulted in increasingly stringent and restrictive vehicle emission standards for hydrocarbons, carbon monoxide, NO x , and particulates such as soot and smog. Soot, or smoke, is basically a carbon particle from heating of lubricants or from agglomeration and dehydrogenation of hydrocarbon fuels during combustion processes. Smog is basically a mixture of soot, water vapor, and unburnt fuel. Soot-laden black smoke is readily observed being emitted from exhaust pipes of large trucks powered by diesel engines. However, when filters are used to reduce soot and smoke emissions, some studies show that engine particulate filters or traps collect only 60-90% of the particles. The retained particles progressively block the flow passage and increase back pressures, thus causing reduced engine output power and fuel economy. 
     For typical gasoline engines, the engine outlet temperature is in the range of 320°-370° C. and the temperature of the exhaust after leaving the catalytic converter can be as high as 500° C. However, the maximum engine outlet temperature can be as high as 400° C. The oxygen content in the exhaust is about 1% because of incomplete combustion, and the fuel/air ratio is at stoichiometric ratio. 
     For diesel engines, the outlet temperature is in the range of 540°-650° C. and its maximum temperature can be as high as 800° C. Diesel soot particles have an average size diameter than 0.3 μm and more than 75% of them have a diameter less than 1 μm. When collected on a filter, the bulk density of the soot particles is about 0.07 gm/cm 3 . This indicates that the structure of the soot particles is porous, which facilitates reactions with water and oxygen. Soot oxidizes slowly at 300° C. and rapidly at 400° C. in air or a gas mixture containing 10% oxygen. If a temperature of about 540° C. is reached in the presence of adequate oxygen, soot collected a diesel exhaust filter will burn. The oxygen content of diesel engine exhaust is about 10-12% because the diesel engine&#39;s turbocharger have an air/fuel ratio as high as 25% excess air. 
     Therefore maintaining a reactor to which gasoline engine exhaust with an oxygen content of about 1% is introduced above 300° C. will result in the oxidation of gaseous constituents (such as carbon monoxide and unburned hydrocarbons) and will greatly reduce their release to the atmosphere. Similarly, maintaining a reactor to which diesel engine exhaust with an oxygen content of about 10% about 400° C. will result in the burning and reduced release of soot particles. Such a reactor could complement, or replace, the catalytic converters used with gasoline engines, and could greatly reduce noxious releases from diesel engines, which do not have catalytic converters. 
     A recognized problem for catalytic converters in use with gasoline engines as reported by Ashley in Mechanical Engineering in November 1994 is that from 60% to 85% of the hydrocarbon emissions are generated during the first 200 seconds following cold startup. This is because catalytic converters cannot efficiently remove these pollutants until they attain their effective operating temperature of 300° C. or greater. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a reactor that can be located along the exhaust manifold of an internal combustion engine, such as a diesel engine, gasoline engine, jet engine, or gas turbine. Combustion exhaust, which may contain soot particles, unburned hydrocarbon fuel, carbon dioxide, carbon monoxide, water vapor, nitrogen oxides, and air is directed into a reaction zone. The engine and reactor may be mounted on a vehicle or may be stationary mounted. The reaction zone is surrounded by ceramic foam cells, a ceramic wall, and insulation material. These insulators minimize the loss of energy from the reaction zone and from the reactor itself. The reaction zone and ceramic foam cells are configured so that several heat transfer processes (conduction, convection, and radiation) combine to &#34;trap&#34; energy in the reaction zone and attain temperatures sufficiently high to oxidize soot particles, hydrocarbons, and carbon monoxide, and dissociate noxious emissions such as NO x  and SO x . These oxidation reactions are exothermic so that heat is generated in the reaction zone, and is trapped there, so that the temperatures needed for oxidation are sustained. Further heat is generated in the reaction zone from burning (combustion) of unburned hydrocarbons in the engine exhaust so that temperatures are attained in excess of the exhaust temperature when it enters the reaction zone. 
     Incoming particle-laden exhaust contacts the porous ceramic foam cells and the particles (soot) are deposited on the porous ceramic foam surfaces transferring heat through impinging heat transfer. The particles are heated by conduction from the porous ceramic foam, by the heat trapped in the reaction zone through convection and radiation, and by the heat generated from combustion of the unburned hydrocarbons. The deposited carbon particles are oxidized and burned in the presence of the oxygen in the exhaust to toxic carbon monoxide. The carbon monoxide is in turn oxidized to harmless carbon dioxide in the reactor. The oxidation and combustion of these deposited carbon particles also releases energy, and in turn increase the reactor temperature. 
     The present invention includes the injection of water in the form of atomized droplets or steam into the reaction zone. The water will react with unburned hydrocarbons, soot particles, and through gasification, regasification, and water shift reaction. 
     
         C.sub.m H.sub.n +m H.sub.2 O→mCO+(m+n/2) H.sub.2 (gasification) 
    
     
         C+H.sub.2 O→CO+H.sub.2 (regasification) 
    
     
         CO+H.sub.2 O→CO.sub.2 +H.sub.2 (water shift reaction) 
    
     Carbon monoxide, carbon dioxide, and hydrogen formed in the above reactions or in the engine exhaust can react by methanation and hydrocracking to form methane and water. 
     
         CO+3H.sub.2→CH.sub.4 +H.sub.2 O (methanation) 
    
     
         CO.sub.2 +4H.sub.2 →CH.sub.4 +2H.sub.2 O (methanation) 
    
     
         C.sub.m H.sub.n +(2m-n/2) H.sub.2 →m CH.sub.4 (hydrocracking) 
    
     The products of these reactions are carbon dioxide, hydrogen, and methane. Hydrogen and methane are readily oxidized in the reaction zone in exothermic reactions that help the sustain high temperatures in the reaction zone. Alternatively, they are oxidized in an added catalytic oxidizer or commercially available catalytic converter. 
     The present invention has several objectives. First, it uses an engine&#39;s own waste energy and the energy generated from the combustion of the engine&#39;s own emissions to destroy undesirable constituents of the engine&#39;s exhaust and to act as a second combustor. Second, because the reactor retains heat for several hours after the engine is shutdown, there is more efficient restart of the engine during the interval that the reactor is at above-ambient temperatures. The reactor also reduces the duration of the cold-start period from approximately 200 seconds to approximately 100 seconds because of its heat retention properties and traps particulates in the exhaust in the reactor. These effects result in less energy consumption and lower hydrocarbon, smoke, and soot emissions. Third, the reactor does not increase operations and maintenance needs--it does not have moving parts; it does not require catalyst converters (although an embodiment is disclosed and claimed that uses a catalytic converter); it does not require change in the engine combustion process (such as throttling); no filter or trap (which may block the exhaust system, or reduce engine power or fuel economy) is needed; it does not require external oxygen or energy sources for current vehicle designs (although future vehicle designs may require them and a claimed embodiment includes them); neither cleaning nor regeneration is required; a control system is not required; and the reactor is not noisy. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of an embodiment that emphasizes thermal radiation enhancement with neither a catalytic oxidizer layer nor a catalytic converter. 
     FIG. 2 is a cross sectional view of an embodiment that emphasizes thermal radiation enhancement with a catalytic oxidizer layer. 
     FIG. 3 is a cross sectional view of an embodiment that emphasizes thermal radiation enhancement with a catalytic converter. 
     FIG. 4 is a cross sectional view of an embodiment that emphasizes long retention times in the reaction zone. 
     FIG. 5 is a cross sectional view of an embodiment for a compromise between long retention times and thermal radiation enhancement. 
     FIG. 6 is a cross sectional view of an embodiment with assisted air and energy sources. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, engine exhaust 1 typically containing combustion products including smoke, soot particles, unburned hydrocarbons (fuel), carbon dioxide, carbon monoxide, water vapor, nitrogen oxides (NOD enter the present invention through inlet pipe 9 at high temperature. The inlet pipe leads the impinging engine exhaust jet stream directly into a reaction zone 20 onto the stagnation surface of ceramic foam cells 30. Also atomized water droplets or steam from a water tank 100 are introduced into the reaction zone 20 with use of a connecting pipe 101, a pump 102, and an atomizing nozzle 103. The atomized water droplets, or steam, are injected into the reaction zone 20 to mix with engine exhaust constituents and to participate in the gasification and water shift reactions. The connecting pipe could be wrapped about the engine block to better utilize waste heat from the engine and to flash water into steam. 
     The reaction zone has lateral surfaces bordered by porous heat-retaining zone 4. More specifically, the porous heat-retaining zone may be constructed of reticulated foam cells of ceramic materials such as zirconia, mullite, silica, alumina, cordierite, or lava; ceramic oxides of these ceramic materials; combinations of the ceramic materials or of their oxides; or these combinations washcoated with high purity alumina, titania, or zeolites. The surface of the reaction zone opposite from the inlet pipe is bordered by an impervious ceramic wall disk 5. Attached to the impervious ceramic wall disk 5 and extending into the reaction zone 20, are the ceramic foam cells 30, which could be made of the same materials as the porous heat-retaining zone. The porous materials 4 and 30 serve five functions: (1) as energy-retaining media; (2) as sites for filtering and deposition of soot particles; (3) for prolonging the retention time of exhaust in the reactor; (4) for providing shape factors for radiation enhancement; and (5) for uniform thermal and flow mixing. 
     As shown in FIG. 1, there is a niche 35 between the porous heat-retaining zone 4 and the porous ceramic foam cells 30. The porous heat-retaining zone is within an impervious ceramic wall 6, which in turn is bordered by an outer insulating region 7, such as vacuum form ceramic fibers, ceramic fiber blankets, or refractory fibers. The impervious ceramic wall disk 5 and the impervious ceramic wall 6 may be ceramic materials such as zirconia, mullite, silica, alumina, cordierite, or lava; ceramic oxides of these ceramic materials; combinations of the ceramic materials or of their oxides; combinations of metals and ceramics; or magnesia or calcia stabilized or partially-stabilized ceramics. The reactor has a metal casing 8. 
     With the terminology that the inlet to the reactor is the bottom of the reactor and the outlet area is the top, the top of the reactor is a metal enclosure 10 and a metal outlet pipe 11. Bordering top of the impervious ceramic wall disk 5, reaction chamber 20, porous heat-retaining zone 4, impervious ceramic wall 6, and outer insulating region 7 is a metal net mesh 70. Contained between the metal net mesh 70 and the stainless steel enclosure 10 is an outer chamber 40. The metal components are typically stainless steel or a high-temperature alloy. 
     Most of incoming particle-laden exhaust flow jet 1 entering the reaction zone 20 impinges on the stagnation surface of the porous ceramic foam cells 30 and distributes to the niche 35. Some of the incoming flow directly passes into the niche 35 where it mixes with the distributed flow there and then passes through the porous heat-retaining zone 4. Because the porous heat-retaining zone is bordered by the impervious ceramic wall 6, flow from the porous heat-retaining zone is through the metal net mesh 70 into the outer chamber 40 and then out of the reactor through the outlet pipe 11. 
     In the reaction zone 20 several processes act to create sufficiently high temperatures to oxidize and burn soot particles, hydrocarbons, and carbon monoxide, and dissociates noxious emissions such as NO x  and SO x . When the incoming particle-laden exhaust flow 1 contacts the porous heat-retaining material in zone 4 and cells 30, particles are deposited on these surfaces and heat is conducted to these surfaces through impinging heat transfer and conduction. These surfaces, in turn emit heat through radiation, and the hot exhaust transfers heat through convection. As the reaction zone is surrounded by insulating material, the heat generated by the above processes is retained in the reaction zone, with some losses, and temperatures sufficient to oxidize and burn the carbon soot particles, unburned hydrocarbon fuel, and carbon monoxide are attained and the gaseous product leaves the surfaces of the porous zone 4 and cells 30. Oxidation and burning (combustion) of the soot particles, unburnt hydrocarbons, and carbon monoxide, as well as decomposition of nitrogen oxides and sulfur oxides, are exothermic reactions whose heat releases help attain the high temperatures needed to sustain these oxidation and combustion processes. The final products 12 released from the outlet pipe include carbon dioxide, water vapor, and other clean exhaust gases. 
     The engine exhaust 1 mixes with the atomized water droplets or steam 104 and the chemical reactions described in the Summary section convert soot particles (carbon), carbon monoxide, and unburned hydrocarbon into carbon dioxide, H 2  O, hydrogen, and methane. All of the reactions initiated by the introduction of water are exothermic at the temperatures attained in the central reaction zone except gasification. For the introduction of water to have a net exothermic effect, the mass ratio of water to feedstock (engine exhaust) should be in the range of 0.01 to 3.0. The methane and hydrogen produced are fuels that burn to further enhance the high temperatures needed to sustain the oxidation and combustion processes. 
     This range of suitable mass ratios were developed from combustion calculations with exhaust based on combustion of diesel #2 fuel in the engine and an experimental result in which a temperature of 477° C. was sustained in the reactor at an engine load of 400 ft-lb and engine speed of 1800 RPM when no water was introduced. The mole fraction of solid carbon, C(S), carbon monoxide, methane, and hydrogen leaving a reactor is shown as a function of mass ratio of water to exhaust and of the rate with which exhaust is introduced into the reactor. Case 1 (312 kg/hr) represents exhaust compositions from current diesel engines. Case 3 (62 kg/hr) represents a worst case exhaust composition from old diesel engines. Case 2 (139 kg/hr) is an intermediate case. 
     
         __________________________________________________________________________MOLE FRACTIONMass Ratio 0.0 0.2 0.4 0.6 0.8 1.0 2.0 3.0__________________________________________________________________________C (S)(1)   8.5E-5     0.0 0.0 0.0 0.0 0.0 0.0 0.0(2)   1.8E-1     6.2E-2         0.0 0.0 0.0 0.0 0.0 0.0(3)   3.8E-1     2.8E-1         1.8E-1             4.1E-2                 0.0 0.0 0.0 0.0CO(1)   1.6E-2     4.3E-3         2.1E-3             1.6E-3                 1.0E-3                     7.0E-4                         2.3E-4                             6.2E-5(2)   1.1E-2     1.4E-2         1.4E-2             1.0E-2                 8.3E-3                     6.6E-3                         3.0E-3                             1.6E-3(3)   4.8E-3     8.0E-3         1.2E-2             1.3E-2                 1.5E-2                     1.5E-2                         8.6E-3                             5.6E-3CH.sub.4(1)   8.7E-3     2.0E-3         5.0E-4             2.8E-4                 1.7E-4                     2.3E-5                         1.6E-6                             5.2E-7(2)   3.2E-2     6.0E-2         6.5E-2             4.5E-2                 3.4E-2                     2.3E-2                         4.8E-3                             1.3E-3(3)   9.8E-2     1.1E-1         1.2E-1             1.3E-1                 1.4E-1                     1.3E-1                         6.1E-2                             2.8E-2H.sub.2(1)   5.1E-2     6.6E-2         5.7E-2             5.1E-2                 4.4E-2                     3.9E-2                         2.5E-2                             1.7E-2(2)   8.8E-2     1.3E-1         1.6E-1             1.7E-1                 1.7E-1                     1.7E-1                         1.5E-1                             1.2E-1(3)   1.4E-1     1.5E-1         1.7E-1             1.9E-1                 2.0E-1                     2.1E-1                         2.2E-1                             2.1E-1__________________________________________________________________________ 
    
     From the table it is seen that carbon soot leaving the reactor decreases monotonically with water mass ratio, while for the other three materials, depending on case, there might be a peak and then decline for mass ratios above 2. Water mass ratios above three are not considered practical because it would be difficult to sustain high temperatures in the reaction zone with too much water because of the high vaporization energy of water. 
     The embodiment shown in FIG. 1 maximizes shape-related thermal radiation enhancement at the expense of retention time. To achieve more nearly complete oxidation that attainable in the reaction chamber 20, the embodiment shown in FIG. 2 adds a second metal mesh 71 and a catalytic oxidizer layer 200 between the two metal meshes. A commercially available catalytic oxidizer that is particularly effective for hydrogen, light hydrocarbons, and carbon monoxide should be used. The layer should include a commercially available catalyst that can effectively dissociate the nitrogen oxide and sulfur oxide in the exhaust. 
     As an alternative to the catalytic oxidizer used in the embodiment in FIG. 2, a commercially available catalytic converter as are widely used for gasoline engines could be used. FIG. 3 shows an embodiment in which a catalytic converter 300 is used. It is located upstream from the outlet pipe 11 so that the outlet 12 flow is passed directly to the catalytic converter. 
     The embodiments shown in FIG. 4 and FIG. 5 differ from the embodiment shown in FIG. 1 as to the extend of the porous foam cells 30. In the embodiment shown in FIG. 4, the porous ceramic foam cells 32 contact the porous heat-retaining zone 4 for the entire length of the porous ceramic cells. This eliminates the niche 35 shown in FIG. 1, so that reaction zone 21 does not have a niche. The niche has the effect of enhancing temperature in that part of the reaction zone 20 through radiative heat transfer from the surfaces of the porous ceramic foam zone and cells; however, the niche also offered no resistance to transport of the exhaust flow and reduces retention time within the reaction zone. Thus, the embodiment shown in FIG. 4 results in greater retention time at the expense of loss of some shape-related thermal radiation enhancement as compared to the embodiment shown in FIG. 1. 
     In the embodiment shown in FIG. 5, the porous ceramic foam cells 31 contact the porous heat-retaining zone 4 for part of, but not all of the length of the porous ceramic foam cells 31. This results in niche 36 in reaction zone 22 between the porous ceramic foam cells and porous heat-retaining zone that is shorter than the niche 35 in the embodiment shown in FIG. 1. This embodiment is a compromise between retention time and shape-related thermal radiation enhancement. 
     The embodiments shown in FIGS. 4 and 5 differ from the embodiment shown in FIG. 1 only with respect to the shape and extent of the porous ceramic foam cells in the reaction zone. Embodiments with these two configurations of porous ceramic foam cells can have a catalytic oxidizer layer outside of the reaction zone as shown as shown in FIG. 2 or a catalytic converter as shown in FIG. 3. 
     This reactor is installed right before the catalytic converter for gasoline-fueled engines and will be installed right after the engine outlet for diesel-fueled engines. 
     The oxygen (air) content of engine exhaust and its temperature are sufficient for the reactor to operate efficiently under normal operating conditions. However, for certain upset conditions arising from engine loads or to account for future engine development involving low oxygen content (e.g., from not using turbochargers) or low outlet temperatures (e.g., fuel is burned at local areas near the fuel injector, a lean-burn engine), an external energy source or an external source of oxygen (air) may be needed for efficient oxidation and dissociation to occur. FIG. 6 shows an embodiment similar to the embodiment shown in FIG. 4, except for an external source of air 50 that is introduced into the reaction zone with use of a pump 52 and piping 51 and an energy source 60 located in the reaction zone 23. The use of external sources or energy or air is not limited to a variation on the embodiment shown in FIG. 4, but is as readily applicable to other embodiments as well. The energy source could be an electrical source powered from a battery or from utility electricity, or could be solar energy, or could be petroleum-fueled energy directly from a fuel tank.