Reducing oxides of nitrogen using reformate generated from engine fuel, water and/or air

Inlet air (15) humidified in an air bubbling (or other) humidifier (35) that receives water from a tank (36) is sent to a hydrogen generator (27) along with vaporized (23) diesel fuel (22) to produce hydrogen and carbon monoxide (28) for either (a) mixing with the mainstream of exhaust (18) fed to a catalytic converter (30) or (b) regenerating a pair of NOx adsorption traps (38, 39), thereby reducing oxides of nitrogen (NOx), to provide system exhaust (32) which may have less than 0.40 grams/bhp/hr of NOx and 0.28 grams/bhp/hr of non-methane hydrocarbons. In other embodiments, unhumidified air mixed with fuel feeds a homogeneous non-catalytic partial oxidizer (27) to provide the required hydrogen and carbon monoxide.

TECHNICAL FIELD

This invention relates to reducing oxides of nitrogen (NOx) in the exhaust of hydrocarbon-fueled, internal combustion engines (such as gasoline or diesel engines), and more particularly to using hydrogen generators, such as catalytic partial oxidizers (CPOx), non-catalytic (homogeneous) partial oxidizers (POx), or auto thermal reformers (ATR), to generate from engine fuel, water and/or air, streams including hydrogen and carbon monoxide for reducing NOx in catalytic converters or regenerating NOx trap adsorbents.

BACKGROUND ART

The Environmental Protection Agency (EPA) has set, for 2007 and beyond, vehicle internal combustion engine emission requirements; one exemplary requirement for diesel engines, is NOx and non-methane hydrocarbons below 0.20 grams bhp-hr and 0.14 grams/bhp-hr, respectively. This contrasts with current standards of 4.0 grams/bhp-hr and 1.3 grams/bhp-hr, respectively. Thus, the catalytic converters must accomplish a significant reduction in NOx. There currently are no catalyst formulations which are able to adequately reach these restrictive standards; significant development will be required to reduce the cost and improve performance of new catalyst formulations. Apparatus that oxidizes engine fuel to provide a mix that enhances NOx reduction is disclosed in U.S. Pat. No. 5,412,946, in PCT published application WO 01/34950, and U.S. patent application Publication 2001/41153.

One known methodology for NOx reduction is the so-called SCR (Selective Catalytic Reduction) process, as shown inFIG. 1. Therein, a hydrocarbon-fueled engine10receives fuel from a tank12provided by a fuel pump13, as well as air from a turbo compressor14in an air inlet line15. An aqueous solution of urea is carried in a tank16. The urea solution is applied to a hydrolysis unit17together with engine exhaust in a pipe18, wherein heat of the exhaust converts the urea solution to gaseous ammonia. The ammonia then reacts in a selective catalytic converter19with NOx in the exhaust gas to convert the NOx to nitrogen and water, providing reduced NOx in the system exhaust20. The problem is that there is no infrastructure in place to provide the urea solution at stations where fuel, particularly diesel fuel and gasoline, is obtained.

In commonly owned copending U.S. patent application Ser. No. 10/159,369 filed May 31, 2002, hydrogen for reducing NOx in catalytic converters or regenerating NOx trap adsorbents is generated utilizing moisture derived either directly or indirectly from engine exhaust. All of the aforementioned NOx reduction techniques are complicated and expensive.

DISCLOSURE OF INVENTION

Objects of the present invention include: improvement in the reduction of NOx to nitrogen and other harmless gases; achieving NOx reduction that meets EPA 2007 NOx emission requirements; simple, low-cost hydrogen generation for NOx reduction; and generation of hydrogen in and for an internal combustion engine exhaust emission reduction system, from only fuel already available with the engine in addition to water and/or air.

According to the present invention, fuel from the fuel tank of a hydrocarbon-fueled, internal combustion engine and air from the engine air inlet are processed either (a) in a homogeneous non-catalytic partial oxidizer, or (b) along with stored water and heat in the engine's exhaust in a hydrogen generator, which may be a catalytic partial oxidizer, a homogeneous non-catalytic partial oxidizer, or an auto thermal reformer, to generate a stream of reformate, including hydrogen and carbon monoxide, which is used, either directly or following the reaction of NOx with other compounds, to eliminate NOx in the exhaust. For example, the hydrogen-rich stream may either (a) be mixed with the main exhaust stream for processing in a NOx-reducing catalytic converter, or (b) used to regenerate adsorbent in NOx traps following the formation of nitrogen-containing compounds by reaction of NOx in the exhaust with adsorbent in the NOx traps. When unhumidified air (no water) is combined with fuel, a homogeneous, non-catalytic partial oxidizer is used.

Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.

MODE(S) FOR CARRYING OUT THE INVENTION

InFIG. 2, the engine10has the conventional turbo compressor14feeding the air inlet line15, a hydrocarbon fuel tank12, and a fuel pump13. The fuel may typically be diesel fuel, gasoline, natural gas, liquid petroleum gas, or propane. The fuel is fed by a line21to the engine for combustion with the air, and is fed by a second line22through a vaporizing heat exchanger23to a mixer24in a line25that feeds humidified air in a line26to a hydrogen generator27. The hydrogen generator27may be a catalytic partial oxidizer (CPOx), a non-catalytic (homogeneous) partial oxidizer (POx), or an auto thermal reformer (ATR). Within the hydrogen generator, if it is a CPOx, foam monolith or other form of catalyst, which may comprise a group VIII metal, preferably nickel, cobalt, rhodium, iridium or platinum, convert fuel along with hydrocarbons, water and oxygen into a mix of hydrogen, CO and CO2. This is provided through a conduit28to an NOx reducing catalytic converter30along with exhaust in the pipe18, the output of which is exhausted by a pipe32, typically to ambient. The converter30is of the type commonly used in diesel engines, except the catalyst therein may be different. In the converter30, the exhaust—hydrogen, oxides of nitrogen and carbon monoxide—is converted to mainly nitrogen, water, and carbon dioxide, with traces of non-methane hydrocarbons and oxides of nitrogen. With proper adjustment for the particular engine and desired performance range (utilizing valves and possibly a controller responding to sensors, all known in the art), the invention will permit reducing the NOx to 0.40 grams/bhp/hr and non-methane hydrocarbons to 0.28 grams/bhp/hr.

Air from the air inlet15is heated in a heat exchanger34and then fed to a suitable humidifier, such as an air bubbler35, which receives ordinary water from a tank36. The humidified air may be heated further in a heat exchanger39before passing through the line26and mixer24to the hydrogen generator27.

InFIG. 2, the NOx is treated continuously in a known converter. In accordance with the invention, a more effective elimination of NOx comprises utilizing adsorption traps in alternating collection/regeneration cycles as shown inFIG. 3.

Referring toFIG. 3, a pair of NOx adsorbent traps38,44are alternatively connected by corresponding valves40–43to either the conduit28with hydrogen-containing gas from the generator27, or to the pipe18containing engine exhaust. The valves are controlled so that engine exhaust is allowed to flow through one of the traps38,44for a period of time which is less than the time necessary to saturate the adsorbent with NOx, and then the valves are switched so that exhaust flows through the other NOx trap, while the adsorbent in the first NOx trap is regenerated by the hydrogen and carbon monoxide from the generator27. In one cycle, the valves40,43will be open and the valves41and42will be closed; in the next cycle, the valves41and42will be open and the valves40and43will be closed, and so forth. The NOx traps may, for example, contain barium carbonate (BaCO3) as the adsorbent: when the diesel exhaust is adsorbed by the barium carbonate, a reaction generates barium nitrate.
2NOx+BaCO3→Ba(NO3)2+CO2
Then, during the regeneration cycle, the barium nitrate is converted back to barium carbonate, as follows.
3H2+2CO+Ba(NO3)2→BaCO3+N2+3H2O+CO2

A CPOx oxidizer is preferred as the hydrogen generator27because it is very small and can run with low steam carbon ratios and high turndown ratios without soot or carbon formation. However, diesel engine exhaust contains particulates (soot) and oxides of sulfur (SOx), which may deactivate the CPOx catalyst in a relatively short period of time. Therefore, a non-catalytic (homogeneous) partial oxidizer may alternatively be selected as the hydrogen generator27. The percentage of hydrogen produced is only slightly less than that produced by a CPOx. It is easily started by employing a simple spark plug, as is known. Additionally, POX is cheaper than CPOx; control of the O2/C ratio is known (similar to engine O2/fuel ratio), and simpler; SOx and soot do not affect it; and there is no steam/C ratio control problem.

Because the POx has a spark plug to initiate the reaction, it may be utilized with a mixture of ambient air without further humidification, defined herein as “unhumidified air” and fuel, to generate hydrogen and carbon monoxide, according to a second aspect of the invention. Referring toFIG. 4, air in the air inlet line15from the turbocompressor14is passed through the heat exchanger39, over the line26and mixed with heated fuel at the mixer24. This is at the inlet to a homogeneous, non-catalytic partial oxidizer47which includes a spark plug48. The POx47provides reformate in the line28to the converter30in the same fashion as described with respect toFIG. 2.

In this later aspect of the invention, the homogeneous non-catalytic partial oxidizer47may be used to provide hydrogen for regeneration of the NOx trap adsorbent, as is illustrated inFIG. 5.

The embodiments herein heat the fuel before it is utilized for hydrogen generation. However, it is not necessary for the fuel to be heated whenever a homogenous, non-catalytic partial oxidizer is employed, since the spark plug thereof will start the process at any temperature.

The embodiments herein heat the air before it enters the bubbler. However, the air exiting the turbo compressor is hot, typically around 212° F. (100° C.)–390° F. (200° C.), so the heat exchanger34may be omitted if desired. Since the spark plug in the POx47can start a reaction at any temperature, the heat exchangers23and39ofFIGS. 4 and 5may be omitted, if desired. If necessary, the water could be preheated, preferably by exhaust, which could be allowed to bubble through the water tank36or which could be fed to a heat exchanger; but an electric heater could be used instead if desired.

In the embodiments ofFIGS. 2 and 3, the water storage tank36is separate from the air bubbler35; however, if desired to save components and space, the water may be stored in the bubbler which then also comprises the storage tank, and the tank36may be omitted. The invention may be practiced using other humidifiers, such as evaporative plate humidifiers, misters, or others; in such a case, water must be stored on board the vehicle in some form of suitable tank. If more H2is needed in the converter30or the traps38,44, a small water-gas-shift converter may be used between the hydrogen generator and the converter or traps. This would use water from the tank to convert only some of the CO to H2.

Thus, although the invention has been shown and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without departing from the spirit and scope of the invention.