Patent Application
20100018476
The present disclosure relates generally to a hydrogen generator, and more particularly, to a hydrogen generator located on-board a mobile vehicle.
Various technologies have been implemented by engine manufacturers to meet diesel engine emission requirements mandated by the Environmental Protection Agency (EPA). Selective Catalytic Reduction (SCR) is one common technology used to control emission of NOx from diesel engines. The basic principle of SCR is the reduction of NOx to N2 and H2O by a reductant in the presence of a catalyst. In typical automotive SCR systems, a gaseous or liquid reductant (most commonly ammonia or urea) is added to the exhaust gas stream of the engine. The reductant reduces the NOx from the exhaust in a catalytic converter at high temperatures. The catalytic converter typically contains a catalyst that will trigger the reducing reaction at the desired temperature. Various catalyst media, such as metal containing zeolite or metal containing catalyst coated on an alumina porous carrier media, have been used with automotive SCRs. The particular metal catalyst and the carrier media are typically selected based on the exhaust gas temperature.
There is considerable discussion among engine manufacturers about the relative merits of different reductants used to reduce NOx. Specifically, while ammonia generally offers good NOx reduction, it is toxic and difficult to handle safely. Urea, on the other hand, is safer to handle but not quite as effective. In both cases, the reductant must be pure, to prevent impurities from clogging an inlet surface of the catalyst. A major issue with urea reductants is the lack of distribution infrastructure available to support this technology for automotive uses. For this reason, the EPA has been reluctant to certify diesel engines fitted with an SCR system employing ammonia or urea catalyst.
To alleviate the necessity of supplying the reductant from external sources, NOx reduction technologies employing in-situ reductant production have been proposed. These technologies use various combinations of fuel (or other hydrocarbon additives), air and water to produce an H2/CO reductant mixture on-board the vehicle for NOx removal. One such exhaust NOx reduction technique using a reductant produced on-board a vehicle is described in U.S. Pat. No. 7,163,668 B2 (the '668 patent) issued to Bartley et al. on Jan. 16, 2007. In the NOx reduction approach described in the '668 patent, diesel fuel is partially oxidized to produce a reductant mixture of hydrogen (H2) and carbon monoxide (CO) with traces of carbon dioxide (CO2) and water (H2O). The mixture is then passed into the exhaust gas stream of an engine. The exhaust, along with the reductant mixture, is then passed through a hydrogen SCR(H—SCR), where the H2 in the mixture reduces the NOx to nitrogen and water.
Although the NOx reduction technique of the '668 patent may alleviate the need to supply the reductant from external sources, the described approach may have some drawbacks. A common problem with such reductant systems is CO and hydrocarbon “slip.” Slip describes exhaust pipe emissions of CO and hydrocarbon that occur when exhaust gas temperature is too cold for the SCR reaction to occur, and/or when the injection device feeds too much reductant into the exhaust gas stream for the amount of NOx present. In the NOx reduction technique of the '668 patent, in addition to the CO tail pipe emissions that result from diesel fuel oxidation, incomplete oxidation of the diesel fuel may also cause hydrocarbon tail pipe emissions to increase. Using diesel fuel to generate the hydrogen gas may also increase the fuel consumption, and, thus the operating costs, of the engine.
The present disclosure is directed at overcoming one or more of the shortcomings set forth above.
In one aspect, a hydrogen generator for use with an engine is disclosed. The hydrogen generator includes an exhaust duct situated to receive exhaust from the engine, and an SCR device located within the exhaust duct. The hydrogen generator also includes a housing in fluid communication with the exhaust duct upstream of the SCR device, an electrolyte solution disposed within the housing, and a plurality of electrodes at least partially submerged in the electrolyte solution. The electrodes are electrically powered to produce hydrogen gas, and the hydrogen gas is directed to mix with the exhaust.
In another aspect, a method of reducing NOx contained in exhaust gas of an engine is disclosed. The method includes passing electric current through electrodes immersed in an electrolyte to produce hydrogen gas, and mixing the hydrogen gas with an exhaust flow from the engine. The method further includes catalyzing the hydrogen/exhaust gas mixture to reduce the NOx in the exhaust gas.
In yet another aspect, a machine is disclosed. The machine includes an engine configured to combust fuel/air mixture to produce exhaust gas containing NOx, a fuel delivery system configured to direct fuel into the engine, and a battery configured to crank engine. The machine also includes a housing containing a supply of electrolyte, and a plurality of electrodes at least partially submerged in the electrolyte. The electrodes are powered by the battery to produce hydrogen gas. The machine also includes an SCR device, which receives a mixture of the hydrogen gas and the exhaust gas, and reduces at least a portion of the NOx to nitrogen and water.
Power source 10 may include an internal combustion engine such as, for example, a diesel engine, a gasoline engine, a natural gas engine, or any other engine apparent to one skilled in the art. During operation, power source 10 may convert heat energy released by the combustion of fuel 5 (a hydrocarbon based fuel) to mechanical energy. The combustion process may also release byproducts, such as exhaust gas 25.
Fuel/air input system 20 may be configured to introduce fuel 5 for combustion into the power source 10. Fuel 5 may be input into power source 10 in a form suitable for efficient combustion. Depending upon the type of power source 10, this suitable form may include a mixture of fuel 5 and air. In some applications, fuel 5 and air may be input separately into power source 10. Fuel/air input system 20 may include valves, compressors, carburetors, injectors, pumps, ducting and other components known in the art.
Exhaust system 30 may direct exhaust gas 25 out of power source 10. Exhaust gas 25 may comprise many chemical species including, among others, NOx, which may be regulated by government agencies. NOx in exhaust gas 25 includes a mixture of nitrogen dioxide (NO2) and nitrogen oxide (NO). Exhaust system 30 may include components and systems designed to reduce the amount of adverse chemical species in the exhaust gas 25 prior to being released to the environment. These components and systems may include, among others, a particulate filter 32 and an SCR system 34. Particulate filter 32 may extract solid particulate matter from the exhaust gas 25, and SCR system 34 may reduce or eliminate the NOx present in the exhaust gas 25. Exhaust system 30 may also include additional filtration and catalytic conversion devices designed to further reduce the amount of chemical species in exhaust gas 25.
Particulate filter 32 may include any filter used in the art to remove particulate matter from the exhaust stream of an engine. In some embodiments, particulate filter 32 may include a flow-through or a wall-flow filter media made of ceramic honeycomb or metal fiber material. Particulate matter contained in exhaust gas 25 may be collected on the filter media while the exhaust gas 25 flows through particulate filter 32. Particulate filter 32 may require periodic regeneration. Regeneration is the process of removing the accumulated particulate matter from the filter media by burning it off. The particulate filter 32 may be regenerated when a temperature of the particulate matter trapped in the particulate filter 32 reaches an ignition temperature. Regeneration of the particulate filter 32 may be carried out passively or actively. In embodiments where passive regeneration is employed, the filter media may include catalysts to lower an oxidation temperature of the trapped particulate matter. In embodiments where active regeneration is employed, the particulate filter 32 may be associated with heaters to heat the filter media to the oxidation temperature of the trapped particulate matter.
SCR system 34 may include any catalytic converter known in the art to reduce NOx to nitrogen and water. SCR system 34 may include a porous substrate with a washcoat to support a catalyst. In some applications, this porous substrate may include a ceramic honeycomb or various metal type substrates. The washcoat may form a rough irregular surface on the porous substrate and may increase the surface area of the substrate. The catalyst may be coated on the surface of the substrate. In some embodiments, the catalyst may be added as a suspension in the washcoat before application to the substrate. The catalyst may include a metal or a metal oxide. In some embodiments, the catalyst may include a precious metal, such as platinum, palladium or rhodium. Exhaust gas 25 may be mixed with a reductant, such as, for example, H2 75 and then passed through the SCR system 34. While in the SCR system 34, chemical reactions may reduce some or all of the NOx present in exhaust gas 25 to N2 and H2O. The catalyst of the SCR system 34 may affect the rate of these reactions. The current disclosure can be used with any known SCR substrate and catalyst.
Hydrogen generator 100 may produce the reductant H2 75, which is mixed with the exhaust. In some embodiments, hydrogen generator 100 may produce a mixture of H2 75 in combination with other liquids or gases. In these embodiments, a gas separator 110 may separate the H2 75 from the mixture. H2 75 produced by hydrogen generator 100 may be input to engine system 400 at multiple locations. In some embodiments, H2 75 may be input to both fuel/air input system 20 and exhaust system 30. It is contemplated that, in some embodiments, H2 75 may be input into only one of these systems. In embodiments where H2 75 is directed into fuel/air input system 20, an inlet duct 120 may direct the H2 75 into the fuel 5 upstream of engine 10. It is contemplated that, in some embodiments, the H2 75 may alternatively or additionally be directed into an air supply prior to mixing with fuel 5. It is also contemplated that, in some embodiments, H2 75 may be input directly into a combustion chamber of power source 10. In embodiments where H2 75 is directed into exhaust system 30, an inlet duct 130 may direct the H2 75 into exhaust gas 25 at a location downstream of engine 10. In some embodiments, H2 75 may be input into the exhaust downstream of particulate filter 32.
Hydrogen generator 100 may produce H2 75 on-board machine 500. For instance, hydrogen generator 100 may be configured to produce H2 75 by electrolysis of an electrolyte. Electrolysis is a method of separating bonded elements and/or compounds in an electrolyte by passing an electric current through the electrolyte. In some embodiments, water may be used as the electrolyte. In these embodiments, electrolysis of water decomposes water into oxygen and hydrogen gas with the aid of an electric current. It is also contemplated that an acid or a base material mixed with water may serve as the electrolyte. In some embodiments, hydrogen generator 100 may produce a mixture of H2 75 and other gases. In these embodiments, gas separator 110 may separate H2 75 from the mixture of gases.
Housing 112 may also include ports that provide access to the inside thereof. These access ports may include, among others, a gas port 114 and an electrolyte port 118. Gas port 114 may serve as an outlet for the gas produced within hydrogen generator 100. Electrolyte port 118 may serve as a conduit for replenishment of electrolyte 128. Although only one gas port 114 and one electrolyte port 118 are depicted in
Electrodes 126 may include an anode electrode 28, and a cathode electrode 26. The electrodes 126 may also include one or more secondary electrodes 24 interposed between anode electrode 28 and cathode electrode 26. In some embodiments, some or all of the secondary electrodes 24 may be electrically connected to each other. Different connection schemes may be used to connect the electrodes. For example, in some embodiments, half of all the secondary electrodes 24 may be connected to the cathode electrode 26, while the other half of secondary electrodes 24 may be connected to the anode electrode 28. In some embodiments, the electrodes 126 may have a fixed spatial relationship to each other. In these embodiments, it is contemplated that housing 112 may include some mechanism to maintain the fixed spatial relationship between electrodes 126. In some embodiments, spacing between adjacent electrodes 126 may be substantially constant. Electrical cables may connect anode and cathode electrodes 28, 26 to poles of a power source (not shown). In some embodiments, an anode cable 122 may electrically connect anode electrode 28 to the negative pole of the power source, and a cathode cable 124 may electrically connect cathode electrode 124 to the positive pole of the power source. In some embodiments, electrical cables 122 and 124 may connect anode electrode 28 and cathode electrode 26 to different connection points on the external surface of housing 112. In these embodiments, additional electrical cables may connect these connection points to appropriate poles of the power source. The power source may be a battery of machine 500 used to crank engine 400 and power other components of machine 500.
Electrodes 126 may be made of any electrically conductive material. In some embodiments, electrodes 126 may be made of a base metal. Non-limiting examples of materials that may be used as electrodes 126 include iron, aluminum, chromium, nickel, tin, and lead. In general, electrodes 126 may have a solid or a porous structure.
Any electrolyte 128 may be used with hydrogen generator 100. In some embodiments, electrolyte 128 may include water. However, other electrolytes such as acidic solutions, aqueous bicarbonate solutions, hydroxide solutions, or mixtures thereof are also contemplated. As mentioned earlier, when a voltage is applied to anode electrode 28 and cathode electrode 26, electrolyte 128 may decompose to produce H2. In embodiments where electrolyte 128 is water (pure or mixed with other electrolytes), the electrolyte 128 may decompose according to Eq. 1 below:
2H2O→2H2+O2 Eq. 1
The resulting H2 and O2 mixture may exit the hydrogen generator 100 through gas port 114, and H2 may be separated from the mixture by gas separator 110. Energy may also be released during the decomposition process. The released energy may increase the temperature of hydrogen generator 100.
Electrolyte 128 may be consumed during operation of hydrogen generator 100. The consumed electrolyte 128 may be replenished through the electrolyte port 118. Although not shown in
As described above, decomposition of electrolyte 128 by electrolysis may produce hydrogen gas as a mixture of gases. H2 75 may then be separated from this gaseous mixture in gas separator 110 prior to mixing with fuel 5 or exhaust gas 25. In some applications, it may be desirable to eliminate gas separator 110 and produce substantially only hydrogen gas in hydrogen generator 100. In these embodiments, an electrochemical reaction may be used to produce H2 75 as substantially the only reaction product, and the H2 75 may be directly mixed with fuel 5 and/or exhaust gases 25. An electrochemical reaction is a chemical reaction between the electrodes and the electrolyte when an electric current passes through them. The electrochemical reaction in such an embodiment may proceed as indicated in Eq. 2 below:
2M+2H2O+2OH−→2M(OH)2+H2+2e− Eq. 2
Any metal (M) can be used as electrodes 126. However, since electrodes 126 may be consumed in the electrochemical reaction, they may need more frequent replacement, as compared to a hydrogen generator 100 producing H2 75 by electrolysis of electrolyte 128. Therefore, in the electrochemical embodiments, low cost and easy availability of the electrode material may be important factors in the selection of electrodes 126.
An elevated temperature may increase the rate of the electrolysis reaction. Therefore, a heater 116 may be provided in hydrogen generator 100 to vary the rate of H2 75 production. In some embodiments, heater 116 may be an external heater. In some embodiments, operation of heater 116 may be controlled to vary the rate of H2 75 production depending upon the need for NOx reduction by machine 500.
An electronic control module (ECM) 50 (shown in
Upstream NOx sensor 54 may be connected on the upstream side of SCR system 34, and may measure the quantity of NOx present in exhaust gases 25 upstream of SCR system 34. Downstream NOx sensor 56 may be connected on the downstream side of SCR system 34, and may measure the quantity of NOx present in exhaust gases 25 downstream of SCR system 34. Using measurements from upstream NOx sensor 54 and downstream NOx sensor 56, ECM 50 may determine the NOx conversion efficiency of SCR system 34.
Hydrogen sensor 58 may measure H2 75 flow from hydrogen generator 100 into the exhaust stream. Hydrogen sensor 58 may be a flow meter or other kind of measurement device that is capable of measuring the quantity of H2 75 flowing through inlet duct 130. Some embodiments may also include measurement devices that measure the concentration of hydrogen gas emanating from hydrogen generator 100 and gas separator 110.
Temperature sensor 52 may include any type of sensor that measures a temperature of hydrogen generator 100. Although
ECM 50 may perform numerous control functions to increase the efficiency and promote safe operation of the hydrogen generator 100 and exhaust system 400. Non-limiting examples of some of the control tasks that may be performed by ECM 50 include: decreasing H2 production in hydrogen generator 100 when NOx content in exhaust gas 25 is low, shutting down hydrogen generator 100 when temperature sensor 52 indicates an excessive temperature or when other sensors in hydrogen generator 100 indicate an abnormal condition, warning a machine operator at the occurrence of an event, etc.
In some embodiments, ECM 50 may control the electric current to heater 116 (
In some embodiments, a portion of the H2 75 produced by hydrogen generator 100 may be input into fuel/air input system 20. The hydrogen enhanced fuel 5 may result in increased engine efficiency and/or less NOx in exhaust gas 25. In some cases, H2 75 produced in excess of what is needed to reduce NOx in SCR system 34 may be diverted to the fuel/air system 20. In some embodiments, excess H2 75 may be stored in a hydrogen storage vessel 115. This stored H2 75 may then be used to respond to rapid increases in H2 demand and/or extended or excessive H2 demands.
The disclosed hydrogen generator may be applicable to any engine system where NOx reduction is desired. The hydrogen gas chemically reduces NOx to nitrogen and water. To illustrate the operation of the hydrogen generator, an exemplary application will now be described.
During operation of machine 500, exhaust gas 25 containing NOx may be released into exhaust system 30 by engine system 400. In exhaust system 30, exhaust gas 25 may flow sequentially through particulate filter 32 and SCR system 34. Particulate matter contained in exhaust gas 25 may be filtered out by particulate filter 32, so that exhaust gas 25 down stream of particulate filter 32 may contain less particulate matter than exhaust gas 25 upstream of particulate filter 32. NOx sensor 54 may measure the NOx content in exhaust gas 25 upstream of SCR system 34. In response to the measured amount of NOx in exhaust gas 25, ECM 50 may instruct hydrogen generator 100 to produce a corresponding amount of H2. Instructing hydrogen generator 100 may include passing electric current from a battery through cathode electrode 26 and anode electrode 28, and/or by controlling heater 116 to increase the temperature of electrolyte 128.
Hydrogen generator 100 may produce H2 75 by an electrochemical reaction. Iron (Fe) electrodes 126 may be partially immersed in electrolyte 128 made of potassium hydroxide solution (KOH+H2O) contained within the hydrogen generator 100. ECM 50 may control hydrogen generator 100 to produce H2 75 to achieve a H2:NOx ratio in exhaust gas 25 of about 2. Hydrogen generator 100 may produce H2 75 according to the electrochemical reaction of Eq. 3 below:
Fe0+KOH+2H2O→Fe(OH)3+K++H2+e− Eq. 3
H2 75 produced by the electrochemical reaction may be input into exhaust system 30 through inlet duct 130. H2 75 may mix with exhaust gas 25 before entering the SCR system 34. The NOx components of exhaust gas 25 may react with the mixed H2 75 in the presence of the catalyst of SCR system 34 in accordance with the chemical reactions of Eq. 4 and Eq. 5 below. These reactions may substantially reduce the NOx content in the exhaust gas 25 released into the atmosphere.
2NO+2H2→N2+2H2O Eq. 4
2NO2+4H2→N2+4H2O Eq. 5
In the hydrogen generator 100 of the current disclosure, H2 75, which is used as the reductant in SCR system 34, may be produced on-board machine 500. On-board production of the reductant may eliminate the need for a distribution network to support the use of the technology. In embodiments of hydrogen generator 100, where H2 75 is produced by an electrochemical reaction, the consumable electrodes 126 may need to be supplied to hydrogen generator 100 periodically. However, in these embodiments, selection of a commonly available material as electrodes 126 may minimize the need for a dedicated distribution network.
Since the reactions within hydrogen generator 100 of the current disclosure produce only non-toxic gases, dangers associated with the release of these gases to the atmosphere may be minimized. In embodiments of the hydrogen generator 100 producing H2 75 by an electrochemical reaction, gas separation systems may also be unnecessary, thereby decreasing the cost of the hydrogen generator 100. In addition, since water or another non-fuel electrolyte is used to produce H2 75, the fuel efficiency (and thus the operating cost) of machine 500 may be minimally affected.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed on-board hydrogen generator. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed hydrogen generator. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
