Abstract:
A hydrogen generator for use with an engine is disclosed. The hydrogen generator has an exhaust duct situated to receive exhaust from the engine, and an SCR device located within the exhaust duct. The hydrogen generator also has 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.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to a hydrogen generator, and more particularly, to a hydrogen generator located on-board a mobile vehicle. 
       BACKGROUND 
       [0002]    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 NO x  from diesel engines. The basic principle of SCR is the reduction of NO x  to N 2  and H 2 O 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 NO x  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. 
         [0003]    There is considerable discussion among engine manufacturers about the relative merits of different reductants used to reduce NO x . Specifically, while ammonia generally offers good NO x  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. 
         [0004]    To alleviate the necessity of supplying the reductant from external sources, NO x  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 H 2 /CO reductant mixture on-board the vehicle for NO x  removal. One such exhaust NO x  reduction technique using a reductant produced on-board a vehicle is described in U.S. Pat. No. 7,163,668 B2 (the &#39;668 patent) issued to Bartley et al. on Jan. 16, 2007. In the NO x  reduction approach described in the &#39;668 patent, diesel fuel is partially oxidized to produce a reductant mixture of hydrogen (H 2 ) and carbon monoxide (CO) with traces of carbon dioxide (CO 2 ) and water (H 2 O). 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 H 2  in the mixture reduces the NO x  to nitrogen and water. 
         [0005]    Although the NO x  reduction technique of the &#39;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 NO x  present. In the NO x  reduction technique of the &#39;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. 
         [0006]    The present disclosure is directed at overcoming one or more of the shortcomings set forth above. 
       SUMMARY OF THE INVENTION 
       [0007]    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. 
         [0008]    In another aspect, a method of reducing NO x  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 NO x  in the exhaust gas. 
         [0009]    In yet another aspect, a machine is disclosed. The machine includes an engine configured to combust fuel/air mixture to produce exhaust gas containing NO x , 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 NO x  to nitrogen and water. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration of an exemplary disclosed engine system; 
           [0011]      FIG. 2  is a diagrammatic illustration of an exemplary disclosed hydrogen generator for use with the engine of  FIG. 1 ; and 
           [0012]      FIG. 3A  and  FIG. 3B  are exemplary embodiments of an exemplary disclosed electrode for use with the hydrogen generator of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  illustrates a machine  500  having an engine system  400 . The machine  500  may be a mobile or stationary machine. Non-limiting examples of the machine  500  include automobiles, trains, generators, construction equipment, etc. The engine system  400  may include various systems and components that cooperate to convert chemical energy contained in a fuel to mechanical work. Engine system  400  may include, among others, a power source  10 , a fuel/air input system  20 , an exhaust system  30 , and a hydrogen generator  100 . Power source  10  may be coupled between fuel/air input system  20  and exhaust system  30 . Fuel/air input system  20  may input a fuel  5  and air into the power source  10  for combustion. Exhaust system  30  may remove exhaust gases  25  produced by the combustion process from power source  10 . 
         [0014]    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 . 
         [0015]    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. 
         [0016]    Exhaust system  30  may direct exhaust gas  25  out of power source  10 . Exhaust gas  25  may comprise many chemical species including, among others, NO x , which may be regulated by government agencies. NO x  in exhaust gas  25  includes a mixture of nitrogen dioxide (NO 2 ) 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 NO x  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 . 
         [0017]    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. 
         [0018]    SCR system  34  may include any catalytic converter known in the art to reduce NO x  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, H 2    75  and then passed through the SCR system  34 . While in the SCR system  34 , chemical reactions may reduce some or all of the NO x  present in exhaust gas  25  to N 2  and H 2 O. 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. 
         [0019]    Hydrogen generator  100  may produce the reductant H 2    75 , which is mixed with the exhaust. In some embodiments, hydrogen generator  100  may produce a mixture of H 2    75  in combination with other liquids or gases. In these embodiments, a gas separator  110  may separate the H 2    75  from the mixture. H 2    75  produced by hydrogen generator  100  may be input to engine system  400  at multiple locations. In some embodiments, H 2    75  may be input to both fuel/air input system  20  and exhaust system  30 . It is contemplated that, in some embodiments, H 2    75  may be input into only one of these systems. In embodiments where H 2    75  is directed into fuel/air input system  20 , an inlet duct  120  may direct the H 2    75  into the fuel  5  upstream of engine  10 . It is contemplated that, in some embodiments, the H 2    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, H 2    75  may be input directly into a combustion chamber of power source  10 . In embodiments where H 2    75  is directed into exhaust system  30 , an inlet duct  130  may direct the H 2    75  into exhaust gas  25  at a location downstream of engine  10 . In some embodiments, H 2    75  may be input into the exhaust downstream of particulate filter  32 . 
         [0020]    Hydrogen generator  100  may produce H 2    75  on-board machine  500 . For instance, hydrogen generator  100  may be configured to produce H 2    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 H 2    75  and other gases. In these embodiments, gas separator  110  may separate H 2    75  from the mixture of gases. 
         [0021]      FIG. 2  illustrates an exemplary hydrogen generator  100  that may be located on-board machine  500  and used in conjunction with engine system  400 . Hydrogen generator  100  may be disposed at any location relative to engine system  400 . In some applications, hydrogen generator  100  may be mounted on engine system  400 . It is also contemplated that in some applications, hydrogen generator  100  may be formed integral with engine system  400 . Hydrogen generator  100  may include a housing  112 . Housing  112  may be made of any material that can safely contain an electrolyte  128 , and can withstand temperatures produced during electrolysis of electrolyte  128 . Although housing  112  of a rectangular shape is depicted in  FIG. 2 , housing  112  may be of any shape. Housing  112  may be of unitary construction, or may include multiple parts (for instance, a body and a lid) attached together. 
         [0022]    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  FIG. 2 , it is contemplated that other embodiments may include multiple gas ports  114  and/or multiple electrolyte ports  118 . Multiple electrodes  126  may also be included within housing  112 . A portion of these electrodes  126  may be at least partially immersed in electrolyte  128 . 
         [0023]    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 . 
         [0024]    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.  FIGS. 3A and 3B  show two embodiments of an electrode having a porous structure. The electrode surface area in contact with the electrolyte  128  may be higher for electrodes  126  having a porous structure. Consequently, gas production with electrodes  126  having a porous structure may also be higher. Electrodes  126  having a porous structure may include open cell foams, high porosity sintered metal fibers, metal mesh and the like. 
         [0025]    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 H 2 . In embodiments where electrolyte  128  is water (pure or mixed with other electrolytes), the electrolyte  128  may decompose according to Eq. 1 below: 
         [0000]      2H 2 O→2H 2 +O 2   Eq. 1 
         [0026]    The resulting H 2  and O 2  mixture may exit the hydrogen generator  100  through gas port  114 , and H 2  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 . 
         [0027]    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  FIG. 2 , hydrogen generator  100  may include sensors and alarms to detect a low amount of electrolyte  128 , and warn an operator when the electrolyte level drops below a preset value. Hydrogen generator  100  may also include valves and other safety features for the safe operation of hydrogen generator  100 . These safety features may include gas release valves and pressure indicators that maintain the pressure within housing  112  within acceptable limits. 
         [0028]    As described above, decomposition of electrolyte  128  by electrolysis may produce hydrogen gas as a mixture of gases. H 2    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 H 2    75  as substantially the only reaction product, and the H 2    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: 
         [0000]      2M+2H 2 O+2OH − →2M(OH) 2 +H 2 +2 e   −   Eq. 2 
         [0029]    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 H 2    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 . 
         [0030]    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 H 2    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 H 2    75  production depending upon the need for NO x  reduction by machine  500 . 
         [0031]    An electronic control module (ECM)  50  (shown in  FIG. 1 ) may be used to control the rate of H 2    75  production based on the needs of machine  500 . In some embodiments, ECM  50  may be part of a larger control system of machine  500 . ECM  50  may be any control device that affects the operation of exhaust system  30  based on inputs from multiple sensors. These sensors may include, among others, an upstream NO x  sensor  54 , a downstream NO x  sensor  56 , a hydrogen sensor  58 , and a temperature sensor  52 . 
         [0032]    Upstream NO x  sensor  54  may be connected on the upstream side of SCR system  34 , and may measure the quantity of NO x  present in exhaust gases  25  upstream of SCR system  34 . Downstream NO x  sensor  56  may be connected on the downstream side of SCR system  34 , and may measure the quantity of NO x  present in exhaust gases  25  downstream of SCR system  34 . Using measurements from upstream NO x  sensor  54  and downstream NO x  sensor  56 , ECM  50  may determine the NO x  conversion efficiency of SCR system  34 . 
         [0033]    Hydrogen sensor  58  may measure H 2    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 H 2    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 . 
         [0034]    Temperature sensor  52  may include any type of sensor that measures a temperature of hydrogen generator  100 . Although  FIG. 2  depicts the temperature sensor  52  as being positioned to measure a temperature of electrolyte  128 , temperature sensor  52  can alternatively be positioned to measure a temperature anywhere within hydrogen generator  100 . 
         [0035]    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 H 2  production in hydrogen generator  100  when NO x  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. 
         [0036]    In some embodiments, ECM  50  may control the electric current to heater  116  ( FIG. 2 ) or electric current to cathode electrode  26  and anode electrode  28  to regulate the amount of H 2    75  produced based on the NO x  conversion efficiency. For instance, if NO x  sensor  56  indicates an excessive concentration of NO x , H 2    75  production in hydrogen generator  100  may be increased. ECM  50  may also control H 2  production based on a desired ratio of H 2 :NO x . The rate of NO x  reduction in SCR system  34  may be affected by the relative concentrations of NO x  and H 2 . Typically, a 1:1 molar ratio of NO to H 2  will enable efficient reduction of NO, and a 1:2 molar ratio of NO 2  to H 2  will enable efficient reduction of NO 2 . Typically, a H 2 :NO x  ratio between about 1 and about 3 may enable efficient NO x  removal from exhaust gas  25 . 
         [0037]    In some embodiments, a portion of the H 2    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 NO x  in exhaust gas  25 . In some cases, H 2    75  produced in excess of what is needed to reduce NO x  in SCR system  34  may be diverted to the fuel/air system  20 . In some embodiments, excess H 2    75  may be stored in a hydrogen storage vessel  115 . This stored H 2    75  may then be used to respond to rapid increases in H 2  demand and/or extended or excessive H 2  demands. 
       INDUSTRIAL APPLICABILITY 
       [0038]    The disclosed hydrogen generator may be applicable to any engine system where NO x  reduction is desired. The hydrogen gas chemically reduces NO x  to nitrogen and water. To illustrate the operation of the hydrogen generator, an exemplary application will now be described. 
         [0039]    During operation of machine  500 , exhaust gas  25  containing NO x  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 . NO x  sensor  54  may measure the NO x  content in exhaust gas  25  upstream of SCR system  34 . In response to the measured amount of NO x  in exhaust gas  25 , ECM  50  may instruct hydrogen generator  100  to produce a corresponding amount of H 2 . 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 . 
         [0040]    Hydrogen generator  100  may produce H 2    75  by an electrochemical reaction. Iron (Fe) electrodes  126  may be partially immersed in electrolyte  128  made of potassium hydroxide solution (KOH+H 2 O) contained within the hydrogen generator  100 . ECM  50  may control hydrogen generator  100  to produce H 2    75  to achieve a H 2 :NO x  ratio in exhaust gas  25  of about 2. Hydrogen generator  100  may produce H 2    75  according to the electrochemical reaction of Eq. 3 below: 
         [0000]      Fe 0 +KOH+2H 2 O→Fe(OH) 3 +K + +H 2   +e   −   Eq. 3 
         [0041]    H 2    75  produced by the electrochemical reaction may be input into exhaust system  30  through inlet duct  130 . H 2    75  may mix with exhaust gas  25  before entering the SCR system  34 . The NO x  components of exhaust gas  25  may react with the mixed H 2    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 NO x  content in the exhaust gas  25  released into the atmosphere. 
         [0000]      2NO+2H 2 →N 2 +2H 2 O  Eq. 4 
         [0000]      2NO 2 +4H 2 →N 2 +4H 2 O  Eq. 5 
         [0042]    In the hydrogen generator  100  of the current disclosure, H 2    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 H 2    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. 
         [0043]    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 H 2    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 H 2    75 , the fuel efficiency (and thus the operating cost) of machine  500  may be minimally affected. 
         [0044]    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.