Abstract:
A combined gasoline and hydrogen fueling system for a gasoline-powered internal combustion engine, including, preferably, a rapid-start catalytic reformer for producing reformate gas containing hydrogen from gasoline. The reformate from the reformer is swept by air into the intake manifold of the cold engine where it is mixed with intake air and then drawn into the cylinders and ignited conventionally to start the engine. A computer-based reformer control system optimizes the amount of reformate formed and the resulting reformate/air mixture. The reformer control system interfaces or is integral with a computer-based gasoline and air supply system for the engine, the two systems cooperating to optimize a mixture of gasoline and reformate in the intake manifold at all times during warming of the engine and its exhaust catalyst to steady-state operating temperature. Preferably, flow of reformate is terminated thereafter.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to internal combustion engines; more particularly, to a method for fueling an internal combustion engine using both a hydrocarbon fuel, such as gasoline, diesel fuel or ethanol, and hydrogen; and 
        most particularly, to method and apparatus for starting an internal combustion engine using a hydrogen-containing fuel gas, preferably catalytically reformed gasoline or diesel fuel, to minimize cold-start hydrocarbon engine emissions.        
 
       BACKGROUND OF THE INVENTION  
       [0003]     At cold start-up of a hydrocarbon fuel powered internal combustion engine, fuel combustion typically is incomplete, resulting in significant and undesirable amounts of unburned hydrocarbons in the engine exhaust. Further, these residual hydrocarbons are incompletely oxidized by an exhaust gas catalytic converter which is also cold, such that a cold-starting engine typically emits significant amounts of unburned hydrocarbons to the atmosphere. This situation continues to pertain until the engine and the converter reach their respective intended operating temperatures.  
         [0004]     What is needed in the art is a means for starting an internal combustion engine and fueling it while producing an engine exhaust containing significantly reduced amounts of unburned hydrocarbons.  
         [0005]     It is a principal object of the present invention to provide an internal combustion engine exhaust having substantially reduced amounts of unburned hydrocarbons under all conditions of engine operation.  
         [0006]     It is a further object of the invention to provide a system for fueling an engine whereby steady-state hydrocarbon fuel, such as raw gasoline or diesel fuel, is withheld until engine operating conditions permit complete combustion of the steady-state fuel.  
       SUMMARY OF THE INVENTION  
       [0007]     Briefly described, a fueling system for an internal combustion engine includes means for providing a hydrogen-containing gas for starting the engine to prevent formation of engine exhaust containing unburned hydrocarbons. Such means includes a hydrogen supply system, such as a hydrogen-filled pressure vessel or a liquid-fuel catalytic reformer. In a currently preferred embodiment, a rapid-start catalytic reformer produces reformate gas from a liquid fuel, such as gasoline, diesel fuel or ethanol, the reformate containing hydrogen and carbon monoxide. Preferably, the reformer is supplied with the same fuel as is the engine at steady state. With combustion pre-heating, the reformer begins producing reformate in a very short period of time. The reformate is swept by air into the intake manifold of the cold engine where it is mixed with intake air and then drawn into the cylinders and ignited conventionally to start the engine. A computer-based reformer control system optimizes the amount of reformate formed and the resulting reformate/air mixture. The reformer control system interfaces with a computer-based hydrocarbon fuel and air supply system for the engine which begins injecting hydrocarbon fuel into the reformate in the manifold as the engine warms. The two control systems cooperate in response to engine torque requirements to optimize the mixture of hydrocarbon fuel and reformate in the intake manifold at all times during warming of both the engine and the exhaust catalyst to their respective steady-state operating temperatures, and to minimize amounts of unburned hydrocarbons in the engine&#39;s exhaust at all times.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0009]      FIG. 1  is a schematic diagram of a prior art engine fueling control function responsive to torque demand, using gasoline as the hydrocarbon fuel;  
         [0010]      FIG. 2  is a schematic diagram of an onboard hydrocarbon reformate generation system for supplying hydrocarbon reformate to an engine manifold; and  
         [0011]      FIG. 3  is a schematic diagram of an engine fueling control function in accordance with the invention, combining the prior art gasoline fueling function shown in  FIG. 1  with a novel reformate engine fueling function. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]     The following description and the drawings are directed to method and apparatus for operation of an internal combustion engine fueled at steady-state by gasoline. It should be understood that similar methods and apparatus for engines employing other hydrocarbon fuels at steady-state, such as diesel fuel, ethanol, and the like, are fully comprehended by the invention.  
         [0013]     Referring to  FIG. 1 , a prior art engine management function  10  includes an engine intake air flow control valve (throttle)  12 , an engine mass air flow sensor  14 , an exhaust air-to-fuel ratio sensor  16 , an exhaust air-to-fuel ratio control means  18 , at least one fuel injector  20  disposed in an engine intake manifold  22 , and an engine fuel injector control means  24 . Prior art function  10  is managed by a programmable electronic engine control module  26 .  
         [0014]     In prior art function  10 , for any given torque requirement, the gasoline requirement is calculated  28  (typically from a look-up table in the controller) and forwarded  30 . Similarly, a desired combustion air-to-fuel ratio is calculated  32  (also from a look-up table) and forwarded  34 . The two values are multiplied  36  to yield a desired baseline engine air flow  38  which is forwarded to an engine air flow control algorithm  40  which sets the opening of intake air control valve  12 . The resulting actual air flow is determined by engine mass air flow sensor  14 , and the output air flow value is multiplied  41  by the desired fuel-to-air ratio  42  to yield a non-adjusted required fuel value  43 . The exhaust air-to-fuel ratio sensor  16  provides an output  44  to control means  18  which adjusts  46  the injected fuel trim value required to maintain the desired fuel-to-air ratio  42 , in known fashion.  
         [0015]     This amount is summed  48  with (subtracted from) the non-adjusted fuel value  43  to provide an adjusted required fuel amount  50  which fuel injector control means  24  causes fuel injector  20  to inject into manifold  22 .  
         [0016]     Referring to  FIG. 2 , a reformate fueling system  60  is provided for symbiotic attachment to an internal combustion engine  62  across a functional interface  64 . Engine  62  may be a motive engine for a vehicle  65 , for example, an automobile or truck, in known fashion, and reformate fueling system  60  is preferably carried onboard such a vehicle. Engine  62  comprises intake manifold  22  and fuel injection fuel rail  67 . Reformate fueling system  60  may also draw from and utilize an existing engine air filter  66 , engine coolant system  68 , and fuel tank  70 , containing liquid hydrocarbon fuel  74  such as, for example, gasoline  74   a , diesel fuel  74   b  or ethanol  74   c .  
         [0017]     In reformate generation system  60  for fueling engine  62  in accordance with the invention, a catalytic fuel reformer  72  is connected to a hydrocarbon fuel supply subsystem originating in fuel tank  70  (a recirculating fuel system is shown). Reformer  72  receives fuel  74  delivered by fuel pump  75  from fuel tank  70  via a dedicated reformer fuel injector  76 . Preferably and additionally, bypass fuel flows through injector  76  and through a pressure regulator  78 , supplying fuel rail  67  in known fashion, the excess fuel returning  80  to tank  70 . As can be appreciated in the art, while a recirculating fuel system is shown in  FIG. 2 , the present invention can be used with other fuel systems as well, such as with non-circulating “dead headed” fuel systems (not shown).  
         [0018]     Reformer  72  is also supplied with metered air  82  originating in engine air filter  66 . Air blower  84  draws air through filter  66  and discharges air under pressure through mass air flow sensor  86 . A reformer air flow control valve  88  regulates the mass air flow. Air is warmed by passage through a reformate/inlet air heat exchanger  90 , whereby the air is heated and the hot reformate is partially cooled, and the air then passes into reformer  72 .  
         [0019]     Reformer  72  includes an air and fuel injection and mixing chamber  92  in communication with reforming chamber  94 . At start-up, fuel injected into chamber  92  by injector  76  is ignited by a spark igniter  96  extending into chamber  92 . This provides a hot combustion exhaust which passes through the reformer, rapidly warming the catalytic elements therein. When ignition is terminated, the warmed catalytic elements in chamber  94  begin reforming the fuel/air mixture continuously supplied to the reformer to yield a hydrogen containing fuel gas, hydrocarbon reformate  98 . From heat exchanger  90 , reformate  98  is preferably passed through an additional heat exchanger  100 , which further cools reformate  98  by heat exchange with coolant  102  from engine coolant system  68 , and is discharged into intake manifold  22 .  
         [0020]     Referring to  FIGS. 1, 2 , and  3 , in a combined hydrocarbon fuel and reformate fueling system  300  for an internal combustion engine, a reformer management function  110  interfaces with engine management function  10 ′ across a functional interface  112 . The principal engine fueling function steps in function  10 ′ are identical with those described hereinabove under function  10  and shown in  FIG. 1 .  
         [0021]     Engine management function  10 ′ chooses when to initiate and engage reformate fueling system  60  to produce reformate for fueling engine  62 , for example, when the engine is cold and it is desirable to prevent generation of exhaust gas containing unburned hydrocarbons. Reformer energy output demand is scheduled as a percentage of the fuel flow energy required for the demanded engine torque. Varying the reformate fraction permits optimization of exhaust composition and engine performance. The reformate fraction may comprise from 0% to 100% of the fuel for engine  62  at any given time. Preferably at engine startup, the engine is 100% fueled by reformate. Alternately, initial cranking may include from a fraction up to 100% hydrocarbon fuel for a short time to avoid potential delays in starting the engine while the reformer is starting up.  
         [0022]     Engine function  10 ′ calculates  114  a reformate fueling fraction  116  and communicates that fraction to reformer function  110 . The hydrocarbon fuel flow required  30  to meet the torque demand imposed on the engine is also supplied to reformer function  110 . The conversion efficiency  118  of the reformer is calculated  119 , based on stored programmed data. The reformate fueling fraction  116 , hydrocarbon fuel flow requirement  30  to meet the torque demand of the engine, and reformer efficiency  118  are combined  120 , by algorithm, to determine the actual flow  122  of hydrocarbon fuel required at the reformer.  
         [0023]     As described above, air is required in the reformer for reforming the hydrocarbon fuel. This air required for the reforming process must be accounted for in determining the total air flow through the engine. Control of engine air-to-fuel ratio is maintained through adjustment of direct engine intake air flow to compensate for the actual fuel flow and air flow used in production of reformate. A desired air-to-fuel ratio  124  for the reformer is calculated  126 , based on stored program data. Required hydrocarbon fuel flow  122  is multiplied  128  by ratio  124  to yield the desired reformer air flow  130  which is then set by reformer air flow control valve  88 . Reformer mass air flow sensor  86  determines the actual reformer air flow  132  which is multiplied  134  by the desired reformer fuel-to-air ratio  124  to yield a commanded reformer hydrocarbon fuel flow  136  to which reformer injector  76  responds to inject the commanded flow of hydrocarbon fuel into reformer  72 .  
         [0024]     The actual reformer air flow  132  is added  138  to the air flow measured by engine mass air flow  14  and is multiplied  41 ′ by the desired combustion fuel-to-air ratio  42  to yield an equivalent fuel flow. However, because reformate is inherently less powerful than hydrocarbon fuel, the commanded reformer hydrocarbon fuel flow  136  must be combined  140  with the reformer efficiency  118  to yield a flow of reformer fuel  142  which is the torque equivalent of required torque hydrocarbon fuel  30 . The torque equivalent reformer fuel  142  is subtracted  144  from the gross required torque hydrocarbon fuel  30 , which difference depends upon the relative percentages of simultaneous fueling by reformate and hydrocarbon fuel together. In setting the desired baseline engine air flow  146 , the commanded reformer hydrocarbon fuel is added  148  to the output of  144  and then multiplied  36 ′ by the desired combustion air-to-fuel ratio  34 .  
         [0025]     Further, the torque equivalent reformer fuel  142  is subtracted  48 ′ from output  41 ′, adjusted  46  by any fuel in the engine exhaust, as in the prior art, and a required injection value  50 ′ is forwarded to engine fuel injector control means  24  to cause fuel injector  20  to inject amount  50  into manifold  22 .  
         [0026]     Proper engine torque output is maintained during reformer operation through two mechanisms. First, the process controls the reformer to produce reformate energy output equivalent to the engine controller demand independent of reformer efficiency. The reformer fuel input is adjusted, based on the current energy conversion efficiency of the reformer. Second, the engine controller adjusts hydrocarbon fueling for error in the actual reformer energy output, relative to the reformer energy demand, should the demand exceed the output capacity of the reformer system, or should system dynamics cause momentary delays in reformer response.  
         [0027]     Combined engine management function  10 ′ and reformer function  110  are thus capable of fueling engine  62  at any desired ratio of reformate to hydrocarbon fuel, from 100% reformate to 100% hydrocarbon fuel. Preferably, engine  62  is fueled predominately or exclusively by hydrogen-containing fuel gas, such as hydrogen gas or reformate gas, either when engine  62  is cold, as at startup, or when exhaust air-to-fuel ratio sensor  16  detects fuel levels in the exhaust that are at or above a predetermined acceptance level. Preferably, engine  62  is fueled as little as possible by a hydrogen-containing gas for fuel economy reasons.  
         [0028]     Thus, for example, in a typical operation, at cold engine and reformer start-up, fueling fraction  114  is nearly or 100% reformate. Reformer  72  is quickly preheated by ignition of air/fuel mixture in chamber  92  and begins producing reformate  98  in chamber  94  shortly thereafter. Reformate  98  is passed immediately to intake manifold  22  and thence to the cylinders of engine  62  where it is combusted to start the engine, producing an exhaust substantially free of unburned hydrocarbons. The engine immediately begins to warm, as does the exhaust catalytic converter. In accordance with an algorithm programmed into engine management controller  26 ′ and dependent at least upon engine temperature, unburned fuel levels in the exhaust, and engine torque requirements, hydrocarbon fueling system  10 ′ begins injecting small amounts of hydrocarbon fuel into manifold  22 , while simultaneously reducing the reformate fueling fraction  116 . Preferably, when the engine and exhaust converter have reached their respective steady-state operating temperatures, the reformate fueling fraction is set to an optimum value to provide good fuel economy and low engine emissions. This value may be as low as 0% reformate fuel, depending on specific needs for vehicle operation.  
         [0029]     It is understood that, while in the preferred embodiment described, a reformer is used to convert a hydrogen fuel such as gasoline, diesel fuel or ethanol, into a hydrogen-containing gas (reformate), the fueling system can operate alternatively using hydrogen gas fed directly from a storage vessel.  
         [0030]     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.