Abstract:
A power system includes an internal combustion engine having a primary combustion chamber and a secondary combustion chamber, a first fuel being supplied to the primary combustion chamber, a second fuel being burned in the secondary combustion chamber so as to ignite the first fuel; a reformer that reforms a fuel by a dehydrocyclization reaction to generate an aromatic-rich high-octane-value liquid fuel together with a hydrogen-rich gaseous fuel; a gas/liquid separator that separates the liquid fuel from the gaseous fuel; and devices for respectively supplying the liquid fuel as the first fuel to the primary combustion chamber and the gaseous fuel as the second fuel to the secondary combustion chamber. Thus, the power system improves the combustion efficiency of the internal combustion engine.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a power system and, in particular, a power system that includes an internal combustion engine having primary and secondary combustion chambers. 
   2. Description of the Related Art 
   As such an internal combustion engine, an arrangement is known in which a lean primary gas mixture is supplied to a primary combustion chamber via a primary intake valve, a rich secondary gas mixture is supplied to a secondary combustion chamber via a secondary intake valve, and the flame generated by combustion of the secondary gas mixture induces ignition and combustion of the primary gas mixture (for example, Japanese Patent Publication No. 61-31301). In this internal combustion engine, excellent combustion efficiency can be obtained by burning the lean primary gas mixture. Furthermore, since the combustion occurs uniformly, it is possible to reduce pollutants such as nitrogen oxides and carbon monoxide. 
   However, since the conventional arrangement employs, as the secondary gas mixture, a hydrocarbon fuel which has a low combustion rate, it is difficult to further improve the combustion efficiency by fully increasing the leanness of the primary gas mixture. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to provide a power system in which the combustion efficiency of the internal combustion engine can be further improved. 
   In order to accomplish the above object, an aspect of the present invention provides a power system that includes an internal combustion engine having a primary combustion chamber and a secondary combustion chamber, a first fuel being supplied to the primary combustion chamber, a second fuel being burned in the secondary combustion chamber to generate a flame for igniting the first fuel; a reformer that reforms fuel by a dehydrocyclization reaction to generate an aromatic-rich high-octane-value liquid fuel together with a hydrogen-rich gaseous fuel; a gas/liquid separator that separates the liquid fuel from the gaseous fuel; and devices for respectively supplying the liquid fuel as the first fuel to the primary combustion chamber and the gaseous fuel as the second fuel to the secondary combustion chamber. 
   Hydrogen has a wide combustible gas mixture range and an extremely fast combustion rate. Using a hydrogen-rich gaseous fuel as the second fuel for igniting the first fuel enables the first fuel to be completely burned even when the leanness of the primary gas mixture, which is the first fuel, in the primary combustion chamber is fully increased. Moreover, since part of the fuel supplied to the primary combustion chamber can be reformed by the dehydrocyclization reaction into an aromatic-rich high-octane-value liquid fuel and a hydrogen-rich gaseous fuel, it is unnecessary to prepare hydrogen in advance as the second fuel. 
   The above-mentioned object, other objects, characteristics, and advantages of the present invention will become apparent from an explanation of a preferred embodiment that will be described in detail below by reference to the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of a power system; and 
       FIG. 2  is a cross sectional view of an internal combustion engine. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In a power system  1  shown in  FIG. 1 , a fuel tank  2  is connected to the inlet side of a reformer  5  via a first supply pipe  4  having a first open/close valve  3 , and the outlet side of the reformer  5  is connected to the inlet side of a gas/liquid separator  8  via a second supply pipe  7  having a second open/close valve  6 . A liquid outlet a side of the gas/liquid separator  8  is connected to a first inlet side of a first gas mixture preparation device  11  via a third supply pipe  10  having a third open/close valve  9 . A gas outlet b side of the gas/liquid separator  8  is connected to the inlet side of a hydrogen separator  14  via a fourth supply pipe  13 , which is connected to first and second ports of a three-way valve  12 . A hydrogen outlet c side of the hydrogen separator  14  is connected to a first inlet side of a second gas mixture preparation device  17  via a fifth supply pipe  16  having a fourth open/close valve  15 . A hydrocarbon gas outlet d side of the hydrogen separator  14  is connected to a second inlet side of the first gas mixture preparation device  11  via a sixth supply pipe  19  having a fifth open/close valve  18 . A third port of the three-way valve  12  is connected to a second inlet side of the second gas mixture preparation device  17  via a seventh supply pipe  21 . The outlet side of the first gas mixture preparation device  11  is connected to a first fuel inlet side of an internal combustion engine  23  via an eighth supply pipe  22 . The outlet side of the second gas mixture preparation device  17  is connected to a second fuel inlet side of the internal combustion engine  23  via a ninth supply pipe  24 . 
   The fuel tank  2  contains fuel which is used as fuel for the internal combustion engine and is reformed by a dehydrocyclization reaction in the reformer  5 . As such a fuel, a hydrocarbon, an alcohol, an ether, etc. can be used. The reformer  5  reforms the fuel supplied from the fuel tank  2  by a dehydrocyclization reaction to generate an aromatic-rich high-octane-value liquid fuel and a hydrogen-rich gaseous fuel. 
   The gas/liquid separator  8  has a function of separating the high-octane-value liquid fuel and the gaseous fuel from the product from the reformer  5 . The whole or a part of the liquid fuel separated in the gas/liquid separator  8  is supplied to the first gas mixture preparation device  11  via the third supply pipe  10  having the third open/close valve  9 . On the other hand, the whole or a part of the gaseous fuel separated in the gas/liquid separator  8  is separated into hydrogen and a hydrocarbon gas in the hydrogen separator  14 . The whole or a part of the hydrogen separated in the hydrogen separator  14  is supplied to the second gas mixture preparation device  17  via the fifth supply pipe  16  having the fourth open/close valve  15 . On the other hand, the whole or a part of the hydrocarbon gas separated in the hydrogen separator  14  is supplied to the first gas mixture preparation device  11  via the sixth supply pipe  19  having the fifth open/close valve  18 . Switching over the three-way valve  12  allows the whole or a part of the gaseous fuel separated in the gas/liquid separator  8  to be fed to the second gas mixture preparation device  17  while bypassing the hydrogen separator  14 . The fuel tank  2  is connected to a third inlet side of the first gas mixture preparation device  11  via a tenth supply pipe  26  having a sixth open/close valve  25 . 
   As shown in  FIG. 2 , a piston  29  is slidably fitted within a cylinder bore  28  of a cylinder block  27  of the internal combustion engine  23 . Formed in a cylinder head  30  are a primary combustion chamber  31 , a secondary combustion chamber  33 , a primary intake port  34 , an exhaust port (not illustrated), and a secondary intake port  35 . The primary combustion chamber  31  is defined by the piston  29 , the secondary combustion chamber  33  communicates with the primary combustion chamber  31  via a torch nozzle  32 , the primary intake port  34  and the exhaust port open into the primary combustion chamber  31 , and the secondary intake port  35  opens into the secondary combustion chamber  33 . The primary intake port  34  is opened and closed by the primary intake valve  36 , the secondary intake port  33  is opened and closed by the secondary intake valve  37 , and the exhaust port is opened and closed by an exhaust valve (not illustrated). Electrodes of a spark plug  38  screwed into the cylinder head  30  face the secondary combustion chamber  33 . The primary intake port  34  is the first fuel inlet side, to which the eighth supply pipe  22  is connected. The secondary intake port  35  is the second fuel inlet side, to which the ninth supply pipe  24  is connected. 
   The first gas mixture preparation device  11  functions as a device for preparing a primary gas mixture from air and at least one selected from the fuel within the fuel tank  2 , the high-octane-value liquid fuel separated by the gas/liquid separator  8 , and the hydrocarbon gas separated by the hydrogen separator  14 , and feeds the primary gas mixture to the primary combustion chamber  31  via the eighth supply pipe  22  and the primary intake port  34  of the internal combustion engine  23 . 
   The second gas mixture preparation device  17  functions as a device for preparing a secondary gas mixture from hydrogen and air or from air and the hydrogen-rich gaseous fuel, and feeds the secondary gas mixture to the secondary combustion chamber  33  via the ninth supply pipe  24  and the secondary intake port  35  of the internal combustion engine  23 . 
   The reformer  5  is packed with a catalyst that is active in accelerating a dehydrocyclization reaction. This type of catalyst is desirably a crystalline aluminosilicate such as, for example, a zeolite and, in particular, a ZSM-5 zeolite having an MFI structure, which preferably contains at least one selected from gallium, zinc, and platinum. The temperature of the dehydrocyclization reaction is set at 400° C. to 700° C. 
   Table 1 shows the results of reforming in which a dehydrocyclization reaction was carried out using n-pentane as the fuel and, as the catalyst, each of a protonated ZSM-5 (H-ZSM-5), a Ga-modified ZSM-5 (Ga-ZSM-5), and a Zn-modified ZSM-5 (Zn-ZSM-5). The gallium and zinc contents were 2 wt % of the weight of the catalyst. The reforming conditions were a weight hourly space velocity (WHSV) of 2 h −1 , a reforming temperature of 550° C., and a reforming pressure of 0.1 MPa. 
   
     
       
             
             
           
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
               TABLE 1 
             
           
           
             
                 
                 
             
             
                 
               Reformed fuel components (wt %) 
             
           
        
         
             
                 
                 
                 
               Paraffinic 
               Aromatic 
             
             
                 
               Catalyst 
               Hydrogen 
               hydrocarbon gas 
               hydrocarbon 
             
             
                 
                 
             
           
        
         
             
                 
               H-ZSM-5 
               2.0 
               54.9 
               43.1 
             
             
                 
               Ga-ZSM-5 
               3.0 
               46.4 
               50.6 
             
             
                 
               Zn-ZSM-5 
               3.6 
               44.8 
               51.6 
             
             
                 
                 
             
           
        
       
     
   
   It is clear from Table 1 that the use of H-ZSM-5 as the catalyst can sufficiently promote the dehydrocyclization reaction. It was also found that, when a catalyst obtained by modifying H-ZSM-5 with gallium or zinc was used, the yields of the aromatic hydrocarbon and hydrogen increased as compared with the case where H-ZSM-5 was used. 
   In the above-mentioned arrangement, fuel within the fuel tank  2  is supplied to the reformer  5  via the first supply pipe  4  with the first open/close valve  3  open. In the reformer  5 , the fuel is reformed by the dehydrocyclization reaction, thereby generating the aromatic-rich high-octane-value liquid fuel and the hydrogen-rich gaseous fuel. 
   The product from the reformer  5  is fed into the gas/liquid separator  8  through the second supply pipe  7  with the second open/close valve  6  open. In the gas/liquid separator  8 , the high-octane-value liquid fuel and the gaseous fuel are separated from each other, and the high-octane-value liquid fuel is fed to the first gas mixture preparation device  11  through the third supply pipe  10  with the third open/close valve  9  open. The gaseous fuel separated in the gas/liquid separator  8  is fed into the hydrogen separator  14  through the fourth supply pipe  13  with the first and second ports of the three-way valve  12  connected through. 
   In the hydrogen separator  14 , the gaseous fuel is separated into hydrogen and the hydrocarbon gas, and the hydrocarbon gas is fed into the first gas mixture preparation device  11  through the sixth supply pipe  19  with the fifth open/close valve  18  open. On the other hand, the hydrogen separated in the hydrogen separator  14  is fed into the second gas mixture preparation device  17  through the fifth supply pipe  16  with the fourth open/close valve  15  open. 
   In the first gas mixture preparation device  11 , the primary gas mixture is prepared from, for example, the fuel supplied from the fuel tank  1 , the aromatic-rich high-octane-value liquid fuel, the hydrocarbon gas, and air, and the primary gas mixture is fed into the primary intake port  34  of the internal combustion engine  23  through the eighth supply pipe  22 . In this case, the fuel supplied from the fuel tank  1 , the aromatic-rich high-octane-value liquid fuel, and the hydrocarbon gas can be used at any ratio. On the other hand, in the second gas mixture preparation device  17 , the secondary gas mixture is prepared from air and hydrogen or the hydrogen-rich gaseous fuel, and the secondary gas mixture is fed to the secondary intake port  35  of the internal combustion engine  23  through the ninth supply pipe  24 . 
   In the internal combustion engine  23 , when the primary and secondary intake valves  36  and  37  open during the intake stroke of the piston  29 , the primary gas mixture is supplied from the primary intake port  34  into the primary combustion chamber  31 , and the secondary gas mixture is supplied from the secondary intake port  35  into the secondary combustion chamber  33 . During the following compression stroke, the secondary gas mixture within the secondary combustion chamber  33  is ignited by a spark discharge of the spark plug  38 , and the resulting flame shoots into the primary combustion chamber  31  through the torch nozzle  32 , thereby igniting the primary gas mixture within the primary combustion chamber  31  and making it burn. This enables a lean gas mixture with a high overall air-fuel ratio to be burned. The piston  29  then moves to the expansion stroke, and when the exhaust valve is opened during the following exhaust stroke, the exhaust gas is discharged via the exhaust port and an exhaust pipe. In this way, the internal combustion engine  23  operates. 
   Table 2 shows the result of reforming in which a dehydrocyclization reaction was carried out using, as a fuel, isooctane (2,2,4-trimethylpentane), which is a major component of high-octane gasoline and, as a catalyst, a Ga-modified ZSM-5 (Ga-ZSM-5). The gallium content was 1.5 wt % of the weight of the catalyst. The reforming conditions were a weight hourly space velocity (WHSV) of 2 h −1 , a reforming temperature of 530° C., and a reforming pressure of 0.1 MPa. 
   
     
       
             
             
           
             
             
             
             
             
           
         
             
                 
               TABLE 2 
             
           
           
             
                 
                 
             
             
                 
               Reformed fuel components (wt %) 
             
           
        
         
             
                 
                 
               Paraffinic 
               Aromatic 
               Unreacted 
             
             
               Catalyst 
               Hydrogen 
               hydrocarbon gas 
               hydrocarbon 
               component 
             
             
                 
             
             
               Ga-ZSM-5 
               1.5 
               24.7 
               30.2 
               43.6 
             
             
                 
             
           
        
       
     
   
   Although an unreacted component is generated when isooctane is used as the fuel, such a fuel is also usable in the present invention. 
   In accordance with the present invention, the above-mentioned arrangement allows the first fuel to be completely burned even when its leanness is fully increased, thus further improving the combustion efficiency and reducing the pollutants in the exhaust gas. Since it is possible to generate hydrogen by reforming the fuel of the fuel tank, it is unnecessary to prepare hydrogen in advance, thus simplifying the arrangement of the power system. 
   Although an embodiment of the present invention is explained in detail above, the present invention can be modified in a variety of ways without departing from the spirit and scope of the present invention.