Abstract:
The purpose of the present invention is to provide an engine with reforming cylinders which are fuel reforming devices capable of supplying a reformed fuel according to the outputs of outputting cylinders. The engine is provided with the outputting cylinders for burning the fuel and the reforming cylinders which are the fuel reforming devices for reforming the fuel through the reciprocating motions of pistons. The amount of reformed fuel supplied to all the outputting cylinders is changed according to the outputs of the outputting cylinders while maintaining the amount of supplied fuel and the amount of suctioned gas, which are supplied into one reforming cylinder.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an engine, and more specifically, to an engine including a fuel reforming device. 
       BACKGROUND ART 
       [0002]    A premixing engine supplying reformed gas fuel, obtained by premixing intake air and exhaust air in liquid fuel has conventionally been known. The premixing engine features reformation of liquid fuel into gas fuel that can be combusted in a diluted state to be combusted, and thus can achieve smaller amounts of smoke and NOx discharged, as described in Patent Literature 1 for example. 
         [0003]    An engine described in Patent Literature 1 reforms fuel by using one of a plurality of cylinders as a reforming cylinder serving as a fuel reforming device to mix the liquid fuel with intake air and exhaust air and compressing the mixture. The reformed fuel can be reformed only when predetermined intake gas temperature, composition, compression rate, and fuel air equivalence ratio are achieved. Thus, the engine is incapable of decreasing the produced amount of reformed fuel by changing the fuel air equivalence ratio achieved by the reformed fuel or changing the intake gas amount, in accordance with an output from outputting cylinders. Thus, the engine might fail to supply an amount of reformed fuel in accordance with the output from the outputting cylinders, and thus might not be able to operate with an appropriate amount of fuel. 
       CITATION LIST 
     Patent Literature 
       [0004]    PTL 1: Japanese Unexamined Patent Application Publication No. 2007-332891 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    The present invention has been made in light of the aforementioned circumstances, and an object of the present invention is to provide an engine including a fuel reforming device that can supply reformed fuel in accordance with an output from an outputting cylinder. 
       Solution to Problem 
       [0006]    Specifically, in the present invention, an engine includes an outputting cylinder configured to combust fuel, and a reforming cylinder configured to reform the fuel through back and forth movement of a piston. An amount of reformed fuel supplied to the outputting cylinder is changed in accordance with an output from the outputting cylinder, while maintaining an amount of supplied fuel and an amount of suctioned gas to one reforming cylinder. 
         [0007]    In the present invention, at least one of a compression rate and an expansion rate of the reforming cylinder is changed based on temperature of reformed fuel discharged from the reforming cylinder. 
         [0008]    In the present invention, the reforming cylinder includes an expansion chamber a volume of which changes in accordance with the back and forth movement of the piston, and a reaction chamber with a constant volume, and the expansion chamber and the reaction chamber are in communication with each other. 
         [0009]    In the present invention, the reforming cylinder is coupled with an intake air pipe through which intake air from outside is supplied and an EGR pipe through which exhaust air from the outputting cylinder is supplied, and the reforming cylinder is provided with a fuel injection device that supplies fuel to a mixture of the intake air and the exhaust air supplied to the reforming cylinder and an additive injection device that supplies an additive based on an amount of supplied fuel and an amount of the mixture. 
       Advantageous Effects of Invention 
       [0010]    The present invention has the following advantageous effects. 
         [0011]    Specifically, in the present invention, the amount of reformed fuel supplied to the outputting cylinder is changed, while maintaining the amount of reformed fuel discharged from each reforming cylinder and a fuel air equivalence ratio of the reformed fuel. Thus, the reformed fuel can be supplied in accordance with the output of the outputting cylinder. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a schematic view illustrating one embodiment of an engine according to the present invention. 
           [0013]      FIG. 2  is a schematic view illustrating a configuration of an outputting cylinder and a reforming cylinder in one embodiment of the engine according to the present invention. 
           [0014]      FIG. 3  is a side sectional view illustrating a variable valve device in one embodiment of the engine according to the present invention. 
           [0015]      FIG. 4  is a partially enlarged plan view of the variable valve device in one embodiment of the engine according to the present invention. 
           [0016]      FIG. 5  is a partially enlarged plan view illustrating a case where a hydraulic cylinder in the variable valve device in one embodiment of the engine according to the present invention is not protrudent. 
           [0017]      FIG. 6  is a schematic view of a control configuration in one embodiment of the engine according to the present invention. 
           [0018]      FIG. 7( a )  is a diagram illustrating a relationship between a crank angle of one cam and opening and closing timings of an intake valve in one embodiment of the engine according to the present invention, and  FIG. 7( b )  is a diagram illustrating a relationship between the crank angle and a valve lift of the intake valve. 
           [0019]      FIG. 8  is a chart representing a state in a reaction chamber at a crank position of a reforming cylinder in one embodiment of the engine according to the present invention. 
           [0020]      FIG. 9  is a partially enlarged side view illustrating a case where a hydraulic cylinder in a variable valve device in another embodiment of the present invention is not protrudent. 
           [0021]      FIG. 10  is a partially enlarged side view illustrating a case where a hydraulic cylinder in a variable valve device in another embodiment of the present invention is protrudent. 
           [0022]      FIG. 11  is a diagram illustrating opening and closing timings of an intake valve in accordance with a profile of one cam in the variable valve device in another embodiment of the present invention,  FIG. 11( a )  illustrating a relationship between a crank angle and the opening and closing timings of the intake valve and  FIG. 11( b )  illustrating a relationship between the crank angle and a valve lift of the intake valve. 
           [0023]      FIG. 12  is a diagram illustrating the opening and closing timings of the intake valve in accordance with a profile of the other cam in the variable valve device in another embodiment of the present invention,  FIG. 12( a )  illustrating a relationship between the crank angle and the opening and closing timings of the intake valve and  FIG. 12( b )  illustrating a relationship between the crank angle and the valve lift of the intake valve. 
           [0024]      FIG. 13  is a chart representing a state in a reaction chamber at a crank position of a reforming cylinder in a variable valve device in another embodiment of the present invention. 
           [0025]      FIG. 14  is a schematic view illustrating a configuration of a reforming cylinder in still another embodiment of the present invention. 
           [0026]      FIG. 15  is a schematic view illustrating a control configuration for calculating the amount of an additive in the reforming cylinder according to still another embodiment of the present invention. 
           [0027]      FIG. 16  is a chart representing a state in a reaction chamber at a crank position of the reforming cylinder in still another embodiment of the present invention. 
           [0028]      FIG. 17  is a schematic view illustrating a configuration of a reforming cylinder in yet still another embodiment of the present invention. 
           [0029]      FIG. 18  is a schematic view illustrating a configuration in an embodiment in which a reaction chamber is arranged in a piston of the reforming cylinder in yet still another embodiment of the present invention. 
           [0030]      FIG. 19  is a schematic view illustrating a configuration in an embodiment in which a reaction chamber is arranged in a cylinder block of the reforming cylinder in yet still another embodiment of the present invention. 
           [0031]      FIG. 20  is a chart representing a relationship between a crank position of the reforming cylinder and fuel injection timings in yet still another embodiment of the present invention. 
           [0032]      FIG. 21  is a schematic view illustrating flow of supply air in the reaction chamber in the reforming cylinder in yet still another embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0033]    An engine  1  as one embodiment of an engine according to the present invention is described with reference to  FIG. 1  to  FIG. 8 . 
         [0034]    As illustrated in  FIG. 1  and  FIG. 2 , the engine  1  is a four-cylinder diesel engine using light oil or heavy oil as a fuel. The engine  1  mainly includes: four outputting cylinders  2 ; a supercharger  14 ; three reforming cylinders  15  serving as a fuel reforming device; an intake air intercooler  33 ; a reformed fuel intercooler  34 ; an EGR gas intercooler  35 ; a variable valve device  36  (see  FIG. 3 ); and an ECU  60  as a control device. The engine  1  according to the present embodiment is a four-cylinder diesel engine. However, this should not be construed in a limiting sense. 
         [0035]    As illustrated in  FIG. 2 , the outputting cylinders  2  generate driving force through combustion of fuel, and transmit the driving force to an output shaft. The outputting cylinders  2  include four cylinders. Each of the outputting cylinders  2  includes an output cylinder  3 , an outputting piston  4 , an outputting connecting rod  5 , and a secondary fuel injection device  6 . 
         [0036]    The outputting cylinders  2  have the outputting piston  4  incorporated in the output cylinder  3  in a slidable manner. The output cylinder  3  has one side closed by an unillustrated cylinder head, and the other side open. The outputting piston  4  is coupled with an outputting crankshaft  7 , serving as the output shaft, via the outputting connecting rod  5 . The outputting cylinders  2  have a compression rate of 13 or more (for example, about 13 to 18), to prevent preignition or misfire from occurring. 
         [0037]    The outputting crankshaft  7  is provided with an outputting crank angle detection sensor  8 . The outputting cylinders  2  each include a combustion chamber  9  defined by an inner wall of the output cylinder  3  and an end surface of the outputting piston  4 . The outputting cylinders  2  are each provided with the secondary fuel injection device  6  that can inject fuel into the combustion chamber  9 . The secondary fuel injection device  6  includes an injector with a hole-type nozzle. The outputting cylinders  2  are coupled with an intake pipe  11  via an outputting intake valve  10  and to an exhaust pipe  13  via an outputting exhaust valve  12 . In the present embodiment, the number of outputting cylinders  2  may be one or more than one. 
         [0038]    As illustrated in  FIG. 1  and  FIG. 2 , the supercharger  14  performs adiabatic compression on outer air, and supplies the resultant air to the combustion chamber  9  of the outputting cylinder  2 . The supercharger  14  includes a turbine  14   a  and a compressor  14   b . The turbine  14   a  is coupled with the exhaust pipe  13  and thus can be supplied with exhaust air from the combustion chamber  9 . The compressor  14   b  is coupled with the intake pipe  11 , and can suck outer air, as intake air, and supply the intake air into the combustion chamber  9 . Thus, the supercharger  14  can achieve the adiabatic compression with the turbine  14   a  converting pressure of the exhaust air into rotational driving force to be transmitted to the compressor  14   b  and the compressor  14   b  sucking the outer air. 
         [0039]    The reforming cylinders  15 , serving as the fuel reforming device, reform a higher hydrocarbon fuel, such as light oil, into a lower hydrocarbon fuel (for example, methane), to prevent preignition. The reforming cylinders  15 , serving as the fuel reforming device, include three cylinders (see  FIG. 1 ). The reforming cylinders  15  perform the reforming of the fuel by performing the adiabatic compression on a result of injecting fuel onto a mixture (hereinafter simply referred to as “supply air”) of the intake air and the exhaust air (EGR gas). The reforming cylinders  15  each include a reforming cylinder head  16 , a reforming cylinder  17 , a reforming piston  18 , a reforming connecting rod  19 , a main fuel injection device  20 , and the like. 
         [0040]    As illustrated in  FIG. 2 , the reforming cylinder  17  of the reforming cylinder  15  has one side closed by the reforming cylinder head  16 , and incorporates the reforming piston  18  provided in a slidable manner. The reforming piston  18  is coupled with a reforming crankshaft  21  via the reforming connecting rod  19 . The reforming crankshaft  21  is provided with a reforming crank angle detection sensor  22 . The reforming piston  18  of the reforming cylinder  15  is coupled with the outputting crankshaft  7 , via a reforming cylinder speed change device  59  described later, in an interlocking manner. The reforming piston  18  can move back and forth with the driving force transmitted from the outputting crankshaft  7  to the reforming crankshaft  21 . In the present embodiment, the driving force is transmitted from the outputting crankshaft  7  to the reforming cylinders  15 . However, this should not be construed in a limiting sense. The driving force may be transmitted from an independent driving source. The reforming cylinder  15  may be provided for each outputting cylinder  2 , or one reforming cylinder  15  may be provided for a plurality of outputting cylinders  2 . Furthermore, a cylinder serving as both the outputting cylinder  2  and the reforming cylinder  15  may be used. 
         [0041]    The reforming cylinder  15  includes a reaction chamber  23  defined by the reforming cylinder head  16 , the reforming cylinder  17 , and an end surface of the reforming piston  18 . The reaction chamber  23  has a volume changeable in accordance with the back and forth movement of the reforming piston  18 . The reaction chamber  23  performs the adiabatic compression on the supply air and the fuel, in accordance with the volume change. The compression rate of the reaction chamber  23  is set to be 15 or more (for example, about 15 to 20). The volume of the reaction chamber  23  (the amount of exhaust air from the reforming cylinder  15 ) is set to be smaller than the amount of exhaust air from one of the outputting cylinders  2 . 
         [0042]    The main fuel injection device  20  supplies fuel into the reaction chamber  23 . The main fuel injection device  20  is provided to the reforming cylinder head  16 . The main fuel injection device  20  can supply an appropriate amount of fuel into the reaction chamber  23  at an appropriate timing. The main fuel injection device  20  includes a nozzle such as a pintle nozzle, a swirl injector, and an air-assist injector. 
         [0043]    Each of the reforming cylinders  15  is coupled with a supply pipe  25  via a reforming intake valve  24 . The intake air can be partially supplied to the supply pipe  25  through the intake pipe  11 . The supply pipe  25  is coupled with the exhaust pipe  13  via an EGR pipe  28 . Thus, the exhaust air from the combustion chamber  9  of the outputting cylinders  2  can be partially supplied to the supply pipe  25  as the EGR gas through the EGR pipe  28 . Thus, the mixture (hereinafter, simply referred to as “supply air”) of the intake air and the EGR gas can be supplied from the supply pipe  25  to the reaction chamber  23  of each of the reforming cylinders  15 . 
         [0044]    Each of the reforming cylinders  15  is coupled with an exhaust pipe  27  via a reforming exhaust valve  26 . The exhaust pipe  27  is coupled with the intake pipe  11 , which is more on the downstream side than the supply pipe  25 , via a mixer  27   a . Each of the reforming cylinders  15  can discharge the lower hydrocarbon fuel (hereinafter simply referred to as “reformed fuel”), as a result of the reforming, from the reaction chamber  23  to the intake pipe  11  via the exhaust pipe  27 . The exhaust pipe  27  is provided with a reformed fuel temperature sensor  29  that is more on the upstream side of the reformed fuel intercooler  34  described later. The reformed fuel temperature sensor  29  detects the temperature of the reformed fuel immediately after being discharged from the reforming cylinders  15 . In the present embodiment, the fuel reforming device includes the three reforming cylinders  15 . However, this should not be construed in a limiting sense. The fuel reforming device may include one or a plurality of reforming cylinders  15 . 
         [0045]    The intake pipe  11  is provided with a first intake regulating valve  30  that is more on the downstream side than a coupled position of the supply pipe  25 , and is more on the upstream side than a coupled position of the exhaust pipe  27 . The first intake regulating valve  30  changes an outputting intake air flow amount A 1 . The first intake regulating valve  30  includes an electromagnetic flow amount control valve. The first intake regulating valve  30  can change the opening of the first intake regulating valve  30 , based on a signal acquired from the ECU  60  as the control device described below. The first intake regulating valve  30 , which is the electromagnetic flow amount control valve in the present embodiment, may be any valve as long as the outputting intake air flow amount A 1  can be changed. 
         [0046]    The supply pipe  25  is provided with a second intake regulating valve  31  that is more on the upstream side than a coupled position of the EGR pipe  28 . The second intake regulating valve  31  changes a reforming intake air flow amount A 2 . The second intake regulating valve  31  includes an electromagnetic flow amount control valve. The second intake regulating valve  31  can change the opening of the second intake regulating valve  31 , based on a signal acquired from the ECU  60  described below. The second intake regulating valve  31 , which is the electromagnetic flow amount control valve in the present embodiment, may be any valve as long as the reforming intake air flow amount A 2  can be changed. 
         [0047]    The EGR pipe  28  is provided with an EGR gas regulating valve  32 . The EGR gas regulating valve  32  changes an EGR gas flow amount A 3 . The EGR gas regulating valve  32  includes an electromagnetic flow amount control valve. The EGR gas regulating valve  32  can change the opening of the EGR gas regulating valve  32 , based on a signal acquired from the ECU  60  described below. The EGR gas regulating valve  32 , which is the electromagnetic flow amount control valve in the present embodiment, may be any valve as long as the EGR gas flow amount A 3  can be changed. 
         [0048]    In the engine  1  with this configuration, a mixture ratio between the intake air and the reformed fuel discharged from the reaction chamber  23  of each of the reforming cylinders  15  can be changed with the first intake regulating valve  30 . Furthermore, in the engine  1 , a mixture ratio between the intake air and the EGR gas supplied to the reaction chamber  23  can be changed with the second intake regulating valve  31  and the EGR gas regulating valve  32 . 
         [0049]    The intake air intercooler  33 , the reformed fuel intercooler  34 , and the EGR gas intercooler  35  cool gas. The intake air intercooler  33  is provided to the intake pipe  11 . The intake air intercooler  33  can cool the intake air after the adiabatic compression by the compressor  14   b . The reformed fuel intercooler  34  is provided to the exhaust pipe  27 . The reformed fuel intercooler  34  can cool the reformed fuel discharged from the reaction chamber  23  of each of the reforming cylinders  15 . The reformed fuel intercooler  34  includes a heat radiator or a heat exchanger that uses air or water as a cooling medium. The EGR gas intercooler  35  is provided to the EGR pipe  28 . The EGR gas intercooler  35  can cool the exhaust air heated by the combustion of the fuel. 
         [0050]    As illustrated in  FIG. 3  to  FIG. 5 , the variable valve device  36  opens and closes the reforming intake valve  24  and the reforming exhaust valve  26  at predetermined timings. The variable valve device  36  includes a mechanism for opening and closing the reforming intake valve  24 . The mechanism includes a swing arm shaft  37 , a first swing arm  38 , a second swing arm  41 , a push rod  43 , a valve arm  44 , a cam shaft  45 , an intake air switching unit  48  (see  FIG. 5 ), and the like, and is driven in accordance with a rotational movement of the reforming crankshaft  21  to open and close the reforming intake valve  24 . The variable valve device  36  includes a mechanism for opening and closing the reforming exhaust valve  26 . The mechanism includes a third swing arm  55 , a fourth swing arm  56 , an exhaust air switching unit  57  (see  FIG. 5 ), and the like, and is driven in accordance with a rotational movement of the reforming crankshaft  21  to open and close the reforming exhaust valve  26 . The third swing arm  55 , the fourth swing arm  56 , the exhaust air switching unit  57 , and the like have the same configurations as the first swing arm  38 , the second swing arm  41 , the intake air switching unit  48 , and the like, and thus will not be described in detail. 
         [0051]    As illustrated in  FIG. 4  and  FIG. 5 , the swing arm shaft  37  extends in parallel with an axial direction (hereinafter, a description is given with the axial direction of the reforming crankshaft  21  defined as “front and rear direction”) of the reforming crankshaft  21 . 
         [0052]    The first swing arm  38  is a substantially rectangular parallelepiped member. The first swing arm  38  has one end in the longitudinal direction swingably supported by the swing arm shaft  37 . The first swing arm  38  has a lower portion of the other end in the longitudinal direction rotatably supporting the first cam roller  39 . The other end of the first swing arm  38  has an upper surface on which a rod support member  40 , having a semispherical recess facing upward, is attached. 
         [0053]    The second swing arm  41  is a substantially rectangular parallelepiped member. The second swing arm  41  has one end in the longitudinal direction disposed adjacent to the first swing arm  38  and swingably supported by the swing arm shaft  37 . Thus, the second swing arm  41  is swingably supported by the swing arm shaft  37  while being disposed adjacent to the first swing arm  38 . The second swing arm  41  has a lower portion of the other end in the longitudinal direction rotatably supporting a second cam roller  42 . 
         [0054]    As illustrated in  FIG. 3 , the push rod  43  is a substantially columnar member with which the first swing arm  38  and the valve arm  44  are coupled with each other in an interlocking manner. The push rod  43  has a semispherical lower end that is swingably fit in the recess of the rod support member  40  of the first swing arm  38 . The push rod  43  has an upper end swingably fit in the one end of the valve arm  44 . 
         [0055]    The valve arm  44 , with which the push rod  43  and an intake air coupling member  24   a  are coupled with each other, is swingably supported by a valve arm shaft  44   a  extending in the front and rear direction. The valve arm  44  has one end coupled with the upper end of the push rod  43 , and the other end coupled with the intake air coupling member  24   a.    
         [0056]    As illustrated in  FIG. 3  and  FIG. 5 , the cam shaft  45  is disposed below the other end of first swing arm  38  and the second swing arm  41  in the longitudinal direction, while extending in the front and rear direction. The cam shaft  45  is coupled with the reforming crankshaft  21  via a gear and the like in an interlocking manner, and rotates when the reforming crankshaft  21  rotates. The cam shaft  45  includes a first cam  46  and a second cam  47  that are formed while being apart from each other in the axial direction (front and rear direction) by a predetermined distance. The first cam  46  and the second cam  47  have different profiles. The first cam  46  is disposed on the cam shaft  45  in such a manner as to be in contact with the first cam roller  39  of the first swing arm  38  from below. The second cam  47  is disposed on the cam shaft  45  in such a manner as to be in contact with the second cam roller  42  of the second swing arm  41  from below. 
         [0057]    The cam shaft  45  further includes a third cam  53  and a fourth cam  54 , for the reforming exhaust valve  26 , formed thereon. The third cam  53  and the fourth cam  54  have different profiles. The third swing arm  55  and the fourth swing arm  56 , for the reforming exhaust valve  26 , are coupled with an exhaust air coupling member disposed on an upper end of the reforming exhaust valve  26  via the push rod  43  and the valve arm  44 . 
         [0058]    When the first swing arm  38  swings to a side opposite to the cam shaft  45 , the reforming intake valve  24  opens via the push rod  43  fit in the rod support member  40  of the first swing arm  38 , the valve arm  44 , and the intake air coupling member  24   a  (see  FIG. 3 ). Similarly, when the third swing arm  55  for the reforming exhaust valve  26  swings to the side opposite to the cam shaft  45 , the reforming exhaust valve  26  opens via the push rod  43  fit in the rod support member of the third swing arm  55  and the valve arm  44  (see  FIG. 3 ). 
         [0059]    As illustrated in  FIG. 5 , the intake air switching unit  48  switches an operation state of the first swing arm  38  and the second swing arm  41 , and switches opening and closing timings of the reforming intake valve  24 . The intake air switching unit  48  includes a hydraulic pump  49 , an electromagnetic intake-valve switching valve  50 , a hydraulic piston  51 , and a receiving member  52 , and further includes oil paths formed by these members, the swing arm shaft  37 , and the first swing arm  38 . 
         [0060]    The electromagnetic intake-valve switching valve  50  switches a flow path of hydraulic oil supplied to the hydraulic piston  51 , upon receiving a control signal. The hydraulic oil pumped by the hydraulic pump  49  is supplied to the hydraulic piston  51  of the first swing arm  38  via the electromagnetic intake-valve switching valve  50 . 
         [0061]    The hydraulic piston  51  is a hydraulic actuator disposed on the first swing arm  38 . The hydraulic piston  51  has a semispherical bottom portion that is movable toward the cam shaft  45 . The bottom portion of the hydraulic piston  51  protrudes toward the cam shaft  45 , in accordance with the switching of the flow path of the hydraulic oil by the electromagnetic intake-valve switching valve  50 . 
         [0062]    As illustrated in  FIG. 4  and  FIG. 5 , the receiving member  52  is a plate-shaped member attached to a side surface of the second swing arm  41  on a side of the cam shaft  45 . The receiving member  52  extends to a side surface of the first swing arm  38  on a side of the cam shaft  45  from the second swing arm  41 . The receiving member  52  has an extending end portion that faces and overlaps with the hydraulic piston  51  of the first swing arm  38  in bottom view. The receiving member  52  does not come into contact with the first swing arm within a movable range of the second swing arm  41 . When the bottom portion of the hydraulic piston  51  protrudes, a bottom portion of the receiving member  52  comes into contact with the bottom portion. 
         [0063]    Similarly, as illustrated in  FIG. 5 , the exhaust air switching unit  57  switches an operation state of the third swing arm  55  and the fourth swing arm  56 , and switches opening and closing timings of the reforming exhaust valve  26 . The exhaust air switching unit  57  includes the hydraulic pump  49 , an electromagnetic exhaust-valve switching valve  58 , the hydraulic piston  51 , and the receiving member  52 , and further includes oil paths formed by these members, the swing arm shaft  37 , and the third swing arm  55 . 
         [0064]    The electromagnetic exhaust-valve switching valve  58  switches the flow path of the hydraulic oil supplied to the hydraulic piston  51 , upon receiving a control signal. The hydraulic oil pumped by the hydraulic pump  49  is supplied to the hydraulic piston  51  of the third swing arm  55  via the electromagnetic exhaust-valve switching valve  58 . 
         [0065]    As illustrated in  FIG. 2 , the reforming cylinder speed change device  59  changes reforming cylinder rotational speed Nr. The reforming cylinder speed change device  59  has an input side coupled with the outputting crankshaft  7  and an output side coupled with the reforming crankshaft  21 . The reforming cylinder speed change device  59  transmits the driving force, from the outputting crankshaft  7  rotating at target rotational speed Np of the engine  1 , to the reforming crankshaft  21  at appropriate reforming cylinder rotational speed Nr. Thus, the reforming cylinder speed change device  59  can rotate the reforming cylinders  15  at the appropriate reforming cylinder rotational speed Nr, while the outputting cylinders  2  are rotating at the target rotational speed Np. The reforming cylinder speed change device  59  may be a gear-type stepped speed change device, a belt-type or hydraulic stepless speed change device, or the like with which the rotational speed on the output side can be appropriately changed from that on the input side. 
         [0066]    As illustrated in  FIG. 2 , the ECU  60  as the control device controls the engine  1 . Specifically, the ECU  60  controls the secondary fuel injection device  6 , the main fuel injection device  20 , the first intake regulating valve  30 , the second intake regulating valve  31 , the EGR gas regulating valve  32 , the electromagnetic intake-valve switching valve  50 , the electromagnetic exhaust-valve switching valve  58 , and the like. The ECU  60  stores therein various programs and data for controlling the engine  1 . The ECU  60  may be connected to a CPU, a ROM, a RAM, an HDD, and the like via a bus, or may be a one-chip LSI or the like. 
         [0067]    As illustrated in  FIG. 6 , the ECU  60  stores therein various programs for controlling fuel injection; a main fuel injection amount map M 1  for calculating a main fuel injection amount Qm based on a target rotational speed Np and target output Wt of the engine  1 ; an intake air flow amount map M 2  for calculating an outputting intake air flow amount A 1  supplied to the combustion chamber  9  of the outputting cylinder  2 , based on the target rotational speed Np and the main fuel injection amount Qm; a mixture flow amount map M 3  for calculating a reforming intake air flow amount A 2  and an EGR gas flow amount A 3  supplied to the reaction chamber  23  of the reforming cylinder  15  based on the target rotational speed Np and the main fuel injection amount Qm; a secondary fuel injection amount map M 4  for calculating a secondary fuel injection amount Qs for ignition that is injected into the combustion chamber  9  based on the target rotational speed Np and the main fuel injection amount Qm; and the like. 
         [0068]    As illustrated in  FIG. 2 , the ECU  60  is coupled with the secondary fuel injection device  6 , and can control fuel injection of the secondary fuel injection device  6 . 
         [0069]    The ECU  60  is coupled with the main fuel injection device  20 , and can control fuel injection of the main fuel injection device  20 . 
         [0070]    The ECU  60  is coupled with the reformed fuel temperature sensor  29 , and can acquire the temperature of the reformed fuel detected by the reformed fuel temperature sensor  29 . 
         [0071]    The ECU  60  is coupled with the first intake regulating valve  30 , and can control opening/closing of the first intake regulating valve  30 . 
         [0072]    The ECU  60  is coupled with the second intake regulating valve  31 , and can control opening/closing of the second intake regulating valve  31 . 
         [0073]    The ECU  60  is coupled with the EGR gas regulating valve  32 , and can control opening/closing of the EGR gas regulating valve  32 . 
         [0074]    The ECU  60  is coupled with the outputting crank angle detection sensor  8 , and can acquire an outputting crankshaft angle θ 1  detected by the outputting crank angle detection sensor  8 . 
         [0075]    The ECU  60  is coupled with the reforming crank angle detection sensor  22 , and can acquire a reforming crankshaft angle θ 2  detected by the reforming crank angle detection sensor  22 . 
         [0076]    As illustrated in  FIG. 5 , the ECU  60  is coupled with the electromagnetic intake-valve switching valve  50 , and can control the electromagnetic intake-valve switching valve  50 . 
         [0077]    The ECU  60  is coupled with the electromagnetic exhaust-valve switching valve  58 , and can control the electromagnetic exhaust-valve switching valve  58 . 
         [0078]    The ECU  60  is coupled with the reforming cylinder speed change device  59  (see  FIG. 2 ), and can control the reforming cylinder speed change device  59 . 
         [0079]    The ECU  60  is coupled with an unillustrated cooling water temperature sensor, and can acquire the temperature of cooling water detected by the cooling water temperature sensor. 
         [0080]    An operation mode of the components of the engine  1  according to one embodiment of the present invention is described below. 
         [0081]    First of all, paths of intake air and exhaust air in the engine  1  are described. 
         [0082]    As illustrated in  FIG. 2 , the outer air sucked in by the compressor  14   b  of the supercharger  14  is discharged to the intake pipe  11  as intake air in an adiabatically compressed state. The intake air is cooled by the intake air intercooler  33 , and then is supplied to the combustion chamber  9  of the outputting cylinder  2  through the intake pipe  11 . The intake air is partially supplied to the reaction chamber  23  of the reforming cylinder  15  via the supply pipe  25  coupled with the intake pipe  11  and the reforming intake valve  24 . 
         [0083]    The exhaust air from the combustion chamber  9  of the outputting cylinder  2  rotates the turbine  14   a  of the supercharger  14  through the exhaust pipe  13 , and then is discharged outside. The exhaust air is partially supplied to the reaction chamber  23  of the reforming cylinder  15  as the EGR gas, through the EGR pipe  28  and the supply pipe  25  coupled with the EGR pipe  28 . 
         [0084]    The supply air (the intake air and the EGR gas) supplied to the reaction chamber  23  is adiabatically compressed by the reforming piston  18  in the reaction chamber  23  together with the injected fuel. The supply air and the reformed fuel are adiabatically expanded in accordance with the movement of the reforming piston  18 . Then, the supply air and the reformed fuel are discharged from the reaction chamber  23  due to the compression caused by the movement of the reforming piston  18 , and then is recirculated to the intake pipe  11 , via the reforming exhaust valve  26  and through the exhaust pipe  27 , to be supplied to the combustion chamber  9 . 
         [0085]    Next, how the ECU  60  calculates various predetermined amounts is described. As illustrated in  FIG. 6 , the ECU  60  calculates the main fuel injection amount Qm from the main fuel injection amount map M 1 , based on the target rotational speed Np and target output Wt of the engine  1  determined in accordance with an operation amount on an unillustrated operation device and the like. 
         [0086]    The ECU  60  calculates an outputting intake air flow amount A 1  for supplying to the combustion chamber  9  of the outputting cylinder  2 , from the intake air flow amount map M 2 , based on the target rotational speed Np and the main fuel injection amount Qm. 
         [0087]    The ECU  60  calculates the reforming intake air flow amount A 2  and the EGR gas flow amount A 3  supplied to the reaction chamber  23  of the reforming cylinder  15 , from the mixture flow amount map M 3  based on the target rotational speed Np and the main fuel injection amount Qm. 
         [0088]    The ECU  60  calculates the secondary fuel injection amount Qs of the igniting fuel supplied to the combustion chamber  9  of the outputting cylinder  2 , from the secondary fuel injection amount map M 4 , based on the target rotational speed Np and the main fuel injection amount Qm. 
         [0089]    The ECU  60  acquires the outputting crankshaft angle θ 1  detected by the outputting crank angle detection sensor  8  and the reforming crankshaft angle θ 2  detected by the reforming crank angle detection sensor  22 , and calculates strokes of the outputting cylinders  2  and the reforming cylinders  15 . 
         [0090]    Next, an operation mode of the variable valve device  36  with the configuration described above is described. The operation mode of the variable valve device  36  for the intake valve  24  is the same as the operation mode of the variable valve device  36  for the exhaust valve  26 . Thus, a detailed description on the operation mode of the variable valve device  36  for the exhaust valve  26  is omitted. 
         [0091]    As illustrated in  FIG. 7 , the first cam  46  (see  FIG. 5 ) has a cam profile that maintains a state where the first swing arm  38  has been swung to be closest to the cam shaft  45  during all the strokes of the reforming cylinders  15  in a single cycle. More specifically, the first cam  46  has a cam profile that maintains a state where the reforming intake valve  24  is closed during all the strokes of the reforming cylinders  15  in a single cycle. The second cam  47  (see  FIG. 5 ) has a cam profile that causes the second swing arm  41  to swing in accordance with the stroke of the outputting cylinders  2 . Specifically, the second cam  47  has a profile designed in such a manner that the reforming intake valve  24  starts to open at a timing ( 51 ) earlier than a top dead point (hereinafter, referred to as an “intake air top dead point”) T of the intake stroke of the reforming piston  18 , and that the maximum valve lift of the reforming intake valve  24  is achieved at the intake air top dead point T of the reforming piston  18 . Thus, the second cam  47  has the cam profile that causes the reforming intake valve  24  to open and close in accordance with the stroke of the outputting cylinders  2 . 
         [0092]    As illustrated in  FIG. 5 , when the ECU  60  is controlling the electromagnetic intake-valve switching valve  50  of the variable valve device  36  in such a manner that the bottom portion of the hydraulic piston  51  does not protrude toward the cam shaft  45 , the first swing arm  38  swings about the swing arm shaft  37  in accordance with the profile of the first cam  46 . The second swing arm  41  swings about the swing arm shaft  37  in accordance with the profile of the second cam  47 . 
         [0093]    When the first cam  46  and the second cam  47  further rotate in a direction indicated by a white arrow, the first swing arm  38  stays in the state of having been swung to be closest to the cam shaft  45  in accordance with the profile of the first cam  46 . The second swing arm  41  swings to a side opposite to the cam shaft  45  in accordance with the profile of the second cam  47 . In this process, the receiving member  52  of the second swing arm  41  that has been swung to the side opposite to the cam shaft  45  enters a recess formed on the side surface of the first swing arm  38  on the side of the cam shaft  45 . Thus, the first swing arm  38  stays in the state of having been swung to be closest to the cam shaft  45  without coming into contact with the receiving member  52 . In other words, the reforming intake valve  24  of the reforming piston  18  stays in a closed state. Thus, the opening and closing timings of the reforming intake valve  24  are determined in accordance with the operation of the first swing arm  38 , and not in accordance with the operation of the second swing arm  41 . 
         [0094]    The first swing arm  38  enters a state of being supported by the second swing arm  41 , when the hydraulic piston  51  comes into contact with the receiving member  52  of the second swing arm  41 . Thus, when the first cam  46  and the second cam  47  further rotate in the direction indicated by the white arrow, the first swing arm  38  swings in accordance with the second swing arm  41  to which the receiving member  52  is attached, and not in accordance with the profile of the first cam  46 . Thus, when the second swing arm  41  swings toward the cam shaft  45  in accordance with the profile of the second cam  47 , the first swing arm  38  also swings toward the cam shaft  45 . Thus, the reforming intake valve  24  of the reforming piston  18  is closed in accordance with the profile of the second cam  47 . When the first swing arm  38  swings to the side opposite to the cam shaft  45 , the reforming intake valve  24  opens in accordance with the profile of the second cam  47  (see  FIG. 2 ). All things considered, the opening and closing timings of the reforming intake valve  24  are determined in accordance with the operation of the second swing arm  41 . 
         [0095]    The ECU  60  can change the opening and closing timings of the reforming exhaust valve  26  by switching the electromagnetic exhaust-valve switching valve  58  of the variable valve device  36 , as in the operation mode of switching the opening and closing timings of the reforming intake valve  24  with the variable valve device  36 . The third cam  53  that makes the third swing arm  55  swing has a cam profile for maintaining the state where the reforming exhaust valve  26  is closed. 
         [0096]    As illustrated in  FIG. 5 , when the ECU  60  controls the electromagnetic exhaust-valve switching valve  58  of the variable valve device  36  in such a manner that the bottom portion of the hydraulic piston  51  of the third swing arm  55  does not protrude toward the cam shaft  45 , the third swing arm  55  and the fourth swing arm  56  swing independently from each other. More specifically, the third swing arm  55  stays in a state of having been swung to be closest to the cam shaft  45  in accordance with the profile of the third cam  53 . The fourth swing arm  56  swings in accordance with the profile of the fourth cam  54 . Thus, the opening and closing timings of the reforming exhaust valve  26  are determined in accordance with the operation of the third swing arm  55 , and not in accordance with the operation of the fourth swing arm  56 . 
         [0097]    When the ECU  60  controls the electromagnetic exhaust-valve switching valve  58  of the variable valve device  36  in such a manner that the bottom portion of the hydraulic piston  51  of the third swing arm  55  protrudes toward the cam shaft  45 , the third swing arm  55  enters a state of being supported by the fourth swing arm  56 , with the hydraulic piston  51  being in contact with the receiving member  52  of the fourth swing arm  56 . Thus, the third swing arm  55  swings in accordance with the swinging of the fourth swing arm  56  to which the receiving member  52  is attached, and not in accordance with the profile of the third cam  53 . Thus, the opening and closing timings of the reforming exhaust valve  26  are determined in accordance with the operation of the fourth swing arm  56 , and not in accordance with the operation of the third swing arm  55 . In the present embodiment, the compression rate and the expansion rate are controlled through cam switching by the hydraulic piston  51 . However, this should not be construed in a limiting sense. Any mechanism, for example, an overhead variable valve mechanism or the like, capable of changing the compression rate and the expansion rate may be employed. 
         [0098]    Next, how fuel is reformed with the reforming cylinders  15  will be described with reference to  FIG. 8 . 
         [0099]    As illustrated in  FIG. 8 , when the reforming cylinder  15  is in the intake stroke, the reforming piston  18  moves from the top dead point to the bottom dead point. Thus, the internal pressure of the reaction chamber  23  of the reforming cylinders  15  drops due to the volume increase caused by the movement of the reforming piston  18 . When the reforming cylinder  15  is in the intake stroke, the reforming intake valve  24  opens for supplying the supply air and the exhaust air to the reaction chamber  23 . The ECU  60  controls the opening and closing of the second intake regulating valve  31  based on the acquired reforming crankshaft angle θ 2 , in such a manner that the intake air is supplied into the reaction chamber  23  of the reforming cylinders  15  by the calculated reforming intake air flow amount A 2 , due to the drop in the internal pressure while the reforming cylinder  15  is in the intake stroke (for example, while the reforming piston  18  is close to the bottom dead point). Furthermore, the ECU  60  controls the opening and closing of the EGR gas regulating valve  32  in such a manner that the EGR gas is supplied into the reaction chamber  23  of the reforming cylinders  15  by the calculated EGR gas flow amount A 3 . Thus, the supply air at an oxygen concentration suitable for fuel reforming is supplied to the reaction chamber  23  (supply air suction in  FIG. 8 ). 
         [0100]    When the reforming cylinder  15  is in a compression stroke, the reforming piston  18  moves from the bottom dead point to the top dead point. Thus, the internal pressure of the reaction chamber  23  of the reforming cylinder  15  increases due to the volume decrease caused by the movement of the reforming piston  18 . Thus, the supply air supplied to the reaction chamber  23  is adiabatically compressed by the reforming piston  18 . When the supply air is adiabatically compressed, a high-temperature and high-pressure state is achieved in the reaction chamber  23  of the reforming cylinder  15 . 
         [0101]    When the reforming cylinder  15  is in the compression stroke, the ECU  60  controls the main fuel injection device  20  based on the acquired reforming crankshaft angle θ 2 , in such a manner that the fuel is supplied to the reaction chamber  23  of the reforming cylinder  15  by the calculated main fuel injection amount Qm. Thus, the fuel is injected into the reaction chamber  23  of the reforming cylinder  15  in the high-temperature and high-pressure state (fuel injection in  FIG. 8 ). The fuel for achieving a fuel air equivalence ratio required for reforming to the lower hydrocarbon fuel by using the supply air supplied to the reaction chamber  23  is supplied to the reaction chamber  23 . 
         [0102]    The injected fuel in the reaction chamber  23  is dispersed and is quickly mixed (premixed) with the supply air in the reaction chamber  23  in the high-temperature and higher pressure state to be evaporated. The reforming reaction of the fuel premixed with the supply air starts when the reforming piston  18  reaches a portion close to the top dead point to achieve the highest-temperature and highest-pressure state in the reaction chamber  23 . 
         [0103]    When the reforming cylinder  15  is in an expansion stroke, the reforming piston  18  moves from the top dead point to the bottom dead point. Thus, the internal pressure of the reaction chamber  23  of the reforming cylinder  15  drops due to the volume increase caused by the movement of the reforming piston  18 . The reformed fuel is adiabatically expanded due to the volume increase in the reaction chamber  23 . Thus, the reformed fuel is cooled to be in a pressure drop state, whereby the reforming reaction stops (reforming stop in  FIG. 8 ). 
         [0104]    When the reforming cylinder  15  is in an exhaust stroke, the reforming piston  18  moves from the bottom dead point to the top dead point. Thus, the internal pressure of the reaction chamber  23  of the reforming cylinder  15  rises due to the volume decrease caused by the movement of the reforming piston  18 . When the reforming cylinder  15  is in the exhaust stroke, the reforming exhaust valve  26  opens for discharging the reformed fuel from the reaction chamber  23 . Thus, the reformed fuel is discharged from the reaction chamber  23  via the reforming exhaust valve  26 , to be recirculated to the intake pipe  11  through the exhaust pipe  27  (fuel discharge in  FIG. 8 ). 
         [0105]    The reformed fuel is supplied as high temperature fuel gas to the exhaust pipe  27 , due to residual heat, in the heat of the supply air, not used for endothermic decomposition reaction in the reforming. The high temperature reformed fuel supplied to the exhaust pipe  27  is cooled by the reformed fuel intercooler  34  of the exhaust pipe  27 . Thus, self-preignition in the outputting cylinders  2  is prevented. The reformed fuel cooled by the reformed fuel intercooler  34  is supplied to the intake pipe  11  via the mixer  27   a.    
         [0106]    Next, control on a mass balance between the fuel supplied to the outputting cylinders  2  and the fuel reformed by the reforming cylinders  15  is described. 
         [0107]    An amount Gf of reformed fuel, which is a total amount of reformed fuel supplied to the outputting cylinders  2  in a single cycle, is calculated based on the following Formula 1, from an output side fuel air equivalence ratio φp representing the fuel air equivalence ratio in the outputting cylinder  2 , an output side intake air amount Gair, the number of outputting cylinders Kp, the target rotational speed Np of the outputting cylinder corresponding to the target rotational speed of the engine  1 , and an output side theoretical mixture ratio αp. 
         [0000]    
       
         
           
             
               
                 
                   Gf 
                   = 
                   
                     
                       φ 
                        
                       
                           
                       
                        
                       
                         p 
                         · 
                         Gair 
                         · 
                         Kp 
                         · 
                         Np 
                       
                     
                     
                       
                         2 
                         · 
                         α 
                       
                        
                       
                           
                       
                        
                       p 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
         [0108]    An amount gf of supplied fuel to one reforming cylinder  15  is calculated based on the following Formula 2, from a reformation side fuel air equivalence ratio φr representing the fuel air equivalence ratio in the reforming cylinder  15 , an EGR rate ψegr, an amount gi of reformation side suctioned gas for each cylinder, and a reformation side theoretical mixture ratio αr. 
         [0000]    
       
         
           
             
               
                 
                   gf 
                   = 
                   
                     
                       φ 
                        
                       
                           
                       
                        
                       
                         r 
                         · 
                         
                           ( 
                           
                             1 
                             - 
                             
                               ψ 
                                
                               
                                   
                               
                                
                               egr 
                             
                           
                           ) 
                         
                         · 
                         gi 
                       
                     
                     
                       
                         ( 
                         
                           φ 
                            
                           
                               
                           
                            
                           
                             r 
                             · 
                             ψ 
                           
                            
                           
                               
                           
                            
                           egr 
                         
                         ) 
                       
                       + 
                       
                         α 
                          
                         
                             
                         
                          
                         r 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
         [0109]    An amount Gf of reformed fuel is also calculated based on the following Formula 3, from the amount gf of supplied fuel to the reforming cylinders  15 , the number of reforming cylinders Kr supplied with the fuel and the supply air, and the reforming cylinder rotational speed Nr. 
         [0000]    
       
         
           
             
               
                 
                   Gf 
                   = 
                   
                     gf 
                     · 
                     Kr 
                     · 
                     
                       Nr 
                       2 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
         [0110]    The following Formula 4, obtained by applying Formulae 1 and 2 to Formula 3, represents the relationship between: the product of the number of reforming cylinders Kr supplied with the fuel and the supply air and the reforming cylinder rotational speed Nr; and the product of the number of outputting cylinders Kp and the outputting cylinder target rotational speed Np. Thus, the product of the rotational speed and the number of cylinders in the outputting cylinders  2  and in the reforming cylinders  15  represents the mass balance between the fuel supplied to the outputting cylinders  2  and the fuel reformed by the reforming cylinders  15 . 
         [0000]    
       
         
           
             
               
                 
                   
                     Kr 
                     · 
                     Nr 
                   
                   = 
                   
                     
                       
                         φ 
                          
                         
                             
                         
                          
                         
                           p 
                           · 
                           Gair 
                           · 
                           
                             ( 
                             
                               
                                 φ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   r 
                                   · 
                                   ψ 
                                 
                                  
                                 
                                     
                                 
                                  
                                 egr 
                               
                               + 
                               
                                 α 
                                  
                                 
                                     
                                 
                                  
                                 r 
                               
                             
                             ) 
                           
                         
                       
                       
                         φ 
                          
                         
                             
                         
                          
                         
                           r 
                           · 
                           gi 
                           · 
                           α 
                         
                          
                         
                             
                         
                          
                         
                           p 
                            
                           
                             ( 
                             
                               1 
                               - 
                               
                                 ψ 
                                  
                                 
                                     
                                 
                                  
                                 egr 
                               
                             
                             ) 
                           
                         
                       
                     
                     · 
                     Kp 
                     · 
                     Np 
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
         [0111]    The ECU  60  calculates the output side fuel air equivalence ratio φp, the output side intake air amount Gair, and the output side theoretical mixture ratio αp, from: the main fuel injection amount Qm calculated from the main fuel injection amount map M 1  based on the target rotational speed Np and the target output Wt of the engine  1  determined from an operation amount on an unillustrated operation tool or the like; the number of outputting cylinders Kp; and the opening of the first intake regulating valve  30  and the second intake regulating valve  31 . Similarly, the ECU  60  calculates: the reformation side fuel air equivalence ratio φr; the EGR rate ψegr; and the amount gi of reformation side suctioned gas for each cylinder and the reformation side theoretical mixture ratio αr. 
         [0112]    The ECU  60  sets the number of reforming cylinders Kr supplied with the fuel and the supply air to be the minimum number, and calculates the reforming cylinder rotational speed Nr based on Formula 4, from the output side fuel air equivalence ratio φp, the output side intake air amount Gair, the output side theoretical mixture ratio αp, the reformation side fuel air equivalence ratio φr, the EGR rate ψegr, the amount gi of reformation side suctioned gas, and the reformation side theoretical mixture ratio αr calculated as described above, and controls the reforming cylinder speed change device  59 . 
         [0113]    Upon determining that Formula 4 is not satisfied by controlling the reforming cylinder speed change device  59  in the state where the number of reforming cylinders Kr supplied with the fuel and the supply air is set to be the minimum number, the ECU  60  controls the opening of the first intake regulating valve  30 , the second intake regulating valve  31 , and the EGR gas regulating valve  32 , to increase the number of reforming cylinders Kr supplied with the fuel and the supply air, and controls the main fuel injection device  20 , the electromagnetic intake-valve switching valve  50 , and the electromagnetic exhaust-valve switching valve  58  corresponding to the number of reforming cylinders Kr to which the fuel and the supply air are started to be supplied. Then, the ECU  60  calculates the reforming cylinder rotational speed Nr based on Formula 4, from the newly set number of reforming cylinders Kr, and controls the reforming cylinder speed change device  59 . 
         [0114]    Specifically, the ECU  60  controls the main fuel injection device  20  in such a manner that one reforming cylinder  15  not supplied with fuel is supplied with fuel. Furthermore, the ECU  60  controls the electromagnetic intake-valve switching valve  50  and the electromagnetic exhaust-valve switching valve  58  in such a manner that the first swing arm  38 , corresponding to the reforming cylinder  15  not supplied with the supply air, swings in accordance with the profile of the second cam  47 , and that the third swing arm  55  swings in accordance with the profile of the fourth cam  54 . The ECU  60  newly sets the number of reforming cylinders Kr supplied with the fuel and the supply air, and calculates the reforming cylinder rotational speed Nr based on Formula 4, from the output side fuel air equivalence ratio φp, the output side intake air amount Gair, the output side theoretical mixture ratio αp, the reformation side fuel air equivalence ratio φr, the EGR rate ψegr, the amount gi of reformation side suctioned gas, and the reformation side theoretical mixture ratio αr calculated as described above, to control the reforming cylinder speed change device  59 . 
         [0115]    As described above, the ECU  60  of the engine  1  sets the number of reforming cylinders Kr supplied with the fuel and the supply air to a predetermined number, and controls the reforming cylinder speed change device  59  in such a manner that Formula 4 is satisfied. Upon determining that Formula 4 is not satisfied by controlling the reforming cylinder speed change device  59 , the ECU  60  controls the opening of the first intake regulating valve  30 , the second intake regulating valve  31 , and the EGR gas regulating valve  32 , and the main fuel injection device  20 , the electromagnetic intake-valve switching valve  50 , and the electromagnetic exhaust-valve switching valve  58  corresponding to the number of reforming cylinders Kr to which the supplying of the fuel and the supply air starts or stops, in such a manner that the number of reforming cylinders Kr supplied with the fuel and the supply air increases or decreases. Next, the ECU  60  calculates the reforming cylinder rotational speed Nr based on Formula 4, from new number of reforming cylinders Kr and controls the reforming cylinder speed change device  59 . As a result, in the engine  1 , the amount of reformed fuel supplied to the outputting cylinders  2  is changed, while maintaining the amount of reformed fuel discharged from each of the reforming cylinders  15  and the fuel air equivalence ratio of the reformed fuel. In other words, the mass balance between the fuel reformed by the reforming cylinders  15  and the fuel supplied to the outputting cylinders  2  remains unchanged even when the output of the outputting cylinders  2  changes. Thus, the reformed fuel can be supplied in accordance with the output of the outputting cylinders  2 . 
         [0116]    In the present embodiment, the engine  1  changes the reforming cylinder rotational speed Nr of the reforming cylinders  15  and the number of reforming cylinders Kr to control the amount of reformed fuel. However, this should not be construed in a limiting sense. For example, the engine  1  may be configured to control the reforming cylinder speed change device  59  for changing the reforming cylinder rotational speed Nr in such a manner that the amount of reformed fuel supplied to the outputting cylinders  2  is changed, while maintaining the amount of reformed fuel discharged from each of the reforming cylinders  15  and the fuel air equivalence ratio achieved by the reformed fuel. The engine  1  may also be configured to control the variable valve device  36  for controlling the opening and closing of the reforming intake valve  24  and the reforming exhaust valve  26  and for changing the number of reforming cylinders Kr in such a manner that the amount of reformed fuel supplied to the outputting cylinders  2  is changed, while maintaining the amount of reformed fuel discharged from each of the reforming cylinders  15  and the fuel air equivalence ratio of the reformed fuel. 
         [0117]    Next, an operation mode of a variable valve device  36   a  according to another embodiment is described with reference to  FIG. 9  to  FIG. 13 . 
         [0118]    As illustrated in  FIG. 9 , when the ECU  60  controls the electromagnetic intake-valve switching valve  50  of the variable valve device  36   a  in such a manner that the bottom portion of the hydraulic piston  51  does not protrude toward the cam shaft  45 , the first cam roller  39  of the first swing arm  38  rotates while being in contact with a first cam  46   a . More specifically, the first swing arm  38  swings about the swing arm shaft  37  in accordance with the profile of the first cam  46   a . The second cam roller  42  of the second swing arm  41  rotates while being in contact with a second cam  47   a . More specifically, the second swing arm  41  rotates about the swing arm shaft  37  in accordance with the profile of a second cam  47   a . The first swing arm  38  and the second swing arm  41  swing independently from each other. 
         [0119]    When the first cam  46   a  and the second cam  47   a  rotate in a direction indicated by a white arrow, the first swing arm  38  and the second swing arm  41  simultaneously swing toward the side opposite to the cam shaft  45 , in accordance with the profiles of the respective cams. When the first swing arm  38  swings toward the side opposite to the cam shaft  45 , the reforming intake valve  24  opens via the push rod  43  fit in the rod support member  40  of the first swing arm  38 , the valve arm  44 , and an intake air coupling member  24   a  (see  FIG. 3 ). 
         [0120]    When the first cam  46   a  and the second cam  47   a  further rotate in the direction indicated by the white arrow, the first swing arm  38  swings toward the cam shaft  45  in accordance with the profile of the first cam  46   a  before the second swing arm  41  does. In this process, the first swing arm  38  has a side surface facing the cam shaft  45  provided with a recess, and thus does not come into contact with the receiving member  52 . Thus, the receiving member  52  does not hinder the swinging toward the cam shaft  45 . After the first swing arm  38  has been swung toward the cam shaft  45 , the second swing arm  41  swings toward the cam shaft  45  in accordance with the profile of the second cam  47   a . When the first swing arm  38  swings downward, the reforming intake valve  24  closes (see  FIG. 3 ). In this manner, the first swing arm  38  and the second swing arm  41  operate independently from each other, and thus the opening and closing timings of the reforming intake valve  24  are determined in accordance with the operation of the first swing arm  38 , and not in accordance with the operation of the second swing arm  41 . 
         [0121]    As illustrated in  FIG. 11 , the profile of the first cam  46   a  is designed in such a manner that the reforming intake valve  24  starts to open at a timing (S 1 ) before the top dead point (hereinafter, referred to as an “intake air top dead point”) T is reached by the reforming piston  18  in an intake stroke, and that the maximum valve lift of the reforming intake valve  24  is achieved when the intake air top dead point T is reached by the reforming piston  18 . The profile of the first cam  46   a  is designed in such a manner that the reforming intake valve  24  starts to close at a timing before the reforming piston  18  reaches the bottom dead point (hereinafter, referred to as an “intake air bottom dead point”) B in the intake stroke, and is completely closed at a timing (S 2 ) before the reforming piston  18  reaches the intake air bottom dead point B. Thus, the first cam  46   a  is designed in such a manner that the reforming intake valve  24  opens and closes at timings earlier than the opening and closing timings of the reforming intake valve  24  determined by the second cam  47   a  described later. 
         [0122]    As illustrated in  FIG. 10 , when the ECU  60  controls the electromagnetic intake-valve switching valve  50  of the variable valve device  36   a  in such a manner that the bottom portion of the hydraulic piston  51  protrudes toward the cam shaft  45 , the bottom portion is pressed toward the cam shaft  45  by the hydraulic oil supplied to the hydraulic piston  51 . The hydraulic piston  51  pressed by the hydraulic oil slides toward the cam shaft  45  to protrude from the side surface of the first swing arm  38  facing the cam shaft  45 . The bottom portion of the hydraulic piston  51  comes into contact with the receiving member  52  attached to the second swing arm  41 . 
         [0123]    The first swing arm  38  enters a state of being supported by the second swing arm  41  when the hydraulic piston  51  comes into contact with the receiving member  52  of the second swing arm  41 . Thus, the first swing arm  38  swings in accordance with the second swing arm  41  to which the receiving member  52  is attached, and not in accordance with the profile of the first cam  46   a . More specifically, when the second swing arm  41  swings toward the cam shaft  45  in accordance with the profile of the second cam  47   a , the first swing arm  38  also swings toward the cam shaft  45 . When the first swing arm  38  swings toward the cam shaft  45 , the reforming intake valve  24  is closed (see  FIG. 3 ). All things considered, when the reforming intake valve  24  is closed, the first swing arm  38  integrally operates with the second swing arm  41 , and the opening and closing timings of the reforming intake valve  24  are determined in accordance with the operation of the second swing arm  41 . 
         [0124]    As illustrated in  FIG. 12 , the profile of the second cam  47   a  is designed in such a manner that the reforming intake valve  24  starts to open at a timing (S 1 ) before the reforming piston  18  reaches the intake air top dead point T, and the maximum valve lift of the reforming intake valve  24  is achieved when the reforming piston  18  reaches the intake air top dead point T. The profile is also designed in such a manner that the reforming intake valve  24  starts to close at a timing close to when the reforming piston  18  reaches the intake air bottom dead point B, and is completely closed at a timing (S 3 ) thereafter. More specifically, the second cam  47   a  is designed in such a manner that the reforming intake valve  24  opens and closes at timings later than the opening and closing timings of the reforming intake valve  24  defined by the first cam  46   a  as described above. In the present embodiment, the reforming intake valve  24  starts to close at a timing close to when the reforming piston  18  reaches the intake air bottom dead point B. However, the present invention is not limited to this. More specifically, the reforming intake valve  24  may start to close when the reforming piston  18  reaches the intake air bottom dead point B. 
         [0125]    The ECU  60  can change the opening and closing timings of the reforming exhaust valve  26  by switching the electromagnetic exhaust-valve switching valve  58  of the variable valve device  36   a , as in the operation mode in which the opening and closing timings of the reforming intake valve  24  are switched by the variable valve device  36   a . The third cam  53   a  that swings the third swing arm  55  starts to open and close the reforming exhaust valve  26  at a timing earlier than the opening and closing timings of the reforming exhaust valve  26  defined by the fourth cam  54   a  that swings the fourth swing arm  56 . 
         [0126]    As illustrated in  FIG. 9 , when the ECU  60  controls the electromagnetic exhaust-valve switching valve  58  of the variable valve device  36   a  in such a manner that the bottom portion of the hydraulic piston  51  of the third swing arm  55  does not protrude toward the cam shaft  45 , the third swing arm  55  and the fourth swing arm  56  swing independently from each other. More specifically, the third swing arm  55  operates in accordance with the profile of the third cam  53   a  and the fourth swing arm  56  operates in accordance with the profile of the fourth cam  54   a . Thus, the opening and closing timings of the reforming exhaust valve  26  are determined in accordance with the operation of the third swing arm  55 , and not in accordance with the operation of the fourth swing arm  56 . 
         [0127]    As illustrated in  FIG. 10 , when the ECU  60  controls the electromagnetic exhaust-valve switching valve  58  of the variable valve device  36   a  in such a manner that the bottom portion of the hydraulic piston  51  of the third swing arm  55  protrudes toward the cam shaft  45 , the third swing arm  55  enters a state of being supported by the fourth swing arm  56  with the hydraulic piston  51  coming into contact with the receiving member  52  of the fourth swing arm  56 . Thus, the third swing arm  55  swings in accordance with the swinging of the fourth swing arm  56  to which the receiving member  52  is attached, and not in accordance with the profile of the third cam  53   a . Thus, the opening and closing timings of the reforming exhaust valve  26  are determined in accordance with the operation of the fourth swing arm  56 , and not in accordance with the operation of the third swing arm  55 . In the present embodiment, the compression rate and the expansion rate are controlled by switching the cams with the hydraulic piston  51 . However, this should not be construed in a limiting sense. Any mechanism, for example, an overhead cam variable valve mechanism or the like, capable of changing the compression rate and the expansion rate may be employed. 
         [0128]    Next, how the compression rate and the expansion rate in the reforming cylinders  15  are controlled is described. 
         [0129]    Upon determining that reformed fuel temperature Tf is higher than an upper limit value Tu based on a signal acquired from the reformed fuel temperature sensor  29 , the ECU  60  controls the electromagnetic intake-valve switching valve  50  of the intake air switching unit  48  in such a manner that the first swing arm  38  that opens and closes the reforming intake valve  24  swings in accordance with the profile of the first cam  46   a  (see  FIG. 11 ). More specifically, the ECU  60  controls the electromagnetic intake-valve switching valve  50  in such a manner that the supply air supplied to the reforming cylinders  15  is reduced. Thus, the substantial compression rate of the reforming cylinders  15  is reduced, whereby the temperature of the reformed fuel adiabatically compressed by the reforming cylinders  15  is prevented from rising. 
         [0130]    Upon determining that the reformed fuel temperature Tf is higher than the upper limit value Tu based on a signal acquired from the reformed fuel temperature sensor  29 , the ECU  60  controls the electromagnetic exhaust-valve switching valve  58  of the exhaust air switching unit  57  in such a manner that the third swing arm  55  that opens and closes the reforming exhaust valve  26  swings in accordance with the profile of the fourth cam  54   a  (see  FIG. 12 ). More specifically, the ECU  60  controls the electromagnetic exhaust-valve switching valve  58  in such a manner that the reformed fuel is discharged at a timing close to when the reforming cylinder  15  reaches the bottom dead point. Thus, the substantial expansion rate of the reforming cylinders  15  increases, and the temperature drop of the reformed fuel adiabatically expanded by the reforming cylinders  15  is facilitated. 
         [0131]    Upon determining that the reformed fuel temperature Tf is higher than the upper limit value Tu based on a signal acquired from the reformed fuel temperature sensor  29 , the ECU  60  may control the electromagnetic intake-valve switching valve  50  of the intake air switching unit  48  in such a manner that the first swing arm  38  that opens and closes the reforming intake valve  24  swings in accordance with the profile of the first cam  46   a  (see  FIG. 11 ), and may control the electromagnetic exhaust-valve switching valve  58  of the exhaust air switching unit  57  in such a manner that the third swing arm  55  that opens and closes the reforming exhaust valve  26  swings in accordance with the profile of the fourth cam  54   a  (see  FIG. 12 ). Thus, in the reforming cylinders  15 , the substantial compression rate decreases, and the substantial expansion rate increases. 
         [0132]    Upon determining that cooling water temperature Tw of the engine  1  acquired from an unillustrated cooling water sensor is equal to or lower than a lower limit value T 1  or that it is within a predetermined time period from the start time of the engine, the ECU  60  controls the electromagnetic intake-valve switching valve  50  of the intake air switching unit  48  in such a manner that the first swing arm  38  that opens and closes the reforming intake valve  24  swings in accordance with the profile of the second cam  47   a  regardless of the reformed fuel temperature Tf acquired from the reformed fuel temperature sensor  29  (see  FIG. 12 ). More specifically, the ECU  60  controls the electromagnetic intake-valve switching valve  50  in such a manner that the supply air supplied to the reforming cylinders  15  increases. Thus, in the reforming cylinders  15 , the substantial compression rate increases, pressure and temperature after the adiabatical compression by the reforming cylinders  15  rise, and the fuel reforming reaction is facilitated. 
         [0133]    As described above, in the engine  1  including the outputting cylinders  2  and the reforming cylinders  15  that reform fuel through back and forth movement of the reforming piston  18 , the opening and closing timings of at least one of the reforming intake valve  24  and the reforming exhaust valve  26  are changed by using the variable valve device  36   a  based on a signal acquired from the reformed fuel temperature sensor  29 . When the reformed fuel temperature Tf is higher than the upper limit value Tu, the temperature of the reformed fuel is maintained within a defined range in the engine  1 , with the substantial expansion rate of the reforming cylinders  15  increasing and the substantial compression rate of the reforming cylinders  15  decreasing. Thus, the reformed fuel can be supplied in a stable state regardless of the operation condition, whereby the output of the engine can be prevented from degrading. 
         [0134]    In the engine  1 , when the result of the determination indicates that the cooling water temperature Tw acquired from the cooling water sensor is equal to or lower than the predetermined value or that it is within a predetermined time period from the start time of the engine  1 , the opening and closing timings of the reforming intake valve  24  are changed by using the variable valve device  36   a  regardless of the reformed fuel temperature Tf. Thus, in the engine  1 , the substantial compression rate of the reforming cylinders  15  increases, so that the fuel reforming can be ensured even when the engine  1  or the outer air is at a low temperature. Thus, the reformed fuel is supplied in the stable state regardless of the operation condition, whereby the degradation of the engine output can be prevented. 
         [0135]    Reforming cylinders  15   a  in an engine according to still another embodiment of the present invention are described with reference to  FIG. 14  to  FIG. 16 . 
         [0136]    The reforming cylinders  15   a , serving as the fuel reforming device, reform a higher hydrocarbon fuel such as light oil into a lower hydrocarbon fuel (for example, methane) to prevent preignition. The reforming cylinders  15   a  adiabatically compress a result of injecting fuel to a mixture (hereinafter simply referred to as “supply air”) of intake air and exhaust air (EGR gas) to reform the fuel. The reforming cylinders  15   a  each include the reforming cylinder head  16 , the reforming cylinder  17 , the reforming piston  18 , the reforming connecting rod  19 , the main fuel injection device  20 , and an additive injection device  61 . 
         [0137]    The additive injection device  61  supplies water as an additive into the reaction chamber  23 . The additive injection device  61  is provided to the reforming cylinder head  16 . The additive injection device  61  can supply an appropriate amount of water as the additive into the reaction chamber  23  at an appropriate timing. The additive injection device  61  is coupled with an additive storage tank  62  via an unillustrated additive injection pump. The additive storage tank  62  is provided with a remaining additive sensor  62   a . The additive injection device  61  includes a nozzle such as a pintle nozzle, a swirl injector, and an air-assist injector. In the present embodiment, the additive injection device  61  is directed toward the inside of the reaction chamber  23  from the reforming cylinder head  16 . However, this should not be construed in a limiting sense. Alternatively, the additive injection device  61  may be provided to inject water into the supply pipe  25 . The intake pipe  11  is provided with an intake air detection sensor  11   a  that is more on the upstream side than the coupled position of the supply pipe  25 . The intake air detection sensor  11   a  detects an intake air flow amount A 0  as a total intake air flow amount from the outer air and an absolute humidity H of the intake air. 
         [0138]    The ECU  60  as the control device controls the engine  1 . Specifically, the ECU  60  controls the secondary fuel injection device  6 , the main fuel injection device  20 , the additive injection device  61 , the first intake regulating valve  30 , the second intake regulating valve  31 , the EGR gas regulating valve  32 , and the like. The ECU  60  stores therein various programs and data for controlling the engine  1 . The ECU  60  may be connected to a CPU, a ROM, a RAM, an HDD, and the like via a bus, or may be a one-chip LSI or the like. 
         [0139]    As illustrated in  FIG. 6 , the ECU  60  stores therein: various programs for controlling fuel injection; the main fuel injection amount Qm map M 1  for calculating the main fuel injection amount Qm based on the amount of an additive (water in the present embodiment) with which the thermal decomposition reaction per unit fuel of the fuel used can be most facilitated and based on the target rotational speed Np and the target output Wt of the engine  1 ; the intake air flow amount map M 2  for calculating the outputting intake air flow amount A 1  for supplying to the combustion chamber  9  of the outputting cylinder  2 , based on the target rotational speed Np and the main fuel injection amount Qm; the mixture flow amount map M 3  for calculating the reforming intake air flow amount A 2  and the EGR gas flow amount A 3  for supplying to the reaction chamber  23  of the reforming cylinder  15   a  based on the target rotational speed Np and the main fuel injection amount Qm; the secondary fuel injection amount map M 4  for calculating the secondary fuel injection amount Qs for ignition to be injected into the combustion chamber  9  based on the target rotational speed Np and the main fuel injection amount Qm; and the like. 
         [0140]    The ECU  60  is coupled with the intake air detection sensor  11   a  and can acquire the intake air flow amount A 0  and the absolute humidity H of the intake air detected by the intake air detection sensor  11   a.    
         [0141]    The ECU  60  is coupled with the remaining additive sensor  62   a  and can acquire a signal indicating a remaining amount of the additive in the additive storage tank  62  detected by the remaining additive sensor  62   a.    
         [0142]    An operation mode of the components of the engine  1  according to one embodiment of the present invention is described below with reference to  FIG. 14  to  FIG. 16 . 
         [0143]    First of all, paths of intake air and exhaust air in the engine  1  are described. 
         [0144]    As illustrated in  FIG. 14 , the outer air sucked in by the compressor  14   b  of the supercharger  14  is discharged to the intake pipe  11  as intake air in an adiabatically compressed state. The intake air is cooled by the intake air intercooler  33 , and then is supplied to the combustion chamber  9  of the outputting cylinder  2  through the intake pipe  11 . The intake air is partially supplied to the reaction chamber  23  of the reforming cylinder  15   a  via the supply pipe  25  coupled with the intake pipe  11  and the reforming intake valve  24 . 
         [0145]    The exhaust air from the combustion chamber  9  of the outputting cylinder  2  rotates the turbine  14   a  of the supercharger  14  through the exhaust pipe  13 , and then is discharged outside. The exhaust air is partially supplied to the reaction chamber  23  of the reforming cylinder  15   a  as the EGR gas, through the EGR pipe  28  and the supply pipe  25  coupled with the EGR pipe  28 . 
         [0146]    The supply air (the intake air and the EGR gas) supplied to the reaction chamber  23  is adiabatically compressed by the reforming piston  18  in the reaction chamber  23  together with the injected fuel and water as the additive. The supply air and the reformed fuel are adiabatically expanded due to the movement of the reforming piston  18 . Then, the supply air and the reformed fuel are discharged from the reaction chamber  23  as a result of the compression due to the movement of the reforming piston  18 , and then are recirculated to the intake pipe  11 , via the reforming exhaust valve  26  and through the exhaust pipe  27 , to be supplied to the combustion chamber  9 . 
         [0147]    As illustrated in  FIG. 15 , the ECU  60  calculates an amount Wsu of water with which the reforming reaction of the fuel supplied to the reforming cylinders  15  by the main fuel injection amount Qm is most facilitated, based on the main fuel injection amount Qm and an amount Wb of the additive (water in the present embodiment) with which the reforming reaction per unit fuel used can be most facilitated. 
         [0148]    The ECU  60  calculates an amount of water Wex in the EGR gas supplied to the reaction chamber  23  of the reforming cylinder  15 , from an exhaust air recirculation rate ψ based on the main fuel injection amount Qm, the reforming intake air flow amount A 2 , and the EGR gas flow amount A 3 . 
         [0149]    The ECU  60  calculates the amount of water Win in the intake air supplied to the reaction chamber  23  of the reforming cylinder  15   a  from the reforming intake air flow amount A 2  and the absolute humidity H detected by the intake air detection sensor  11   a.    
         [0150]    The ECU  60  calculates an amount of water Wad supplied to the reaction chamber  23  via the additive injection device  61 , from the amount of water Wsu with which the reforming reaction of the fuel supplied by the main fuel injection amount Qm can be most facilitated, the amount of water Wex in the EGR gas, and the amount of water Win supplied in the intake air supplied to the reaction chamber  23 , based on the following Formula 1. 
         [0000]        Wad=Wsu−Win−Wex   [Formula 5]
 
         [0151]    Next, how the fuel is reformed in the reforming cylinders  15  is described with reference to  FIG. 16 . 
         [0152]    As illustrated in  FIG. 16 , when the reforming cylinder  15   a  is in the intake stroke, the reforming piston  18  in the reforming cylinders  15   a  moves from the top dead point to the bottom dead point. Thus, the internal pressure of the reaction chamber  23  of the reforming cylinder  15   a  drops due to the volume increase as a result of the movement of the reforming piston  18 . When the reforming cylinder  15  is in the intake stroke, the valve opens for supplying the supply air and the exhaust air to the reaction chamber  23 . The ECU  60  controls the opening and closing of the second intake regulating valve  31  based on the acquired reforming crankshaft angle θ 2 , in such a manner that the intake air is supplied into the reaction chamber  23  of the reforming cylinders  15   a  by the calculated reforming intake air flow amount A 2 , due to the decreased internal pressure while the reforming cylinder  15  is in the intake stroke (for example, while the reforming piston  18  is close to the bottom dead point). Furthermore, the ECU  60  controls the opening and closing of the EGR gas regulating valve  32  in such a manner that the EGR gas is supplied into the reaction chamber  23  of the reforming cylinders  15   a  by the calculated EGR gas flow amount A 3 . Thus, the supply air at an oxygen concentration suitable for fuel reforming is supplied to the reaction chamber  23  (supply air suction in  FIG. 16 ). 
         [0153]    When the reforming cylinder  15   a  is in the compression stroke, the reforming piston  18  moves from the bottom dead point to the top dead point. Thus, the internal pressure of the reaction chamber  23  of the reforming cylinders  15   a  rises due to the volume decrease as a result of the movement of the reforming piston  18 . Thus, the supply air supplied to the reaction chamber  23  is adiabatically compressed by the reforming piston  18 . With the adiabatical compression of the supply air by the reforming cylinders  15   a , the high-temperature and high-pressure state is achieved in the reaction chamber  23 . 
         [0154]    When the reforming cylinder  15   a  is in the compression stroke, the ECU  60  controls the main fuel injection device  20  based on the acquired reforming crankshaft angle θ 2 , in such a manner that the fuel is supplied to the reaction chamber  23  of the reforming cylinder  15  by the calculated main fuel injection amount Qm. Thus, the fuel is injected into the reaction chamber  23  of the reforming cylinder  15   a  in the high-temperature and high-pressure state (fuel supply in  FIG. 16 ). The fuel, achieving a fuel air equivalence ratio required for reforming to the lower hydrocarbon fuel by using the supply air supplied to the reaction chamber  23 , is supplied to the reaction chamber  23 . 
         [0155]    The ECU  60  controls the additive injection device  61  based on the acquired reforming crankshaft angle θ 2 , in such a manner that water as the additive is supplied to the reaction chamber  23  of the reforming cylinder  15   a , by the amount Wad calculated based on Formula 1 described above. 
         [0156]    The injected fuel in the reaction chamber  23  is dispersed and is quickly mixed (premixed) with the supply air in the reaction chamber  23  in the high-temperature and higher pressure state to be evaporated. The reforming reaction of the fuel premixed with the supply air starts when the reforming piston  18  reaches a point close to the top dead point to achieve the highest-temperature and highest-pressure state in the reaction chamber  23  (a gray area in  FIG. 16 ). The reforming reaction of the higher hydrocarbon fuel is facilitated by water added as the additive. The higher hydrocarbon reacts with water in the high-temperature and high-pressure state, and thus is reformed into carbon oxide and hydrogen as in the following Chemical Formula 1, or is reformed into carbon dioxide and hydrogen as in the following Chemical Formula 2. Hydrogen generated by the reforming reaction separates carbon from the higher hydrocarbon to contribute to the reforming to obtain the lower hydrocarbon. 
         [0000]      C n H m   +n H 2 O           n CO+( n+m/ 2)H 2   [Chemical Formula 1]
 
         [0000]      C n H m +2 n H 2 O           n CO 2 +(2 n+m/ 2)H 2   [Chemical Formula 2]
 
         [0157]    When the reforming cylinder  15   a  is in an expansion stroke, the reforming piston  18  moves from the top dead point to the bottom dead point. Thus, the internal pressure of the reaction chamber  23  of the reforming cylinder  15   a  drops due to the volume increase caused by the movement of the reforming piston  18 . The reformed fuel is adiabatically expanded due to the volume increase in the reaction chamber  23 . Thus, the reformed fuel is cooled to be in a pressure drop state, whereby the reforming reaction stops (reforming stop in  FIG. 16 ). 
         [0158]    When the reforming cylinder  15   a  is in the exhaust stroke, the reforming piston  18  moves from the bottom dead point to the top dead point. Thus, the internal pressure of the reaction chamber  23  of the reforming cylinder  15   a  rises due to the volume decrease caused by the movement of the reforming piston  18 . When the reforming cylinder  15   a  is in the exhaust stroke, the reforming exhaust valve  26  opens for discharging the reformed fuel from the reaction chamber  23 . Thus, the reformed fuel is discharged from the reaction chamber  23  via the reforming exhaust valve  26 , to be recirculated to the intake pipe  11  through the exhaust pipe  27  (fuel discharge in  FIG. 16 ). 
         [0159]    The reformed fuel is supplied as high temperature fuel gas to the exhaust pipe  27 , due to residual heat, in the heat of the supply air, not used for endothermic decomposition reaction in the reforming. The high temperature reformed fuel supplied to the exhaust pipe  27  is cooled by the reformed fuel intercooler  34  of the exhaust pipe  27 . Thus, self-preignition in the outputting cylinders  2  is prevented. The reformed fuel cooled by the reformed fuel intercooler  34  is supplied to the intake pipe  11  via the mixer  27   a.    
         [0160]    Upon determining that the remaining amount of water as the additive in the additive storage tank  62  is smaller than a reference value based on a signal acquired from the remaining additive sensor  62   a , the ECU  60  controls one or a plurality of the secondary fuel injection device  6 , the main fuel injection device  20 , the second intake regulating valve  31 , and the EGR gas regulating valve  32  so that at least one of the secondary fuel injection amount Qs, the main fuel injection amount Qm, the reforming intake air flow amount A 2 , and the exhaust air recirculation rate ψ is increased or reduced. For example, when the absolute humidity H is high, the ECU  60  performs control in such a manner that the opening of the second intake regulating valve  31  increases and the opening of the EGR gas regulating valve  32  decreases, and thus the reforming intake air flow amount A 2  increases. Thus, the amount of water Wsu supplied to the reaction chamber  23  includes the amount of water Win in the intake air with an increased rate and the amount of water Wad supplied to the reaction chamber  23  via the additive injection device  61  decreased, in accordance with Formula 1. 
         [0161]    As described above, in the engine  1  including the reforming cylinders  15   a  supplied with the supply air and the fuel, water as the additive is supplied from the additive injection device  61  to the reforming cylinders  15   a , based on the amount of supplied fuel and the supply air amount. The ECU  60  of the engine  1  calculates the amount of water Wsu with which the reforming reaction of the fuel supplied to the reforming cylinders  15   a  by the main fuel injection amount Qm is most facilitated, the amount of water Win in the intake air, and the amount of water Wex in the EGR gas, and performs control in such a manner that water in the amount Wad, required for the amount of water Wsu to be in the reforming cylinders  15   a , is supplied from the additive injection device  61 . In the engine  1  according to the present invention having the configuration described above, the amount of water supplied from the additive injection device  61  is changed in accordance with the amount of water in the supply air changing in accordance with the operation state and the operation environment. Thus, in the engine  1 , an appropriate amount of water as the additive, for facilitating the reforming reaction, can be supplied from the additive injection device  61 . 
         [0162]    In the engine  1 , when the storage amount of the additive storage tank  62  drops below the reference value, the ECU  60  controls one or a plurality of the secondary fuel injection device  6 , the main fuel injection device  20 , the second intake regulating valve  31 , and the EGR gas regulating valve  32  so that at least one of the secondary fuel injection amount Qs, the main fuel injection amount Qm, the reforming intake air flow amount A 2 , and the exhaust air recirculation rate ψ increases or decreases. With this configuration, water in the intake air and the exhaust air is used so that the amount of water Wad that needs to be supplied from the additive injection device  61  can be reduced. Thus, the appropriate amount of additive for promoting the reforming reaction can be supplied. 
         [0163]    Reforming cylinders  15   b  of an engine according to yet still another embodiment of the present invention are described with reference to  FIG. 17  to  FIG. 21 . 
         [0164]    The reforming cylinders  15   b , serving as the fuel reforming device, reform a higher hydrocarbon fuel such as light oil into a lower hydrocarbon fuel (for example, methane) to prevent preignition. The reforming cylinders  15   b  adiabatically compress a result of injecting fuel to a mixture of intake air and exhaust air (EGR gas) to reform the fuel. The reforming cylinders  15   b  each include the reforming cylinder head  16 , the reforming cylinder  17 , the reforming piston  18 , the reforming connecting rod  19 , a reaction chamber  64 , and the main fuel injection device  20 . 
         [0165]    The reforming cylinders  15   b  each include an expansion chamber  63  defined by the reforming cylinder head  16 , the reforming cylinder  17 , and an end surface of the reforming piston  18 . The volume of the expansion chamber  63  changes in accordance with the back and forth movement of the reforming piston  18 . The supply air and the fuel are adiabatically compressed through the change in the volume of the expansion chamber  63 . 
         [0166]    The reaction chamber  64  is formed in the reforming cylinder head  16  of the reforming cylinder  15   b . The reaction chamber  64  is a space where the supply air and the fuel are premixed, and the reforming reaction occurs. The reaction chamber  64  of the reforming cylinder head  16  has a substantially spherical shape. The shape of the reaction chamber  64  is not limited to the substantially spherical shape, and may be any shape, such as an elliptical shape, with which swirling current can be generated. The reaction chamber  64  is provided with the main fuel injection device  20 . The main fuel injection device  20  injects the fuel only into the reaction chamber  64 . Thus, the main fuel injection device  20  is positioned in such a manner that the injected fuel does not reach the inside of the expansion chamber  63  through a communication hole  65 . The main fuel injection device  20  includes a nozzle such as a pintle nozzle, a swirl injector, and an air-assist injector. 
         [0167]    A communication hole  65 , communicating between the expansion chamber  63  and the reaction chamber  64 , is formed in the reforming cylinder head  16 . The communication hole  65  is deviated to one side of the reaction chamber  64  to have an axis not passing the center of the reaction chamber  64 . Thus, in the reforming cylinder  15   b , gas that has flowed into the reaction chamber  64  from the expansion chamber  63  through the communication hole  65 , swirls in the reaction chamber  64 , whereby the swirling flow is generated. The communication hole  65  is formed to face an end surface of the reforming piston  18 . Thus, the communicated state of the expansion chamber  63  and the reaction chamber  64  is maintained regardless of the position of the top dead point of the reforming piston  18 . Thus, the top dead point of the reforming piston  18  can be set at any position in the reforming cylinder  15   b . In the present embodiment, the number of communication hole  65  is one. However, this should not be construed in a limiting sense. A plurality of the communication holes  65  may be formed as long as the swirling flow is generated in the reaction chamber  64 . 
         [0168]    The compression rate of the reforming cylinders  15   b  is set to be equal to or higher than 15 (for example, about 15 to 20) considering the heat loss. In the reforming cylinder  15   b , the volume ratio of the reaction chamber  64  to the expansion chamber  63 , in a state of having the smallest volume due to the reforming piston  18  being positioned at the top dead point, is 3:7. Thus, in the reforming cylinder  15   b , when the fuel that has been reformed in the reaction chamber  64  is adiabatically expanded in the expansion chamber  63 , the amount of reformed fuel oxidized in the reaction chamber  64  by oxygen in the unreacted supply air remaining in the expansion chamber  63  can be reduced. 
         [0169]    In the present embodiment, the reaction chamber  64  is formed in the reforming cylinder head  16 . However, this should not be construed in a limiting sense. For example, as illustrated in  FIG. 18 , the reaction chamber  64  may be formed in the reforming piston  18 . The reaction chamber  64  in the reforming piston  18  has a substantially spherical shape. The communication hole  65 , communicating between the expansion chamber  63  and the reaction chamber  64 , is formed in the reforming piston  18 . The communication hole  65  is deviated to one side of the reaction chamber  64  to have an axis not passing the center of the reaction chamber  64 . Thus, in the reforming cylinder  15   b , gas that has flowed into the reaction chamber  64  from the expansion chamber  63  through communication hole  65 , swirls in the reaction chamber  64 , whereby the swirling flow is generated. In this embodiment, the main fuel injection device  20  is provided to the reforming cylinder head  16 . The main fuel injection device  20  injects the fuel into the reaction chamber  64  through the communication hole  65  formed in the reforming piston  18 . Thus, the supply air and the fuel can be premixed in the reaction chamber  64  formed in the reforming piston  18  that moves back and forth. 
         [0170]    As illustrated in  FIG. 19 , the reaction chamber  64  may be formed in a cylinder block  66  where the reforming cylinder  17  is formed. The reaction chamber  64  in the cylinder block  66  has a substantially spherical shape. The communication hole  65 , communicating between the expansion chamber  63  and the reaction chamber  64 , is formed in the cylinder block  66 . The communication hole  65  is deviated to one side of the reaction chamber  64  to have an axis not passing the center of the reaction chamber  64 . Thus, in the reforming cylinder  15   b , gas that has flowed into the reaction chamber  64  from the expansion chamber  63  through communication hole  65 , swirls in the reaction chamber  64 , whereby the swirling flow is generated. In this embodiment, the main fuel injection device  20  is provided to the reaction chamber  64 . 
         [0171]    As illustrated in  FIG. 17 , the reforming cylinder  15   b  is coupled with the supply pipe  25  via the reforming intake valve  24  and with the exhaust pipe  27  via the reforming exhaust valve  26 . The exhaust pipe  27  is coupled with the intake pipe  11 . Thus, the intake air from the intake pipe  11  can be partially supplied to the supply pipe  25 . The supply pipe  25  is coupled with the exhaust pipe  13  through the EGR pipe  28 . Thus, the exhaust air from the combustion chamber  9  of the outputting cylinder  2  can be partially supplied through the EGR pipe  28  as the EGR gas. Thus, the mixture (hereinafter simply referred to as “supply air”) of the intake air and the EGR gas from the supply pipe  25  can be supplied to the expansion chamber  63  of the reforming cylinder  15   b . The exhaust pipe  27  is coupled with the intake pipe  11 , more on the downstream side than the supply pipe  25 , via the mixer  27   a . In the reforming cylinder  15   b , the lower hydrocarbon fuel (hereinafter simply referred to as “reformed fuel”), obtained by reforming the mixture, can be discharged into the intake pipe  11  from the expansion chamber  63  through the exhaust pipe  27 . 
         [0172]    The intake pipe  11  includes the first intake regulating valve  30  that is more on the downstream side than the coupled position of the supply pipe  25 , and is more on the upstream side than the coupled position of the exhaust pipe  27 . The first intake regulating valve  30  includes an electromagnetic flow amount control valve. The first intake regulating valve  30  can change the opening of the first intake regulating valve  30  in accordance with a signal acquired from the ECU  60  as the control device described later. The first intake regulating valve  30 , which is the electromagnetic flow amount control valve in the present embodiment, may be any valve that can change the flow amount of the intake air. 
         [0173]    The supply pipe  25  is provided with the second intake regulating valve  31  that is more on the upstream side than the coupled position of the EGR pipe  28 . The second intake regulating valve  31  includes an electromagnetic flow amount control valve. The second intake regulating valve  31  can change the opening of the second intake regulating valve  31  in accordance with a signal acquired from the ECU  60  described later. The second intake regulating valve  31 , which is the electromagnetic flow amount control valve in the present embodiment, may be any valve that can change the flow amount of the intake air. 
         [0174]    The EGR pipe  28  is provided with the EGR gas regulating valve  32 . The EGR gas regulating valve  32  includes an electromagnetic flow amount control valve. The EGR gas regulating valve  32  can change the opening of the EGR gas regulating valve  32  in accordance with a signal acquired from the ECU  60  described below. The EGR gas regulating valve  32 , which is the electromagnetic flow amount control valve in the present embodiment, may be any valve that can change the flow amount of the EGR gas. 
         [0175]    In the engine  1  with this configuration, the mixture ratio between the intake air and the reformed fuel discharged from the expansion chamber  63  of the reforming cylinder  15   b  can be changed with the first intake regulating valve  30 . In the engine  1 , the mixture ratio between the intake air and the EGR gas supplied to the expansion chamber  63 , can be changed with the second intake regulating valve  31  and the EGR gas regulating valve  32 . 
         [0176]    The intake air intercooler  33 , the reformed fuel intercooler  34 , and the EGR gas intercooler  35  cool gas. The intake air intercooler  33  is provided to the intake pipe  11 . The intake air intercooler  33  can cool the intake air adiabatically compressed by the compressor  14   b . The reformed fuel intercooler  34  is provided to the exhaust pipe  27 . The reformed fuel intercooler  34  can cool the reformed fuel discharged from the expansion chamber  63  of the reforming cylinders  15 . The reformed fuel intercooler  34  includes a heat radiator or a heat exchanger using air or water as the cooling medium. The EGR gas intercooler  35  is provided to the EGR pipe  28 . The EGR gas intercooler  35  cools the exhaust air heated by fuel combustion. 
         [0177]    The ECU  60  as the control device controls the engine  1 . Specifically, the ECU  60  controls the secondary fuel injection device  6 , the main fuel injection device  20 , the first intake regulating valve  30 , the second intake regulating valve  31 , the EGR gas regulating valve  32 , and the like. The ECU  60  stores therein various programs and data for controlling the engine  1 . The ECU  60  may be connected to a CPU, a ROM, a RAM, an HDD, and the like via a bus, or may be a one-chip LSI or the like. 
         [0178]    As illustrated in  FIG. 6 , the ECU  60  stores therein: various programs for controlling fuel injection; the main fuel injection amount map M 1  for calculating the main fuel injection amount Qm based on the target rotational speed Np and the target output Wt of the engine  1 ; the intake air flow amount map M 2  for calculating the outputting intake air flow amount A 1  for supplying to the combustion chamber  9  of the outputting cylinder  2 , based on the target rotational speed Np and the main fuel injection amount Qm; the mixture flow amount map M 3  for calculating the reforming intake air flow amount A 2  and the EGR gas flow amount A 3  for supplying to the expansion chamber  63  of the reforming cylinder  15  based on the target rotational speed Np and the main fuel injection amount Qm; the secondary fuel injection amount map M 4  for calculating the secondary fuel injection amount Qs for ignition to be injected into the combustion chamber  9  based on the target rotational speed Np and the main fuel injection amount Qm; and the like. 
         [0179]    An operation mode of the components of the engine  1  according to one embodiment of the present invention is described below. 
         [0180]    First of all, paths of intake air and exhaust air in the engine  1  are described. 
         [0181]    As illustrated in  FIG. 17 , the outer air sucked in by the compressor  14   b  of the supercharger  14  is discharged to the intake pipe  11  as intake air in an adiabatically compressed state. The intake air is cooled by the intake air intercooler  33 , and then is supplied to the combustion chamber  9  of the outputting cylinder  2  through the intake pipe  11 . The intake air is partially supplied to the expansion chamber  63  of the reforming cylinder  15   b  via the supply pipe  25  coupled with the intake pipe  11  and the reforming intake valve  24 . 
         [0182]    The exhaust air from the combustion chamber  9  of the outputting cylinder  2  rotates the turbine  14   a  of the supercharger  14  through the exhaust pipe  13 , and then is discharged outside. The exhaust air is partially supplied to the expansion chamber  63  of the reforming cylinder  15   b  as the EGR gas, through the EGR pipe  28  and the supply pipe  25  coupled with the EGR pipe  28 . 
         [0183]    The supply air (the intake air and the EGR gas) supplied to the expansion chamber  63  is supplied to the reaction chamber  64  through the communication hole  65 . The supply air and the reformed fuel are discharged from the reaction chamber  64  to the expansion chamber  63 , due to the suction caused by the movement of the reforming piston  18 . The reforming piston  18  discharged from the expansion chamber  63  due to the compression caused by the movement of the reforming piston  18  is recirculated to the intake pipe  11 , via the reforming exhaust valve  26  and through the exhaust pipe  27 , to be supplied to the combustion chamber  9 . 
         [0184]    Next, how the ECU  60  calculates various predetermined amounts is described. As illustrated in  FIG. 6 , the ECU  60  calculates the main fuel injection amount Qm from the main fuel injection amount map M 1 , based on the target rotational speed Np and the target output Wt of the engine  1  determined in accordance with an operation amount on an unillustrated operation device and the like. 
         [0185]    The ECU  60  calculates the outputting intake air flow amount A 1  for supplying to the combustion chamber  9  of the outputting cylinder  2 , from the intake air flow amount map M 2 , based on the target rotational speed Np and the main fuel injection amount Qm. 
         [0186]    The ECU  60  calculates the reforming intake air flow amount A 2  and the EGR gas flow amount A 3  for supplying to the expansion chamber  63  of the reforming cylinder  15   b , from the mixture flow amount map M 3  based on the target rotational speed Np and the main fuel injection amount Qm. 
         [0187]    The ECU  60  calculates the secondary fuel injection amount Qs of the igniting fuel supplied to the combustion chamber  9  of the outputting cylinder  2 , from the secondary fuel injection amount map M 4 , based on the target rotational speed Np and the main fuel injection amount Qm 
         [0188]    The ECU  60  acquires the outputting crankshaft angle θ 1  detected by the outputting crank angle detection sensor  8  and the reforming crankshaft angle θ 2  detected by the reforming crank angle detection sensor  22 , and calculates strokes of the outputting cylinders  2  and the reforming cylinders  15   b.    
         [0189]    Next, how fuel is reformed with the reforming cylinders  15  will be described with reference to  FIG. 20  and  FIG. 21 . 
         [0190]    As illustrated in  FIG. 20 , when the reforming cylinder  15   b  is in the intake stroke, the reforming piston  18  moves from the top dead point to the bottom dead point. Thus, the internal pressure of the expansion chamber  63  of the reforming cylinder  15   b  drops due to the volume increase caused by the movement of the reforming piston  18 . When the reforming cylinder  15   b  is in the intake stroke, the reforming intake valve  24  opens for supplying the supply air. The ECU  60  controls the opening and closing of the second intake regulating valve  31  based on the acquired reforming crankshaft angle θ 2 , in such a manner that the intake air is supplied into the expansion chamber  63  of the reforming cylinder  15   b  by the calculated reforming intake air flow amount A 2 , while the reforming cylinder  15   b  is in the intake stroke (for example, while the reforming piston  18  is close to the bottom dead point). Furthermore, the ECU  60  controls the opening and closing of the EGR gas regulating valve  32  in such a manner that the EGR gas is supplied into the expansion chamber  63  of the reforming cylinder  15   b  by the calculated EGR gas flow amount A 3 . Thus, the supply air (the intake air and the EGR gas) at an oxygen concentration suitable for fuel reforming is supplied to the expansion chamber  63  (supply air suction in  FIG. 20 ). 
         [0191]    When the reforming cylinder  15   b  is in the compression stroke, the reforming piston  18  moves from the bottom dead point to the top dead point. Thus, the internal pressure of the expansion chamber  63  of the reforming cylinder  15   b  increases due to the volume decrease caused by the movement of the reforming piston  18 . Thus, the supply air supplied to the expansion chamber  63  is adiabatically compressed by the reforming piston  18 . As illustrated in  FIG. 21 , the internal supply air in the expansion chamber  63  that has been adiabatically compressed flows into the reaction chamber  64  at high speed through the communication hole  65  (supply air flow in in  FIG. 20 ). In this process, the supply air forms a high-speed swirling flow in the reaction chamber  64  due to the positional relationship between the reaction chamber  64  and the communication hole  65 . The reforming cylinders  15   b  adiabatically compresses the supply air, whereby the high-temperature and the high-pressure state is achieved in the reaction chamber  64 . 
         [0192]    As illustrated in  FIG. 20 , when the reforming cylinder  15   b  is in the compression stroke, the ECU  60  controls the main fuel injection device  20  based on the acquired reforming crankshaft angle θ 2 , in such a manner that the fuel is supplied into the reaction chamber  64  of the reforming cylinder  15   b  by the calculated main fuel injection amount Qm. Thus, in the reforming cylinder  15   b , the fuel is injected into the reaction chamber  64  that is in the high-temperature and high-pressure state with the high-sped swirling flow generated (fuel injection in  FIG. 20 ). In the reaction chamber  64 , the fuel is supplied for achieving the fuel air equivalence ratio required for the reforming into the lower hydrocarbon fuel by using the reforming intake air flow amount A 2  of the intake air supplied to the expansion chamber  63  and the EGR gas flow amount A 3  of the EGR gas. 
         [0193]    The fuel injected into the reaction chamber  64  is dispersed and is quickly mixed (premixed) with the supply air in the reaction chamber  64  that is in the high-temperature and higher pressure state and has the high-speed swirling flow, to be evaporated. The injected fuel in the reaction chamber  64  partially adheres to an inner wall of the reaction chamber  64 . The inner wall of the reaction chamber  64  has no object sliding thereon such as the reforming piston  18  in the expansion chamber  63 . Thus, the fuel adhered on the inner wall of the reaction chamber  64  is exposed to the high-speed swirling flow in the high-temperature and high-pressure state to be evaporated and mixed with the supply air. 
         [0194]    The reforming reaction of the fuel premixed with the supply air starts when the reforming piston  18  reaches a point close to the top dead point, that is, when the supply air and the fuel are in the highest-temperature and highest pressure state (fuel reforming in  FIG. 20 ). In this process, the internal pressure of the reaction chamber  64  drops below the internal pressure of the expansion chamber  63  as the reforming reaction proceeds, and thus the mixture of the supply air and the fuel does not flow into the expansion chamber  63 . 
         [0195]    When the reforming cylinder  15   b  is in the expansion stroke, the reforming piston  18  moves from the top dead point to the bottom dead point. Thus, the internal pressure of the expansion chamber  63  of the reforming cylinder  15   b  drops due to the volume increase caused by the movement of the reforming piston  18 . Thus, the reformed fuel in the reaction chamber  64  moves to the expansion chamber  63  (fuel flow out in  FIG. 20 ). The reformed fuel flowed out from the reaction chamber  64  to the expansion chamber  63  is adiabatically expanded by the volume increase of the expansion chamber  63 . Thus, the reformed fuel is cooled by the adiabatical expansion, and thus the low pressure state is achieved, whereby the reforming reaction stops (reforming stop in  FIG. 20 ). 
         [0196]    When the reforming cylinder  15   b  is in the exhaust stroke, the reforming piston  18  moves from the bottom dead point to the top dead point. Thus, the internal pressure of the expansion chamber  63  of the reforming cylinder  15   b  increases due to the volume drop caused by the movement of the reforming piston  18 . When the reforming cylinder  15   b  is in the exhaust stroke, the reforming exhaust valve  26  is opened for discharging the reformed fuel from the expansion chamber  63 . Thus, the reformed fuel is discharged from the expansion chamber  63  via the reforming exhaust valve  26 , to be recirculated to the intake pipe  11  through the exhaust pipe  27  (fuel discharge in  FIG. 20 ). 
         [0197]    The reformed fuel is supplied as high temperature fuel gas to the exhaust pipe  27 , due to residual heat, in the heat of the supply air, not used for endothermic decomposition reaction in the reforming. The high temperature reformed fuel supplied to the exhaust pipe  27  is cooled by the reformed fuel intercooler  34  of the exhaust pipe  27 . Thus, self-preignition in the outputting cylinders  2  is prevented. The reformed fuel cooled by the reformed fuel intercooler  34  is supplied to the intake pipe  11  via the mixer  27   a.    
         [0198]    As described above, the reforming cylinder  15   b  has different spaces for adiabatic compression of the supply air and the fuel reforming. The reaction chamber  64  of the reforming cylinder  15   b  has no object sliding on the inner wall such as the reforming piston  18  in the expansion chamber  63 . Thus, the fuel is entirely reformed without being scraped off by the reforming piston  18 . Specifically, the predetermined amount of fuel injected into the supply air having a predetermined oxygen concentration is entirely endothermically decomposed to be gasified by the high-speed swirling flow in the reaction chamber  64  that is in the high-temperature and high-pressure state, while the reforming cylinder  15   b  is in the compression stroke. Thus, the fuel is reformed into the lower hydrocarbon fuel. Thus, the supplied reforming intake air flow amount A 2 , the EGR gas flow amount A 3 , and the main fuel injection amount Qm are sufficiently used for generating the reformed fuel in the reforming cylinder  15   b . The top dead point of the reforming piston  18  can be determined to be at any position in the reforming cylinder  15   b . Thus, the supply air amount remaining in the expansion chamber  63  decreases, whereby the oxidization of the reformed fuel at the time of adiabatic expansion is prevented. Thus, the injected fuel and the supply air can be sufficiently premixed quickly. 
       INDUSTRIAL APPLICABILITY 
       [0199]    The present invention can be applied to an engine including a fuel reforming device. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  engine 
               2  outputting cylinder 
               11  intake air pipe 
               15  reforming cylinder 
               15   a  reforming cylinder 
               15   b  reforming cylinder 
               17  reforming cylinder 
               18  reforming piston 
               20  main fuel injection device 
               23  reaction chamber 
               28  EGR pipe 
               36   a  variable valve device 
               61  additive injection device 
               63  expansion chamber 
               64  reaction chamber 
             gf the amount of supplied fuel to reforming cylinder 
             gi the amount of suctioned gas of reforming cylinder 
             the amount of reformed fuel