Abstract:
An internal combustion engine having a reciprocating multi cylinder internal combustion engine with multiple valves. At least a pair of exhaust valves are provided and each supply a separate power extraction device. The first exhaust valves connect to a power turbine used to provide additional power to the engine either mechanically or electrically. The flow path from these exhaust valves is smaller in area and volume than a second flow path which is used to deliver products of combustion to a turbocharger turbine. The timing of the exhaust valve events is controlled to produce a higher grade of energy to the power turbine and enhance the ability to extract power from the combustion process.

Description:
[0001]    This invention was made with Government support under contract DE-FC26-05NT42422 awarded by the Department of Energy. The United States Government has certain rights in this invention. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to internal combustion engines and more specifically to prime mover systems incorporating internal combustion engines and power extraction devices. 
       BACKGROUND OF THE INVENTION 
       [0003]    For over a hundred years, piston engines have been utilized to convert the energy in hydrocarbon based fuel to useful power outputs. Typically, these engines have incorporated variable volume combustion chamber or chambers using a cycle having an intake portion, a compression portion, an expansion portion and an exhaust portion. The variable volume combustion chamber is most typically defined by a reciprocating piston in a cylinder bore and connected by appropriate mechanical devices to a crankshaft or other rotary output component. The engines may be two cycle or four cycle according to the need. 
         [0004]    The consideration of efficiency has always been important but with advances in regulatory limits during the last twenty years, reducing emissions, including nitrous oxides, has become exceedingly important. The usual steps for combustion management to minimize emissions typically decrease efficiency of the engine. In the case of the compression ignition or diesel engine cycle, the need to reduce oxides of nitrogen requires significant alteration to the operating conditions which tends to decrease the otherwise outstanding efficiency of such an engine type. 
         [0005]    A number of attempts have been made to increase efficiency by fully utilizing the energy available in such engines through power extraction devices in the exhaust of the engine. Such power extraction devices may be a turbo supercharger (turbocharger) which receives the exhaust from the engine and drives a compressor connected to the engine intake by appropriate manifolds. The heat of pressurization by the compressor may be supplied to an intercooler or aftercooler to reduce the temperature of the gases flowing into the engine and thus increase the density of the mixture. Another energy extraction device is found in a power turbine which may be used to supply additional power to the engine output via an appropriate mechanical connection or may be used to drive a turbo generator supplying electrical energy for accessory and other loads. 
         [0006]    While some systems have been proposed to provide a separate exhaust for different power extraction devices, such systems do not provide a system having a maximum efficiency. 
         [0007]    Accordingly, what is needed in the art is a prime mover system incorporating an internal combustion engine and power extraction devices which more efficiently utilize the energy available from the internal combustion engine. 
       SUMMARY OF THE INVENTION 
       [0008]    In one form, the invention is a prime mover system having a reciprocating internal combustion engine. The engine has at least one intake valve for admitting combustion air into a variable volume combustion chamber with a volume varying between a minimum and maximum and at least a first and second valve for discharging products of combustion. A first exhaust flow path is provided from the first exhaust valve and a power turbine is fluidly connected to the first exhaust flow path and drives a load. A second exhaust flow path from the second exhaust valve is fluidly connected to a turbocharger having a turbine fluidly connected to the second exhaust flow path and a compressor driven by the turbine for pressurizing air for delivery to the at least one intake valve. A valve actuation system is provided for opening the first exhaust valve to discharge exhaust to the power turbine before the chamber has reached a maximum volume after a combustion event and to open the second exhaust valve to discharge exhaust to the turbocharger turbine after the chamber has reached maximum volume. 
         [0009]    In another form, the invention is a method of operating an internal combustion engine having at least one intake valve for admitting combustion air into a variable volume combustion chamber and at least a first and second exhaust valve for discharging products of combustion. The method includes opening the first exhaust valve to exhaust a portion of the products of combustion approximately before said variable volume combustion chamber reaches its maximum volume after a combustion event to drive a power turbine connected to a load. The second exhaust valve is opened to discharge exhaust to a turbocharger, after the combustion chamber has reached its maximum volume after said combustion event. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows a schematic drawing of a prime mover system embodying the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]      FIG. 1  shows a prime mover system  10  having an internal combustion engine  12  with multiple cylinders in which pistons (not shown) reciprocate to provide variable volume combustion chambers  14 . Although the engine shows three cylinders, it should be apparent to those skilled in the art that a great variety in the number of cylinders may be employed, according to the size and to the duty cycle required of the engine  12 . The combustion chamber  14  has at least one intake valve  16  and preferably an additional intake valve  18  for admitting combustion air from an intake manifold  20  passed via passages  22  and  24 . The air thus introduced into combustion chamber  14  goes through a cycle including an intake portion, compression portion, expansion portion and exhaust portion. The air that has been pressurized is combined with fuel from a fuel system  26  and ignited to combust and drive the expansion portion of the cycle to generate power. 
         [0012]    The combustion process may be a spark ignition in which a combustible hydrocarbon fuel is mixed with intake air from intake manifold  20  and ignited by an ignition device, usually in the form of a spark plug. The mixing of fuel and air may take place in the intake manifold passages  22  and  24  and even in the combustion chamber  14 . Another form of combustion type is compression ignition in which the pressurized air from intake manifold  20  is pressurized to such a degree that when fuel is injected directly into the combustion chamber  14  from fuel system  26  the mixture ignites and produces the expansion portion of the cycle. Many varieties of fuel systems are utilized for this purpose and the current type most in use is a system in which the fuel quantity and timing is controlled electronically and the pressure generated either at each individual cylinder, in the case of a unit injector, or in a high pressure common rail. 
         [0013]    The combustion chambers  14  also have exhaust valve  26  and  28  for each cylinder to discharge products of combustion. The exhaust valve  28  fluidly connects to a first exhaust flow path  30  leading to an exhaust manifold  32  and then to a power turbine  34  via conduit  33 . A second exhaust flow path  36  leads from valve  26  to a second exhaust manifold  38  connecting via conduit  40  to a turbine  42  of a turbocharger  44 . As will be described in detail below, the cross-sectional flow area of the first exhaust passages  30  are smaller than the cross-sectional flow area of the second exhaust passages  36 . Furthermore the total volume of the exhaust passages  30 , exhaust manifold  32 , and conduit  33  is smaller than the volume of the corresponding second exhaust passages  36 , exhaust manifold  38  and passage  40 . 
         [0014]    The valves  14 ,  18 ,  26  and  28  are actuated by appropriate systems. The intake valves  16  and  18  are actuated by a system schematically shown at  46  having mechanical interconnections represented by dashed lines  48 . Like fuel systems, the valve actuation systems can be any one of a variety of systems including hydro-mechanical or piezoelectric. The valves  28  are actuated by a device  50  mechanically interconnected by an appropriate system indicated by dashed line  52 . The valves  26  are actuated by a system  54  through mechanical interconnection represented by  56 . 
         [0015]    The output from power turbine  34  may be used to drive a load  58  which may be a turbo generator or a device that mechanically interconnects with the prime output of internal combustion engine  12 . The gases discharged from power turbine  34  pass through conduit  60  where they pass through an aftertreatment device  62  and finally to an exhaust  64 . The aftertreatment device may be used to remove particulates and reduce oxides of nitrogen through appropriate catalysts and other processes. The output from turbocharger turbine  42  passes through conduit  66  where it joins conduit  60  and passes through the aftertreatment device  62 . 
         [0016]    Intake air for engine  12  is taken from ambient via conduit  68  which feeds a compressor  70  driven by turbine  42  for pressurizing air for delivery through conduit  72  to an aftercooler  74  and conduit  76  to the intake manifold  40 . 
         [0017]    The prime mover system may also include exhaust gas recirculation (EGR) which has a conduit  78  connected to conduit  60  and leading to an optional EGR cooler  80  and appropriate metering device  82  to introduce a portion of the products of combustion via conduit  84  to the inlet conduit  68 . 
         [0018]    Optionally, a combustor  86  may be interposed in line in conduit  33  upstream of power turbine  34 . Combustor  86  receives fuel via a line  88  extending to fuel system  26 . Combustor  86  incorporates an appropriate ignition device and controls to produce additional energy to power turbine  34  as needed. 
         [0019]    In the operation of engine  12 , the combustion chambers  14  have a variable volume which ranges between a minimum and maximum volume. When the combustion chambers  14  incorporate reciprocating pistons it is common to refer to the minimum volume condition as top dead center (TDC) and the maximum volume condition as bottom dead center (BDC). The intake portion of the cycle causes valves  16  and  18  to be open to admit air for combustion into the combustion cylinder. The air thus admitted is compressed to a point where the combustion chamber  14  is at a minimum volume state. At this point combustion occurs and the energy of combustion drives the combustion chamber volume towards a maximum volume condition. When the pistons are defining the variable volume portion of the chamber the combustion event drives the piston towards a maximum volume state and the movement is converted into a rotary output. In the past, the thermal energy of the process has been focused on to the exclusion of the blow down energy of the gases within the chamber. In accordance with the invention, the valves  28  are opened before the combustion chamber reaches maximum volume so that a portion of the energy otherwise supplied to the piston at a lower energy rate is made available to drive the power turbine  34 . 
         [0020]    The valve actuation system  50  provides a faster opening of the valve  28  than valve  26  and the smaller cross sectional flow area and volume between the combustion chamber and the power turbine ensures that the maximum pressure is available at the power turbine  34 . The faster opening rate of valve  28  reduces throttling loses across that valve. The valve actuation system  50  opens the valve  28  at approximately 90 degrees before BDC, or maximum chamber volume. This causes the pressure ratio across turbine  34  to be greater than otherwise is experienced in such a system. The power turbine  34  has a pressure ratio of from between approximately 4-6:1 so that a maximum amount of energy is extracted via the power turbine  34 . The actuation system  50  then closes the valves  28  at approximately BDC or maximum combustion chamber volume and then the actuation system  54  opens valves  26  to provide the exhaust of the products of combustion which are passed to the turbocharger turbine  42  via a larger flow path and larger capacity system. This splitting of the exhaust flows ensures that the energy in the form of pressure is available in an optimum manner to the power turbine  34  and the remaining energy available is passed through a larger flow area to the turbocharger turbine to provide optimum utilization of the energy available from the combustion process. 
         [0021]    Such a system allows much higher power output than is seen from current turbo compounded engine. In addition, the arrangement of the power extraction devices permits an enhanced EGR process in which a minimum of EGR is required to reduce emissions. 
         [0022]    Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.