Abstract:
An aircraft having a user region therein within which pressurized air at selected pressures can be maintained using an environmental control system provided in the aircraft, and a utility region outside a utility boundary wall of the user region within which selected equipment for the aircraft is located. An internal combustion engine, provided as an intermittent combustion engine, is provided in the utility region having an air intake coupled to combustion chambers therein and a rotatable output shaft also coupled to those combustion chambers for generating force with an air transfer duct extends between the user region and the air intake so as to be capable of conveying pressurized air to that air intake.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    Referenced herein is U.S. application Ser. No. 11/713,262 filed Mar. 2, 2007 for “COMBINATION ENGINES FOR AIRCRAFT” by Frederick M. Schwarz, Brian M. Fentress, Andrew P. Berryann, Charles E. Lents and Jorn A. Glahn. 
       BACKGROUND 
       [0002]    The present invention relates to gas turbine engines for aircraft and, more particularly, to gas turbine engines each coupled to a corresponding auxiliary engine. 
         [0003]    Gas turbine engines as continuous combustion, open Brayton cycle internal combustion engines have come to dominate as the power plants for larger, faster aircraft to essentially the exclusion of reciprocating engines, or internal, intermittent combustion engines, earlier used as power plants for these kinds of aircraft. This is largely because of the greater power-to-weight ratio of gas turbine engines versus internal combustion engines, especially in large horsepower engines, or, more appropriately, large thrust engines in which those large thrusts are provided with a relatively small, and so smaller drag, frontal area engine structures relative to reciprocating engines. Gas turbine engines generate such large thrusts for propulsion, or horsepower for engines with an output shaft, by combining large volumes of air with large amounts of fuel, and thereby form a jet of large velocity leading to the capability to provide desired speedy flights. 
         [0004]    In addition to providing thrust, such gas turbine engines have operated integrated drive generators to generate electricity for the aircraft and for the engine electronic controls. The amount of electricity needed for these purposes in the past has tended to be relatively modest typically in the range of a few hundred kilowatts of electrical power but, with recently arriving new aircraft, exceeding a megawatt of power. However, there are some aircraft, usually for military uses, that have come to have needs for still larger amounts of electrical power either on a relative basis, the electrical power needed relative to the capability of the gas turbine engine available, or on an absolute basis with power needs significantly exceeding a megawatt. Furthermore, such demands for electrical power in military aircraft often occur at relatively high altitudes and often occur unevenly over relatively long time durations of use, that is, large peaks repeatedly occur in electrical power demand in the course of those long use durations. 
         [0005]    Corresponding attempts to obtain the added power from the typical aircraft propulsive system, the gas turbine engine, that are needed to operate the concomitant much larger capacity electrical generators, either on a relative or absolute basis, will subtract significantly from the thrust output of the available turbine or turbines. Making up that thrust loss in these circumstances by operating such available turbine engines so as to increase the thrust output thereof causes the already relatively low fuel use efficiency during flight to decrease significantly which can severely limit the length of otherwise long duration uses, and also brings those engines closer to becoming operationally unstable. 
         [0006]    Of course, such problems could be avoided by providing a gas turbine engine of greater thrust capability than is needed to propel the aircraft to thereby provide adequate capacity for generating needed electrical power. However, if that needed power is not needed on a fairly constant basis to propel the aircraft, such a gas turbine engine will often be operating very far from its optimal operating point as it propels the aircraft, and this leads to significantly degraded fuel efficiency thereby limiting the duration of flight in an aircraft using such an engine. 
         [0007]    Another possibility is the addition of a further small auxiliary gas turbine engine for operating the electrical power generator to provide the needed electrical power. Again, however, for uneven electrical power demands over time, the engine will either be have to be oversized or will be operated inefficiently in meeting the power peak demands and with operating excursions bringing it near to becoming unstable. Even more important, this small auxiliary engine will have poor fuel consumption because the fuel consumption performance of all turbomachinery worsens as it is scaled down since high loss boundary layer flows and tip clearance flows represent a larger fraction of the total fluid flow of the smaller engine. 
         [0008]    In the situation of a relatively small aircraft being selected with a small gas turbine engine for propulsion to provide relatively good fuel consumption at altitude and so long flight endurance, the aircraft would need to have a large wing area and high lift devices, and would have to be operated from long runways. However, the endurance problem is still not satisfactorily solved because such engines do not scale down to small sizes so as to maintain the fuel use efficiencies for power generation and, of course, are limited by instability of the compressor in the peaks of electrical power they can supply. 
         [0009]    From the foregoing, gas turbine engines used to propel aircraft can be seen to not be well suited as energy sources for also operating electrical power generators that are required to deliver large quantities of electrical power, especially in situations in which the quantities demanded of that power change substantially over time or in which those quantities must be delivered over long time durations, or both. A more effective alternative is to use a different kind of engine to serve as the energy source for such electrical power generators that is both substantially more fuel efficient and operates stably over a wide range of output powers. Thus, intermittent combustion internal combustion engines can be used, such as gasoline engines operating on the any of the Diesel, Miller, Otto or Wankel cycles. 
         [0010]    Such engines can operate with a fuel efficiency on the order of seventy percent (70%) better than that of a continuous combustion (Brayton cycle) internal combustion gas turbine engine. Furthermore, this better fuel efficiency of these engines is essentially maintained over a wide range of engine output powers in contrast to the significant fuel efficiency decreases that occur in gas turbine engines if operated away from their optimum operating points. Although such intermittent combustion engines are heavy relative to the output power they provide, they can be relatively small if used primarily for energizing electrical power generators in an aircraft, rather than for propulsion of that aircraft, and can thus be positioned in the aft part of the fuselage past the cabin pressure bulkhead where, typically, auxiliary power units are housed in commercial airliners. 
         [0011]    At high altitudes, however, internal combustion engines of all kinds face the possibility of limited power output because of the relatively small air pressures there limiting the number of chemical reactions of oxygen with hydrogen and oxygen with carbon in the burning the engine fuel in the engine combustion chamber or chambers. Gas turbine engines do provide therein very large air flows through use therein, typically, of axial flow compressors to supply compressed air to the subsequent combustor sufficient to sustain the desired combustion process therein. However, such compressors can provide considerably more compressed air than the minimum needed for this purpose thereby allowing some of this compressed air to be delivered through an air transport duct to the air intake of an intermittent combustion internal combustion engine so that, in effect, the compressors of the gas turbine engine serve as a very capable supercharger for that intermittent combustion engine. The usual mounting positions for propulsion gas turbine engines on passenger or cargo aircraft, at least larger ones, are typically under the wings. This arrangement would thereby require an air transport duct to extend from the compressors therein to the aft part of the aircraft fuselage to supply compressed air to an intermittent combustion engine located there which would be both expensive and require aircraft design compromises. Thus, there is a desire to find a more effective and economical source of pressurized air for operating an intermittent combustion internal combustion engine in an aircraft. 
       SUMMARY 
       [0012]    The present invention provides an aircraft having a user region therein bounded at least in part by boundary walls within which pressurized air at selected pressures can be maintained using an environmental control system provided in the aircraft, and a utility region outside a utility boundary wall of the user region within which selected equipment for the aircraft is located. An internal combustion engine, provided as an intermittent combustion engine, is provided in the utility region having an air intake coupled to combustion chambers therein and a rotatable output shaft also coupled to those combustion chambers for generating force. An air transfer duct extends between an opening in the utility boundary wall, so as to be capable of having pressurized air in the user region enter that air transfer duct at one end thereof, and the air intake at an opposite end thereof so as to be capable of conveying pressurized air therein to that air intake. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic representation of a cross section side view of a portion of an aircraft embodying the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Passenger and cargo aircraft flights at substantial altitudes require that the cabins for passengers, and the cargo spaces also, have the air therein maintained at temperatures and pressures sufficient to keep passengers both alive and reasonably comfortable. Thus, in gas turbine engine propelled aircraft, compressed (and therefore hot) air is typically drawn from a low or intermediate stage of compression in such engines and supplied to an air cycle machine in the aircraft used as a refrigeration device in the aircraft cabin and cargo space environmental control system. In an alternative, rather than taking pressurized air from the propulsion turbine engines, that pressurized air can be instead provided by one or more dedicated air compressors to maintain such cabin and cargo space air pressure. Each such compressor has its rotors rotated for compressing air by a corresponding electric motor that is supplied electrical power from electrical generators integrated with the propulsion turbine engines. Either arrangement has a corresponding control system that supplies cooled, pressurized air, drawn from the atmosphere through the engines or dedicated compressors, respectively, to the cabin and cargo space of the aircraft. This atmosphere based air is conditioned in the environmental control system and then mixed in some fraction with recirculated cabin air in a mix manifold in the aircraft, and the result is supplied to both the aircraft cabin and cargo space as the basis for maintaining desired pressures and temperatures therein. 
         [0015]    Cabin and cargo space pressures are maintained by delivering the mixed atmosphere based and recirculation based air to the aircraft cabin and cargo space at pressures exceeding that desired to be maintained the cabin and cargo space, and then having the cabin pressure control system repeatedly measure various relevant conditions to determine how much air to allow to continuously escape from those aircraft locations to the external atmosphere as the basis for setting the air pressures resulting at such locations. The cabin and cargo space air is allowed to escape to the atmosphere through a pressure outflow, or regulating, valve located in the lower aft part of the fuselage as the air escape mechanism to thereby reach the desired air pressure. 
         [0016]    Thus, providing sufficient added pressure in the air delivered to the cabin and cargo space can thereby allow a portion of that cabin and cargo space pressurized air, which would otherwise be allowed to escape to the atmosphere, to instead be conveyed to an intermittent combustion engine in the aft part of the fuselage just behind the cabin pressure bulkhead from the cabin and cargo space. That is, the cabin and cargo space and the environmental system therefor together can be operated as a supercharger supplying compressed air to the intermittent combustion engine provided to operate an electrical generator primarily supplying electrical power for the aircraft. Whatever further portion of the pressurized cabin and cargo space air that is not needed for operation of the intermittent combustion engine, and so must still be jettisoned to the atmosphere to properly maintain air pressure in the cabin and cargo space, is allowed to escape through the pressure regulating valve by the cabin pressure control system. 
         [0017]    Such an arrangement is shown in a schematic representation of a cross section side view of an aft portion of an aircraft in  FIG. 1 . The passenger and cargo space portion of an environmental control system,  10 , is shown there for a passenger airliner,  11 . A fuselage,  12 , of airliner  11  has a cabin pressure bulkhead,  13 , that separates a portion of this fuselage from both a passenger cabin,  14 , and a cargo space,  15 , that, in turn, are separated from one another by a cabin floor,  16 . Environmental control system  10  (not shown for the most part) supplies pressurized air to passenger cabin  14  from a mix manifold therein (not shown) through a cabin air distribution manifold,  17 , thereof (only partially shown) under control of a computer (not shown) at selected pressures and temperatures. Some of this air, so supplied, is drawn through cabin wall vents,  18 , (only a few of them provided in the aircraft being shown) of this control system each having an opening located just above cabin floor  16  to a duct in that wall leading to an opening at the opposite end thereof in cargo space  15  located just below cabin floor  16 . Environmental control system also has a pressure regulating valve,  19 , that operates under control of the computer (again, not shown) to control the amount of air escaping to the atmosphere from cabin  14  and cargo space  15  thereby setting the selected air pressure therein. 
         [0018]    An intermittent combustion engine operated electrical generation system,  20 , is shown for passenger airliner  11  positioned in that aft fuselage portion,  21 , (mounting means for system  20  in aft portion  21  not shown) that is located rearward of cabin  14  and cargo space  15  as separated therefrom by cabin pressure bulkhead  13 . A further escape route for air in cabin  14  and cargo space  15  cabin is provided by a cargo space air duct,  22 , in aft fuselage portion  21  into which air under pressure in cabin  14  and cargo space  15  can flow through an opening in cabin pressure bulkhead  13  and through a check valve,  22 ′, mounted in that opening. Check valve  22 ′ permits air to flow only from cargo space  15  into duct  22  and not in the reverse direction. This air flow in duct  22  is drawn therethrough by having the other end thereof connected to an air intake, or intake manifold,  23 , leading to engine air intake valves,  23 ′, for an intermittent combustion engine,  24 , represented in the example of  FIG. 1  by a schematic piston arrangement as a Diesel or Otto cycle engine but could alternatively be a Wankel engine. 
         [0019]    Valves  23 ′ in engine  24  control the air taken into combustion chambers,  25 , bounded by an engine block,  26 , providing the basic structure of engine  24 , and by pistons,  27 . Each chamber also has an exhaust valve,  28 , through which combustion products are exhausted to an exhaust manifold,  29 , that has an exhaust duct,  29 , extending therefrom to an opening in fuselage  12  to convey this exhaust to the atmosphere outside the aircraft. A rotatable crankshaft,  30 , has a connecting rod,  31 , rotatably coupling it to a corresponding one of each of pistons  27 . A rotatable camshaft,  32 , is used to open and close air intake valves  23 ′ and exhaust valves  28  in a suitable sequence. 
         [0020]    Crankshaft  30 , under the control of a system controller not shown, is rotated by the force on pistons  27  transmitted thereto by corresponding ones of connecting rods  31  due to repeated combustion events in the corresponding combustion chamber  25  which events occur in all of chambers  25  in a suitable sequence before repeating. These events correspondingly use the air quantities taken through valves  23 ′ repeatedly into, and the fuel quantities repeatedly injected into, those chambers for combustion. The fuel quantities are injected by a fuel injection system not seeable in this FIGURE and the magnitudes thereof are used to select the mechanical power output of crankshaft  30  of the intermittent combustion engine. The resulting combustion products are correspondingly repeatedly rejected from those chambers through valves  28 . 
         [0021]    If an Otto cycle engine is used as intermittent combustion engine  24 , the combustion events are initiated by the repeated sparkings of spark plugs not shown in this FIGURE in a suitable sequence across combustion chambers  25  under the control of the system controller. In addition, intermittent combustion engine  24  has a cooling system in which a coolant flows in passageways in engine block  26  (not shown) positioned adjacent to combustion chambers  25  for cooling the engine structure. The remainder of this cooling system is described below. Although the foregoing description is of an intermittent combustion engine employing pistons, other intermittent combustion engine types could alternatively be used such as one operating on the Wankel cycle. 
         [0022]    Crankshaft  30  is suitably fastened to an input shaft,  33 , of a primary electrical power generator,  34 , to transmit the rotation of crankshaft  30  thereto. The resulting rotation of input shaft  33  electrically energizes output electrical conductors,  35 , of generator  34  to thereby generate the desired electrical power thereat for operating aircraft devices (not or not all shown) connected thereto through a cable connector,  35 ′, and the cables extending therefrom shown only partially except for two such cables,  35 ″ and  35 ′″. The demand for electrical power in the aircraft is used as a basis to select the fuel quantities injected in combustion chambers  25  of intermittent combustion engine  24  to have that engine supply sufficient mechanical power crankshaft  30  to sufficiently rotate input shaft  33  of generator  34  to meet that demand. 
         [0023]    Cable  35 ″ provides electrical power to an electrical motor,  36 , that mechanically rotates an emergency supercharger impeller,  37 , under the control of a computer not shown. Emergency supercharger fan  37  is to provide pressurized air to intake manifold  23  of intermittent combustion engine  24  in the event that cabin  14  and cargo space  15  should suffer a decompression event for some reason to thereby create such an emergency and deprive engine  24  of pressurized air from cabin  14  and cargo space  15 . In such an unlikely event, supercharger  37  is likely to be necessary because the peak horsepower available from intermittent combustion engine  24  would be much less, or even perhaps this engine would not be capable of sustaining its operation at high altitudes. An emergency supply duct,  38 , conveys air from the atmosphere between an opening in the wall of fuselage  12  and impeller  37 . A supercharger duct,  39 , conveys air from impeller  37  to cabin and cargo space air duct  22  connected to intake manifold  23  through a check valve,  39 ′, to prevent air supplied through duct  22  from leaking out of the airliner  12  when impeller  37  is not operating. 
         [0024]    The emergency system including motor  36  and emergency supercharger impeller  37  could be chosen to be eliminated in those situations in which electrical generators (not shown) are fully integrated with the gas turbine engines (not shown but typically mounted on the aircraft wings) used to propel airliner  11  so that they could be used to supply sufficient electrical power to operate the aircraft if intermittent combustion engine  24  fails in any manner. Also, as an alternative, this emergency system could be chosen to be replaced by a small “bleed” duct (not shown) extending from the compressors in the gas turbine engines (not shown but typically mounted on the aircraft wings) used to propel airliner  11  through computer controlled valves (not shown) to a connection with duct  22  to supply compressed air to intermittent combustion engine  24  following a cabin decompression event. In such an arrangement, these sources of compressed air can also provide compressed air to substitute for the pressurized air provided from the cabin and cargo space by duct  22  to thereby provide air at greater air pressures at intake  23  in situations of relatively large demands for electrical power. 
         [0025]    Cable  35 ′″ provides electrical power to an electrical motor,  40 , that mechanically rotates a cooling fan,  41 , under the control of a computer not shown, that are used for the remainder of the cooling system for intermittent combustion engine  24  and for cooling primary electrical power generator  34 . Cooling fan  41  is operated to draw air from a vent,  42 , in the wall of aft fuselage portion  21  through a pair of radiators,  43  and  44 , which air, heated by these radiators, is then forced by this fan along a heat removal duct,  45 , out a further vent,  46 , in the wall of aft fuselage portion  21  into the atmosphere outside of airliner  11 . A pair of hoses allows circulation of coolant between the passageways in engine block  26  of engine  24 , indicated above, and radiator  43  to thereby cool that engine. Similarly, a pair of hoses allows circulation of oil used in electrical power generator  34  and radiator  44  to thereby cool that generator. Such cooling is primarily required when engine  24  and generator  34  are operated with airliner  12  on the ground and there is no cold atmosphere present about aft fuselage portion  21 . 
         [0026]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.