Abstract:
Hybrid aircraft propulsion systems are disclosed comprising an electrically driven ducted fan, a peripheral duct or enclosure, a combustion-produced source of radiant energy, radiant energy receivers or cold mirrors, and thermophotovoltaic or thermoelectric cell energy converters. An electric motor drives a partially or completely duct enclosed fan. Downstream and within the duct enclosure, radiant energy emitters irradiated receiver fins and thermophotovoltaic cells or thermoelectric cells. The receiver fins heat and expand the fan air, and the thermophotovoltaic cells or thermoelectric cells convert the radiant energy into electrical energy which is available to charge batteries and energize the fan motor. Thrust is provided via the acceleration of air by the fan and by the acceleration of air due to heat driven expansion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/643,479, filed May 7, 2012, the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to aircraft engines capable of being operated by electricity and by the combustion of a liquid, gaseous, or solid fuel. 
     BACKGROUND OF THE INVENTION 
     Conventional aircraft engines utilize reciprocating engines, turbine driven propeller engines, or turbine engines which deliver thrust as a result of a combination of fan action and jet thrust. Reciprocating engines require very high maintenance and turbine engines are very expensive to manufacture because of the exotic materials used in the hot section of the engine. Reciprocating and turbine engines rely entirely on the combustion of a chemical fuel for their operation. 
     Recently, because of advances in electric motor technology and battery energy density, short range small aircraft have been developed that are quiet, non polluting, and have ultra low maintenance requirements. These aircraft, however, have very short flight range because the energy density of lithium ion batteries is only about 190 watt hours per kilogram. Hydrocarbon fuels have energy densities in the range of 12,000 watt hours per kilogram. So it is obvious that even with advances in battery energy density, electrically operated aircraft will have limited distance capabilities. 
     It is, therefore, desirable to retain the beneficial operating characteristics of the electric propulsion system while increasing range. 
     SUMMARY OF THE INVENTION 
     Hybrid aircraft propulsion systems are disclosed comprising an electrically driven ducted fan, a peripheral duct or enclosure, a combustion-produced source of radiant energy, radiant energy receivers or cold mirrors, and thermophotovoltaic or thermoelectric cell energy converters. An electric motor drives a partially or completely duct enclosed fan. Downstream and within the duct enclosure, radiant energy emitters irradiate receiver fins and thermophotovoltaic cells or thermoelectric cells. The receiver fins heat and expand the fan air, and the thermophotovoltaic cells or thermoelectric cells convert the radiant energy into electrical energy which is available to charge batteries and energize the fan motor. Thrust is provided via the acceleration of air by the fan and by the acceleration of air due to heat driven expansion. 
     In certain embodiments, hybrid radiant energy aircraft engines, comprises:
         an electric motor driven tubeaxial fan;   a peripheral duct enclosing the operating components;   an electric motor to drive said fan;   at least one combustion driven source of radiant energy;   radiant energy receiving fins located downstream said fan and located with their major dimensions parallel to the airflow;   optional cold mirrors; and   thermophotovoltaic cells or thermoelectric cells positioned to receive a portion of the radiant energy;   wherein the radiant energy radiators are configured to deliver energy to the receiving fins and the photovoltaic cells;   wherein the tubeaxial fan directs air past the receiver fins;   wherein the receiver fins heat the downstream fan air and expand it or increase its pressure;   wherein optional preheating of the combustion air is provided via heat exchangers;   wherein the thermophotovoltaic cells or thermoelectric cells convert a portion of the radiant energy into electrical energy;   wherein that electrical energy is available to power the fan motor and to charge batteries and for other auxiliary uses; and   wherein the thrust produced is the result of any combination of acceleration of air due to fan action and expansion of the fan air due to heating.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a cross section of one embodiment of the engine of the invention. 
         FIG. 2  is a frontal view of one embodiment of the engine of the invention with the fan and fan motor not shown. 
         FIG. 3  is a frontal view of one embodiment of the engine of the invention with the fan and fan motor not shown. 
         FIG. 4  is a block diagram of the functional components of a typical propulsion system using of one embodiment of the engine of the invention. 
         FIG. 5  is a cross section similar to  FIG. 1  of one embodiment of the engine of the invention. 
         FIGS. 6 and 7  show two iterations of one embodiment of the engine of the invention. 
         FIG. 8  is a cross section of one embodiment of the invention, similar to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Definitions 
     The following definitions are provided for the full understanding of terms used in this specification. 
     As used herein, the article “a” means “at least one,” unless the context in which the article is used clearly indicates otherwise. 
     As used herein, “thermophotovoltaic cell” means any material capable of converting radiant energy into electricity. These cells are sometimes referred to as photovoltaic cells or concentrator photovoltaic cells. 
     As used herein, “thermoelectric cell” means any material capable of converting a temperature differential directly into electricity. 
     As used herein, “duct” means a housing having a basically cylindrical shape, having a hollow center section, having mounting tabs for internal components, and having contours that promote the acceleration of the fan and heated air, and having structural components that allow attachment to the aircraft and transmission of thrust forces. 
     As used herein, “cold mirrors” means a material that reflects short wave radiation and absorbs or is transparent to long wave radiation. 
     As used herein, “optical window” means a transparent covering that prevents the convective cooling of the radiator surface that must be maintained at a specific temperature to be an effective radiator. An example of an optical window would be a silica glass cylindrical element that would house a smaller diameter emitter, and would possibly be evacuated to reduce heat losses and to prevent oxidation of the emitter surface. A portion of the window could be reflective to direct the radiant energy in a certain direction. Alternatively, the optical window could be a flat or curved cover. 
     As used herein, “radiant energy radiator” means an element that supports combustion of a fuel and air or oxygen either internally or at its surface, and that has materials of construction that promote the emission of radiation, preferably at frequencies tuned to the photovoltaic cells. 
     As used herein, “tubeaxial fan” means a fan or propeller connected to a motor and positioned in a duct so that the airflow is parallel to the axis of rotation of the fan and inside the duct. 
     As used herein, “hybrid” means to employ more that one means of producing a propulsive force. In the case of the invention, this is; employing electric motor driven fan means and air heating means, and also photovoltaic or photoelectric means for operation of the electric motor. 
     The present invention teaches the construction and operation of a combined cycle aircraft engine. The engine uses a high efficiency, lightweight electric motor to drive a multibladed tubeaxial fan. The fan is located at the forward section of a peripheral duct. Rearward of the fan are radiant energy radiators that achieve radiance via the combustion of a chemical fuel. The radiators deliver energy to longitudinally located fins that absorb the longer wave radiation, convert it to heat, and conduct that heat energy to the airflow created by the axial fan. The heated air expands and is accelerated rearward producing thrust. The fins may have hollow portions that intercept part of the fan air, preheat it and deliver it to the combustors. In this sense the engine operates as an ultra-low compression ratio Brayton cycle engine. Unlike the normal Brayton cycle engine, the fan power is supplied via an electric motor. 
     Within the duct, and also located in a longitudinal fashion, are thermophotovoltaic cells or thermoelectric cells. These cells convert a wide spectrum of radiated energy into electricity at an efficiency of as much as 41%. This electrical energy is directed to the fan motor and to the battery when appropriate. The engine is highly efficient because the radiant energy is utilized as heat to expand air, and as directly converted photon to electrical energy. Also, as with hybrid ground vehicles, the battery stored energy and the chemically stored energy can be used when conditions require high output, or the engine can operate on battery power when demand is lower or pollution or noise abatement is required. The power density of radiant combustors and thermophotovoltaic cells or thermoelectric cells is greater than 20 watt per centimeter square area (see Spectrolab) so sufficient energy can be generated and converted within a 60 cm diameter by 100 cm long duct to create 78,000 watts of electrical energy continuously while also injecting an equal amount of energy into heat for the acceleration of air. 
     So it can be seen that an engine with only two bearings in the electric motor and no hot end moving parts can be constructed using existing components. The engine is suitable for use in small aircraft and for the propulsion of drones. The engine can operate quietly and in an electric only mode and with range extending capabilities in the radiant energy and electric mode. The electric fan can be entirely enclosed within the peripheral duct, or the fan blade may extend beyond the duct circumference for lower speed, quieter operation. 
     In one embodiment, the invention is directed to hybrid radiant energy aircraft engines, comprising:
         an electric motor driven tubeaxial fan;   a peripheral duct enclosing the operating components;   an electric motor to drive said fan;   at least one combustion driven source of radiant energy;   radiant energy receiving fins located downstream said fan and located with their major dimensions parallel to the airflow;   optional cold minors; and   thermophotovoltaic cells or thermoelectric cells positioned to receive a portion of the radiant energy;   wherein the radiant energy radiators are configured to deliver energy to the receiving fins and the photovoltaic cells;   wherein the tubeaxial fan directs air past the receiver fins, wherein the receiver fins heat the downstream fan air and expand it or increase its pressure;   wherein optional preheating of the combustion air is provided via heat exchangers ( 99 ), as shown in  FIG. 4 , described herein;   wherein the thermophotovoltaic cells or thermoelectric cells convert a portion of the radiant energy into electrical energy;   wherein that electrical energy is available to power the fan motor and to charge batteries and for other auxiliary uses; and wherein the thrust produced is the result of any combination of acceleration of air due to fan action and expansion of the fan air due to heating.       

       FIG. 1  is a cross section of one embodiment of the engine showing the external shroud ( 1 ), the fan ( 2 ), the fan electric motor ( 3 ), the radiant energy combustors ( 4 ), the heat absorbing fins ( 5 ), and the thermophotovoltaic cells or thermoelectric cells ( 6 ). The intake of the engine is to the left and the exhaust to the right. 
       FIG. 2  is a frontal view of one embodiment of the engine of the invention with the fan and fan motor not shown. In this drawing the radiant energy radiators ( 4 ) are protected by transparent shields ( 7 ) that keep the airflow from lowering the temperature of the radiators surfaces. The absorber fins may also be cold mirrors which reflect and focus the short wave radiation onto the thermophotovoltaic cells or thermoelectric cells, while absorbing the longer wave radiation and conducting heat to the air passing by. The direction of the radiant energy and the reflected radiant energy is shown by the arrows. 
       FIG. 3  is a frontal view of one embodiment of the engine of the invention with the fan and fan motor not shown. In this drawing the radiator is located in the central part of the duct, while the thermophotovoltaic cells or thermoelectric cells are located on the internal circumference of the duct. This arrangement provides for a simpler shielding of the radiator. 
       FIG. 4  is a block diagram of the functional components of a typical propulsion system using of one embodiment of the engine of the invention. A battery ( 9 ) stores electrical energy, a controller ( 10 ) regulates the electrical energy going to the fan motor, and a vessel ( 11 ) stores chemical energy fuel for the radiant energy combustors. A pneumatic pathway is shown ( 8 ) wherein air enters a hollow space in fin ( 5 ) and is pre heated and sent to combustor ( 4 ). Wavy arrows indicate direction of the radiant energy from the combustors toward the thermoelectric cells ( 6 ). A regulator ( 13 ) controls the flow of fuel to the combustor(s). 
       FIG. 5  is a cross section similar to  FIG. 1  of one embodiment of the engine of the invention but with the addition of a turbine stage which intercepts the accelerated air before it exits the duct. The turbine disc ( 12 ) is connected to the inlet fan and assists the electric fan motor action. In this mode of operation, the engine could function even after complete electrical failure. 
       FIG. 6  shows one embodiment of the engine of the invention utilizing a small frontal section engine that would operate in a high speed environment. 
       FIG. 7  shows an embodiment of the engine of the invention with a large frontal section engine having a short length and being designed for lower speed operation at high efficiency. 
       FIG. 8  is a cross section similar to  FIG. 1  of one embodiment of the engine of the invention utilizing thermoelectric cells ( 13 ) convert radiant energy into heat and then into electricity. The thermoelectric cells receive energy at the hot side ( 14 ), and reject heat at the cold side ( 15 ). 
     In certain embodiments, the hybrid radiant energy aircraft engine of the invention further comprises duct parallel fins configured to absorb long wave radiation and to reflect and optionally to focus shortwave radiation toward the thermophotovoltaic cells or thermoelectric cells. 
     In certain embodiments, the hybrid radiant energy aircraft engine of the invention further comprises a peripheral generally cylindrical housing, internally shaped to convert heated fan air into thrust. 
     In certain embodiments, the hybrid radiant energy aircraft engine of the invention further comprises optical windows or mechanical shrouds configured to prevent cooling of the radiant energy radiator surfaces. 
     In certain embodiments, the hybrid radiant energy aircraft engine of the invention further comprises at least one radiant energy radiator located on the inner surface of the peripheral housing. 
     In certain embodiments, the hybrid radiant energy aircraft engine of the invention further comprises at least one radiant energy radiator located in the center area of the peripheral housing. 
     In certain embodiments, the hybrid radiant energy aircraft engine of the invention further comprises an electronic control means for regulation of fan motor energy input. 
     In certain embodiments, the hybrid radiant energy aircraft engine of the invention further comprises a control means for regulation of the energy output of the radiant energy radiators. 
     In certain embodiments, the hybrid radiant energy aircraft engine of the invention further comprises an electrical energy storage device located within or on the aircraft that provides electrical energy to the fan motor and which receives electrical energy from the thermophotovoltaic cells or thermoelectric cells. In certain embodiments, the electrical storage device comprises at least one lithium ion battery. In certain embodiments, the electrical storage device comprises an electrochemical storage device. In certain embodiments, the electrical storage device comprises a flow battery. In certain embodiments, the electrical storage device comprises a capacitor or pseudocapacitor. In certain embodiments, the electrical storage device is an electrochemical conversion device, such as a fuel cell. 
     In certain embodiments, the hybrid radiant energy aircraft engine of the invention further comprises multiple radiant energy radiators that can be activated and deactivated separately or in groups. In certain embodiments, the amount of thrust produced is in part controlled by the number of radiators that are activated. In certain embodiments, oxides of nitrogen and unburned hydrocarbon emissions are limited by operating each radiator only at its optimum temperature and air fuel ratio. 
     In certain embodiments, the hybrid radiant energy aircraft engine of the invention further comprises a liquid, gaseous, or solid combustion fuel storage device located within or on the aircraft provides chemical energy to the radiant energy combustors. 
     In certain embodiments, the hybrid radiant energy aircraft engine of the invention, the ratio of energy provided to the fan motor compared to the energy provided to the radiant energy radiators is selected to best match engine performance and energy availability to flight conditions and flight plans. In certain embodiments, the energy ratios are preset for at least one of takeoff, climb, cruise, altitude change, landing operations, and combinations thereof. In certain embodiments, the energy ratios are selected by an electronically stored algorithm that has as an input the throttle setting. 
     In certain embodiments, the energy ratios are selected in response to a computational analysis of the flight plan, energy storage capacity, and other relevant data. 
     In certain embodiments, a single stage axial rotating turbine element located toward the exit end of the engine converts some of the kinetic energy of the exhaust air into shaft power which mechanically assists the fan motor or operates a generator. 
     When ranges are used herein for physical properties, such as molecular weight, or chemical properties, such as chemical formulae, all combinations, and subcombinations of ranges specific embodiments therein are intended to be included. 
     The disclosures of each patent, patent application and publication cited or described in this document are hereby incorporated herein by reference, in its entirety. 
     Those skilled in the art will appreciate that numerous changes and modifications can be made to the preferred embodiments of the invention and that such changes and modifications can be made without departing from the spirit of the invention. It is, therefore, intended that the appended claims cover all such equivalent variations as fall within the true spirit and scope of the invention.