Endothermic Fuel Power Generator and Method

This invention generally relates to power generating systems and methods for supplementing the power output of a propulsion engine such as a turbojet, ramjet, or turboramjet operating at a high mach number, and more specifically to a power generating system and method that includes a high pressure, endothermic reaction to generate cooled air and gaseous fuel for the propulsion engine while also providing mechanical power for driving accessories such as pumps and generators.

An aircraft in flight requires two types of power from its power plant(s). The first of these powers is in the form of thrust to propel the aircraft forward and the second is in the form of mechanical power for driving accessories such as a fuel pump, hydraulic pump and/or an electric generator. For aircraft operating at subsonic or low supersonic velocities, both thrust and accessory power is usually provided by one or more air breathing engines, such as a turbojet. A turbojet is comprised of a casing encompassing an inlet section, a compressor section, a combustor section, a turbine section, and an exhaust nozzle section arranged in flow series so as to keep the overall width of the engine to a minimum and thereby reduce the drag. Air, from the environment surrounding the engine, enters through the inlet section and into the compressor section where it is pressurized. The pressurized air then exits the compressor section and enters the combustor section where it is mixed with fuel and ignited. This hot gas mixture of air and fuel is then expanded across the turbine section and then through the exhaust nozzle section. In the turbine section a portion of the pressure energy of the hot gas is extracted from the gas and converted into mechanical power. The remaining pressure energy of the hot gas is converted in the exhaust nozzle section to thrust for propelling the aircraft forward. The mechanical power output of the turbine section is used to drive the compressor section. Additionally, the engine has an accessory gearbox to which the aircraft's accessories are operably mounted. The accessory gearbox is driven by the compressor and is mounted along the outside of the casing. The disadvantages associated with an accessory gearbox include weight penalties and increased width and drag of the engine.

For aircraft operating at high supersonic or hypersonic velocities, (i.e. a Mach number in the range of 3 to 6), alternative engine configurations like a ramjet or turboramjet can be used to provide thrust. In these alternate engine configurations as well as with the turbojet configuration, the inlet section of the engine operates as a diffuser reducing the velocity of the entering air and as a consequence increasing the air's static temperature and pressure. This diffusion is referred to, by those skilled in the art, as the ram effect and can produce air temperatures within the compressor on the order of 2500.degree. F. and similar temperatures in the casing and accessory gearbox. This temperature is above the melting temperature of metals commonly used in accessory gearboxes and other components, within the engine, such as turbine shafts and blades. Consequently, at these operating conditions a heat sink, usually a tank of some cryogen, must be provided to cool the air exiting compressor. While it is relatively easy to deliver this cooled air to the shafts and blades of the engine, delivering sufficient cooled air to the gearbox is impractical and expensive. Further, at high mach numbers the weight and drag penalties associated with gearboxes are increased.

Consequently, it has been proposed to replace the accessory gearbox with a ram air turbine drivingly coupled to the aircraft's accessories. A ram air turbine is an impulse type turbine wheel which can be interposed into the high velocity air stream surrounding the aircraft when accessory power is required. The turbine wheel extracts kinetic energy from the air stream and converts it to mechanical power. The disadvantages of the ram air turbine include high cost and the significant drag generated when interposed in the air stream. Also, the ram air turbine cannot provide cooling flow for the engine's components.

Accordingly, a need exists for a power generating system and method that can drive the accessories, provide cooling flow, not produce excessive drag and be relativey inexpensive.

An object of the present invention is to provide a power generating system and method that can provide power to drive accessories without substantially increasing the drag on the aircraft.

Another object of the present invention is to provide a power generating system and method that can provide power cooling flow requires by the components of the gas turbine engine.

Yet another object of the present invention is to provide a power generating system and method that can provide a power generating system and method that can operate at any mach number.

Yet still another object of the present invention is to provide a power generating system and method that is relatively inexpensive.

The present invention achieves the above-stated objective by providing a secondary power generating system and method that incorporates a high pressure, endothermic reaction to cool a portion of the air exiting the compressor section and to drive a motor, such as a turbine, that in turn drives the accessories. Additionally, this secondary power generating system also provides gaseous fuel for the combustor. The system includes a heat exchanger in which high pressure endothermic liquid fuel absorbs heat from the air exiting the compressor and as a result is transformed into a high pressure gas. The high pressure gas is expanded across a secondary power system motor that extracts the pressure energy and converts this energy into mechanical power for driving accessories. The gas is then fed into the combustor where it is ignited. Thus, instead of a bulky gearbox or an expensive ram air turbine, the present invention provides a relatively inexpensive heat exchanger, whose shape can be conformed so that it can be mounted within the gas turbine power plant casing or within the aircraft's frame thereby avoiding creating any drag.

These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawing.

The single FIGURE is a schematic, diagram of a secondary power generating system contemplated by the present invention in conjunction with a propulsion engine.

Referring to the drawing, a secondary power system generally denoted by the numeral 10 is shown in conjunction with a propulsion engine 12. It will be understood that the hardware execution of the propulsion engine 12, that embodies this invention, can be any one of a plurality of engine configurations such as, but not limited to, a turbojet, a ramjet, a turboramjet, or a combined cycle engine. Accordingly, the propulsion engine 12 in the sole figure typifies, very schematically, such an engine. The propulsion engine 12 is comprised of, in a flow series arrangement, an inlet section 14, a compressor section 16, a combustor section 18, a turbine section 20 and an exhaust nozzle section 22. The compressor section 16 and the turbine section 20 are operatively coupled by a rotatable shaft 24.

The secondary power system 10 includes a fuel tank 30 having an endothermic fuel, as a low pressure liquid, stored therein. Preferably, the endothermic fuel is Methylcyclohexane or Decalin. A fuel conduit 50 extends from the fuel tank 30 to a first flow path 36 in a heat exchanger 38. A fuel pump 32 operably disposed in the conduit 50 is provided by pressurizing the endothermic fuel and delivering the liquid fuel to the heat exchanger 38. Concurrently, with the liquid fuel being delivered to the first flow path 36, a portion of the hot air exiting the compressor section 16 is fed through a hot air conduit 60 to a second flow path 40 in the heat exchanger 38. The flow paths 36 and 40 are positioned in relation to each other to effect heat exchange therebetween without commingling of the liquid fuel and the hot air.

Within the heat exchanger 38, the high temperature energy of the air in the second flow path 40 is heat transferred to the first flow path 36 and absorbed by the liquid fuel therein. The liquid fuel then vaporizes and exits the heat exchanger 38 in a gaseous state with only a very small pressure drop. This high pressure gaseous fuel flows from the first flow path 36 through a gas conduit 54 to the combustor section 18 where it is ignited.

The secondary power system 10 further includes a gas operated motor, such as a drive turbine 42, disposed within the conduit 54 intermediate the heat exchanger 38 and the combustor section 18. The drive turbine 42 converts a portion of the pressure energy of the gaseous fuel into mechanical energy for rotating a shaft 44 which drives the fuel pump 32 and any other accessory such as a permanent magnet generator 46. A bypass conduit 56 is in fluid communication with the gas conduit 54 both upstream and downstream of the drive turbine 42. A control valve 58 is disposed within the bypass conduit 56 and controls the amount of fuel flow to the drive turbine 42. The cooled air exiting the second flow path 40 passes through cooling flow conduit 62 and back to the propulsion engine 12. Another conduit 66, having a control valve 68, is in fluid communication with the conduit 50 downstream of the fuel pump 32, and the conduit 54 downstream of the drive turbine 42. The conduit 66 delivers liquid fuel to the combustor 18 during the startup of the engine 12 and whenever the ram effect is not large enough to generate sufficient heat the compressor's 16 discharge air flow to initiate the change-of-phase of the endothermic fuel in the heat exchanger 38. Alternatively, it will be apparent to those skilled in the art that the present invention may also form a portion of a compound engine utilizing, perhaps, an independent fuel system to drive the engine 12 at the lower mach numbers.

A method for generating cooled air and gaseous fuel for a propulsion engine 12 and driving the accessories onboard an aircraft operating at a high mach number is also provided. In this method, a low pressure, liquid, endothermic fuel is pressurized and fed to the heat exchanger 38. Consequently, high pressure air having a high temperature energy is bled from the compressor section 16 and also fed to the heat exchanger 38. Within the heat exchanger 38, the high temperature air is placed into a heat transfer relation with the liquid fuel, whereby the temperature energy is extracted from the air and used to transform the liquid fuel into a high pressure, gaseous fuel. The cooled air is then delivered back to the propulsion engine 12. Meanwhile, the high pressure gaseous fuel is partly expanded across the drive turbine 42 of the secondary power system 10 before being delivered to the combustor section 18. The drive turbine 42 converts the pressure energy of the gaseous fuel into mechanical work for driving the accessories. To assure adequate flow of gaseous fuel to the combustor 18, a portion of the gaseous fuel is bypassed around the drive turbine 42.

Thus, a secondary power generating system and method is provided that can drive an aircraft's accessories, can deliver cooling flow and fuel flow to the aircraft's propulsion engine, can operate at high mach numbers, does not create significant drag and is relatively inexpensive.

Various modifications and alternations to the above described system will be apparent to those skilled in the art. Accordingly, the foregoing detailed description of the preferred embodiment of the invention should be considered exemplary in nature and not as limiting to the scope and spirit of the invention as set forth in the following claims.