Patent Application
20080060361
Inlet nozzle 22 uses the forward movement of vehicle 10 to force air into system 16 utilizing a converging type inlet. In some embodiments, inlet nozzle 22 includes components for varying the cross sectional area of nozzle 22 such that the inlet airflow can be optimized.
Isolator 24 regulates the airflow as it enters injection system 12 and combustor 26. Specifically, during ramjet operation, isolator 24 prevents propagation of shockwaves upstream into the inlet airflow during injection of fuel into combustor 26, which can lead to engine unstart. Isolator 24 prevents a shock train from interacting with the inlet airflow by providing a near constant area buffer between inlet nozzle 22 and combustor 26.
Injection system 12 injects fuel into the air stream such that a controlled burning of the fuel can occur within combustor 26. The controlled burning of the fuel in combustor 26 is used to accelerate the air stream through exhaust nozzle 28.
Exhaust nozzle 28 further accelerates the airflow as it exits system 16 to produce thrust. In some embodiments, exhaust nozzle 28 includes components for varying the cross sectional area of nozzle 28 such that the thrust can be optimized.
Since propulsion system 16 is operable in both ramjet and scramjet modes, two very different flow patterns develop within propulsion system 16, particularly within combustor 26. Thus, in order to optimally inject fuel into the air stream during scramjet and ramjet operation such that the controlled burning is optimized and controlled thermal choking is achieved in ramjet operation, injection system 12 is incorporated in propulsion system 16. Injection system 12 comprises multi-height ramp injectors that optimally distribute fuel across the cross section of the airflow during ramjet and scramjet operation. The ramp injectors also provide enhanced turbulence and mixing through vortex generation as the flow spills over the edges of the ramps. The bluff bases of the ramps also provide augmented flame stabilization. Other embodiments of the injector system can include a variety of small tabulators added to the ramps to enhance the fine scale mixing to improve overall combustion efficiency.
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Ramps 30A-30C are radially longer, or taller, than ramps 32A-32F such that they reach further into the core of airstream A, or the center of combustor 26. Ramps 30A-30C fuel the inner portion of airflow A, while ramps 32A-32F are thus left to primarily fuel the outer portion of airflow A. In one embodiment, ramps 30A-30B reach into the inner forty percent of airflow A, while ramps 32A-32F remain within the outer sixty percent of airflow A, as indicated by dashed line B. Since less fuel is required within the core of airflow A, only a few tall ramps are necessary to deliver the required amount of fuel. Around the outer circumference of combustor 26, where more air flows, a plurality of short ramps, along with the lower portions of the tall ramps, distribute the required amount of fuel. The number of tall ramps typically depends on how large the inner cross sectional area is compared to the outer cross sectional area. In the embodiment of the invention shown, three tall ramps and six short ramps are used to fuel the inner forty percent and outer sixty percent, respectively. The number of tall and short ramps, however, can be varied, along with the number of fuel injection nozzles or orifices on each ramp, to control the fueling of the inner and outer portions of airflow A. Thus, for any configuration, the fuel distribution across airflow A can be controlled.
Shorter ramps are less susceptible to heat problems than the taller ramps because they have less surface area extending into the airflow. Thus, in axi-symmetric cross sections, the present invention is particularly advantageous because it reduces the amount of tall ramps extending into airflow A. Both tall ramps 30A-30C and short ramps 32A-32F, however, benefit from external cooling such that they are operable in the high heat environment of airflow A. The present invention, however, also has practical applications for two-dimensional (2-D) combustors. For example, by avoiding wall injectors, the multi-height ramp injectors of the present invention avoid producing flame near the combustor wall. This keeps the combustion process nearer the center of the combustor and away from the wall, which reduced cooling requirements for the combustor.
For any combustor cross section, the multi-height ramps increase the fuel penetration capability of injection system 12 such that the need for bulkier and more complex injectors is eliminated. The pressure at which the fuel is injected into airstream A is reduced as compared to previous designs. Since ramps 30A-30C and 32A-32F are elevated into airstream A, the fuel stream does not need to be injected at a pressure of a magnitude necessary to penetrate the entire radius of airstream A. Thus, the high pressure requirements of wall injectors are eliminated. Additionally, the use of bulky and complex strut-type or pop-in injectors is also eliminated. Thus, no additional components or hydraulic systems are necessary around the exterior of combustor 26. The multi-height ramp injectors of the present invention also have advantages over wall and pop-in strut injectors in that they are able to produce more turbulence in the airflow.
The profiles of ramps 30A-30C and 32A-32F are selected to produce turbulence in airflow A within combustor 26 such that the fuel delivered by ramps 30A-30C and 32A-32F is more efficiently mixed with airflow A. In the embodiment shown, ramps 30A-30C and 32A-32F have generally trapezoidal cross sections with their radially innermost tops narrower than their radially outermost bottoms. In other embodiments, other profiles such as rectangular, triangular or fir tree may be used. In addition, the ramps may be skewed relative to the axial flow direction to further reduce combustor length and enhance low loss mixing and flame stabilization. For example, the ramps may be curved or twisted relative to the axial flow direction along the wall of isolator 24 to generate a swirl component to the flow that can further enhance low loss mixing and flame stabilization. For illustrative purposes,
The fuel injection nozzles or orifices located on ramps 30A-30C and 32A-32C can be positioned anywhere as required. For example, orifices are typically positioned along the tops and side, but could also be positioned on the downstream, bluff surface to optimally control the fueling of the flame stabilization regions. Also, multiple orifices can be used on each surface to optimally distribute the fuel to airflow A. For example, two side orifices may be used, and on tall ramps 30A-30C, one orifice may be used to supply the inner airflow and one orifice may be used to supply the outer airflow. As the injected fuel enters airflow A, it is quickly introduced into turbulence produced by ramps 30A-30C and 32A-32F.
The downstream-most face of each ramp is generally blunt such that a sharp drop-off is produced in the downstream direction as airflow A flows past ramps 30A-30C and 32A-32F. Thus, dead space in airflow A is established and the airflow must circulate back to fill the dead space, thus producing flow separation and turbulence. The blunt based ramps act as flame holders by producing turbulence to increase the residence time of the fuel as it is burned in airflow A. This assists in propagating flame growth toward the inner diameter of airflow A. Thus, the turbulence within this flame holding region acts as an in situ ignition source to augment the core flow combustion process. In other embodiments of the invention, the profile of ramps 30A-30C and 32A-32F produces enough turbulence and inward flame propagation so that step 36 can be omitted, thus reducing the diameter of combustor 26.
The parameters of ramps 30A-30C and 32A-32F, including their number, height and profile, depends on the desired operational parameters of vehicle 10, such as the desired speed range, flight range, cruising speeds, etc., and can thus be varied accordingly. In various other embodiments, the profiles of ramps 30A-30C and 32A-32F can be adjusted depending on the desired mixing characteristics. The height of the ramps can be adjusted depending on the desired proportion of the airflow to be fueled by the first set of ramps and the second set of ramps. Also, the desired cruising speeds of vehicle 10 may determine how much of the speed range falls within ramjet or scramjet operation of propulsion system 16. For example, if vehicle 10 was intended to have a very narrow speed range, meaning its top speed is relatively close to its bottom speed, then the height of the taller ramps could be selected to optimize performance at the cruising speed.
At the upstream most end of ramps 30A-30C and 32A-32F, the ramps are generally flush with the wall of isolator 24. As the ramps extend downward, they gradually increase in height. Ramp 30A has height h1 such that it reaches into the inner forty percent of airflow A, as indicated by cut-off line B. Ramp 32C has height h2 such that it supplies fuel to the outer sixty percent of airflow A. The rate at which ramps 30A-30C and 32A-32F increase in height, or their rise, depends on the design requirements and can be varied accordingly. Low rise ramps produce less drag and therefore require less cooling. High rise ramps enable fueling of the inner portion of the airflow, but require more cooling. Fuel injection system 12 is shown having ramps of two heights, although, in other embodiments, ramps having three, four or more different heights can be used.
Ramps 30A-30C and 32A-32F are shown having a swept profile, meaning that the upstream portions that are flush with the wall of isolator 24 are wider than the downstream portions, at the height of the ramps. This shape helps to keep isolator 24 at a constant cross sectional area to reduce losses in pressure and to avoid mechanical choking. Both the profile of the ramps and the overall diameter of isolator 24 can be varied along their length to control flow through propulsion system 16 to, for example, avoid choking and control pressure losses. However, other shapes or profiles of ramps 30A-30C and 32A-32F are acceptable based on design parameters and acceptable pressure losses. The downstream face of ramps 30A-30C and 32A-32F are generally planar with step 36 of combustor 26 such that a blunt base is formed. Specifically, the bases of the downstream faces are typically flush with step 36, and the face itself is generally perpendicular to the center axis of combuster 26. The downstream face, however, can be inclined slightly downstream to assist in flame spreading across the combustor. The blunt base and inclined faces assist also in producing turbulence in airflow A.
During ramjet combustion within propulsion system 16, fuel must be injected into combustor 26 gradually along the length of combustor 26 in order to prevent choking. Thus, tall ramps, such as ramp 30A, are used to initially fuel airflow A at its center, within the inner forty percent indicated by line B. After combustion has started, and the fuel mass has moved far enough downstream to avoid choking, wall injectors 34A and 34B are used to fuel the outer portion of airflow A. Wall injectors 34A and 34B are positioned within combustor 26 at a point further downstream where the fuel they inject can intercept the combustion process, further increasing the velocity of airflow A. The tall ramps and wall injectors 34A and 34B supply fuel to airflow A such that the flow remains below the choke point. As such, propulsion system 16 can continually increase the velocity of airflow A to a speed sufficient for beginning scramjet operation.
During scramjet combustion within propulsion system 16, airflow A is moving sufficiently fast such that the possibility of choking the mass flow is avoided. As such, the fuel required for sustaining scramjet, or hypersonic, combustion can be injected into airflow A within a short length of combustor 26. Thus, both the tall and short ramp injectors are used to fuel airflow A. Tall injector ramps, such as ramp 30A, are used to fuel the inner area of airflow A, while short injector ramps, such as ramp 32C, are used to fuel the outer area of airflow A. Additionally, the lower portions of the tall injector ramps can be used to fuel the outer portions of airflow A. Since the inner portion of airflow A makes up a lesser portion of the total mass of airflow A, less injection is needed toward the center of airflow A. Typically, the central region of airflow A can be fueled using three tall ramps 30A-30C. Additionally, since only a fractional amount of the mass of airflow A lies in the direct center of airflow A, injector ramps 30A-30C need not extend up to the direct center to supply fuel there. The tall and short ramps are interdispersed with each other with the taller ramps being equally distributed around the circumference of isolator 24 such that the innermost portion of airflow A is well supplied. The outer portion of airflow A is adequately supplied with fuel using the shorter ramps and the lower portions of the taller ramps. Wall injectors 34A and 34B are not needed and shut off because they would be injecting fuel too far downstream for hypersonic combustion.
Injector nozzles or orifices are positioned on multi-height ramps 30A-30C and 32A-32F in any suitable manner such that fuel can be delivered to the necessary locations in airflow A. For example, orifices 38 are positioned on the top, or radially inward, surface of injector ramp 32B, and orifices 40A and 40B are positioned on the sides of injector ramp 32B. Orifices 38 fuel the radially inward portion of airflow A, while orifices 40A and 40B fuel the portions of airflow A between the ramps. In other embodiments, orifices can be positioned on the downstream surfaces of the ramps to directly fuel the recirculation zones produced by the ramps. Such injectors could be separately operated by secondary controllers to coordinate fuel injection. Fuel injection orifices 38,40A and 40B thus need only be pressurized to penetrate a portion of airflow A. Tall ramps 30A-30C need only penetrate the innermost forty percent, while short ramps 32A-32F need only penetrate the outermost sixty percent. Thus, large, high pressure pumps can be eliminated from injection system 12.
Ramps 30A-30C and 32A-32F include internal hollow regions to accommodate components, such as cooling fluid and fuel lines, to bring fuel to orifices 38, 40A and 40B. Typically, orifices 38, 40A and 40B are positioned toward the downstream end of ramp 32B such that the injected fuel is rapidly introduced into turbulence produced by the presence of ramps 30A-30C and 32A-32F in airflow A.
The generally simple construction of ramps 30A-30C and 32A-32F make them easily scalable for different sized engines. Multi-height ramp injection system 12 includes no moving parts. Therefore, supplemental components need not be customized for each design of the system. Additionally, since the height of the ramps is being used to reach the innermost flow regions, problems associated with increasing pressure as scale increases are avoided. The shapes of the ramps, including profile, height, ramp rise, and swept profile, can be scaled up or down as necessary, and the parameters can be adjusted or coordinated to achieve optimal injection and mixing within different combustors.
Thus, multi-height ramp injection system 12 of the present invention achieves several advantages over previous injection system designs. For example, multi-height ramps 30A-30C and 32A-32F increase the turbulence in airflow A as compared to other designs. Thus, more efficient mixing and burning occurs during the combustion process and shorter, smaller propulsion systems can be designed. Also, multi-height ramp injection system 12 reduces the need for supplemental components, such as hydraulic actuators and high pressure pumps, such that the propulsion system can be reduced in overall size and weight. For example, since the multi-height ramps extend into the airflow, the need for increased fuel penetration and their associated pumps are eliminated.
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.
