Patent Publication Number: US-11639700-B2

Title: Airframe integrated scramjet with fixed geometry and shape transition for hypersonic operation over a large Mach number range

Description:
TECHNICAL FIELD 
     The disclosure relates to hypersonic airbreathing propulsion systems. More particularly, the disclosure relates to supersonic combustion ramjet (scramjet) engines. In some embodiments, the disclosure relates to airframe integrated scramjet engines. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       So that the manner in which the features and advantages of the invention can be understood in more detail, description of the invention briefly summarized above may be had by reference to the illustrations in the appended drawings. It is noted, however, that the drawings illustrate only an embodiment of the invention and therefore are not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments. 
         FIG.  1    is a cross-sectional schematic of a portion of an airframe of a hypersonic flight vehicle that includes an embodiment of an airframe integrated scramjet engine. 
         FIG.  2    is an isometric view an embodiment of the scramjet engine of  FIG.  1   . 
         FIG.  3    is a bottom view of the scramjet engine of  FIG.  1   . 
         FIG.  4    is an isometric view of an embodiment of an inlet of the scramjet engine of  FIG.  1   . 
         FIG.  5    is a front view of the embodiment of the inlet of  FIG.  4   . 
         FIG.  6    is a side view of the scramjet engine of  FIG.  1    depicting locations of fuel injection stations. 
     
    
    
     DETAILED DESCRIPTION 
     A scramjet is an airbreathing engine for hypersonic flight. It can be an alternative propulsion system to rockets for space launch and long-distance, high-speed flight. Hypersonic is defined as travel at speeds greater than or equal to Mach 5, with Mach 1 being the speed of sound in air at sea level. In certain embodiments, the scramjet engine may include an inlet, a combustor, and a nozzle. The inlet may be configured to capture airflow and compress it to conditions suitable for combustion of fuel with oxygen in the air. Air entering the combustor from the inlet can be burned with fuel while maintaining a supersonic velocity. The air and combustion products then pass into the nozzle where they are expanded and accelerated before leaving the scramjet engine to provide the hypersonic engine thrust. The scramjet engine is intended to generate a forward thrust force to power a hypersonic flight aircraft or vehicle while it is flying in the atmosphere at a hypersonic speed. If a scramjet engine is able to generate a forward thrust force at a particular flight Mach number it is considered to be operational at that flight Mach number. 
     In some embodiments a scramjet engine can be integrated smoothly into a hypersonic flight aircraft or vehicle airframe that it is designed to power at hypersonic speed. Furthermore, the scramjet engine may involve a transition in cross-sectional shape along its length such that the conflicting requirements of airframe integration and robust combustion can be satisfied. Additionally, the scramjet engine can be configured to generate a thrust force in the direction of motion over a large Mach number range with a fixed geometry. In other words, the scramjet engine may enable acceleration of the hypersonic flight aircraft or vehicle over a large hypersonic Mach number range without changing its shape. The ability to generate a thrust force in the direction of motion over a large hypersonic Mach range means that the scramjet engine is configured to accelerate the hypersonic aircraft or vehicle and can be used as part of a space launch system. 
     Embodiments may be understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood by one of ordinary skill in the art having the benefit of this disclosure that the components of the embodiments, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the disclosure but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated. 
     It will be appreciated that various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure. Many of these features may be used alone and/or in combination with one another. 
     The phrases “coupled to” and “in communication with” refer to any form of interaction between two or more entities, including mechanical, electrical, magnetic, electromagnetic, fluid, and thermal interaction. Two components may be coupled to or in communication with each other even though they are not in direct contact with each other. For example, two components may be coupled to or in communication with each other through an intermediate component. 
     The directional terms “fore” and “aft” are given their ordinary meaning in the art. That is, “fore” refers to a forward or leading portion of a hypersonic flight aircraft or vehicle airframe and “aft” refers to a rearward or trailing portion of a hypersonic flight aircraft or vehicle airframe. 
       FIGS.  1 - 6    illustrate different views of airframe integrated scramjet engine embodiments and related components. In certain views each engine may be coupled to, or shown with, additional components not included in every view. Further, in some views only selected components are illustrated, to provide detail into the relationship of the components. Some components may be shown in multiple views, but not discussed in connection with every view. Disclosure provided in connection with any figure is relevant and applicable to disclosure provided in connection with any other figure or embodiment. 
       FIG.  1    shows a schematic cross-section of a portion of a hypersonic flight aircraft comprising a vehicle airframe  190  which includes an airframe-integrated scramjet engine  100  according to the present disclosure. The vehicle airframe  190  is made up of the vehicle forebody  191 , an intermediate portion of the airframe  193  and the vehicle aftbody  192 . The disclosed scramjet engine  100  is one that is attached to the vehicle airframe  190  such that the vehicle forebody  191  compresses air captured by the scramjet engine  100 , and the vehicle aftbody  192  continues to expand exhaust from the scramjet engine  100  after it leaves the scramjet engine  100 . 
     The disclosed scramjet engine  100  may be smoothly integrated into the vehicle airframe  190 . This means that the scramjet engine  100  is attached to the vehicle airframe  190  such that air flowing along the vehicle forebody  191  passes smoothly into and around the scramjet engine  100  with minimal disruption or turbulence and/or that exhaust from the scramjet engine  100  flows smoothly onto and over the vehicle aftbody  192 . 
       FIG.  2    illustrates a capture shape  134 , shape transition  146 , and exit shape  164  of a disclosed scramjet engine  100 . As shown in  FIG.  2   , the disclosed scramjet engine  100  comprises a capture shape  134  that can be integrated smoothly with the forebody  191  of the hypersonic flight aircraft or vehicle airframe  190 , a contracting and expanding shape transition  146  over its length, and an exit shape  164  that can be integrated smoothly with the aftbody  192  of the hypersonic flight aircraft or vehicle airframe  190 . The shape transition  146  is a feature of the disclosed scramjet engine  100  that enables both the capture shape  134  and the exit shape  164  to be independently specified to meet geometric requirements of integrating smoothly with a range of different hypersonic flight aircraft or vehicle airframes  190 . Another feature of the shape transition  146  is that it enables an internal shape of the disclosed scramjet engine  100  to be configured for the generation of robust combustion and a thrust force in the direction of motion over a large Mach range. 
     An operational Mach range of a scramjet engine is the range of Mach number over which the scramjet engine generates a thrust force in the direction of motion. The minimum Mach number at which the disclosed scramjet engine  100  is operational is Mach 5. A large operational Mach range for a scramjet is considered to be an increase in Mach number of 3. The disclosed scramjet engine  100  has a minimum operational range from Mach 5 to Mach 8, so it can be considered to have a large operational Mach range. In some embodiments the disclosed scramjet engine  100  may have an operational Mach range from Mach 5 to Mach 12. 
     The disclosed scramjet engine  100  shown in  FIG.  2    can be integrated smoothly with the airframe  190  at the capture shape  134  and the exit shape  162  in order to generate a net thrust. If this is not the case, the thrust force generated by the scramjet engine  100  can be negated by external drag generated by the aerodynamic interaction between the hypersonic flight aircraft or vehicle airframe  190  and the scramjet engine  100 . In other embodiments, variations of the shape transition  146  may allow the scramjet engine  100  to be installed on differently shaped hypersonic flight aircraft or vehicles airframes  190 . 
     The capture shape  134  of the disclosed scramjet  100  is configured to capture a high proportion of available airflow at the upper Mach number of the disclosed scramjet engine&#39;s  100  operational range, but spill air at lower Mach numbers within its operational Mach range. 
     The disclosed scramjet engine  100  may be used to power a hypersonic flight aircraft or vehicle  190  during hypersonic flight. For example, the scramjet engine  100  may power a hypersonic flight aircraft or vehicle airframe  190  at hypersonic speeds within its operational Mach range without a change in geometry during hypersonic flight. 
       FIG.  3    illustrates an embodiment of the scramjet engine  100  according to the present disclosure. As shown, the disclosed scramjet engine  100  can comprise three general components. These components are (1) an inlet  120 , which is configured to capture hypersonic airflow and compress and heat the airflow to conditions suitable for combustion of fuel through the action of shock waves and airflow dilation; (2) a combustor  140 , where fuel and air are burned so as to add energy to the airflow passing through the scramjet engine  100 ; and (3) a nozzle  160 , where combustion products (e.g., water and carbon dioxide) and any unburned air or fuel are expanded to generate a thrust force. The inlet  120  comprises a surface that extends from the capture shape  134  to a throat  129  of the disclosed scramjet engine  100 . The combustor comprises a surface that extends from the throat  129  to a nozzle entrance  128 . The nozzle  160  comprises a surface that extends from the nozzle entrance  128  to the exit shape  164  of the disclosed scramjet engine  100 . 
       FIG.  4    depicts an embodiment of the inlet  120  of the scramjet engine  100  according to the present disclosure. The capture shape  134  of the inlet  120  can be configured to be smoothly integrated with the forebody  191  of the hypersonic flight aircraft or vehicle airframe  190 . In other embodiments, the capture shape  134  of the inlet  120  can be adjusted to facilitate smooth integration with any suitable hypersonic flight aircraft or vehicle airframe, including winged hypersonic aircraft or hypersonic missiles. For example, the forebody  191  can include a convex shape, a concave shape, a planar shape, etc. 
     The capture shape  134  of the inlet  120  is a closed shape that comprises a bodyside leading edge  130 , a pair of side leading edges  122 , and a pair of cowl leading edges  125 . The bodyside leading edge  130  is attached directly to the forebody  191  along its entire length. The pair of side leading edges  122  are attached to each end of the bodyside leading edge  130  and are projected aft and away from the forebody  191  at an angle less than 90 degrees to the forebody  191 . The pair of cowl leading edges  125  are attached to aft ends of the side leading edges  122  and are disposed between the side leading edges  122  to join at a cowling notch  126 . The cowling notch  126  may be configured to allow excess airflow to be spilled from the inlet  120  as further described below. 
     The inlet  120  may be a mixed contraction inlet. The capture shape  134  of the inlet  120  is configured to provide external and internal air compression or contraction, that enables the scramjet engine  100  to be self-starting over its operational Mach range. Self-starting means that supersonic airflow will be established through the scramjet engine  100  at applicable hypersonic flight Mach numbers. If supersonic flow is not established, then the scramjet engine  100  cannot produce a thrust force in the direction of motion at hypersonic flight conditions. The inlet  120  is configured to provide the required amount of airflow compression to make possible robust combustion of fuel and air in the combustor  140 . 
     The throat  129  of the disclosed scramjet  100  can be disposed aft of the cowling notch  126 . The throat  129  can have a cross-sectional area that is smaller than the capture shape  134 . The throat  129  can be in communication with the inlet  120  and the combustor  140  such that air collected by the inlet  120  flows from the inlet  120  through the throat  129  and into the combustor  140 . The throat  129  can have a rounded shape. For example, the rounded shape may be elliptical, circular, oval, or any other suitable shape that does not contain any sharp corners. 
       FIG.  5    illustrates a view of the inlet  120  according to the present disclosure looking downstream.  FIG.  5    depicts the inlet  120  having a smooth shape transition from the capture shape  134  to the rounded throat  129 . The smooth shape transition is depicted as imposed contour lines  131  that are substantially evenly spaced from the capture shape  134  to the rounded throat  129 . The smooth shape transition of the inlet  120  can lead to low internal drag and therefore the opportunity for greater overall thrust from the disclosed scramjet engine  100 . 
     As shown in  FIG.  3   , the rounded throat  129  connects directly to an entrance of the combustor  140 . The shape and cross-sectional area of the rounded throat  129  are the same as the combustor entrance. The cross-sectional area of the combustor  140  may increase along its length from the combustor entrance to a combustor exit. The combustor  140  has a rounded cross-section without sharp corners along its full length. The combustor  140 , having a rounded cross-section, is superior to a combustor  140  having a cross-section that includes corners (e.g., square, rectangular, etc.) in terms of a lower structural weight required to contain a specified pressure, and a smaller surface area over which the airflow passes needed to enclose a specified flow area. Fluid dynamic problems associated with hypersonic corner flows are also not present with the rounded cross-section of the combustor  140   
     The area and cross-sectional shape of the combustor  140  are varied along its length such that fuel can be burned efficiently over the operational Mach number range of the scramjet engine  100 , without any adjustment to its physical shape. This is accomplished by including multiple fuel injectors in the engine and making use of different combinations of the fuel injectors and the metering level of fuel from each fuel injector. 
     As illustrated in  FIG.  3   , the combustor  140  includes a single backward facing step  141  around the circumference of its rounded cross-sectional area. 
       FIG.  6    shows a side view of the scramjet engine  100  according to the present disclosure, indicating possible locations of four fuel injection stations  142 ,  143 ,  144 ,  145  along the length of the scramjet engine  100 . As depicted in  FIG.  6   , the fuel injection stations  142 ,  143 ,  144 ,  145  can be located: 
     on the bodyside  133  of the inlet  120  (station  1   142 ); 
     upstream of the backward facing step  141  (station  2   143 ); 
     adjacent the backward facing step  141  (station  3   144 ); and 
     downstream of the backward facing step (station  4   145 ). 
     The pressure, temperature and velocity of air entering the disclosed scramjet engine  100  changes as it accelerates from Mach 5 to higher Mach numbers. This means that shock waves and other features of the hypersonic airflow within the scramjet engine  100  will also change. The disclosed scramjet engine  100  has a fixed geometry, so there is no movement of the shape or geometry of the scramjet engine  100  over its full length during hypersonic flight. To have a large operational Mach number range, fuel injection stations  142 ,  143 ,  144 ,  145  may be used, individually or in different combinations, and at different fuel metering levels, to maximize the combustion efficiency of the disclosed scramjet engine  100  with a goal of burning more than 80% of the oxygen in the air that is captured by the disclosed scramjet engine  100 . 
     The use of the fuel injection stations  142 ,  143 ,  144 ,  145 , individually or in combination, and at different fuel metering levels, varies depending on the flight Mach number. For example, at the upper portion of the operational Mach range, where mixing between fuel and air is the greatest challenge, fuel is injected at station  1   142  on the bodyside  133  of the inlet  120  at metering levels of up to 50% of a total fuel metering level in order to take advantage of the inlet length to increase mixing between fuel and air; the remaining fuel would be injected at stations  2  and  3  upstream  143 ,  144  and adjacent to the backward facing step  141 . At the intermediate portion of the operational Mach range, fuel is injected at stations  2  and  3   143 ,  144  upstream and adjacent to the backward facing step  141  only, at metering levels ranging between 40% and 60% of the total fuel metering from each station. At the lower portion of the operational Mach range, injection of fuel upstream of the backward facing step  141  can create a large pressure rise in the disclosed scramjet engine  100  that could lead to an engine unstart. Fuel is therefore injected at stations  2  and  3   143 ,  144  upstream of the backward facing step  141  at a combined metering level of less than 70%, with up to 30% injected at station  4   145  downstream of the backward facing step  141 . 
       FIG.  3    depicts one embodiment of the nozzle  160  of the scramjet engine  100  according to the present disclosure. As depicted, the nozzle  160  extends aft from the combustor  140 . The nozzle  160  includes an expanding shape transition from the rounded cross-sectional shape of the combustor  140 , to an exit shape  164  that integrates smoothly with the hypersonic flight aircraft or vehicle airframe  190  (not shown in  FIG.  3   ). The nozzle  160  has a smoothly varying cross-sectional shape that expands in area along its length and is ended at the exit shape  164 . The exit shape  164  can be adjusted to meet the requirement of being smoothly integrated with the hypersonic flight aircraft or vehicle airframe  190 . Other embodiments of the nozzle  160  with different exit shapes  164  allow smooth airframe integration on hypersonic flight aircraft or vehicles that have curved or other aft body shapes. 
     While the invention has been shown or described in some of its forms, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following claims. 
     Any methods disclosed herein comprise one or more steps or actions for performing the described method. The method steps and/or actions may be interchanged with one another. In other words, unless a specific order of steps or actions is required for proper operation of the embodiment, the order and/or use of specific steps and/or actions may be modified. 
     References to approximations are made throughout this specification, such as by use of the term “substantially.” For each such reference, it is to be understood that, in some embodiments, the value, feature, or characteristic may be specified without approximation. For example, where qualifiers such as “about” and “substantially” are used, these terms include within their scope the qualified words in the absence of their qualifiers. For example, where the term “substantially perpendicular” is recited with respect to a feature, it is understood that in further embodiments, the feature can have a precisely perpendicular configuration. 
     Similarly, in the above description of embodiments, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure. This method of disclosure, however, is not to be interpreted as reflecting an intention that any claim require more features than those expressly recited in that claim. Rather, as the following claims reflect, inventive aspects lie in a combination of fewer than all features of any single foregoing disclosed embodiment. 
     The claims following this written disclosure are hereby expressly incorporated into the present written disclosure, with each claim standing on its own as a separate embodiment. This disclosure includes all permutations of the independent claims with their dependent claims. Moreover, additional embodiments capable of derivation from the independent and dependent claims that follow are also expressly incorporated into the present written description. 
     Without further elaboration, it is believed that one skilled in the art can use the preceding description to utilize the invention to its fullest extent. The claims and embodiments disclosed herein are to be construed as merely illustrative and exemplary, and not a limitation of the scope of the present disclosure in any way. It will be apparent to those having ordinary skill in the art, with the aid of the present disclosure, that changes may be made to the details of the above-described embodiments without departing from the underlying principles of the disclosure herein. In other words, various modifications and improvements of the embodiments specifically disclosed in the description above are within the scope of the appended claims. Moreover, the order of the steps or actions of the methods disclosed herein may be changed by those skilled in the art without departing from the scope of the present disclosure. In other words, unless a specific order of steps or actions is required for proper operation of the embodiment, the order or use of specific steps or actions may be modified. The scope of the invention is therefore defined by the following claims and their equivalents.