Patent Application
20190301400
The present invention generally relates to vehicle propulsion systems comprised of scramjets and rockets and, more particularly, to combinations of rockets and scramjet nozzles allowing for a non-two dimensional, non-toroidal, non-plug cluster system, in combination with a three dimensional aerospike nozzle, fully termed Rockets Embedded in Scramjet Nozzle (RESN).
Hypersonic vehicles utilizing air breathing supersonic combustion ramjet (scramjet—a ramjet in which combustion occurs within a supersonic gas flow regime) engines traditionally require external devices to accelerate the vehicle in flow regimes where the scramjet engine may be inoperable. Scramjet engines require a very high-speed airflow at an inlet to compress a mixture of air and fuel to be ignited to provide a volume of gases at high pressure which expands against an exhaust nozzle and thus provide thrust. Accordingly, these flow regimes in which a scramjet is inoperable include flight in the upper atmosphere where air density and atmospheric pressure are very low, space (vacuum or near vacuum), and at lower freestream Mach numbers, and for take-off from ground. Presently in the current state-of-the-art, it has been suggested to use a combination of turbines and rockets to accelerate the scramjet from ground to Mach 3.5, at which point the ramjet flowpath can be ignited, providing thrust to the vehicle. More specifically, the speed that can be attained with turbine propulsion is limited to about Mach 2-2.5 and rocket propulsion is required to achieve a speed of about Mach 3.5 for efficient use of a ramjet. Vehicles using scramjets must also rely on rockets in the upper atmosphere, where the air density is too low for the scramjet.
It has been traditionally proposed to mount these rockets at an external location on the vehicle that is separate from the internal scramjet flowpath. However, such a configuration leads to increased vehicle weight and thus more fuel; also increasing weight. It follows that a larger scramjet would be needed to accommodate this extra mass.
These design problems are further complicated by the fact that traditional rockets utilizing substantially conical bell nozzles have limitations in their optimal operation. They are often designed for optimal performance at a specific altitude along the vehicle flight path. That is, bell nozzles have a length and expansion angle to provide an area ratio (AR) that will result in thrust within a suitable range for propulsion of a particular vehicle while the AR to provide optimum thrust will vary with ambient air pressure at the exhaust exit plane of the bell nozzle; lower pressures at higher altitudes requiring higher AR for efficient operation. Of course, rocket nozzles must be very robust structures that can develop thrust and transfer that thrust to the vehicle being propelled and thus, as a practical matter, cannot be altered in AR during operation. That is, any rocket nozzle will have a fixed length and fixed shape that is generally optimized in accordance with the rate of expansion of the combustion products of the burning fuel at a chosen ambient pressure. Therefore, the AR cannot be smoothly varied as altitude increases and ambient pressure diminishes. For example, two-stage rockets of a known type that is used to lift a payload into Earth orbit, referred to as two-stage to orbit (TSTO), the first stage will typically have bell nozzles with a small AR (e.g. less than 50) while the second stage that is used only in the low ambient pressure of the upper atmosphere will have a significantly larger AR (e.g. greater than 50 and typically greater than 100) and correspondingly greater length. Thus, the requirement for different rockets with different ARs for respective stages is a major reason for providing different rockets for multi-stage systems for placing satellites in orbit.
So-called aerospike nozzles, similar in overall shape and dimensions to comparable bell nozzles but having a sharply angled exhaust exit edges at different distances from the combustor where fuel is ignited, have addressed this issue by allowing for a reduced effective area ratio at higher pressure altitudes, and an increase in area ratio at lower pressure altitudes using the ambient pressure. In other words, aerospike nozzles provide a limited degree of ambient pressure compensation whereas none is provided by bell nozzles. Aerospike nozzles may be either a two-dimensional (2-D) or three-dimensional (3-D) configuration. The 2-D configuration has a curved surface (e.g. upper surface) at increasing distance (in the direction of flow from an opposing (e.g. lower) surface to develop thrust from exhaust gas expansion and, in a 2-D aerospike nozzle, the terminal edges of upper and lower surfaces being terminated at different distances from the combustor. The sides of the 2-D configuration are joined by further, generally parallel surfaces to confine the expanding gas. This 2-D configuration was proposed for the Venture Star (designated X-33) design but requires a compatible vehicle geometry. 2-D aerospike nozzles have highly rectangular combustor cross-section leading to high heat transfer and corresponding viscous drag resulting in lower performance.
The 3-D configuration is essentially non-rectangular with the terminal edge being either planar or scarfed (e.g. the shape being cut at non-planar locations). A toroidal aerospike nozzle requires a large number of separate nozzles and throats as they surround a circle and is thus unduly complex, structurally.
It is therefore an object of the present invention to provide a solution to all of the above problems and design constraints by the simple expedient of embedding one or more lower expansion ratio rockets within a scramjet nozzle.
It is another object of the present invention to utilize the scramjet nozzle as it already exists within the vehicle for further expansion of rocket exhaust products to increase the effective AR of the rocket(s).
It is another object of the present invention to provide a propulsion system including a scramjet having a relatively small and light weight rocket system with a reduced AR that is capable of a thrust specific impulse greater than a space shuttle main engine and provide substantial gain in specific impulse thrust over a combination of a scramjet and rockets of similar design and type while also achieving a substantial reduction in size and weight.
It is a further object of the invention to provide for earlier and lower speed start of ramjets with higher temperature provided by rocket exhaust flow.
It is yet another object of the present invention to provide for operability of a scramjet over an increased range of altitude and ambient pressures.
It is yet another objective of the present invention to provide small size for the RESN rocket exit areas that would have minimal detrimental effect on ramjet or scramjet performance when only they are in operation during the purely air breathing phase.
In order to accomplish these and other objects of the invention, a propulsion system for a vehicle comprising, one or more rockets having an area ratio in a range of 3 to 50, and a scramjet including a nozzle having the one or more rockets embedded in an interior surface thereof and an aerospike exhaust outlet.
The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which:
Referring now to the drawings, and more particularly to
The rocket nozzles may be of any arbitrary number but five is considered somewhat preferable in view of the increase in complexity for greater numbers of rockets. It is also preferred that the rocket nozzles 40 be located in a two-dimensional array (in axial view) preferably near the periphery of a portion of the scramjet nozzle or even surround the scramjet nozzle. As a perfecting feature of the invention, can be separately controlled to provide a degree of directed thrust either alone or in combination with the scramjet thrust to control yaw and pitch of the vehicle in which the invention is employed as control surfaces of the vehicle become progressively ineffective at very high altitudes, and also at other points in trajectory as they have relatively high thrust compared to the air breathing phase.
The scramjet nozzle 50 is carved out as a scarfed nozzle as shown in
The invention, in its broadest expression is the provision of embedded rockets having a low (e.g. less than 50) AR appropriate to low altitude operation in the nozzle of a scramjet allowing for further rocket flow overall expansion of approximately 900 or higher effective AR which is the ratio of scramjet nozzle exit area to the total rocket throat area. Thus the potential for rocket flow expansion is very high, as is exploited by the present invention. This, in combination with a modified scarfed aerospike exhaust nozzle of limited AR and length as compared with known aerospike nozzles. The AR is computed using a projection of the terminal edge of the nozzle on a plane perpendicular to the nozzle axis divided by the throat area. As can be seen in
This placement of the rockets allows for aerospike characteristics within the scramjet nozzle. At higher altitudes where the pressure within the nozzle is much lower, the flow exiting the rocket can achieve much greater expansion ratios into the much greater volume of the scramjet exhaust nozzle; allowing for more optimal, increased thrust and resulting specific impulse. At lower altitudes, the ambient pressure is higher; leading to higher pressures within the scramjet nozzle. This automatically results in a decrease in expansion, relative to a lower pressure environment, allowing for more optimal rocket performance at lower altitudes. This effect is similar to the altitude compensation effect, alluded to above. However, the effect is much greater and differs from effects of traditional aerospike nozzles which is responsive only to the ambient pressure. In sharp contrast therewith, this invention exploits and is responsive to the pressure within the scramjet nozzle, itself, which is controllable through control of the embedded rockets and which, in most cases, is monotonically related to the ambient pressure and flight Mach number. That is, the rocket flow enters the scramjet nozzle at supersonic speed; continuing to expand and increase the vehicle thrust while also providing substantial gas flow within the scramjet even when the vehicle is stationary. Therefore, the rockets can provide substantial thrust even under conditions where the scramjet or ramjet cannot operate; presenting the possibility of horizontal take-off of a vehicle employing the invention from a standing start. Thereafter, as speed increases, the scramjet structure can be operated at subsonic (as in a ramjet) to supersonic speeds until the scramjet begins to operate with supersonic combustion. Scramjet operation can then be continued until atmospheric pressure falls to a point where the scramjet starves. It is important that, due to the flow from the rockets, scramjet operation can be continued to somewhat higher altitudes than is possible with the scramjet, alone. This expanded range of altitude and speed for scramjet operation is an important aspect of the unexpected and very substantial synergy of the combination of rockets embedded in the scramjet nozzle and the modified aerospike scramjet exhaust nozzle. These meritorious effects of the invention appear to be relatively consistent over the entire speed and altitude range for which scramjet operation is contemplated.
These benefits of the invention have been quantified by computational fluid dynamics (CFD) results which support the achievement of these meritorious effects as will now be described. Specifically, axisymmetric, two-dimensional results are computed to quantify performance benefits of this invention. The configurations and Figures presented here are for quantification purposes and do not embody the full scope of this invention.
To evaluate the performance benefits of this invention, the thrust is compared against a baseline thrust. This baseline thrust is the sum of two thrust values: 1. thrust from the scramjet nozzle with the same isolator inflow conditions and no embedded rocket, and 2. the thrust from the inflow conditions of the embedded rocket. The baseline thrust is then subtracted from the thrust of the simulation and then divided by the gravitational acceleration (for normalization) and rocket mass flow rate to obtain the ISP (specific impulse), a traditional measure of rocket and scramjet performance.
The results are similar for a different isolator entrance condition case, which corresponds to a lower altitude of 93,000 ft. and higher Mach number of 9.5 which would occur just before the scram cutoff at the start of orbital insertion phase. The CFD results are presented in
The same trend is seen for expanding the rocket flow further through the embedded rocket before expanding into the scramjet nozzle. In
In view of the foregoing, it is clearly seen that the invention provides a solution to numerous problems and design constraints of scramjets having bell nozzles or conventional aerospike nozzles by the simple expedient of embedding one or more rockets within a scramjet nozzle. The invention also provides a propulsion system including a scramjet having a relatively small and light weight rocket system with a reduced AR (compared with known aerospike nozzles) that is capable of a specific impulse comparable to or greater than a space shuttle main engine and provides substantial gain in specific impulse over a combination of a scramjet and rockets of similar design and type while also achieving a substantial reduction in size and weight. The invention also provides for earlier and lower speed start of ramjets with higher temperature and reduced intake airflow speed environment provided by rocket exhaust flow as well as operability of a scramjet over an increased range of altitude and ambient pressure. With rockets having an AR in the range of 10-20, the total ISP provided by the invention using comparable total rocket thrust is higher than the space shuttle main engine (SSME) and, within that range, performance appears to be independent of the AR of the rocket(s). That is, the invention provides a substantial gain in ISP and thrust compared to a standalone rocket and scramjet of the same type. The altitude compensating aerospike characteristic provides near optimal thrust performance at an expanded range of altitudes.
The existence of the scramjet nozzle surface allows for high exhaust gas expansion of rockets embedded in the scramjet nozzle which may, themselves be of low expansion and area ratio such as near 10 to 20; outside of which range the meritorious effects of the invention other than thrust gain can be expected to be compromised. The total expansion of the rocket flow allows for substantial performance enhancement creatin specific impulse thrust much larger than if an external rocket such as the SSME were used, approximating about 462-465 seconds at high altitude beyond 150,000 feet. Further, in accordance with a preferred embodiment of the invention, the presence of RESN rocket exhaust does not adversely affect the ISP performance of the scramjet more than 1-3 seconds which is approximately 0.0% of the scramjet ISP at the same flight conditions.
While the invention has been described in terms of a single preferred embodiment, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.
This application claims benefit of priority of U.S. Provisional Application 62/648,967, filed Mar. 28, 2018, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62648967 | Mar 2018 | US |
