Some types of flight propulsion systems for operation in the subsonic, supersonic, and hypersonic regimes include rockets, turbojets, ejector ramjets, and dual mode ramjets. While rockets function at any Mach number, state-of-the art turbojets generally operate over a Mach range from 0 to about 2.5. Ejector ramjets generally operate at lower Mach numbers, e.g., Mach 0 to 2.5, in ducted rocket mode and at higher Mach numbers, e.g., Mach 2.5 to 4.3, in mechanically choked ramjet mode. Dual mode ramjets generally operate at lower Mach numbers, e.g., Mach 4 to 5.5, in thermally choked ramjet mode and at higher Mach numbers, e.g., Mach>5.5, in scramjet mode.
Combined cycle propulsion systems using a graduating series of propulsion systems are being developed to operate over wide Mach ranges. In particular, a Rocket-Based Combined Cycle (RBCC) propulsion system may include a dual mode ramjet and a ducted rocket that share the same flow path. A Turbine Based Combined Cycle (TBCC) propulsion system, in contrast, may combine a turbojet with one or more other types of “airbreathing” propulsion systems such as a ramjet or a dual mode ramjet. Airbreathing engines use atmospheric air as a source of oxygen for combustion as opposed to rockets, which carry and use on-board oxygen sources. Airbreathing flight propulsion systems may need to be larger and more massive to capture and use oxygen from the atmosphere, but airbreathing flight propulsion systems are generally several times more efficient than rockets in terms of specific impulse. In particular, specific impulse, which may be defined as thrust produced per unit of the sum of on-board fuel and oxidizer flow, may be higher for pure airbreathing systems because the on-board oxidizer flow is zero resulting in a larger specific impulse.
Currently published TBCC system proposals typically suffer from four major problems: (1) Insufficient take-off and transonic (M=˜1) push-through thrust; (2) Insufficient thrust between the high end of turbojet operation, e.g., M=1.6 to 3.5, depending on the turbojet design, and the low end of an engine, such as a Dual Mode Ramjet (DMRJ), capable of operating at higher Mach numbers, e.g., M=2.5 to 4 depending on DMRJ design; (3) Inability to smoothly and efficiently transition during vehicle acceleration from one TBCC component propulsion system to another, e.g., from turbojet operation to DMRJ operation; and (4) A lack of thermal protection (a.k.a. cocooning) of the turbojet upon an in-flight shutdown of the turbojet to assure a reliable in-flight restart of the turbojet.
The problems occurring in flight after turbojet shutdown in a TBCC have two major elements. First, rotor core heat needs to be removed from the turbojet to avoid binding between the hot turbine wheel and the cooling and as such contracting turbine housing. Second, turbine bearings and other mechanical structures, control electronics, and seals in the turbojet must remain within safe temperature limits while the turbojet is shutdown, despite heat flowing into the turbojet compartment through radiation and conduction through engine mounts (from other operating propulsion systems), and convection (from seal leakage of inlet and exit flow control panel devices). Cocooning of the turbojet in a TBCC system to protect it from thermal problems adds complexity and mass to the system, and the added mass may be in excess of the available vehicle payload. Accordingly, most, if not all published TBCC systems currently ignore both post-shutdown and restart issues.
Literature available on TBCC engine concepts include three published concepts that typify some of the issues, drawbacks, inadequacies, limitations, requirements, or specific in-flight complications of TBCC propulsion systems.
Melvin Bulman and Adam Siebenhaar, “Combined cycle propulsion: Aerojet innovations for practical hypersonic vehicles,” 17th AIAA International Space Planes and Hypersonic Systems and Technologies Conference, 2011, AIAA 2011-2397 describes a TBCC propulsion system sometimes referred to herein as the “TriJet concept.” The TriJet concept employs an inward turning inlet that supplies airflow to a state-of-the-art turbojet, an ejector ramjet (ERJ) with a bi-propellant rocket primer, and a dual mode ramjet (DMRJ). The TriJet concept further employs two nozzles, one for the state-of-the-art turbojet and a single expansion ramp nozzle (SERN) that integrates the exhaust flows of the ERJ and the DMRJ. Hinged doors operated dependent on the flight Mach number control the inflows to the various engines and the exhaust flows into the nozzles.
Baoxi Wei, Wenhui Ling, Feiteng Luo, and Qiang Gang, “Propulsion Performance Research and Status of TRRE Engine experiment,” 21st AIAA International Space Planes and Hypersonics Technologies Conference, (AIAA 2017-2351) discloses a Turbo-aided Rocket-augmented Ramjet Engine (TRRE) concept. The TRRE concept employs an over-under inlet that supplies airflow to a turbojet, a DMRJ with a flowpath integrated thrust augmentation rocket, and a common SERN that integrates the exhaust flow of the turbojet and the DMRJ. The inflows to the various engines and the exhaust flows into the common nozzle are controlled by hinged doors that are positioned as a function of the flight Mach number.
The US SR-72 concept, or so called “Over-Under” concept, was featured in Aviation Week, “Integrated propulsion breakthrough key to Skunk Works' hypersonic SR-72 concept”, Nov. 1, 2013 Guy Norris|Aviation Week & Space Technology. The Over-Under concept employs a common inlet that supplies airflow to a turbojet and a DMRJ, and a SERN integrates the exhaust flows of the two engines. The turbojet required for the Over-Under concept is currently beyond the state of the art, being required to operate at high temperature and up to Mach 3 to 4.
These concepts or proposals generally address the common TBCC problems of insufficient take-off and transonic push-through thrust, insufficient thrust between the high end of turbojet operation and the low end of DMRJ operation, and transitions during vehicle acceleration from one TBCC integrated propulsion system to another. The current proposals, however, do not address the cocooning problem. Without a solution to this problem, the concepts are not feasible.
The drawings illustrate examples for the purpose of explanation and are not of the invention itself. Use of the same reference symbols in different figures indicates similar or identical items.
Combined cycle propulsion systems (CCPSs) as disclosed herein integrate multiple engine components, e.g., a low-speed propulsion system (LSPS), and a mid-speed propulsion system (MSPS), and a high-speed propulsion system (HSPS), into a module having a common inlet and a common nozzle. The various propulsion systems in a CCPS module generally operate sequentially with some overlap during the transition from one type of propulsion to the next. Depending on the specific configuration, a CCPS module may be laterally symmetric or laterally asymmetric with respect to the common inlet, the common nozzle, and the engines selected for the propulsion systems. Depending on the sizes and masses of modules, flight vehicles can be configured with various combination of CCPS modules, for example, one or more symmetric CCPS modules, one or more pairs of mirrored asymmetric CCPS modules, or a mix of symmetric and asymmetric CCPS modules.
A HSPS flow path in CCPS module 1000 includes inlet 1100 feeding air in an X-direction to a combustor of HSPS 1300 and exhaust from HSPS 1300 exiting to common nozzle 1200. An LSPS flow path in CCPS module 1000 includes a forward transition or bypass duct 1110 from inlet 1100 to an engine of LSPS 1400, and an aft-transition duct 1210 from the engine of LSPS 1400 to the common nozzle 1200. The MSPS flow path includes two parallel (port and starboard) bypass ducts, each including a forward transition duct 1120 from inlet 1100 to an engine of MSPS 1500 and an aft-transition duct 1220 from that MSPS engine to common nozzle 1200. Flows through the various bypass ducts 1110 and 1120 are in respective Xo*, Xp*, and Xs* directions, which may be at different angles and offsets from the X-direction defining flow into the HSPS 1300.
An exemplary configuration of CCPS module 1000 can employ a turbojet in LSPS 1400, two ejector ramjets (ERJs) in MSPS 1500, and a Dual Mode Ramjet (DMRJ) in HSPS 1300, providing the capability to operate such a configuration of CCPS module 1000 over a flight regime range of Mach 0 to 6.
HSPS 1300 in this exemplary and other configurations has a channel that is always open, but peripheral channels 1110 and 1120 can be gradually opened and closed using respective air flow control systems including a set of hinged inlet flow control panels 1122 and 1124 for bypass duct 1110 and a set of hinged inlet flow control panels 1126 and 1128 for each bypass duct 1120. In order to achieve the ability to vary the internal inlet contraction, the hinge point of drive systems 1117 of each forward panel 1122 or 1126 is located inside the internal contraction section of inlet 1100, which starts at a plane defined by a “crotch” 1111 of inlet 1100. That means that the hinge points of drive systems 1117 are a distance D in the X-direction behind crotch 1111. Lowering internal inlet contraction is significant when attempting to start HSPS 1300. (“Start” stands here for achieving supersonic flow inside a duct.) Once started, the contraction in HSPS 1300 can be increased by moving panels 1122 and 1126 into their respective closed positions without “unstarting” the HSPS. When an inlet panel is in a closed configuration, the air flow to the respective channel is blocked. When an inlet flow control panel 1124 or 1126 is open, partially or fully, air flow from inlet tube 1100 is directed into channel 1110 or 1120. In general, air flow from inlet 1100 is thus split, flows through, and exits through all partially or fully open channels, including the channel of HSPS 1300. Flow control panels 1122, 1124, 1126, and 1128 are located in the forward channel transition sections 1110 and 1120. As illustrated these forward transition ducts 1110 and 1120 may have rectangular cross section whose aspect ratios change along their centerlines. Rectangular ducts permit rotation of the rectangular hinged panels 1122, 1124, 1126, or 1128 and appropriate sealing along the duct sidewalls.
Each individual flow control panel system on the inlet side as shown in
The total flow captured (the 100% level) by the inlet of a CCPS module is a function of flight Mach number and altitude of flight. Assuming a typical Mach-altitude flight profile for a hypersonic vehicle, the total flow captured can be expressed as a function of Mach number only. A typical flow management scheme for a CCPS module during flight is illustrated in
The trubojet flow channel is wide open at Mach 0 to maintain a maximum available flow 441 to the turbojet until a point 442, corresponding to Mach 1.8 as an example, where the percentage flow to the turbojet begins to decrease and the percentage to the ejector ramjets begins to increase. Between Mach 1.8 and 2, the turbojet channel of LSPS 1400 receives a decreasing flow 443 that decreases to about 15% of the maximum available flow 410 at a point 444. Flow 443 may initially be used for operation of the turbojet simultaneously with operation of the ejector ramjets and may later be used for cooling the core of the then shut down but windmilling turbojet. After core-cooling, at point 444, the turbine flow through LSPS 1400 is completely shut off.
Percentage air flow 451 to MSPS 1500 may be 20%, for example, during solo operation of the turbojet. The MSPS flow 451, more generally, may be non-zero and may be chosen to reduce drag-inducing spill flow from the common inlet. Additionally, the common nozzle of the CCPS may be too large for the flow received if MSPS flow 451 were zero, which could cause unwanted nozzle performance losses during operation of turbojet alone. At point 452, when percentage air flow to the turbojet starts decreasing, percentage air flow to MSPS 1500 starts increasing to be used in the ejector ramjets of MSPS 1500 for mid-speed thrust production. The ejector ramjets may be employed together with the turbojet to provide thrust until a point 453, when the turbojet is shut down. After the turbojet is shut down, the thrust to further accelerate the vehicle may come only from MSPS 1500, e.g., the ejector ramjets, until about Mach 4.2 at which point 454, the ramjet duct panels are closing, and HSPS flow 430 increases as the ERJ duct panels close. Equal flows between ramjet and DMRJ ducts may be achieved around Mach 4.3. Full DMRJ flow occurs at a point 455 when the ERJ flow is shut off and the DMRJ flow 431 is almost at 100% of inlet flow 410 except for the residual spill flow, which goes to zero at the DMRJ design point at Mach 6. Over the entire acceleration phase from Mach 0 to 6, the sum of all flows is 100% of the total captured flow 410.
A CCPS module employing a DMRJ such as shown in
One configuration of a CCPS module may have port and starboard ejector ramjet systems with each being similar or identical to the system illustrated in
Thermal protection of a turbojet for any CCPS configuration may include two sequential processes, core heat removal and engine compartment cooling. Core heat removal may begin immediately after the turbojet is shut down and may remove core heat from the engine rotor through passive “windmilling.” In particular, after a turbojet 1420 is shut down, i.e., while no fuel is being fed to turbojet 1420, LSPS inlet flow control panel set 1122-1124 and exhaust panel 1294 may remain fully or partly open for air flow and rotation of the engine rotor. Windmilling in this fashion may generally remove heat only when the turbojet 1420 is shut down at below about Mach 2. At Mach 1.8 to 2.0 and at 10,000 ft, a typical flight altitude for this speed, the recovery temperature of the inlet air may be about 170 to 210° F., which is cool enough to remove heat from turbojet 1420. At higher Mach numbers, the inlet air may be above 210° F. and is likely too hot to effectively cool the hot turbojet core. Inlet flow control panel set 1122-1124 is closed after completion of core heat removal and at speeds higher than Mach 2, and a turbine engine air conditioning system (TEACS) 800, shown in
TEACS 800, as shown in
A two-step transition 930 from LSPS operation to MSPS operation in flight process 900 includes an ERJ start-up operation 932 and an LSPS shutdown operation 934. ERJ start-up operation 932 opens flow control panel sets and supplies fuel for stable operation of the ERJs in parallel with ongoing turbojet operation, and once that is accomplished, LSPS shutdown operation 934 gradually shuts down the LSPS, e.g., reduces fuel supplied to turbojet. A thermal management process 940 maintains the LSPS in a safe temperature ranges while the LSPS is shutdown. A windmilling process 942 of thermal management process 940 immediately follows shutdown operation 934 and initially cools a turbine rotor of the turbojet through passive windmilling with the LSPS channel inlet and exit panels open while operating at flight speeds not exceeding Mach 2. A maintenance operation 944 of thermal management process 940 closes/seals inlet flow control panel set 1122-1124 of the turbojet channel, controls exhaust flow control panel 1294 of the turbojet, e.g., so that exhaust flow control panel 1294 may be slightly open, and activates flow from air conditioner system 800 into turbojet 1420. Temperature maintenance operation 944 with closed inlet flow control panel set 1122-1124 may continue while turbojet 1420 is shutdown, including during higher speed operations of flight process 900, e.g., including a mid-supersonic flight operation 945, a HSPS startup operation 950, and high-speed flight operation 956.
Mid supersonic flight operation 945 can be conducted with ERJs 1500 only up to a speed of about Mach 4.2. When accelerating to speeds above about Mach 4.2, HSPS startup operation 950 may employ a two-step transition from the MSPS to the HSPS. A HSPS startup operation 952 starts up and begins stable operation of the HSPS in parallel with ongoing MSPS operation, and then an MSPS shutdown operation 954 gradually shuts down the MSPS and closes of MSPS channel inlet doors 1126 and exhaust flow control panel 1296. A high-speed flight operation 956 may continue supersonic acceleration, cruise, and deceleration using the HSPS only, e.g., only DMRJ thrust.
The operations of flight process 900 are reversible. For example, a reverse of operation 950 provides two-step transition from HSPS to MSPS operation, e.g., from DMRJ operation to RJ only operation. The reverse of operation 950 gradually powers up MSPS during deceleration to suitable flight speeds and then shuts down the HSPS when flight decelerates to about Mach 4.2. A reversal of operation 945 is a supersonic deceleration operation with MSPS RJ thrust only. A reverse of operation 930 is a two-step transition from MSPS to LSPS operation, e.g., from ERJ to turbojet only operation to starting the LSPS. A reverse of operation 925 is a low supersonic deceleration operation with the LSPS thrust, e.g., turbojet only trust. Low supersonic and subsonic deceleration and landing operations will be conducted with the LSPS only, e.g., with the turbojet only.
CCPS module 1000 as described above may employ a LSPS 1400, a MSPS 1500, and a HSPS 1300 in many different configurations.
All or portions of some of the above-described systems and methods can be implemented in a computer-readable media, e.g., a non-transient media, such as an optical or magnetic disk, a memory card, or other solid state storage containing instructions that a computing device can execute to perform specific processes that are described herein. Such media may further be or be contained in a server or other device connected to a network such as the Internet that provides for the downloading of data and executable instructions.
Although particular implementations have been disclosed, these implementations are only examples and should not be taken as limitations. Various adaptations and combinations of features of the implementations disclosed are within the scope of the following claims.
This patent document claims benefit of the earlier filing date of U.S. Provisional Pat. App. No. 62/797,569, filed Jan. 28, 2019, which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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62797569 | Jan 2019 | US |