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Aerospace Propulsion Ramjet Aerospace Engineering Department Main Principle of the Ramjet Basic design The air inlet/diffuser admits air to the engine, reduces air velocity and develops ram pressure. The combustor adds heat and mass to the compressed air by burning a fuel. The nozzle converts some of the thermal energy of the hot combustion products to kinetic energy to produce thrust. Compression is given by the vehicle speed (bad performance at low speed, auxiliary bosster needed to reach interesting performances). No moving parts, flexibility in geometrical design. High thrust per unit frontal area. Ideal Ramjet Cycle 21554654-SESA2005LN2006-Propulsion.pdf RAMJET BASIC OPERATION Ramjet has no moving parts Achieves compression of intake air by forward speed of vehicle Air entering the intake of a supersonic aircraft is slowed by aerodynamic diffusion created by the inlet and diffuser to low velocities Expansion of hot gases after fuel injection and combustion accelerates exhaust air to a velocity higher than that at inlet and creates positive thrust Fuel injectors KEY RESULTS: RAMJET Begin with non-dimensional thrust equation, or specific thrust Ratio of exit to inlet velocity expressed as ratio of Mach numbers and static temperatures. Recall that for a Ramjet Me=M0 Ramjet specific thrust depends on temperature ratio across burner, tb Compare with H&P EQ. (5.27) RAMJET.docx Energy balance across burner Expression for fuel flow rate for certain temperature rise of incoming mass flow and fuel energy, h Useful propulsion metrics Specific impulse, thrust specific fuel consumption, and overall efficiency ( )( )( )h mTUTmTSFCg mTIhT cm mT T c m h mM MTTMa mTTTMMRTRTMMUUUUMa mTfoverallffspo po ft t p o fo b ottoo ooeoeoeoeoeoeoo o 00 43 404341 1 11=== = =||.|

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\| =qu uuutSpecific Thrust Figure 5.9 from Hill and Peterson: Ramjet performance parameters vs. flight Mach number Specific thrust has peak value for set Tmax and Ta Specific thrust increases as maximum allowable combustor exit temperature increases Specific fuel consumption decreases with increasing flight Mach number Efficiencies Figure 5.10 from Hill and Peterson: Ramjet performance parameters vs. flight Mach number Specific thrust has peak value for set Tmax and Ta. Peak is around Mach 2.5 Propulsive, thermal and overall efficiencies increase continually with increasing Flight Mach number Ramjet engine integration Inlet GeometrySlowing down the incoming air to about Mach 0.40.5 is the primary purpose of an inlet system to keep the tip speed of compressor blades below sonic. The installedperformance of a jet engine greatly depends upon the air-inlet system. The type and geometry of the inlet and inlet duct determine the pressure loss and distortion of the air supplied to the engine, which will affect installed thrust and fuel consumption. Roughly, 1% reduction in inlet pressure recovery inlet will reduce thrust by ~ 1.3%. Also, the inlets external geometry including the cowl and boundary-layer diverter will greatly influence the aircraft drag. There are basically four types of inlets. Basic Types of Inlet NACA flush Pitot Conical 2-D ramp NACA Flush Inlet Used by several early jet aircraft but is rarely seen today because of its poor pressure recovery (large losses). However, the NACA inlet tends to reduce aircraft wetted area and weight if the engine is in the fuselage. The NACA inlet is regularly used for applications in which pressure recovery is less important, such as the intakes for cooling air or for auxiliary power units. Pitot inlet It is simply a forward-facing hole (also called normal shock inletin supersonic flight). It works very well subsonically and fairly well at low supersonic speeds. The cowl lip radius has a major influence upon engine performance and aircraft drag. A large lip radius tends to minimize distortion and accommodate additional air required for takeoff , especially at high angles of attack and sideslip. However, it will produce shock-separated flow outside the inlet as speed of sound is approached which greatly increases drag. Hence, supersonic jet cowl lip are nearly sharp. Spike and 2-D Ramp Inlets Better performance than the normal shock inlet at higher supersonic speeds . Supersonic flow over cone (spike) or wedge (2D-ramp) . Spike inlets are typically lighter and have slightly better pressure recovery but with higher cowl drag and more complicated variable geometry mechanisms. Ramp inlets are used up to Mach 2, while spike inlets are used beyond that. Pressure recovery through a shock depends on the strength of the shock. N-S: (M0= 2 M1= 0.57, p1/p0 = 72%) (M0= 1.1 M1= 0.91, p1/p0 = 99.9%) An oblique shock does not reduce the air speed all the way to subsonic. Final transition from super to subsonic speed occurs through a normal shock. Speed reduction and pressure recovery depends on the wedge or cone angle. Example: 1. O-S: (= 10, M0= 2 = 39, M1= 1.66, p1/p0 = 98.6%). 2. N-S: (M1= 1.66 M2= 0.65, p2/p1 = 87.2%). Then, p2/p0 = 87.2 98.6% = 86% The greater the number of oblique shocks, the better the pressure recovery. Theoretical optimal is the isentropic rampinlet (infinite O-S) with 100% pressure recovery, which works properly only at its design Mach number, so rarely used Flight Range of Ramjet Propelled Vehicles Consumption of air-breathing engines (Pratt & Whitney) The hypersonic funnel (Mc Donnell Douglas) RAMJET POWERED MISSILES Boeing/MARC CIM-10A BOMARC A Surface-to-Air Missile Aerojet General LR59-AG-13 liquid rocket; Two Marquardt RJ43-MA-3 ramjets SOME DETAILS ON BOMARC MISSILE Flight testing started in 1952 First launch from Cape Canaveral in September of 1952 Bomarc A became fully operational in 1959 Numerous deployments from Florida to Maine defended U.S. eastern sea board Booster on Bomarc A was source of problems Fuel was too corrosive to store in missile, so fueling took place immediately before launch (increasing time to launch) Fueling process was also quite hazardous, involving three steps (white fuming nitric acid, analine-furfuryl alcohol, and kerosene) New model that utilizes a solid fuel booster Bomarc B became operational in 1961, and featured a safer solid fuel booster and more powerful sustainers Boeing built 700 Bomarc missiles between 1957 and 1964, and Bomarc in active service until 1972 Length 46 ft. 9 in, Wingspan 18 ft. 2 in, Speed Mach 2.8, Range 250 miles, Ceiling 65,000 ft, Cost: $ 1,154,000 per shot Propulsion: One Aerojet General LR59-AG-13 liquid rocket Two Marquardt RJ43-MA-3 ramjets videoplayback_29.FLV HyFly RAMJET CONCEPT Hypersonic Flight Demonstration Program Cruise Flight Mach Number ~ 6 Range 600 nm (1111 km) HyFly RAMJET CONCEPT HyFly program was initiated in 2002 by DARPA (Defense Advanced Research Projects Agency) and U.S. Navy's ONR (Office of Naval Research) to develop and test a demonstrator for a hypersonic Mach 6+ ramjet-powered cruise missile Prime contractor for HyFly missile is Boeing, Aerojet builds sustainer engine Air-launched from F-15E and accelerated to ramjet ignition speed by solid-propellant rocket booster Engine runs on conventional liquid hydrocarbon fuel (JP-10) Much easier to handle than cryogenic fuels (LH2) used on other hypersonic scramjet vehicles Sustainer engine of HyFly is a dual-combustion ramjet (DCR) (very complex) Two different air inlet systems Operate as a "conventional" ramjet with subsonic combustion Operate at hypersonic speeds as a scramjet First scramjet engine (hybrid or otherwise) to demonstrate operability with LH2 fuel RAMJET POWERED MISSILES Orbital Sciences GQM-163 Coyote: Ducted rocket/ramjet engine, Flight speed up to Mach 2.8 at seal-level Hercules MK 70 rocket booster RUSSIA'S P-700 GRANIT LONG-RANGE ANTI-SHIP MISSILE (SS-N-19 SHIPWRECK) Launched by two solid-fuel boosters before sustained flight with ramjet Maximum speed believed ~ Mach 2.25 Range is estimated at 550 to 625 km Weight: 7,000 kg, Length: 10 m, Diameter: 0.85 m Altitude up to 65,000 ft J58 SR-71 ENGINE: RAMJET/TURBOJET HYBRID MAIN IDEA: TURBO-RAMJET J58 TURBO-RAMJET From Ramjet to Scramjet (Supersonic Combustion Ramjet or SCRJ) Beyond Mach = 5 (hypersonic domain), ramjet is less and less efficient. Increasing of air stagnation temperature and pressure tends to limit the performance and to increase the thermal and mechanical loads on the combustion chamber walls To bypass these issues, the solution is to maintain the flow supersonic from the air inlet to the engine exit and to achieve the combustion in the supersonic flow A geometrical throat is therefore no longer needed to accelerate the flow and produce the thrust ; transition from subsonic to supersonic flow can also be achieved, without geometry variation, by heat addition Two variants of scramjet : pure scramjet dual mode ramjet allowing transition from subsonic to supersonic combustion RAMJET VS. SCRAMJET Large temp rise associated with deceleration from high speed to M~0.3 for combustion Solution for increased flight speed: decelerate to lower supersonic speeds in combustor Combustion very difficult (flame support) in a high speed flow Vehicle cooling requirements become very challengingvideoplayback_23.FLV Boeing X-51 WaveRider Scramjet videoplayback_30.FLV Scientific Issues of Ramjet Air intakes : the design is critical (efficiency on the whole flight range, sensitivity to flow distorsions, participation to instabilities) Combustion chamber combustion efficiency lean and rich stability limits wall cooling operating instabilities Combustion Efficien