MAE 5360: Hypersonic Airbreathing Engines Ramjet Overview Mechanical and Aerospace Engineering Department Florida Institute of Technology D. R. Kirk

Ramjet 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 M e =M 0 Ramjet specific thrust depends on temperature ratio across burner,  b –Compare with H&P EQ. (5.27) 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

Thrust and TSFC Performance Summary Ramjet performance parameters vs. flight Mach number Specific thrust has peak value for set T max and Ta Specific thrust increases as maximum allowable combustor exit temperature increases Specific fuel consumption decreases with increasing flight Mach number

Thrust per unit Mass and Efficiency Summary Ramjet performance parameters vs. flight Mach number Specific thrust has peak value for set T max and Ta. Peak is around Mach 2.5 Propulsive, thermal and overall efficiencies increase continually with increasing Flight Mach number

Temperature Dependence of Specific Heats Example: Enthalpy often approximated as h(T)=C p T In combustion chemistry, enthalpy must take into account variable specific heats, h(T)=C p (T)T If C p (T) can be fit with quadratic, solution for flame temperature for certain classes of problems  < 1 and T < 1250 K leads to closed form solutions For higher order fits or  > 1 and/or T > 1250 K, iterative closure schemes are required for solution of flame temperature Also will discuss a definition of enthalpy that accounts for chemical bonds 1 st law concepts defining heat of reaction, heating values, etc.

Normal Shock Total Pressure Loss As M 1 ↑ p 02 /p 01 ↓ very rapidly Total pressure is indicator of how much useful work can be done by a flow –Higher p 0 → more useful work extracted from flow Loss of total pressure are measure of efficiency of flow process Example: Supersonic Propulsion System Engine thrust increases with higher incoming total pressure which enables higher pressure increase across compressor Modern compressors desire entrance Mach numbers of around 0.5 to 0.8, so flow must be decelerated from supersonic flight speed Process is accomplished much more efficiently (less total pressure loss) by using series of multiple oblique shocks, rather than a single normal shock wave

Ramjet Powered Missile Boeing/MARC CIM-10A BOMARC A Surface-to-Air Missile Aerojet General LR59-AG-13 liquid rocket; Two Marquardt RJ43-MA-3 ramjets

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 (LH 2 ) 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 LH 2 fuel

Ramjet Missile Concept Orbital Sciences GQM-163 Coyote: Ducted rocket/ramjet engine, Flight speed up to Mach 2.8 at seal-level Hercules MK 70 rocket booster

Russian 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 Engine

Ramjet/Turbojet Hybrid Engine Operating Modes

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 challenging

X-51 Scramjet

Interstellar Ramjet: ‘Hydrogen Breathing Engine’ In this concept, interstellar hydrogen is scooped to provide propellant mass –Hydrogen is ionized and then collected by an electromagnetic field Onset of ramjet operation is at a velocity of about 4% speed of light Typically, interstellar ramjets are very large systems A ramjet sized for a 45-year manned mission to Alpha Centauri would have a ram intake 650 km in diameter and weigh 3000 metric tons including payload

Summary Ramjet develops no static thrust Relies on ‘ram’ compression of air –Requires high speed flight Performance depends on increase in stagnation temperature across burner (combustor) Efficiencies (thermal, propulsive, and overall) increase with increasing flight Mach number

Homework Assignment 1: Ramjet Analysis