MAE 5360: Hypersonic Airbreathing Engines

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

2. Ramjet Operation Fuel injectors • 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

3. Key Results: Ideal 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 • 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

4. Thrust and TSFC Performance Summary • 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

5. Thrust per unit Mass and Efficiency Summary • 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

6. Ideal Ramjet Performance: QR=48,000 kJ/kg, g=1.4, Ta=220K • Ideal ramjet performance using n-Decane fuel, qualitatively similar to behavior of real ramjets • Require supersonic flight speed for acceptable specific thrust and reasonably low TSFC • Highest specific thrust is around flight Mach number of 2.3-2.7 for Tmax of 2,000 K – 4,000 K • This is an example of a common result that the conditions for minimum fuel consumption (maximum range) are quite different from those for which the engine size per unit thrust is minimum

7. Ideal Ramjet Performance: QR=141,800 kJ/kg, g=1.4, Ta=220K • Ideal ramjet performance using hydrogen fuel, qualitatively similar to behavior of real ramjets • Require supersonic flight speed for acceptable specific thrust and reasonably low TSFC • Highest specific thrust is around flight Mach number of 2.3-2.7 for Tmax of 2,000 K – 4,000 K • This is an example of a common result that the conditions for minimum fuel consumption (maximum range) are quite different from those for which the engine size per unit thrust is minimum

8. Non-Ideal Ramjet Performance (Pd=1.0, Pb=1.0, Pn=1.0, Pe=Pa)

9. Non-Ideal Ramjet Performance (Pd=0.8, Pb=0.9, Pn=0.9, Pe=Pa)

10. Non-Ideal Ramjet Performance (Pd=f(M0), Pb=1.0, Pn=1.0, Pe=Pa)Pd=1-0.1*(M0-1)1.5

11. Temperature Dependence of Specific Heats Example: • Enthalpy often approximated as h(T)=CpT • In combustion chemistry, enthalpy must take into account variable specific heats, h(T)=Cp(T)T • If Cp(T) can be fit with quadratic, solution for flame temperature for certain classes of problems f < 1 and T < 1250 K leads to closed form solutions • For higher order fits or f > 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 • 1st law concepts defining heat of reaction, heating values, etc.

12. Normal Shock Total Pressure Loss 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 • As M1 ↑ p02/p01 ↓ very rapidly • Total pressure is indicator of how much useful work can be done by a flow • Higher p0→ more useful work extracted from flow • Loss of total pressure are measure of efficiency of flow process

13. 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

14. HyFly Ramjet Concept • Hypersonic Flight Demonstration Program • Cruise Flight Mach Number ~ 6 • Range 600 nm (1111 km) http://www.globalsecurity.org/military/systems/munitions/hyfly.htm

15. HyFly Ramjet Concepthttp://www.designation-systems.net/dusrm/app4/hyfly.html • 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

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

17. 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

18. J58 SR-71 Engine: Ramjet/Turbojet Hybrid Engine http://aerostories.free.fr/technique/J58/J58_01/page8.html

19. Ramjet/Turbojet Hybrid Engine Operating Modes

20. 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

21. X-51 Scramjet

22. 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 http://www.daviddarling.info/encyclopedia/I/interstellar_ramjet.html

23. 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

24. Homework Assignment 1: Ramjet Analysis