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

2. Ramjet Operation Ramjet has no moving parts
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 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 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
Hypersonic Flight Demonstration Program
Cruise Flight Mach Number ~ 6
Range 600 nm (1111 km)

15. HyFly Ramjet Concept http://www. designation-systems
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
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

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

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