MAE 4261: AIR-BREATHING ENGINES
Ramjet Analysis Overview
Mechanical and Aerospace Engineering Department
Florida Institute of Technology
D. R. Kirk
RAMJET BASIC 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
KEY RESULTS: RAMJET
U

T
 M o  e  1
m o ao
Uo 
RTe M e Te

RTo M o To
Ue M e

Uo M o


 Tt 4

 4

T



 Mo
 1  M o t b  1  M o 
 1
m o ao
 Tt 3

 0

m f h  m o c p Tt 4  Tt 3 
m f  m o
I sp 
c pTo
h
T
m f g
TSFC 
m f
T
TU 0
 overall 
m f h
 4   0 
• 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)
• 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
WHAT DID WE LEARN?
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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
WHAT DID WE LEARN?
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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 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
MISS BOMARC
http://home.att.net/~ferguspcj/mbomarc/bomarc01.htm
HyFly RAMJET CONCEPT
http://www.globalsecurity.org/military/systems/munitions/hyfly.htm
• Hypersonic Flight Demonstration Program
• Cruise Flight Mach Number ~ 6
• Range 600 nm (1111 km)
HyFly RAMJET CONCEPT
http://www.designation-systems.net/dusrm/app4/hyfly.html
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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
http://www.orbital.com/
Hercules MK 70 rocket booster
RUSSIA'S P-700 GRANIT LONG-RANGE ANTI-SHIP
MISSILE (SS-N-19 ‘SHIPWRECK’)
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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
http://aerostories.free.fr/technique/J58/J58_01/page8.html
MAIN IDEA: TURBO-RAMJET
J58 TURBO-RAMJET
RAMJET VS. SCRAMJET
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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
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
• Next step: We desire an engine that develops static thrust
– Put in a device to mechanically compress air (compressor)
– Put in a device to power compressor (turbine)
• Solution: Turbojet engine
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