MAE 4261: AIR-BREATHING ENGINES

Ramjet Analysis Overview

Mechanical and Aerospace Engineering Department

Florida Institute of Technology

D. R. Kirk

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

Fuelinjectors

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, 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

hm

TUT

mTSFC

gm

TI

h

Tcmm

TTcmhm

MMT

TM

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T

M

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WHAT DID WE LEARN?

• 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?

• 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 MissileAerojet 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

• Hypersonic Flight Demonstration Program • Cruise Flight Mach Number ~ 6• Range 600 nm (1111 km)

http://www.globalsecurity.org/military/systems/munitions/hyfly.htm

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

RAMJET POWERED MISSILESOrbital 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’)

• 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

• 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