Engine

Engine

0.5

1.0

1.5

2 .00.

Turbojet and low-by-pass ratio Turbofan (0.3-1) High-by-pass ration turbofan (≥5) Turboprop Reciprocating engine/propeller

Subsonic o Large diameter with fans with wide –chord fan bade

o Bypass-ratios 1. From six-to-one to as high as nine-to-one 2. Typical five to one

Turbojet engine T= mair(Ve-V∞)+(Pe-P∞)Ae The jet engine takes in mass flow of cool air mair at velocity essentially equal to V∞ and exhaust a mass flow of hot air and combustion product mair+mfuel at velocity V∞. The mass fuel is added usually small compare to the mass of air. mair/mfuel~0.05

Exhaust nozzle o Subsonic, Sonic –Convergent o Supersonic—Convergent and Divergent mair = V∞Aiρ∞

Inlet-Diffusero Subsonic, Sonic –Divergent Duct o Supersonic—Convergent and Divergent Duct

By Pass Ratio Mass flow passing through the fan, externally to the core divided by the mass flow through the core itself o The higher the by pass ratio the higher the propulsion

o o o o

o

efficiency. By pass ratio are on the order of 5 Typical value of thrust specific fuel consumption for these turbofan engines or 0.6 lb/ (lbh)- almost half of conventional turbojet engine The low by pass ratio turbofans is much closer to that of turbojet than that of a propeller by pass ratio between 0 and 1 Used in many high performance jet fighter plane Small initial decrease at low subsonic Mach numbers, the thrust increasing for increasing Mach number well above Mach 1 Ct for the low by pass ratio turbofan gradually increase as M∞ increases for subsonic and transonic speed, and begins to rapidly increase at Mach 2 and beyond

Ct = weight of the fuel burned per unit thrust per unit time

=weight of fuel burned for given time/ (thrust output) (time increment) Ct =lb/lb.s = 1/s; N/N.s = 1/s F 119 Turbofan engine o Two dimensional thrust vectoring exhaust nozzle o The convergent/divergent nozzle vectors thrust 20 degrees either up or down o Nozzle position management—automatically controlled by the full- authority digital electronic control Subsonic – high-by-pass ratio turbofan engine Supersonic - turbojet engine or low-by-pass ratio turbofan engine

M < 0.3 – incompressible flow M ≥ 0.3 – compressible Mach Number Region Subsonic Sonic Transonic Supersonic Hypersonic Hypervelocity

Mach Number M<1 M=1 0.8 ≤ M ≤ 1.3 M≥1 5 ≤ M ≤ 10 M > 10

At subsonic speeds the Concorde was inefficient, requiring high engine power that drained the fuel tank rapidly.