1.1 introduction to propulsion
DESCRIPTION
jetTRANSCRIPT
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Gas Turbine and Jet Propulsion
Xin ZhangRoom: 2577C. Telephone: (852) 3469-2220Email: [email protected]
1.1. Introduction to propulsion
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Why propulsion Aircraft is a feasible alternative for long distance travel (>3 hrs)
Aircraft is a good option for high-speed travel (>300km/h)
What is propulsion To push forward or drive an object forward
Thrust is generated through the application of Newton's ? law of action and reaction.
In an aircraft engine a working fluid is accelerated and the reaction to this acceleration produces a thrust force on the engine
Net force on CV = Momentum flux out Momentum flux in
Thrust is produced if there is an increase in momentum of the working fluid
Momentum
Control Volume (CV)
Momentum in Momentum out
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The environmental impact of air transport
Environmental noise a local nuisance near airports*, a major constraint on the growth of air transport
NOx emissions a threat to local air quality and public health
Carbon emissions (fuel burn) a contributor to global warming .. currently 3% of global carbon emissions + contrails
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* En route noise may be an issue with new propulsion systems
WHO guidelines for community noise
Noise-induced hearing impairment
Interference with speech communication
Sleep disturbance
Cardiovascular and physiological effects
Mental health effects
effects of noise on performance
effects of noise on residential behaviour and annoyance
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Newtons laws of motion
First law
Second law
Third law
When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force.
The vector sum of the forces on an object is equal to the mass m of that object multiplied by the acceleration vector of the object
When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body
= 0 = 0= =
Lateral and longitudinal accelerations
Longitudinal acceleration:
Lateral acceleration:
sV
tVa
=
=211
RVa
22=
R
V1
V2
s
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Classification of gas turbine engines
There are four main types of aerospace propulsive devices:
Piston engine Gas turbine engines Airbreathing Ramjets Rockets
The list is given in ascending order of vehicle flight speed.
Method of thrust generation
Engine type Working fluid
Cycle Thrust generation
Piston Air Intermittent Propeller, rotor
Gas turbine Air Continuous Jet, fan, propeller, rotor
Ramjet Air Continuous Jet
Rocket Various Continuous Jet
In addition to thermodynamic cycle, the method of thrust generation can differ for each of these engines
Newtons 2nd law of motion
Force = rate of change of momentum
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Variants and hybrids
Obvious examples Turbine powered
Turbojet Turbofan Turboprop and turboshaft Propfan
Non-continuous combustion Less obvious hybrids
Turboramjet
Turborocket
Ram-rocket
Liquid air cycle engines (LACE)
Q. What dictates choice of engine types?
A1: Vehicle mission vs. engine capability
The vehicle must operate within a flight corridor which is governed by Lift limit (loss of lift at high altitude and/or low speed) Aerodynamic force limit (excessive structural loading at high speed and
low altitude) Temperature limit (excessive aerodynamic heating at high speed)
Engine capability is determined by
Ability to provide sufficient thrust Ability to operate with adequate fuel economy, as indicated by, for
example, the engines specific impulse:
= where FN is the thrust, is the total mass flowrate of stored propellant
(fuel+oxidiser), and is the Earths gravitational constant at sea level.
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Q. What dictates choice of engine types?
A2: Economics Development cost Purchase cost Operation cost
A3: Reliability and safety Mean time between overhaul (MTBO) Mean time between failure (MTBF)
A4: Technology and legislation Aerothermodynamics Materials Emissions Others (fuels, lubrication, cooling).
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Rocket propulsion
O2
Fuel
Combustionchamber
Propelling nozzle
Rocket propulsion
O2
Fuel
Combustionchamber
Propelling nozzle
Working fluid is the exhaust products (no momentum in)
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Propeller propulsion
Air
Propeller propulsion
Air
Working fluid is Air (momentum inflow from incoming air)
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Lorins concept for jet propulsion (1913)
Air Fuel Exhaust
Combustionchamber Propelling nozzle
Lorins concept for jet propulsion (1913)
Air Fuel Exhaust
Combustionchamber Propelling nozzle
Working fluid is Air & Exhaust gases
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Lorins concept for jet propulsion (1913)
Air Fuel Exhaust
Combustionchamber Propelling nozzle
No rotating parts ~ Ramjet principle
Requires high speed flight velocity
Vin
Combustionchamber
Compressor
Exhaust
Turbine Propelling nozzle
Vjet
Whittles turbo-jet 1930(Co-inventor Ohain 1936)
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Vin
Combustionchamber
Compressor
Exhaust
Turbine Propelling nozzle
Vjet
Whittles turbo-jet 1930(Co-inventor Ohain 1936)
The compressor and the turbine are turbomachines: Machines which transfer energy from or to working fluid through the fluid-dynamic action of rotating blade-rows
Vin
Combustionchamber
Compressor
Exhaust
Turbine Propelling nozzle
Thrust ~ mass flow x (Vjet Vin)
Vjet
Whittles turbo-jet 1930(Co-inventor Ohain 1936)
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Gas turbine cycle
P3
P2
2
4
5
3
Entropy
Turbine entry temperature
2 3 45
Work input to actual compressor is greater than work input for the ideal one!Actual turbine produces less work than the reversible, adiabatic one!
=
Gas turbine cycle
P3
P2
Entropy
Turbine entry temperature
= WorkoutHeatin = Heatin HeatoutHeatin
Heat in
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Gas turbine cycle
P3
P2
Entropy
Turbine entry temperature
= WorkoutHeatin = Heatin HeatoutHeatin
Heat out
Gas turbine cycle
P3
P2
Entropy
Turbine entry temperature
= WorkoutHeatin = Heatin HeatoutHeatin
Useful work+Lost work
Lost work
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Gas turbine cycle
P3
P2
Entropy
Turbine entry temperature
= WorkoutHeatin = Heatin HeatoutHeatin
Useful work+Lost work
Lost work
Gas turbine cycle
Entropy
Turbine entry temperature
= WorkoutHeatin = Heatin HeatoutHeatin
Useful work+Lost work
Lost work
As turbine entry temperature (TET) and pressure ratio rises useful work to heat input rises
Higher efficiency
Higher specific work ~ thrust : weight
Pressure ratio