predicting engine exhaust plume spectral radiance & transmittance engineering project mane 6980...
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Predicting Engine Exhaust Plume Spectral Radiance & Transmittance
Engineering ProjectMANE 6980 – Spring 2010 Wilson Braz
IR Radiation Introduction Infrared (a.k.a. thermal) portion of
electromagnetic spectrum spans approximately 0.5m to 1000m
IR Radiation Introduction (cont.) All matter emits energy Perfect emitters are called ‘blackbodies’ Max Planck, in 1900, was the first to derive the equation
describing ‘spectral’ radiation emission from a blackbody
Planck unwittingly revolutionized physics with the introduction of the Planck constant h which describes the size of ‘quanta’ in quantum mechanics
1
12,
5
2
kThce
hcTi
Planck’s Law
800K
700K
600K
500K
400K
Definitions Radiance - energy flux per unit solid angle
Spectral – modifier that denotes units are given as a function of wavelength (or frequency) E.g. ‘spectral radiance’ = radiance per unit
wavelength
Transmissivity – Fractional amount of energy pass Absorptivity – Fractional amount of energy
absorbed by a medium
srm
W
2
srm
W2
Exhaust Plume Radiation Exhaust plume is gaseous and opaque Radiation is absorbed, emitted, and transmitted
through media at different wavelengths Molecular resonances cause different behaviors at
varying wavelengths, so spectral analysis is of interest – CO2 and H2O predominant elements in IR of plume
Beer’s Law describes transmissivity
Kirchoff’s Law describes emissions
Sae
TT ,,,,,, SS ,1, and
Effects of Soot in plume Combustion process is never 100% efficient
A small portion of fuel does not completely combust, and carbon molecules coalesce into small particles
Carbon particles, or soot, emit and absorb too
Absorption varies significantly with size and particle density
Effects of soot is considered in this project
Plume IR problem break-down
The method of calculating plume emissions broken down into 2 major steps Gaseous spectral radiance and
transmissivity calculations, dominated by CO2 and H2O
Soot
Chemical Reactions of Combustion Fuel (CH2) combines with Oxygen (O2) and
results in water (H2O), carbon dioxide (CO2), and heat energy 2 CH2 + 3 O2 = 2 H2O + 2 CO2
Given mass flow of air and fuel, and the temperatures of plume, we can calculate the particle concentrations using ideal gas law
MODTRAN for Radiance and Transmittance due to CO2 and H2O MODTRAN uses various techniques for calculating CO2
and H20 radiance. Leverage these methods to obtain solutions for C02 and
H2O
‘Standard Atmosphere’ ‘Plume (no soot)’
GE-T700 – 100%MC100% Burn Efficiency (No soot)
MODTRAN Inputs (ppmv) H2O = 40874 CO2 = 39334 O3 = 0.0686 N2O = 0.0 CO = 176.7 CH4 = 4.284 O2 = 144863 NO = 0.0 SO2 = 0.0 NO2 = 148.54 NH3 = 0.001 HNO = 0.0
Temp = 533°K Path = 1 meter Soot = 0 Integrated Radiance = 0.0141 W/cm2 sr (1 – 12
Modeling particulate
Several techniques have been devised for particulate modeling
Proper usage depends upon particle size parameter where D is particle diameter and m is wavelength in the particle fluid.
mD
Turbine engine exhaust soot
For soot, is generally < 0.3 therefore Mie Scattering Theory is used.
Mie equation yield:
mD
22222 42
36
nn
n
C
a
Concentration of Soot in turbine engines from literature
A study performed on the sooting properties of various jet fuels in jet turbines yielded very small soot concentrations.
These values may, or may not be indicative of actual soot concentration in turbo-shaft engines.
Results will be presented for increasing levels of soot concentration
Recommend correlating results with measurements of plume radiance and transmittance
8101.2 C m3 soot per m3 plume
Results
MODTRAN and additional procedure to calculate soot radiant emissions
Published measured values Predicted values