A Study on Infrared Signature of Aircraft Exhaust Plume

Transcription

1 A Study on Infrared Signature of Aircraft Exhaust Plume Pyung Ki Cho a*, Seung Wook Baek a and Bonchan Gu a a Korea Advanced Institute of Science and Technology 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Korea *Corresponding Author: chopk@kaist.ac.kr ABSTRACT In this study, Radiative property modeling was performed to study aircraft exhaust plume IR signature. Line-by-line modeling which is known as the most accurate method for calculating radiative property was used with HITEMP-2010 radiation database. Layered integration method for solving radiative transfer equation was introduced to 1D line of sight. Radiative intensity for mixture composed with CO 2, H 2 O and CO was calculated and reliability and suitability of the modeling was evaluated by comparing with result from other researchers. We confirmed that not only radiative property but also radiative intensity had specific values depending on temperature, pressure and composition of mixture gas. Keyword: Radiation Database, Line-by-Line Method, IR Signature, Exhaust Plume. 1. Introduction For a main topic for radiative heat transfer research, radiative property of combustion gas in combustion system is important for accurate calculating radiative heat transfer and makes possible to predict composition, temperature and concentration of combustion gas. As these needs are to the fore, high performance radiation databases such as HITEMP and CDSD was developed and it is available to get radiative property more accurately and efficiently with development in computer performance. The high performance radiation database has been successful for a number of applications. The applications are remote-sensing of the terrestrial atmosphere from spectrometer, environmental, and industrial problems (Rhothman, 2010). On the other hand, the issue of battle depends upon survivability of tactical aircraft such as combat and UAV (Unmanned Aerial Vehicle) in modern war. Infrared signature (IR) is emitted from various parts of aircrafts which are nose, engine inlet, flat, and others. Especially, engine nozzle and exhaust plume emit the strongest infrared signature in aircraft. These aircraft IR signatures that would be source for IR detector threaten its survivability in battleground. For this reason some researches about IR signature in aircraft have been conducted. In this situation, it is needed to study predicting and analyzing IR signature from aircraft exhaust plume in view of IR detector by computing the radiative property precisely.

2 Radiative property can be obtained from experimental measuring, band model and by using radiation database. After development for radiation database, research for radiative property has been conducted experimentally and numerically together. Ferriso, C. C. et al. studied about emissivity of CO 2 and H 2 O mixture in main band from high temperature plume of hypersonic rocket burner. Radiative property comparison with experimental result from micro wave plasma source and calculation from CDSD radiation database was conducted by Depraz, S. et al. Most of radiative property researches with radiation database were studied for getting the accurate property but also comparing with experimental data. Many researches about IR signature emitted from aircraft have been conducted as well. Mahulikar, S. P. et al. studied IR signature prediction for aircraft survivability and Yi, K. J. et al. suggested radiation shield to reduce solid IR signature on engine exhaust system and verified the its effects. In this study, we have investigated the verification on radiative intensity with radiation database to predict IR signature from exhaust plume. 2. Fundamental As real gas is non-gray gas, radiative property of real gas varies and has specific values depending on temperatures, pressures, wavelength (wavenumber) and compositions of gases. There are many methods for calculating radiative property, Line-by-line method is the most accurate in those. In this study, Line-by-line method was applied to calculate radiative property with using HITEMP 2010 radiation database. Radiation database contains 18 spectroscopic parameters derived from quantum mechanics. We only analyzed radiative properties for CO 2, H 2 O and CO which are typical gas components of plume. Radiation database provides line intensity (or line strength) on specific wavenumber when energy transition occurs. The absorption coefficient can be expressed as pressure, or density, or number of absorption molecules in unit volume. SS PP NN νν, and SS νν are commonly used for line intensity. The line intensity given from radiation database is SS NN NN νν. To convert from SS νν to SS PP νν, Eq. (2) is introduced (Šimečková 2006). SS = SS νν PP PP = SS νν ρρ ρρ = SS νν NN NN (1) SS PP NN νν PP = SS LL(TT ss) TT ss νν PP 0 TT (2) We can convert the line intensity to line intensity on particular temperature and pressure by using next equation because the line intensity is defined on 296K, 1atm.

3 SS NN νν (TT) = SS NN νν (TT 0 ) QQ(TT exp ( 0) EE llhcc ) kktt 0 QQ(TT) exp ( EE llhcc kkkk ) [1 exp hcccc kkkk ] [1 exp hcccc kktt 0 ] (3) Absorption coefficient for mixture can be calculated from multiplication with line intensity and line shape function for each species, and then adding up all of absorption coefficient for every species. nnnnnn PP αα νν,mmmmmm = SS νν,iiiiii (TT)φφ iiiiii (νν νν ) iiiiii νν (4) Incident radiative energy into medium gas is exponentially attenuated by molecules. Transmissivity is expressed as follow equation. Optical length ll means thickness of medium gas layer. ττ νν = exp( αα νν ll) (5) Radiative energy passing through medium is governed by radiative transfer equation (RTE). The changes of the radiation energy due to the medium should be considered of the effects of absorption, emission and scattering in the medium. But it is possible to neglect the scattering effects in aircraft propulsion system because most of the system generates very few solid particles such as soot in the plume contrary to the rocket propulsion system. So RTE can be expressed as follow. II νν = αα ννii bbbb αα νν II νν = αα νν (II bbbb II νν ) (6) Radiative intensity for the line of sight was calculated by RTE with Layered integration method. Medium on the line of sight is composed of several medium layers and these layers under local thermodynamic equilibrium have a specific length. This means that temperature, pressure and each mole fraction are homogeneous in the each medium layer. II νν,1 (ss 1 ) = II νν,0 (0)ττ νν,1 + II bbbb,1 (TT 1 ) (1 ττ νν,1 ) (7) The radiation energy from the (n 1) th layer is absorbed by the (n) th layer and also emitted by the (n) th layer itself. On the right side of the above equation, the first term represents the radiation energy after absorption by the medium and the second term means the emitting from the medium.

4 II νν,2 (ss 2 ) = II νν,1 (ss 1 )ττ νν,2 + II bbbb,2 (TT 2 ) (1 ττ νν,2 ) (8) II νν,nn (ss nn ) = II νν,nn 1 (ss nn 1 )ττ νν,nn + II bbbb,nn (TT nn ) (1 ττ νν,nn ) The radiation energy passing through the medium from the first layer to the (n) th layer can be express as follow. nn II νν,nn = II νν,0 (0)ξξ 0 + II bbbb,pp TT pp (1 ττ νν,pp ) ξξ pp pp=1 nn ξξ pp = ττ νν,kk, ξξ nn = 1 kk=pp+1 (9) 3. Results and Discussions All radiative properties were calculated with radiation database HITEMP By using the properties, we have conducted simulation for the spectral radiative intensity and compared with the experimental results to verify the validity of this study before applying to plume IR signature analysis. All conditions for the analysis study were set to be identical to the reference experiment study and the reference date was caught by digitizing. Fig. 1 Spectral intensity of rocket exhaust plume Deimling, L. et al. s experimental study was chosen as the reference study and they measured IR signature with high temperature and pressure rocket plume. Temperature

5 and pressure are constant and the rocket plume is composed of CO 2, H 2 O, CO and N 2. The each mole percentage is 22.3%, 9.2%, 8.6% and 50%. The peak intensity is observed in near 4.3 µm because of radiation emission by CO 2 and the relatively low intensity from 6 µm to 8 µm is due to emission by H 2 O and the peak intensity in near 2.7 µm is emission by both CO 2 and H 2 O. We confirmed that the present work and the experiment result have a good agreement except for near 3.5 µm. This error is occurred by not gas mixture but solid particle emission because there is no gas component emitting radiation in the region. Solid particles such as soot particles are emitting and scattering the radiation itself. As previously stated, rocket propulsion system has a lot of solid particles due to unburned fuel. However, we neglected scattering effects in this study. Fig. 2 Temperature profile Fig. 3 Spectral intensity of mixture gas with varying temperature

6 Simmons, F. S. et al. s research was chosen as another reference experimental study and they had experiment for mixture of CO 2, H 2 O and N 2 when the temperature changed along the distance. Total optical length is 60cm and it is consist of 10 cells which have a length of 6cm each. Figure 2 is demonstrating to the temperature profile with distance in the experimental setting. The calculated condition is at P = 1atm, with 3.7% CO 2, 7.1% H 2 O and 98.2% N 2, and the spectral range is from 3000 cm -1 to 4200 cm -1. As before the work, we have confirmed that the intensity of gas with varying temperature corresponds with the intensity measurement. The intensity in the near 3700 cm -1 (2.7 µm) is emission by CO 2, and the other wide intensity region is due to emission by H 2 O. 4. Conclusion In this study, The IR signature of hot mixture gas is analyzed to verify the validity of the analysis and agreement with experimental study. We confirmed that the intensity has a characteristic value depending on temperature, composition of mixture, and the emission by CO 2 is dominant in the 4.3 µm, however, in the 2.7 µm, H 2 O emits stronger intensity than CO 2 for the mixture gas radiation. The simulated results are in good agreement with the reference experimental studies. We investigated intensity of mixture gas at not only constant temperature but also varying temperature and we would expand our study to real aircraft plume through this work. Acknowledgment This work has been supported by the Low Observable Technology Research Center program of the Defense Acquisition Program Administration and Agency for Defense Development. REFERENCES Rothman, L. S., Gordon, I. E., Barber, R. J., Do the, H., Gamache, R. R., Goldman, A., Perevalov, V. I., Tashkun, S. A., & Tennyson, J HITEMP, the high-temperature molecular spectroscopic database, Journal of Quantitative Spectroscopy & Radiative Transfer, 111(15), Ferriso, C. C., Ludwig, C. B., & Acton, L Spectral-Emissivity Measurements of the 4.3-n CO 2 Band between 2650K and 3000K, Journal of the Optical Society of America, vol. 56, Depraz, S., Perrin, M. Y., Ph. Rivière, & Soufiani, A Infrared emission spectroscopy of CO 2 at high temperature. Part II: Experimental results and comparisons with spectroscopic databases, Journal of Quantitative Spectroscopy and Radiative Transfer, 113(1),

7 Mahulikar, S. P., Hemant, R., Sonawane, G., & Arvind Rao, Infrared signature studies of aerospace vehicles, Progress in Aerospace Sciences, vol. 43, Yi, K. J., Baek, S. W., Kim, M. Y., Lee, S. N., and Kim, W. C The Effects of Heat Shielding in Jet Engine Exhaust Systems on Aircraft Survivability, Numerical Heat Transfer, Part A, 66, Šimečková, M., Jacquemart, D., Rothman, L. S., Gamache, R. R., & Goldman, A Einstein A-coefficients and statistical weights for molecular absorption transitions in the HITRAN database, Journal of Quantitative Spectroscopy & Radiative Transfer, 98, Deimling, L., Liehmann, W., Eisenreich, N., Weindel, M., & Eckl, W Radiation Emitted from Rocket Plumes, Propellants, Explosives, Pyrotechnics, 22(3), pp Simmons, F. S., Arnold, C. B., & Lindquist, G. H Measurement of temperature profiles in flames by emission-absorption spectroscopy, National Aeronautics and Space Administration, CR-WRL F.