1. Institute of Aerospace Thermodynamics H. Kamoun, G. Lamanna, B. Weigand Institute of Aerospace Thermodynamics, Universität Stuttgart 70569 Stuttgart Germany J. Steelant ESTEC-ESA, 2200 AG Noordwijk, The Netherlands Thermal characterisation of an ethanol flashing jet using differential infrared thermography Eucass 2011, St Petersburg

2. 2 Institute of Aerospace Thermodynamics Contents Motivation & Objectives Differential Infrared Thermography Experimental Setup Uncertainty analysis Results Summary

3. 3 Institute of Aerospace Thermodynamics Contents Motivation & Objectives Differential Infrared Thermography Experimental Setup Uncertainty analysis Results Summary

4. 4 Institute of Aerospace Thermodynamics Motivation & Objectives Flashing: Sudden exposure of a superheated pressurized liquid to a low pressure environment  Fast phase transition Relevant in many technical application  Accidental release of flammable and toxic pressure-liquefied gases in nuclear and chemical industry.  Benefit in propulsion system  enhanced atomisation P T P inj P sat (T inj ) P∞P∞ T sat (P ∞ )T inj Liquid Vapor RpRp ΔTΔT

5. 5 Institute of Aerospace Thermodynamics Motivation & Objectives Flash-atomisation/vaporisation model  Temperature data for validation Non-intrusive methods are needed New method  Differential Infrared Thermography (DIT)

6. 6 Institute of Aerospace Thermodynamics Contents Motivation & Objectives Differential Infrared Thermography Experimental Setup Uncertainty analysis Results Summary

7. 7 Institute of Aerospace Thermodynamics Differential Infrared Thermography Problem:  Spray emissivity: ε unknown  For a liquid or a gas ε = f (T, λ, density) DIT

8. 8 Institute of Aerospace Thermodynamics Differential Thermography - Liquid: ethanol, T inj = 389K, p am = 0.2bar, p inj = 10bar T Back = 286 K T Back = 366 K

9. 9 Institute of Aerospace Thermodynamics Contents Motivation & Objectives Differential Infrared Thermography Experimental Setup Uncertainty analysis Results Summary

10. 10 Institute of Aerospace Thermodynamics Experimental Setup High-pressure liquid supply system Liquid tank Optical setup Vacuum chamber Vacuum Pump

11. 11 Institute of Aerospace Thermodynamics Experimental Setup Heated modified diesel injector with D=150 μm and L/D= 6.6  Short injection and transient times → Constant backpressure  Constant injection conditions (i.e. pressure & temperature)  Reproducible test conditions Courtesy of Bosch GmbH

12. 12 Institute of Aerospace Thermodynamics Experimental Setup Heated background Cooled background 303 K<T Back <389 K 280 K<T Back <290 K

13. 13 Institute of Aerospace Thermodynamics Differential Infrared Thermography

14. 14 Institute of Aerospace Thermodynamics IR Kamera Resolution: 640x512 pixel Detector: InSb Detector cooling: Stirling Cooler Spectral range: 1.5 - 5µm Integrationmode: Snapshot Calibration range: 5°C – 300°C FLIR Orion SC7000 Series

15. 15 Institute of Aerospace Thermodynamics Contents Motivation & Objectives Differential Infrared Thermography Experimental Setup Uncertainty analysis Results Summary

16. 16 Institute of Aerospace Thermodynamics Uncertainty analysis The choice of the background temperatures  If I spray < I Background1,2 and for the spray dilute region ( ε spray <<1) A calculation of the spray temperature is impossible Key point: the selection of the background temperature should enhance the contrast between spray and surroundings

17. 17 Institute of Aerospace Thermodynamics Uncertainty analysis The sensitivity to measurement errors in e.g. the temperature recorded by the infrared camera T Cam1 For a given T spray and T back1,2,the temperature recorded by the camera and the spray temperature error can be computed as a function of ε spray

18. 18 Institute of Aerospace Thermodynamics Uncertainty analysis Liquid: ethanol, T inj = 389K, p am = 0.2bar, p inj = 10bar The best results are obtained when the spray temperature distribution is intermediate between the two background values

19. 19 Institute of Aerospace Thermodynamics Uncertainty analysis T back1 =286 K, T back1 =366 K Max error: 4K T back1 =337K, T back1 =366 K Max error: 25K

20. 20 Institute of Aerospace Thermodynamics Uncertainty analysis (Outlook) Influence of multiple scattering inside the spray:  Neglecting infrared scattering may lead to an overestimation of the emitted spray radiation  Further investigation are needed to evaluate this effect on the temperature results  Comparison of the temperature results with Global Rainbow Thermometry data to validate the assumption made here.

21. 21 Institute of Aerospace Thermodynamics Contents Motivation & Objectives Differential Infrared Thermography Experimental Setup Uncertainty analysis Results Summary

22. 22 Institute of Aerospace Thermodynamics Results (Validation) Liquid: ethanol, T inj = 403K, p am = 1 bar, p inj = 10bar the window does not affect the temperature results good agreement with the temperature measured by the thermocouples Despite the good agreement a validation of the DIT can be accomplished only upon  comparison with other non- intrusive thermographic technique (e.g. GRT)  estimation of infrared scattering from a cloud of finely atomised droplets.

23. 23 Institute of Aerospace Thermodynamics Results r x Example of flash a atomising spray. Liquid: Ethanol, T inj = 389 K, p am = 0.2 bar, p inj = 10 bar Near the nozzle exit: narrow temperature profile Downstream: flatter temperature profile Rapidly decay of the temperature downstream the nozzle

24. 24 Institute of Aerospace Thermodynamics Results (Axial Profile) Liquid: ethanol, T inj = 342 K, p inj = 10bar Superheating R p ↑ → Cooling rate ↑

25. 25 Institute of Aerospace Thermodynamics Contents Motivation & Objectives Differential Infrared Thermography Experimental Setup Uncertainty analysis Results Summary

26. 26 Institute of Aerospace Thermodynamics Summary and Outlook The potential of the differential infrared thermography (DIT) for the characterisation of the temperature evolution in am flashing jet has been explored Experiments were carried out under vacuum condition employing ethanol as test fluid. The best results are obtained when the spray temperature is intermediate between the two background values The temperature showed a decay along the spray centreline With increasing superheat level, the cooling rate increases Results with a good agreement with the thermocouple measurement. Outlook further investigation are needed to evaluate the effect of radiative, infrared scattering on the temperature measurement

27. 27 Institute of Aerospace Thermodynamics Thank You

28. 28 Institute of Aerospace Thermodynamics

29. 29 Institute of Aerospace Thermodynamics Backup

30. 30 Institute of Aerospace Thermodynamics Experimental Setup Requirements:  Reproducible test conditions P ∞ : from 0.02 bar to 0.4 bar T ∞ =20°C T inj : from 35 °C to 140°C P inj = 10 bar  Good Vacuum (P ∞ =390 Pa)  Possibility to vary independently injection pressure and temperature Problem:  Maintaining a constant backpressure Solution:  Fast response injection

31. 31 Institute of Aerospace Thermodynamics Injector Requirements:  Short injection and transient times → Constant backpressure  Constant injection conditions (i.e. pressure & temperature)  Reproducible test conditions  heated, modified diesel injector Courtesy of Bosch GmbH

32. 32 Institute of Aerospace Thermodynamics Results (Axial Profile) Liquid: ethanol, p am = 0.1 bar, p inj = 10bar

33. 33 Institute of Aerospace Thermodynamics Results (Axial Profile) Liquid: ethanol, T inj = 389 K, p inj = 10bar

34. 34 Institute of Aerospace Thermodynamics Vacuum Chamber Water cooling → to prevent temperature gradients in the test chamber Chamber temperature controlled through 3 thermocouples