Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

3.1 Development of optical diagnostics for two phase flows

The main results are:
- The development of innovative non-intrusive diagnostics in two-phase flow combustion.
- The combination of adavanced optical diagnostics to investigate simultaneously the gaseous and liquid phases

-- For LEMTA, this development concerns mainly the implementation of two colors laser-induced fluorescence (applied to droplet temperature measurement) in combusting monodisperse droplet streams, the extension of this technique to the measurement of temperature distribution within combusting droplets (for stationary and periodic phenomena), which was the first measurement of this kind.
The experimental techniques applied to monodisperse droplet streams are highly useful laboratory tools, which can provide very accurate data (droplet temperature) on single droplets behaviour (even in combustion).

Finally, the extension of two colors laser-induced fluorescence to polydisperse spray has been carried out: it constitutes a more flexible tool able to operate closest to real spray conditions and also closest to real aero-engines configurations.
For CORIA and ONERA, the development concerns mainly the rainbow technique. The theoretical work carried out at CORIA on the description of the rainbow in the Nussenzveig framework gives the possibility of a more accurate process of the ONERA experimental records by taking into account the ripple structure. Nowadays, we focus our efforts on the effect of radial gradient of temperature in rainbow and LIF measurements.

-- Two kinds of diagnostics have been combined
- Two colors laser induced fluorescence applied to droplet temperature measurement has been combined with planar laser induced fluorescence (PLIF)applied to concentration measurement of fuel vapor in the close vicinity of the droplet. The relationship between the droplet temperature and the surrounding fuel vapour concentration has been demonstrated and quantified.

- The temperature measurement of the liquid droplets by two colors laser-induced fluorescence has been combined with the size measurement by PDA. With the use of these two measurements, the heating of the droplet and its evaporation can be directly monitored.

Two kinds of benefits of these results can be distinguished:
- The development of these new measurement techniques allows collecting new experimental data on selected test cases. It will promote the development of new physical models and validation tools for the computer codes. It should improve the efficiency and predictive capabilities of the calculation tools for the engine disigners.
- The development of the measurement techniques has already promoted cooperations with instrumentation manufacturers (especially DANTEC Dynamics) and manufacturing agreement will be expected shortly for two colors laser-induced fluorescence applied droplet temperature measurements.
Furthermore, the priciples of the techniques will be published in archival scientific literature.
Further applications of two/three colors LIF on real fuels (like kerozene or diesel or automotive petrol) can be forseen in the next future. The technique is operational on simple single component fuels (ethanol, acetone). Further application on real fuel requires extension of the calibration principles for the real fuel. Then the techniques may be then used in industrial sprays and combustors.

Extension of the PLIF technique for fuel vapour concentration measurements in sprays operating with more realistic aeronautical fuels such as kerosene or surrogates is currently under study at ONERA. New molecules will be probed in the future to determine their ability to provide information on equivalence ratio and temperature of the gas phase. Application of the technique to gas turbines operating at real conditions (typically air preheated at 800 K and 3.0 MPa) is foreseen in the short term.
LEMTA, ONERA and CORIA participates to a new french program that aims to improve the measurements techniques and especially to address their extension to multicomponent fuels.

One of the objectives of this collaboration is the development of the Global rainbow technique to measure the droplet temperature/ Composition in real complex sprays.

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