Sprays thermometry using two color LIF and SLIPI

• Knowing the droplets temperature is of great importance in spray-assisted combustion devices as it directly affects the droplet evaporation rate. This information helps optimizing the fuel/air mixture formation for the improvement of combustion devices. To measure the temperature of spray droplets, optical techniques such as Rainbow-Refractrometry (for point-wise) and the two-color LIF ratio thermometry (for 2D) have been preferred to thermocouples due to their non-intrusive nature. However, in optically dense sprays, these techniques are affected by unwanted impedes such as multiple scattering of light, intensity reduction along the light propagation (laser extinction) and attenuation of the signal travelling from the incident plane to the detector. The multiple light scattering contains false signals emerging from the non-illuminated portions of the sprays and leads to erroneous measurement results as well as image blur. Thanks to SLIPI (Structured Laser Illumination Planar Imaging) these issues can be efficiently addressed. In addition, by using two-color LIF (Laser Induced Fluorescence), effects of laser extinction and signal attenuation can be canceled out from the image ratio. In this study, SLIPI is combined with the two-color/band LIF ratio approach using a temperature sensitive dye. Here Fluorescein is excited at 447 nm and emits a LIF signal peaking at 520 nm. This signal becomes redshifted as the temperature increases. We demonstrate, for the first time, the application of this novel approach for measuring the local temperature of a hollow cone (HC) spray in 2D. The water temperature in the presented measurements ranges from 20°C to 90°C while the liquid injection pressure is set to 20 bars. The measurement is calibrated in-situ with a thermocouple and the results from both the conventional and SLIPI two-color LIF detection schemes are compared. It is found that the SLIPI ratio shows a significant improvement in signal sensitivity and accuracy when compared to the results of the conventional planar imaging.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Annan teknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Other Engineering and Technologies (hsv//eng)

Nyckelord

spray imaging

temperature mapping

multiple scattering

SLIPI

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