Spray diagnostics with CAVILUX HF

Author: Lukas Weiß

Description

The Institute of Engineering Thermodynamics at the Friedrich-Alexander University of Erlangen-Nürnberg is using CAVILUX HF laser illumination in various applications (Figure 1 – 3). The full potential of the laser lighting can be seen in shadowgraphy of fluid flows in injection nozzles. The camera, nozzle and illumination are aligned in this order at an optical rail. The laser illuminates through the transparent nozzle directly into the camera. Different phases of the liquid fuel lead to changes in the refractive index of the fluids. This can be captured by the camera. The field of view is 5 mm x 5 mm. The objective is a Navitar Long Distance Microscope. The depth of field can be adjusted with the aperture of the optics. However, this results in significant light losses. The high brightness of the CAVILUX laser illumination solves this challenge. The speed of the fluid stream in the nozzle is about 100 – 200 m/s which is captured by the camera with 200 kHz. Very short exposure times are needed to reduce motion blur. The camera does not provide short enough shutter times. Therefore the light source is the only option to reduce the motion blur. The pulsed mode of CAVILUX HF that creates short pulses at high frequencies allows to capture high quality images.

The visualization of fluid flows in the injection nozzles and the cavitation of the flows created in the nozzle would not be possible without CAVILUX HF laser illumination


Figure 1: Spray of fuel oil captured at 20.000 fps. Use of an effervescent nozzle. Field of view of 5 mm x 20 mm)


Figure 2: Video: Spray of fuel oil captured at 100.000 fps. Field of view 1,5 mm x 1,5 mm with nozzle size of 0,7 mm.


Figure 3: Fuel spray in engine


Figure 4: Flow in transparent nozzle.

About the author

Lukas Weiß, M. Sc.
Friedrich-Alexander Universität Erlangen-Nürnberg
Institute of Engineering Thermodynamics – LTT

Am Weichselgarten 8
91058 Erlangen
GERMANY

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Fuel Injection Measurements with CAVILUX Smart Diode Laser

Oil spray

Author: Prof. Dr.-Ing. Reinhold Kneer

Description

The form of a fluid jet is highly determined by the collapse of the jet near the nozzle. This phenomenon is also known as primary collapse. Based on this knowledge various experimental, numerical and theoretical studies about the primary collapse have been performed worldwide in the past. However, especially under the conditions in diesel engines the mechanisms of the collapse have not been sufficiently understood. This lack of understanding originates in the lack of established data about form, size and velocity of the fragments in liquid jets. Motivated by the belief that the spatial resolutions that have been reached in current literature are too small to visualize the smallest of fluid structures but there are possibilities to improve the situation. The Institute of Heat and Mass Transfer (WSA) of the RWTH Aachen University has recently developed a new double-pulse backlight microscope [1]. The images that have been acquired with this measurement method contain information about primary fluid structures with a special resolution that has not been reached so far.

application_image

The double-pulse back illumination microscopy creates photographic images of the area of interest of the primary collapse with high special resolution and at the same time low motion blur at two different times during the injection. Amongst other settings this is enabled with the use of a pulsed light source (CAVILUX Smart by the company Cavitar Ltd.). The light source emits the two short light pulses (pulse duration: 10 ns) within short time (1 μs). In addition the light is monochromatic and incoherent which is a major advantage in microscopic imaging. The microscopic optic in its current development state is able to visualize the area of the primary collapse of diesel jets with 600 nm/pixel and a special resolution of 2 μm. Based on the acquired double images not only the size, form and amount of primary fluid structures can be identified with appropriate analysis tools but also the velocity can be measured.

[1] Reddemann, M. A., Mathieu, F., Kneer, R. (2013) Transmitted light microscopy for visualizing the turbulent primary breakup of a microscale liquid jet, Experiments Fluids, 54(11).

About the author

Prof. Dr.-Ing. Reinhold Kneer
RWTH Aachen University, Institute of Heat and Mass Transfer

Augustinerbach 6
D-52056 Aachen
GERMANY

Tel. (0241) 80-95400
FAX (0241) 80-92145

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Fuel Injection in Diesel Jet

Fuel injection

The target is to monitor fuel injection and to measure soot concentration inside a diesel jet during the combustion.

Frame rate: 25.000 fps

Laser pulse length: 800 ns

Working distance: ~ 500 mm

Camera optics: 100 Macro Carl Zeiss

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