The Clean Combustion Laboratory supports an extensive range of laser diagnostics methods for the measurements of velocity, mixing, temperature and reactive scalar fields in reacting and non-reacting flows.
Our lasers can be tuned to excite laser induced fluorescence (LIF) from species such as OH, CH2O, NO, CO, CH and PAH. A two-color TSI, laser/phase Doppler velocimetry system (LDV/PDA) is also available for single-point measurements of velocity, droplet size and number density. A small number of engines, dynamometers and gas analysers are also present.
This may be performed at low repetition rates of 10Hz as well as high repetition rates of up to 10kHz. Existing facilities include two low repetition rate (10Hz) Nd:YAG lasers (Spectra Physics, PRO-350) each providing an output of 1.4J/pulse at 532nm with a pulse duration of 9ns. These lasers can pump two existing dye lasers (Sirah, PrecisionScan, PRSC-LG-24-EG).
Also available is a state-of-the-art, high-speed LIF imaging system comprising two high-speed, Nd-YAG lasers (Edgewave, IS6II-E and HD30II-E) with a repetition rate of up to 10kHz and outputs of 3 and 12mJ/pulse, respectively. These can pump two high-speed dye lasers (Sirah-Credo).
Capabilities exist to measuring soot volume fractions using laser-induced incandescence (LII). Recent equipment added to this laboratory include a mode-locked picosecond Nd:YAG laser (Ekspla, PL2251 Series, 50mJ/pulse, 30ps and 80ps pulsewidth) as well as very fast photomultiplier tubes. Such acquisitions enable single point measurements of temperature using rotational CARS, as well as fast detection of LIF-PAH and LII signals which are essential for soot measurements in laminar and turbulent sooting flames.
This set-up is highly relevant in the visualisation of liquid fragments in the primary and secondary regions of atomising sprays. It consists of a two-dimensional backlight illumination system developed to include two lasers, two lenses and two cameras both operated in a PIV mode and synchronised to the lasers using a LaVISION high-speed controller. Two x 5kHz Edgewave laser heads (Figure 1: 1 and 2) are used in order to provide two 532nm-beams. Each beam is split into two using a 50:50 beam-splitter (9 and 10).
The four split beams are guided into two diffusing optics (7 or 8), using laser-line mirrors (11 to 14) and finally into the probe volume (15). The two laser heads are typically time shifted by 5µs (for high Weber number) to 40µs (for dripping mode break-up). On the collection side of each viewing angle, there is a long-distance microscope (QM100, Figure 1: 5 or 6) coupled to a LaVISION HSS6 camera (3 or 4) operating in PIV mode.
Figure 1 shows one Edgewave, 10kHz laser pumping a Sirah-Credo dye laser. Two reactive species, namely CH2O and OH were imaged recently using this set-up. The collection side includes lenses with very narrow depth of field allowing for accurate “out-of-plane” resolution, two intensified high-speed CMOS cameras (LaVision-Star 6) with 5.4kHz frame rate at full resolution of 1024x1024 pixels and four intensified CCD cameras (LaVision, Imager intense) with a dual-frame rate of 10Hz and a resolution of 1376 x 1040 pixels.