CW-LCE Measurements
High spatial resolution continuous wave laser cavity extinction (CW-LCE) technique is designed to measure the soot volume fraction from low- soot-producing flames. A laser beam cavity is realised by placing two partially reflective concave mirrors on either side of the laminar diffusion flame under investigation. This configuration makes the beam convergent inside the cavity, allowing a spatial resolution within 200 μm, whilst increasing the absorption by an order of magnitude. The measurements of soot distribution across test low sooting methane flame show good agreement with results using laser-induced incandescence (LII) in the range from around 20 ppb to 15 ppm. The set up can also be used to measure any absorptive probe volume.
Schematic of the cavity (BS beam splitter; ND neutral density filter; PD photodiode; PRM partial reflective mirror).
Soot volume fraction measured using cavity extinction (blue circles) and LII (red line) for a standard methane flame.
Further details in: Tian, B., Gao, Y., Balusamy, S., & Hochgreb, S. (2015). Applied Physics B: Lasers and Optics, 120(3), 469–487. [https://doi.org/10.1007/s00340-015-6156-3]
Tian, B., Gao, Y., Zhang, C., & Hochgreb, S. (2018). Combustion and Flame, 192, 224–237. [https://doi.org/10.1016/j.combustflame.2018.01.037]