Abstract
Multi-pass cavity line-of-sight extinction (MPC-LOSE) and laser-induced incandescence (LII) techniques are deployed to measure the soot volume fraction in a series of nitrogen-diluted flames, which produce only ppm volume mass fractions of soot. The separate suppression effects on soot formation of direct fuel dilution and indirect effects of temperature and residence time are interpreted by using a numerically calculated flow velocity and temperature field using a one-step fast chemistry model. The experimentally determined rate of soot formation is shown to obey approximately the same function of the local temperature for all dilution cases. The results show that a simple one-step reaction model using previously measured activation energies can account for the dilution effect with good accuracy. The results show that the direct effect of dilution on concentration is comparable to the effects of changing the temperature estimated local temperature and residence time.
Highlights
Soot from combustion sources is both a significant atmospheric pollutant, as well as a contributor to climate change [1,2]
Line-of-sight extinction (LOSE) methods [9,10,11] have been widely used for soot detection and measurement, as they can yield absolute values of soot volume fraction in uniform or symmetric systems, and are relatively simple and inexpensive to implement using a low power continuous wave (CW) laser and photodiodes
A high spatial resolution of 200 μm can be achieved by using concave cavity mirrors in the optical set-up
Summary
Soot from combustion sources is both a significant atmospheric pollutant, as well as a contributor to climate change [1,2]. Understanding the process of soot production, and creating predictive models is part of the research into the development of clean, sootfree combustion systems. We investigate inert-diluted hydrocarbon flames, which typically produce significantly lower soot than in undiluted flames, presenting challenges to usual measurement methods [3,4,5,6,7,8]. Line-of-sight extinction (LOSE) methods [9,10,11] have been widely used for soot detection and measurement, as they can yield absolute values of soot volume fraction (fv) in uniform or symmetric systems, and are relatively simple and inexpensive to implement using a low power continuous wave (CW) laser and photodiodes. Laser-induced incandescence (LII) imaging produces twodimensional maps of relative soot volume fractions, but requires calibration. The techniques are complementary, and have been used together in the past [12,13]
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