Laser induced incandescence determination of the ratio of the soot absorption functions at 532 nm and 1064 nm in the nucleation zone of a low pressure premixed sooting flame

摘要

In this work, the two-excitation wavelength laser induced incandescence (LII) method has been applied in a low-pressure premixed methane/oxygenitrogen flame (equivalence ratio 2.32) to determine the variation of the ratio of the soot absorption functions at 532 nm and 1064 nm E(m,532nm)/E(m, 1064 nm) along the flame. This method relies on the comparison of LII signals mea sured upon two different excitation wavelengths (here 532 nm and 1064 nm) and with laser fluences selected in such a way that the soot particles are equally laser-heated. The comparison of the laser fluences at 532 nm and 1064 nm leads to an easy determination of E(m, 532 nm)/ E(m, 1064 nm). The reliability of the method is demon strated for the first time in a low pressure flame in which the soot nucleation zone can be spatially resolved and which contains soot particles acting differently with the laser fluence according to their residence time in the flame. The method is then applied to determine the profile of E(m, 532 nm)/E(m, 1064 nm) along the flame. A very im portant decrease of this ratio is observed in the region of nascent soot, while the ratio remains constant at high dis tance above the burner. Implication on temperature determi nation from spectrally resolved measurement of flame emis sion is studied.