Laser-induced incandescence for soot diagnostics at high pressures
The influence of pressure on laser-induced incandescence (LII) is investigated systematically in premixed, laminar, sooting ethylene/air flames at 1-15 bar with wavelength-, laser fluence-, and time-resolved detection. In the investigated pressure range the LII signal decay rate is proportional to pressure. This observation is consistent with the prediction of heat-transfer models in the free-mol. regime. Pressure does not systematically affect the relation between LII signal and laser fluence. With appropriate detection timing the pressure influence on LII signal's proportionality to soot vol. fraction obtained by extinction measurements is only minor compared with the variation obsd. in different flames at fixed pressures. The implications for particle sizing and soot vol. fraction measurements using LII techniques at elevated pressures are discussed.
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