Laser-induced fluorescence diagnostics of a propane/air flame with a manganese fuel additive

Abstract

Laser-induced fluorescence (LIF) has been used to investigate the effects of MMT, a managanese-containing fuel additive, on a premixed propane/air flame burning at 40 torr. The emphasis was placed on the chemistry of formation of prompt nitric oxide. No measurable effect due to the MMT on the gas-phase chemistry of this flame was observed. LIF profiles as a function of burner height were made for OH, H, O, CH, NO, CO, Mn, MnO, and temperature using OH rotational excitation scans. Photochemical interferences were observed when exciting O, H, CO, and NO deep in the ultraviolet (205–230 nm), due either to laser-generated trace species or concomitant LIF from other species. Low laser power is required to avoid these problems. The interferences were significantly more severe in this propane flame than seen previously for a methane flame under similar conditions, most certainly due to absorption and photochemical activity of pyrolytic and partially oxidized fragmentary hydrocarbons with two or more carbons. This suggests caution when applying laser diagnostics (including excimer lasers) to flames with complex hydrocarbon fuels. Mn and MnO LIF detection strategies were developed on an atmospheric pressure burner and applied to this low pressure flame. The Mn LIF signals are strong but those from MnO are of low intensity and in a region of strong LIF from C 2 molecules.