An experimental investigation of premixed fuel-rich lowpressure propene/oxygen/argon flames by laser spectroscopy and molecular-beam mass spectrometry

A fuel-rich, nonsooting (C/O=0.773) premixed laminar propene flame at 50 mbar was investigated by combining laser techniques and molecular beam sampling mass spectrometry (MBMS) to contribute to the understanding of the regime between stoichiometric and sooting flames, where models have difficulties in predicting important flame features. As a quantity of paramount influence, the temperature profile was measured by laser-induced fluorescence (LIF) of the OH radical: also, the burnt gas temperature was determined from the Stokes/anti-Stokes Raman intensities of CO and H₂. In addition, absolute OH concentrations were obtained using LIF.

The profiles of several hydrocarbons including radical species were measured by MBMS with particular attention to intermediate species, which were discussed as precursors of the first aromatic ring. Quantitative data were obtained for a variety of stable compounds, and semiquantitative profiles were determined for several other species, thus providing a broad database for modeling studies. The analysis of the data shows that C₆H₆ formation via acetylene plays only a minor role under our flame conditions, whereas significant contributions from the propargyl recombination are noted. Furthermore, additional reaction sequences via C₆H_x (x>6) species should be considered in this flame for the formation of C₆H₆ an aromatic compounds: here, the recombination of allyl and propargyl addition to propene seem to be important steps. It was concluded that fuel-specific aspects need to be considered in the formation of higher hydrocarbons in general and of the first aromatic ring in particular.