Direct numerical simulations of probe effects in low-pressure flame sampling

Speciation studies of low-pressure flames using intrusive sampling and molecular beam mass spectrometry analysis are essential towards developing and validating combustion models. In order to assess potential probe-induced effects, direct numerical simulations of a realistic experimental configuration were carried out using a finite-volume fully compressible code as well as detailed descriptions of chemical kinetics and molecular transport. A 50 mbar rich propene/oxygen/argon flame was modeled for which experimental data are available. The effects of the probe and supporting flange, non-adiabaticity, sampling location, and compressibility when there is suction through the sampling orifice were assessed. Results showed that even under adiabatic conditions, the presence of the probe-flange assembly affects the flow field two-dimensionally. Furthermore, the effects of heat loss and compressibility were found to be significant at the sampling location. Important radicals for fuel oxidation such as OH and HCO, and for soot formation such as C3H3 are affected by the sampling procedure and their concentrations at the sampling location can differ notably compared to unperturbed one-dimensional flames.