Laminar burning velocities of methane + formic acid + air flames: Experimental and modeling study

Laminar burning velocities of methane + formic acid + air flames were determined using the heat flux method at 1 atm and initial gas temperature of 353 K. For fuel mixtures containing 75 or 50% mole fraction of HCOOH, a range of equivalence ratios from 0.7 to 1.3 was covered. In stoichiometric mixtures burning velocities were measured varying fuel composition from pure methane to 85% of formic acid. Due to the relatively high initial temperature close to the operational limit of the present burner, an extrapolation procedure had to be used leading to rather high experimental uncertainties up to ± 2 cm/s. New measurements have been compared with the predictions of the recent kinetic model of the authors and the model of Glarborg et al. [34]. Both models failed, and the reasons for the disagreement were analysed. A modification of the rate constant of reaction HOCO(+M)=H+CO₂(+M) was suggested that dramatically improved the present model performance. This model was then compared with the predictions of the model developed by Marshall and Glarborg [19] at the conditions of the available experimental data for HCOOH flames. The comparison indicates some inconsistencies in the recent measurements of the burning velocity of formic acid.