Chemical structure of atmospheric pressure premixed laminar formic acid/hydrogen flames

The work presents an experimental and kinetic modeling study of laminar premixed formic acid [HC(O)OH]/H 2 /O 2 /Ar flames at different equivalence ratios ( phi= 0.85, 1.1 and 1.3) stabilized on a flat burner at atmospheric pressure, as well as laminar flame speed of HC(O)OH/O 2 /Ar flames ( phi= 0.5-1.5) at 1 atm. Flame structure as well as laminar flame speed were simulated using three different detailed chemical kinetic mechanisms proposed for formic acid oxidation. The components in the fuel blends show different consumption profiles, namely, hydrogen is consumed slower than formic acid. According to kinetic analysis, the reason of the observed phenomenon is that the studied flames have hydrogen as a fuel but also as an intermediate product formed from HC(O)OH decomposition. Comparison of the measured and simulated flame structure shows that all the mechanisms satisfactorily predict the mole fraction profiles of the reactants, main products, and intermediates. It is noteworthy that the mechanisms proposed by Glarborg et al., Konnov et al. and the updated AramcoMech2.0 adequately predict the spatial variations in the mole fractions of free radicals, such as H, OH O and HO 2 . However, some drawbacks of the mechanisms used were identified; in particular, they predict different concentrations of CH 2 O. As for laminar flame speed simulations, the Konnov et al. mechanism predicts around two times higher values than in experiment, while the Glarborg et al. and updated AramcoMech2.0 show good agreement with the experimental data. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The work investigates laminar premixed formic acid flames and flame speed, using experimental and kinetic modeling methods. Different chemical kinetic mechanisms were used to simulate flame structure and speed, with hydrogen consumed slower than formic acid due to its dual role as fuel and intermediate product. Despite satisfactory predictions for most components, discrepancies were identified in predicting formaldehyde concentrations.