Effects of hydrogen content on laminar burning velocity and Markstein length in outwardly propagating spherical SNG–air premixed flames

Abstract

As the hydrogen content of the five synthetic natural gas (SNG) fuels fixed with the Wobbe index increases, the unstretched laminar burning velocity and Markstein length also increase. For the addition of hydrogen to natural gas pipelines, an experiment was conducted using up to 19% hydrogen gas (SNG H19). By comparing the error rates with the measured laminar burning velocities and the four reaction mechanisms, Aramco 2.0 was selected as the optimized mechanism for the SNG mixtures. The unstretched laminar burning velocities were compared with those of Aramco 2.0 for SNG–air premixed flames under elevated pressures up to 0.5 MPa for equivalence ratios (ϕ) of 0.7–1.4. The results showed that the measured laminar burning velocities were consistent with the numerical values under lean and stoichiometric conditions; however, the deviations increased under rich conditions as the hydrogen content increased. The laminar burning velocities estimated using the four mixing laws were evaluated under elevated pressure and rich conditions. Consequently, the results predicted by mass-fraction mixing and Q/k models were in good agreement with the measured values. The Markstein length decreases linearly as the hydrogen content increases, but all Markstein lengths are positive; therefore, no instability occurs in the SNG–air premixed flames. The measured Markstein lengths were compared with the theoretical Markstein lengths and reasonably traced well to the isothermal surface at 600 K. When the hydrogen content reaches up to SNG H19, the theoretical Markstein lengths overpredict the results, except for ϕ values of 0.7 and 1.4.