An experimental study of laminar ammonia/methane/air premixed flames using expanding spherical flames

The fundamental flame properties of ammonia/methane/air mixtures were experimentally investigated using expending spherical flames in a constant pressure chamber. The laminar flame speeds, Markstein lengths and flammability limits were reported for ammonia/methane fuel blends with the equivalence ratios varying from 0.6 to 1.4, at room temperature (298 K) and different pressures (1.0, 5.0 atm). The measured flame properties are compared to those from one dimensional freely propagating flames to assess the accuracy of three existing detailed chemical mechanisms for ammonia/methane/air mixtures. Results show that for ammonia/methane/air mixtures, the laminar flame speeds have a linear correlation with the methane volume fraction. Over the whole ranges of equivalence ratio and methane volume fraction considered, the mechanism of Okafor et al. can accurately predict the laminar flame speeds. With increasing methane content in the fuel mixture, both upper and lower flammability equivalence ratio limits are broadened, and the flammability concentration limits decrease uniformly. In addition, pressure has a pronounced impact on upper limits, while its impact on lower limits is negligible. Sensitivity analysis shows that radicals H, OH (H, OH and CH3) play crucial roles in flame propagation of fuel lean (rich) flames. For fuel lean flame propagation, linear correlations between laminar flame speeds and radical concentrations of H + OH are observed for a wide range of pressures and methane volume fractions.

Automated summary

Experimental investigation of flame properties in ammonia/methane/air mixtures shows significant influence of gas composition and pressure on flame speeds and flammability limits. Linear correlation between flame speed and methane volume fraction is observed, with accurate prediction using Okafor et al. mechanism.