(52d) Combustion Properties of Outwardly-Propagating Spherical CH4-NH3/Air Flames

Fundamental combustion characteristics of methane (CH₄)-ammonia (NH₃) blends are studied to evaluate the potential as a low-carbon fuel since their utilization can be considered as an interim technology for responding to global warming. The propagation of spark-ignited spherical laminar premixed CH₄-NH₃/air flames at normal temperature and pressure is experimentally investigated and also computationally predicted using a detailed kinetic mechanism. The fundamental unstretched laminar burning velocities and Markstein numbers are determined and the associated flame structure is investigated. Results show that the laminar burning velocities are reduced with NH₃ substitution, while their tendency with varying fuel-equivalence ratio is similar to the pure CH₄/air flames. Predicted flame structure exhibits that nitrogen oxide (NO_x) formation is enhanced with NH₃ substitution, but at fuel-rich conditions the increased amount of NO_x emissions is much lower than that under fuel-lean conditions. Markstein numbers of CH₄-NH₃/air flames are similar to the pure CH₄/air flames, implying that the flamefront instabilities are not significantly affected by NH₃ substitution. Measured and predicted tendencies of the laminar burning velocities and Markstein numbers for various conditions show encouraging agreement, but quantitative discrepancies among the measurements and predictions at some conditions merit additional consideration.