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

Ku, J. W., Sungkyunkwan University
Ahn, Y. J., Sungkungkwan University
Kwon, O. C., Sungkyunkwan University
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 (NOx) formation is enhanced with NH3 substitution, but at fuel-rich conditions the increased amount of NOx 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.