A comparative study on the laminar C1–C4 n-alkane/NH3 premixed flame

Abstract

This work aims to comparatively investigate the NH3 blending effects on the combustion of light alkanes, CH4/C2H6/C3H8,/nC4H10. The laminar burning velocity (Su0) and burned gas Marstein length of the stoichiometric alkane/NH3 blends were measured at 298 K, 0.1 MPa using expanding spherical flame and compared with the six mechanisms. Detailed kinetic analyses were conducted using a newly developed mechanism. The results show that the Su0 of each alkane exhibits a distinctive response to NH3 introduction, which amplified the difference of Su0 for the binary fuels. The C2H6/NH3 blend exhibits the maximum Su0 at low ammonia fraction but exceeds by nC4H10/NH3 at intermediate and high ammonia fraction. The Su0 reduction caused by NH3 blending is dominated by the scavenging effect on the OH and H radicals and less affected by the C-N interactions under all studied conditions. Consequently, the Su0 of larger alkanes are less influenced by the NH3 blending because of their diverse production sources of OH and H radicals. Due to the competitive effect of increased mixture Zel’dovich number and decreased Lewis number, burned gas Markstein length of the binary fuels tend to increase firstly and then decrease with increased NH3 fractions. In addition, ammonia blending energy fraction may be a more proper criterion in practical engineering usage compared with mole fraction, since the energy fraction of NH3 governs the relative reduction of Su0 and CO2 emissions independent of the alkane types, and these parameters are the major concerns in NH3 blending combustion.