Laminar burning characteristics of diluted n-butanol/air mixtures

Experimental and numerical studies on laminar burning characteristics of diluted n-butanol/air premixed mixtures were conducted. Experiments were conducted using the spherically expanding flames at different dilution ratios of nitrogen at the initial pressure of 0.1MPa and temperature of 428 K. Both measured and computed results show that with the increase of dilution ratio of nitrogen, the laminar flame speed of n-butanol/air mixtures is decreased. This is attributed to the decrease of adiabatic flame temperature of the mixtures. In addition, effective Lewis numbers of n-butanol/air mixtures at varied dilution ratios were deduced, and flame instability was analyzed. Results show that in the case of equivalence ratio less than 1.4, flame tends to stabilize with nitrogen dilution for the n-butanol/air mixture. In contrast, in the case of equivalence ratio equals to and larger than 1.4, the flame tends to become unstabilized when mixtures are diluted with nitrogen. The measured laminar flame speeds are in good agreement with the computed laminar flame speeds at different nitrogen dilution ratios. Results show a linear relationship between the normalized laminar flame speed and nitrogen dilution ratio. Sensitivity analysis was conducted using the recently developed detailed kinetic mechanism. Results indicate that the three-body reactions are dominant at large dilution ratio.