Laminar Burning Speeds and Flammability Limits of CH4/O2 Mixtures With Varying N2 Dilution at Sub-Atmospheric Conditions

Abstract

This paper presents experimentally determined laminar burning speeds (SL) of premixed methane/oxygen/nitrogen mixtures at sub-atmospheric conditions obtained by using the constant-pressure spherical flame method. The goal of the conducted experiments was to investigate the effects of nitrogen dilution and pressure reduction on the laminar flame speed and flammability limits of methane/oxygen mixtures. Nitrogen content was varied between 3.1 and 79.3 volume percent. SL at a target pressure of 0.5 bar was investigated. Actual pressure levels ranged between 0.506 and 0.568 bar. Experiments at 1 bar were conducted as a benchmark case of the setup compared to results from literature. The laminar flame speed is found to increase with decreasing nitrogen content and decreasing pressure. The obtained results show good agreement with simulated data using the several chemical reaction mechanisms within 4.8% for near stochiometric mixtures. The upper flammability limit (UFL) is shown to be pressure-sensitive while the lower flammability limit (LFL) remains stationary for both pressure levels compared to reference data at 1 bar. Furthermore, the LFL is shown to stay at 6% vol methane content, independent of nitrogen dilution ratio.