Effects of fuel composition and initial pressure on laminar flame speed of H2/CO/CH4 bio-syngas

Abstract

Biomass-derived syngas composition varies considerably depending on different feedstocks and processing techniques and thereby complicates the combustion control. A study on the effects of variations in the fuel composition and initial pressure on the characteristics of premixed H2/CO/CH4 flames was conducted using the spherical expanding flame method and CHEMIKIN package. Experimental measurements and numerical simulations were performed at an initial temperature of 303 K, equivalence ratios of 0.6–1.5 and pressures of 0.1–0.5 MPa with a wide range of H2/CO/CH4 compositions. The thermal and chemical kinetic analyses are also presented. The measured laminar flame speed was compared with simulations using the Li mechanism. The experimental data show a reasonable agreement with the calculated values, especially at fuel-lean and low pressure conditions. With the increase of H2 fraction in the fuel, the laminar flame speed increases significantly, but for the CH4 enrichment flame, the behavior is quite the contrary that it has the lowest laminar flame speed. With the increase of CO fraction in the fuel, the laminar flame speed does not change much. The thermal and chemical kinetic analyses indicate that the CO addition has more effect on the adiabatic flame temperature but only plays a small role in the chemical effect compared to that of the H2 addition. On the other hand, at elevated pressures, the Li mechanism gives slight overestimations for lean mixtures but underestimations for rich mixtures. The laminar flame speed decreases with the increase of initial pressure under tested equivalence ratio which is mainly due to the increasing unburned mixture density and decreasing H, OH radicals concentrations.