Enhancement of biogas combustion by co-firing dimethyl ether in a gas turbine model combustor

Abstract

To improve the combustion intensity of biogas which is a renewable gas turbine fuel with methane (CH4) and CO2 as major components, dimethyl ether (DME, CH3OCH3) was used to co-fire with biogas in a gas turbine model combustor in this work. Swirl combustion characteristics of biogas/DME mixtures under different DME contents in fuel mixtures (α) and CO2 contents in biogas mixtures (β) were measured. Numerical simulation and kinetic analysis were performed to provide insights into the effects of DME co-firing and CO2 content on combustion characteristics. It was observed that flame shape and flame size remain almost unchanged with varying DME content and CO2 content at the fixed air flow rate, which are associated with the nearly unchanged flow field. The flame displays a purple color with DME co-firing due to the enhanced formaldehyde (CH2O) chemiluminescence. DME co-firing can effectively improve the flame stability and lower the lean blowout limit (LBO). The decreased LBO is associated with the enhanced fuel reactivity, which results in the reduced ignition delay time and the increased laminar flame speed, OH peak value and high-level OH area. However, increasing CO2 content raises LBO, which is associated with the decreased laminar flame speed, OH peak value and high-level OH area. The ignition delay time can hardly follow the LBO trend with varying CO2 content as it cannot account for the thermal effect caused by CO2 addition. Furthermore, the NO emissions increase with DME co-firing and exceed 20 ppm in pure DME combustion due to the increased temperature level and high-T area, while the amplitude of combustion acoustics is elevated by ∼30–70% with increasing DME content. In contrast, both the NO emissions and amplitude of combustion acoustics attenuate with increasing CO2 content.