Mapping the stability of free-jet biogas flames under partially premixed combustion

• Published in: Energy (Oxford) Vol. 220; p. 119749
• Main Authors: Abdallah, Muhammed S., Mansour, Mohy S., Allam, Nageh K.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.04.2021; Elsevier BV
• Subjects: Biogas; Carbon dioxide; Combustion; Combustion chambers; Combustion stability; Equivalence ratio; Extinguishing; Flame stability; Flow stability; Fluid dynamics; Fluid flow; Jet flow; Optimization; Partially premixed combustion; Premixing; Reynolds number; Slot burner; Slot burner; Biogas; Partially premixed combustion; Flame stability
• ISSN: 0360-5442; 1873-6785
• DOI: 10.1016/j.energy.2020.119749

Enhancement of biogas combustion characteristics will increase the possibility of the direct utilization of such an eco-friendly fuel in practical combustors. We report a full study of biogas combustion under partially premixed mode to investigate the stability of biogas free-jet flames using a concentric flow slot burner was used to evaluate the biogas combustion characteristics. Five mixtures of biogas ranging from 0%CO2 up to 40%CO2 were investigated to study the effect of CO2 proportion on the stability of biogas flames. A new well-defined stability procedure was followed by studying the four major observed phenomena in biogas flames: Stable Flame, Partially-lifted Flame, Fully-lifted Flame, and Extinction. Each phenomenon was clearly defined in addition to describing the operating conditions in terms of Reynolds Number (Re) and Equivalence ratio (ϕ). The effect of the premixing ratio (LD) on the combustion stability of biogas flames was also studied for five premixing ratios LD3, LD5, LD7, LD10, and LD16 to optimize the flame stability. The temperature of stable biogas flames was also measured at different CO2 percentages. The results showed that LD10 is the optimum premixing ratio to generate a stable biogas flame at all tested CO2 proportions. Partially premixed combustion in slot burner manages to sustain a stable biogas flame up to 30%CO2. However, increasing the CO2 to 40% eventually led to a weak and unstable flame regardless of the premixing ratio. •Biogas with up to 30% level of CO2 upgrading has appropriate combustion characteristics.•LD10 is the most appropriate premixing ratio to operate a stable flame.•The premixing ratio LD16 was the optimum premixing ratio to reach the operating conditions.•Increasing the CO2 content would decrease the temperature of the flame.•A full map of operational conditions is presented to guide the future research work.