Numerical and Experimental Analysis of the Effect of a Swirler with a High Swirl Number in a Biogas Combustor

Abstract

Climate change as a worldwide phenomenon is the cause of multinational agreements such as the Kyoto Protocol and the Paris Agreement with the goal of reducing greenhouse gas emissions. Biogas is one of the most promising biofuels for the integration of clean energy sources; however, biogas has the disadvantage of a low calorific value. To overcome this problem, mechanical devices such as swirlers are implemented in combustion chambers (CCs) to increase their combustion efficiencies. A swirler induces rotation in the airstream that keeps a constant re-ignition of the air–fuel mixture in the combustion. We present the numerical modeling using computational fluid dynamics (CFD) and experimental testing of combustion with biogas in a CC, including an optimized swirler in the airstream with a swirl number (Sn) of 2.48. A turbulence model of the renormalization group (RNG) was used to analyze the turbulence. Chemistry was parameterized using the laminar flamelet model. The numerical model allows visualizing the recirculation zone generated at the primary zone, and partially at the intermediate zone of the CC caused by the strong swirl. Temperature distribution profiles show the highest temperatures located at the intermediate and dilution zones, with the last one being a characteristic feature of biogas combustion. A strong swirl in the airstream generates low-velocity zones at the center of the CC. This effect centers flame, avoiding hot spots near the flame tube and flashback at the structural components. Regarding pollutant emissions, the goal of a biogas that generates less pollutants than nonrenewable gases is accomplished. It is observed that the mole fraction of NO in the CC is close to zero, while the mole fraction of CO2 after combustion is lowered compared to the original mole fraction contained in the biogas (0.25). The mole fraction of CO2 obtained in experimental tests was 0.0127. Results obtained in the numerical model for temperatures and mole fractions of CO2 and NO show a behavior similar to that of the experimental model. Experimental results for mole fraction of CO emissions are also presented and have a mean value of 0.0009. This value lies within allowed pollutant emissions for CO according to national environmental regulations.