Flow field, flame structure and emissions quantifications of oxygenated glycerol in a swirl flame combustor

• Glycerol is combusted in spray form assisted by the premixed methane swirl flame. • OH* chemiluminescence imaging shows two distinct heat release zones. • The glycerol spray results in reduced strength of recirculation flow. • Lower NO and CO emissions can be achieved by regulating the operating conditions. • Dual-fuel injection strategy is an effective way to combust glycerol. The growing production of biodiesel results in the supply glut of crude glycerol byproduct. One option is to utilise the glycerol as supplementary fuel for combined heat and power generation, thereby partially substituting conventional fossil fuel while improving the economics of biodiesel production. In the present study, the spray combustion and emissions characteristics of glycerol were examined using a swirl flame burner. Due to the inherent low heating value of glycerol, the swirling air was premixed with methane to form a co-fired globally lean flame. Both the crude glycerol and pure glycerol spray flames emitted strong spectral intensity of yellowish-orange in the flame brush, overwhelming the bluish flame of fuel-lean methane. The dual heat release zone indicated by the OH* chemiluminescence marks the spatial locations of the swirling premixed flame and centrally injected spray flame. The sooting region of the flame was found to extend downstream beyond the heat release zone. The presence of spray reduced the intensity of the central reverse flow, while the size of the central recirculation zone was also affected. By employing a globally lean-flame and preheating approach, the NO emission was kept low while the higher atomising air-to-liquid ratio led to lower CO emissions. By employing a dual-fuel injection strategy, the glycerol can be effectively burned under swirl and moderately heated condition.