Comparative chemiluminescence investigation of OH* radicals in laminar and turbulent multi-fuel air- and oxy-fuel flames on semi-industrial and laboratory scale including NOX-formation

Chemiluminescence emitted by the de-excitation of excited hydroxyl radicals (OH*), allows for several insights into combustion processes. The presented study investigates air- and oxy-fuel combustion of natural gas with hydrogen enrichment up to 100%, using both small-scale laminar flames and turbulent high-impulse flames (50–100 kW). The obtained results from the laminar 1 kW flames from the laboratory burner are then used, to interpret the influence of turbulence and chemistry influence from an industrial scale multi-fuel multi-oxidizer burner. The measurements performed for the laboratory burner were also compared to simulations. Experimental data were compared to 1D simulations, showing good agreement in trends. However, in turbulent flames, turbulence effects far exceeded those of combustion chemistry. While laminar flames exhibited the highest chemiluminescence intensity in CH 4 -air combustion in both experiments and simulations, the maximum in turbulent combustion experiments occurred in oxy-fuel combustion, with hydrogen and natural gas performing similarly. Oxy-fuel flames showed similar chemiluminescence intensities, increased by 2 orders of magnitude, compared to turbulent air-fuel combustion. Additionally, the changes in flame shape and reaction zone size for hydrogen-enrichment in air-fuel combustion were investigated in terms of NO X formation, where OH* imaging proved its potential for emission reduction. • Laminar and turbulent flames are compared via OH* chemiluminescence imaging. • Natural gas enriched with 0 to 100% H 2 is used as fuel. • The investigations include lab-scale and industry ready burners from 1 to 100 kW. • Insights into differences between laminar and turbulent flames are presented. • The flames are investigated for shape and length, heat release and NO X formation.