EFFECTS OF HYDROGEN ADDITION ON A CONFINED LEAN NON-PREMIXED NATURAL GAS SWIRLED FLAME

Advanced combustion approaches in gas turbines suggest the use of alternative fuels to reduce pollutants emissions and to improve performances. Alternative fuels include, among others, by-products of biomass gasification and refinery wastes. Many of these fuels contain hydrogen, which may have a significant effect on combustion performances. Moreover, conventional hydrocarbon fuels blended with hydrogen have also been proposed as a cross-over strategy for the hydrogen-energy based infrastructure of the future.
The flame structure and flow field modifications induced in a confined lean non-premixed natural gas swirled flame by hydrogen addition were experimentally investigated. The hydrogen content was varied between 0% and 100% of the total volumetric fuel flow; correspondingly input thermal power varied from 20kW to 7kW while equivalence ratio varied form 0.71 to 0.17. Two different typology of fuels injection were considered: coaxial and transverse with respect to the swirled air stream.
When hydrogen is added to natural gas, preliminary results showed an unexpected increase in pollutants emissions (both CO and NO_x) and soot formation (only for axial fuel injection). With increasing hydrogen content, temperature measurements and visual inspection of the flame indicate the appearance of a hotter and more reactive zone close to the burner efflux. For the axial fuel injection, PIV measurements evidenced also a toroidal vortex around the fuel jet which is responsible for the increasing soot formation. Such behavior was not detected for transverse fuel injection due to an increase in the mixing of fuel and air.