Highly radiating hydrogen flames: Effect of toluene concentration and phase

Adapting H2 as a carbon-free fuel for industrial applications requires new, innovative approaches, especially when radiant heat transfer is required. One possible option is to dope hydrogen with bio-oils, containing aromatics that help produce highly sooting flames. The potential doping effects of toluene on a H2-N2 (1:1 vol) flames were studied. Flames with 1%–5% toluene, based on the mole concentration of H2, were measured using a combination of techniques including: still photographs and laser-based techniques. Toluene was mixed with H2-N2 fuel mixture as either a vapor carried by N2, or as a dilute spray. Spray flames produced substantially more PAH, with significantly more soot near the nozzle exit plane, than the prevaporized flames. Increasing the dopant concentration from 1% to 3% of the H2 had a marked effect on soot loading in the flame, although the further increasing the dopant concentration to 5% had a far smaller effect on the soot produced in the flame. Correlations of formation rates were non-linear with toluene concentration in cases where toluene represents less than 10% of the fuel, although expected linear relationships were obsered beyond this regime up to 1:1 toluene/H2 blends.