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Abstract In line with the global drive to decarbonise energy systems, there is an urgent need to develop new dry low-NOx (DLN type) combustion concepts to enable efficient utilisation of alternative fuels, such as hydrogen. New combustor configurations require a detailed study of flame behaviour, including stabilisation, structure and dynamics, as well as other performance parameters such as combustor emissions. In this work, a piloted single-nozzle lean direct injection (LDI) burner was investigated where hydrogen was injected into the main air stream in a jet-in-crossflow configuration. Hydrogen was injected relatively close to the combustor inlet to create a partially premixed mixture in order to avoid flashback. The main flame was surrounded by 12 circumferential premixed hydrogen-air pilot flames. The flame stabilisation and the dynamics of the main flame were studied in the presence of the pilot flames, taking into account the complex interactions between them. The bulk air velocity of the main flame was varied from 30 m/s to 90 m/s, while the equivalence ratio was varied from 0.2 to 0.6. Two pilot schemes were employed; P1 - the pilot flow rate was kept proportional to the air flow rate of the main flame, and P2 - the pilot flow rate was kept constant irrespective of main air flow rate conditions. The equivalence ratio of the pilot was kept stoichiometric for both schemes. Flame structure and dynamics were evaluated from OH* chemiluminescence measurements utilising both, a photomultiplier tube and a high-speed intensified imaging system. The lean blow off limit was observed to increase from 0.1 to 0.13 as the bulk air velocity was increased from 30 m/s to 90 m/s. At all bulk air velocities tested, the amplitude of the acoustic pressure oscillations was the highest at ϕg = 0.4 and decreased on either side (for richer or leaner mixtures). The results also showed that for a fixed main bulk air velocity, the flame stabilisation was characterised by extinction and auto-ignition events at low equivalence ratios (around 0.2 to 0.3), while for higher equivalence ratios, lifted flames were observed. The flame root and flame tip positions, estimated from OH* chemiluminescence images, increased as the global equivalence ratio was changed from 0.15 to 0.4, beyond which the flame root position decreased slightly while the flame tip position remained more or less at the same value. The results from this work will help develop a detailed understanding of the flame behaviour in lean hydrogen flames and hence inform design efforts towards the development of new architectures for stable, low-emission 100% hydrogen combustors.
Dere et al. (Mon,) studied this question.