CFD based exploration of the dry-low-NO x hydrogen micromix combustion technology at increased energy densities

Injector Design Space Exploration for an Ultra-Low NOx Hydrogen Micromix Combustion System

“…The mixing process in a micromix system is significantly improved by the principle of the jet-in-cross-flow. The flame anchoring, which is essential for the reduction in NOx formation, is achieved primarily by the recirculation vortices and by the momentum flux ratio of the crossflow streams [63] [17]. The conceptual micromix combustor design conceived at Cranfield University is shown as in Figure 2.…”

“…If, however, the penetration depth increases beyond this critical value, the hydrogen penetrates the shear layer between the two streams and hence enters into a hot inner recirculation zone [63], as shown in Figure 6. This further increases the residence time of the mixture, subsequently leading to an increase in NOx emissions [17]. Hence the determination of this critical penetration depth (ycrit) is of vital importance to the design of the micromix system.…”

“…The spatial discretisation of the computational domain consists of approximately 2.1 million hexahedral elements. The Φ used for this numerical study is assumed to be 0.43, an assumption based on the previous analysis carried out by Aachen [21]. A detailed analysis on the effect of varying Φ on the hydrodynamic instability characteristics of this concept is required to derive the lean limit of hydrogen combustion at a given temperature and pressure condition and will be carried out in future work.…”

“…This kind of flame structure isn't typical of a micromix combustor. The micromix principle aims to combust all the injected fuel in the thin inter-vortex shear layer thus avoiding high fuel concentration and, high-temperature peak and consequently reduced NOx formations [61] [62].…”

“…As a part of this study, the influence of varying the air feed panel hydraulic diameter and the hydrogen inlet diameter and their subsequent impact on the momentum flux ratio and NOx emission characteristics are analyzed. A reference geometry is scaled based on the previous work carried out by Aachen [17], such that the momentum flux ratio was kept constant but with an increased heat release for the current analysis. The reference geometry design parameters are shown in Table 3.…”