On the effective Lewis number formulations for lean hydrogen/hydrocarbon/air mixtures

Fuel flexibility, stability and emissions in premixed hydrogen-rich gas turbine combustion: Technology, fundamentals, and numerical simulations

“…Non-equidiffusivities (also known as preferential diffusion) i.e. the non-unity of Lewis number have been shown to lead to strong changes in combustion intensity when flames are subject to stretch which is the case under real turbulent combustion conditions [46]. This is true for laminar flames subject to strain and curvature, as well as for turbulent flames, highlighting the relevance of estimating changes in the Lewis number when fuel composition is modified.…”

“…This is true for laminar flames subject to strain and curvature, as well as for turbulent flames, highlighting the relevance of estimating changes in the Lewis number when fuel composition is modified. Such estimations are straightforward for a single fuel but it is more subtle when operating with a blend of fuels as reported in a recent study by Bouvet and co-workers [46]. The researchers re-iterated the importance of Lewis number and performed a comparison of different formulations to evaluate it for fuel mixtures.…”

“…6 for CH 4 -CO-H 2 blends. Bouvet et al [46] compared this volume-based Lewis number estimation to other formulations already in use by the combustion community, the diffusion based [47] and heat release based [48] formulations:…”

“…Bouvet et al [46] relied on laminar flame calculations while Dinkelacker et al [47] investigated turbulent combustion regimes. More research is needed in this area to clarify which formulation should be preferred when modeling fuel mixtures.…”

Research on Cellular Instabilities of Lean Premixed Syngas Flames under Various Hydrogen Fractions Using a Constant Volume Vessel

“…Hydrodynamic instability, which is caused by the expansion across the flame sheet [12,13], is present in all flames [14][15][16]. Diffusive-thermal instability, which is caused by the preferential diffusion of mass and heat [17,18], is only present in the flames with Lewis number (Le) < 1 [19][20][21][22]. Body-force instability, which is caused by the effect of buoyancy [23], is only apparent when the laminar propagation speed of the flame is low [24].…”