Evaluation of burning velocity of premixed lean NH3/H2 highly turbulent flames using NH PLIF signal

Journal article, 2026

NH₃/H₂ flames are a promising route to carbon-neutral combustion, yet their turbulent burning rates remain poorly characterized. Using simultaneous PLIF of NH₃, NH and OH together with Rayleigh scattering in a jet flame stabilized on a McKenna burner, we show that conventional flamelet-based turbulent burning velocities (U_T,F) drastically underestimate the true bulk consumption velocity (U_T), by factors of up to 25× and 9× when evaluated from NH₃- and OH-PLIF data, respectively. To overcome this limitation, we introduce a new bulk metric U^*_T, derived from the strong NH–heat-release-rate correlation observed in unstretched laminar simulations; it inherently accounts for reaction-zone broadening, stretch and flame–flame interactions. U*T substantially exceeds U_T,F, with the residual gap to _UT traced to the breakdown of NH–HRR proportionality under strain. The framework also yields local burning velocities u^*_c that grow with downstream distance, providing a physically motivated, semi-quantitative characterization of highly turbulent NH₃/H₂ combustion.