General heat release rate surrogates for NH3/H2/N2 and H2 flames using Raman/Rayleigh/LIF accessible species

Accurate estimation of the heat-release rate (HRR) is essential for understanding and controlling ammonia–hydrogen combustion, yet conventional experimental surrogates are strongly dependent on operating conditions and typically rely on radicals measured by laser-induced fluorescence (LIF). Building upon the QSSA-based HRR reconstruction introduced in our previous work (Zhu et al., 2025), the present study evaluates the robustness and experimental practicality of the existing QSSA-based reconstruction framework rather than proposing a new surrogate. This framework reconstructs absolute HRR in NH 3 / H 2 / N 2 and pure H 2 counterflow flames from Raman/Rayleigh-accessible major species, optionally augmented by LIF-measurable OH . Its robustness is rigorously tested using five detailed kinetic mechanisms over an extended operating space comprising premixed flames ( ϕ = 0.8 – 1.2 , P = 1 – 10 atm, and the full fuel-blend range) and non-premixed flames (varying N 2 dilution and strain rates of 40–150 s −1 ). Consistent with the role of OH established in our previous work, the extended validation confirms that major-stable-species-only reconstruction loses fidelity as the hydrogen fraction increases, whereas including OH reduces the error by several-fold, with some cases approaching or exceeding an order-of-magnitude improvement over conventional indicators such as [ OH ] [ NH 3 ] , [ NH ] , or [ O ] [ NH 2 ] . Most importantly, this study provides the first comprehensive multidimensional error-propagation analysis of the existing QSSA-based reconstruction framework using experimental Raman/Rayleigh major-species data and simulated OH proxies. The analysis quantifies the effects of temperature uncertainty, species-dependent relative and absolute measurement errors, and spatial misregistration, and establishes practical diagnostic limits for NH 3 precision and OH –major-species co-registration. The novelty therefore lies in the extended validation and, principally, in translating an existing reconstruction method into quantitative uncertainty bounds and experimental requirements for high-fidelity HRR diagnostics. Novelty and significance statement The QSSA-based HRR reconstruction and the beneficial role of OH were introduced and demonstrated in our previous work (Zhu et al., 2025); neither is claimed as a new contribution of the present study. Here, the existing QSSA-based reconstruction framework is rigorously validated across five detailed kinetic mechanisms and an extended range of pressure, fuel composition, equivalence ratio, dilution, strain rate, and premixed/non-premixed configurations. More importantly, this study provides the first comprehensive multidimensional error-propagation analysis of the existing QSSA-based reconstruction framework, covering temperature uncertainty, species-dependent relative and absolute measurement errors, and spatial misregistration between major-species and OH fields. The resulting quantitative limits on NH 3 precision, radical noise, and spatial co-registration constitute the principal novelty and provide actionable requirements for future Raman/Rayleigh/LIF-based HRR diagnostics.