Development of a Skeletal Mechanism with NOx Chemistry for CH4/H2 Combustion over a Wide Range of Hydrogen-Blending Ratios

Abstract

An accurate and efficient skeletal mechanism is critical to describe the combustion chemistry of CH₄/H₂ with nitrogen oxides (NO_x) through computational fluid dynamics (CFD) simulations. In this paper, the performance of the 11 classical/state-of-the-art detailed C/H/O/N mechanisms (1995–2020) for predicting combustion of CH₄, H₂, and their mixtures is comprehensively and quantitatively evaluated. Based on the best-performing one Glarborg2018, a 60-species and 566-reaction skeletal C_1–2/H/O/N mechanism with NO_x chemistry for CH₄/H₂ combustion over a wide range of hydrogen-blending ratios from 0 to 100% is developed using the directed relation graph with error propagation (DRGEP), sensitivity analysis (SA), and quasi-steady-state-approximation (QSSA) methods. Also, the present newly developed skeletal mechanism is comprehensively evaluated against large numbers of available experimental data (∼3500 data points) for combustion of CH₄, H₂, and their mixtures, in terms of ignition delay times, laminar burning velocities, flame structures (i.e., temperature and species (reactants, intermediates, and final products, including CH₄, H₂, O₂, CO, CO₂, CH₂O, C₂H₄, C₂H₆, N₂, and H₂O) concentrations), NO_x emissions, as well as NO formation and reduction via different submechanisms. Results show that Glarborg2018 performs best in predicting NO from combustion of CH₄, H₂, and their mixtures, especially at high temperatures. The present newly developed skeletal mechanism can reasonably well predict NO_x emissions in CH₄/H₂ combustion over a wide range of hydrogen-blending ratios from 0 to 100% at low-/intermediate-/high-temperature levels (e.g., 650–2200 K), which is superior to the existing skeletal ones; in particular, thermal NO, prompt NO, NO formed via NNH and N₂O-intermediate, as well as NO reduced by HCCO/CH_i=0–3 and H can be separately reproduced. In conclusion, the present newly developed skeletal C_1–2/H/O/N mechanism preserves comparable prediction accuracy compared to its parent Glarborg2018 and is applicable to model combustion of CH₄, H₂, and their mixtures with NO_x chemistry over a wide range of low, intermediate, and high temperatures.