Fire (Oct 2024)
RANS Simulation of Minimum Ignition Energy of Stoichiometric and Leaner CH<sub>4</sub>/Air Mixtures at Higher Pressures in Quiescent Conditions
Abstract
Minimum ignition energy (MIE) has been extensively studied via experiments and simulations. However, our literature review reveals little quantitative consistency, with results varying from 0.324 to 1.349 mJ for ϕ = 1.0 and from 0.22 to 0.944 mJ for ϕ = 0.9. Therefore, there is a need to resolve these discrepancies. This RANS study aims to partially address this knowledge gap. Additionally, it presents other flame evolution parameters essential for robust combustion design. Using the reactingFOAM solver, we predict the threshold energy required to ignite the fuel mixture. For this, the single step using the Arrhenius law is selected to model ignition in the flame kernel of stochiometric and lean CH4/air mixtures, allowing it to develop into a self-sustained flame. The ignition power density, an energy quantity normalised with volume, is incrementally varied, keeping the kernel critical radius rs constant at 0.5 mm in the quiescent mixture of two equivalence ratios ϕ 0.9 and 1.0, for varied operating pressures of 1, 5, and 10 bar at the constant initial temperature of 300 K. The minimum ignition energy is validated with twelve independent 1-bar datasets both numerically and experimentally. The effect of pressure on MIEs, which diminish as pressure rises, is significant. At ϕ = 1.0 (and 0.9), the flame temperature reached 481.24 K (457.803 K) at 1 bar, 443.176 K (427.356 K) at 5 bar, and 385.56 K (382.688 K) at 10 bar. The minimum ignition energy was validated using twelve independent 1-bar datasets from both numerical simulations and experiments. The results show strong agreement with many experimental findings. Finally, a mathematical formulation of MIE is devised; a function of pressure and equivalence ratio shows a slightly curved relationship.
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