Numerical investigation of strained extinction at engine-relevant pressures: Pressure dependence and sensitivity to chemical and physical parameters for methane-based flames

摘要

Resistance to extinction by stretch and and laminar flame speed are important properties of any combustible mixture. Recent work has shown that extinction by stretch controls the overall structure of several important types of methane-based turbulent flames. The parameter used to quantify this phenomena, Extinction Strain Rate (ESR), is numerically studied here for methane-based flames across a range of pressures relevant to gas turbines and internal combustion engines, 1-40 atm. The pressure trends are compared with those of laminar flame speed which is historically better studied. Current kinetic models agree that ESR of lean flames is a non-monotonic function of pressure and that ESR of rich flames increases significantly with pressure, but are found to differ significantly in their numerical predictions of ESR, particularly at higher pressures. To better identify the source of model prediction differences and what governs the overall accuracy of the ESR predictions, various model sensitivity analyses were conducted. Pressure-dependent kinetics are shown to be vital to determining ESR pressure trends as are molecular collision efficiencies. Yet, reactions sensitivities for ESR largely mirror those for laminar flame speed calculations. Sensitivity to the transport parameter, Lennard Jones diameter, significantly exceeds reaction sensitivities for the fuel, oxidizer and bath gas. Thermodynamic parameter ESR sensitivities vary widely with pressure, but at least for enthalpy, appear insignificant when uncertainties are considered. This study informs and motivates further efforts to understand the phenomena of flame extinction by stretch at elevated pressures. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.