Effects of CO2 Dilution on Methane Ignition in Moderate or Intense Low-oxygen Dilution(MILD) Combustion: A Numerical Study

Abstract

Abstract: Homogeneous mixtures of CH₄/air under moderate or intense low-oxygen dilution(MILD) combustion conditions were numerically studied to clarify the fundamental effects of exhaust gas recirculation(EGR),especially CO₂ in EGR gases,on ignition characteristics.Specifically,effects of CO₂ addition on autoignition delay time were emphasized at temperature between 1200 K and 1600 K for a wide range of the lean-to-rich equivalence ratio(0.2~2).The results showed that the ignition delay time increased with equivalence ratio or CO₂ dilution ratio.Furthermore,ignition delay time was seen to be exponentially related with the reciprocal of initial temperature.Special concern was given to the chemical effects of CO₂ on the ignition delay time.The enhancement of ignition delay time with CO₂ addition can be mainly ascribed to the decrease of H,O and OH radicals.The predictions of temperature profiles and mole fractions of CO and CO₂ were strongly related to the chemical effects of CO₂.A single ignition time correlation was obtained in form of Arrhenius-type for the entire range of conditions as a function of temperature,CH₄ mole fraction and O₂ mole fraction.This correlation could successfully capture the complex behaviors of ignition of CH₄/air/CO₂ mixture.The results can be applied to MILD combustion as "reference time",for example,to predict ignition delay time in turbulent reacting flow.

Key words: moderate or intense low-oxygen dilution combustion, ignition delay time, autoignition, methane

摘要： Homogeneous mixtures of CH₄/air under moderate or intense low-oxygen dilution(MILD) combustion conditions were numerically studied to clarify the fundamental effects of exhaust gas recirculation(EGR),especially CO₂ in EGR gases,on ignition characteristics.Specifically,effects of CO₂ addition on autoignition delay time were emphasized at temperature between 1200 K and 1600 K for a wide range of the lean-to-rich equivalence ratio(0.2~2).The results showed that the ignition delay time increased with equivalence ratio or CO₂ dilution ratio.Furthermore,ignition delay time was seen to be exponentially related with the reciprocal of initial temperature.Special concern was given to the chemical effects of CO₂ on the ignition delay time.The enhancement of ignition delay time with CO₂ addition can be mainly ascribed to the decrease of H,O and OH radicals.The predictions of temperature profiles and mole fractions of CO and CO₂ were strongly related to the chemical effects of CO₂.A single ignition time correlation was obtained in form of Arrhenius-type for the entire range of conditions as a function of temperature,CH₄ mole fraction and O₂ mole fraction.This correlation could successfully capture the complex behaviors of ignition of CH₄/air/CO₂ mixture.The results can be applied to MILD combustion as "reference time",for example,to predict ignition delay time in turbulent reacting flow.

关键词: moderate or intense low-oxygen dilution combustion, ignition delay time, autoignition, methane

CAO Zhenjun, ZHU Tong. Effects of CO₂ Dilution on Methane Ignition in Moderate or Intense Low-oxygen Dilution(MILD) Combustion: A Numerical Study[J]. Chin.J.Chem.Eng., 2012, 20(4): 701-709.

曹甄俊, 朱彤. Effects of CO₂ Dilution on Methane Ignition in Moderate or Intense Low-oxygen Dilution(MILD) Combustion: A Numerical Study[J]. Chinese Journal of Chemical Engineering, 2012, 20(4): 701-709.

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Effects of CO₂ Dilution on Methane Ignition in Moderate or Intense Low-oxygen Dilution(MILD) Combustion: A Numerical Study

Effects of CO₂ Dilution on Methane Ignition in Moderate or Intense Low-oxygen Dilution(MILD) Combustion: A Numerical Study

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