Homogeneous mixtures of CH

4

/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 CO

2

in EGR gases

on ignition characteristics.Specifically

effects of CO

2

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 CO

2

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 CO

2

on the ignition delay time.The enhancement of ignition delay time with CO

2

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 CO

2

were strongly related to the chemical effects of CO

2

.A single ignition time correlation was obtained in form of Arrhenius-type for the entire range of conditions as a function of temperature

CH

4

mole fraction and O

2

mole fraction.This correlation could successfully capture the complex behaviors of ignition of CH

4

/air/CO

2

mixture.The results can be applied to MILD combustion as "reference time"

for example

to

predict ignition delay time in turbulent reacting flow.