Effects of large-amount dilutions of exhaust gas recirculation (EGR) and dedicated-EGR (DEGR) on the ignition characteristics of stoichiometric methane-air premixed air were experimentally studied by using a micro flow reactor. The flames were formed for various EGR/DEGR ratios and equivalence ratios Φ_A in the DEGR cylinder Stable flames and oscillating flames were observed; the combustion characteristics varied because the mixtures were highly diluted with EGR/DEGR gases. Their ignition temperatures were defined by the positions of the flames referred to a measured temperature profile in the quartz tube. Since EGR gas is composed of inert species such as N_2 and CO_2, the ignition temperatures of the premixed gas with EGR gas were higher than that without EGR gas; the EGR gas dilution interferes the ignition timing in reciprocating engines. On the other hand, the ignition temperature of the premixed gas with the dilution of DEGR gas whose equivalence ratios correspond to Φ_A = 1.6 and 1.8 were lower than that with EGR gas. This is because highly-reactive intermediate species such as H_2 and CO. Particularly, the ignition temperatures of the premixed gases highly diluted (40%) with DEGR gas of Φ_A = 1.6 and 1.8 were lower than that without EGR gas or DEGR gas. Therefore, it was found that gases with DEGR have potential for shorting the ignition delay.
