Reactivity of CO/H2/CH4/Air Mixtures Derived from In-Cylinder Fuel Reformation Examined by a Micro Flow Reactor with a Controlled Temperature Profile

Abstract

ABSTRACT The effects of CO/H2/CH4 mixture compositions on the reactivity are investigated based on weak flame responses in a micro flow reactor with a controlled temperature profile (MFR). The ratios of H2 and CH4 are varied widely at a constant fraction of CO and the effects of variations in the compositions on the reactivity of the stoichiometric CO/H2/CH4 mixtures are evaluated both experimentally and computationally at atmospheric pressure. The results show that a weak flame is stabilized at the higher temperature region in MFR as the CH4 mole fraction increases, which indicates that the reactivity of the CO/H2/CH4 mixtures decreases with the increase of the CH4 mole fraction. Ignition delay times of the CO/H2/CH4 mixtures are also computed using a detailed chemical reaction model. The computed ignition delay times of the CO/H2/CH4 mixtures largely increase as the CH4 mole fraction increases, which is consistent with the variation in the reactivity shown by weak flames in MFR. Rate-of-production analyses using a detailed chemical reaction model show that the OH radical consumption by CH4 increases and that by H2 decreases as the CH4 fraction increases. Consequently, the production rate of CH3 radicals, which are less reactive than H radicals, increases and the production rate of H radicals decreases. This can suppress the OH formation from H radicals. Therefore, the primary factor of the significant reduction of the reactivity of the CO/H2/CH4 mixtures seems to be the increase of the OH radical consumption by CH4 and the CH3 radical production due to the increase in the CH4 fraction.