Effects of hydrogen addition on the laminar premixed flames and emissions of methane and propane

Abstract

In this work, the laminar premixed flames for methane and propane at atmospheric pressure were numerically investigated with respect to different hydrogen concentrations, ranging from 5 % to 25 % (by vol.). Based on the two-dimensional (2D) flame predictions, hydrogen decreased the maximum temperatures and species concentrations such as formaldehyde (CH2O), acetylene (C2H2), carbon monoxide (CO) and nitric oxide (NO) for methane and propane. However, the CH2O mole fractions were raised by a maximum deviation of 10 % when hydrogen was added into the fuel lean and stoichiometric propane mixtures. The decrease in C2H2 eventually lowered the soot volume fractions and number densities. Besides, the axial locations of the maximum species concentrations, soot volume fractions and number densities were also affected by hydrogen. Meanwhile, the addition of hydrogen increased the flame temperatures and laminar burning velocities for the one-dimensional (1D) premixed flames of methane and propane. This trend was identically predicted for the formation of intermediate species such as CH2O, hydroperoxyl (HO2) and hydroxyl (OH) whereas C2H2, CO and NO were lowered, as justified by the sensitivity analyses. For propane at an equivalence ratio (φ) = 1.3, the rates of production (ROPs) of C2H2 were increased linearly with hydrogen, which resulted in higher C2H2 concentrations.