OH and CH2O Laser-Induced Fluorescence Measurements for Hydrogen Flames and Methane, n-Butane, and Dimethyl Ether Weak Flames in a Micro Flow Reactor with a Controlled Temperature Profile

Abstract

Laser-induced fluorescence (LIF) measurements were applied for the first time to a micro flow reactor with a controlled temperature profile to investigate general combustion and ignition characteristics of hydrogen (H2/O2/N2 mixture at O2/N2 = 1:9), methane, n-butane, and dimethyl ether (DME) (fuel/air mixtures). For the hydrogen case, overall flame responses of the H2/O2/N2 mixture against inlet flow velocity were investigated on the basis of the OH-LIF measurement. The existence of the three kinds of flame responses, such as normal flames in the high inlet flow velocity, flames with repetitive extinction and ignition (FREI) in the intermediate inlet flow velocity, and weak flames in the low inlet flow velocity were confirmed at ϕ = 0.6, 1.0, and 1.2. Experimental identification of the hydrogen weak flame was established for the first time. However, the OH-LIF signal level from fuel-rich hydrogen weak flames are quite low, and that at ϕ = 3.0 could not be detected. The reason for the low-level OH-LIF sig...