Impact of Hydrogen and Carbon Monoxide on Lean Premixed Hydrocarbon Flames

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The objectives of this study are (1) to characterize experimentally stretched, lean, premixed flames under laminar and mildly turbulent conditions using particle thermometry and laser-induced fluorescence; (2) to assess enhancement of flame stability and lean-burning limits in premixed hydrocarbon (methane or propane) flames by addition of hydrogen or hydrogen/carbon monoxide mixtures; (3) to develop and validate reduced mechanisms to predict flame behavior (including extinction) of methane/ hydrogen/ carbon monoxide fuel mixtures; and (4) to develop analytical understanding of how multicomponent fuels with different Lewis numbers impact flame stability. The experimental studies and subsequent validation of numerical models rely detailed characterization of counterflow, opposed-jet, premixed flames. Independent variation of the hydrogen and carbon-monoxide concentrations in the fuel feed offer a new mean of exploring and influencing the chemical pathways in lean, premixed hydrocarbon combustion, in particular near extinction. To measure extinction conditions in the counterflow flames, flow fields are probed with laser Doppler velocimetry and temperature fields are measured by observing emissions from micron-size particles with a sensitive infrared camera. Laser-induced fluorescence (LIF) along the flame centerline probes flame structure through measurements of hydroxyl and formaldehyde fluorescence signals. Previous studies have shown that small amounts of hydrogen in the fuel stream can substantially extend the stability limits of stretched, premixed flames, suggesting that this may be a way to enhance the operability of lean, premixed, dry, low-NOx combustion systems. Such systems are used for space heating, power generation, and other industrial applications. This concept is further explored in this study.