Speciation of Organic By-Products from the Thermal Decomposition of Alternative Automotive Fuels

The high-temperature thermal degradation of four alternative automotive fuels (methanol, ethanol, natural gas, and liquefied pteroleum (LP) gas) have been examined as a function of fuel-oxygen equivalence ratio and exposure temperature using fused silica flow reactor instrumentation coupled to in-line GC-TCD and GC-MS detection. Organic speciation for methanol, natural gas, and LP gas wereconsistent with previous measurements. However, several previously undetected organic by-products were observed from ethanol oxidation and pyrolysis. Organic speciation was found to vary significantly between methanol and ethanol and less so between natural gas and LP gas. Non-methane organic gases (NMOG) and specific reactivities of the respective fuels were measured, and trends with respect toproposed reactivity adjustment factors are discussed. A qualitative comparison of NMOG quantified in the flow reactor tests with the results of recent vehicles tests is also reported. The most significatn differences in the comparisons were observed for toxic compounds, including the lack of detection of acetaldehyde, 1,3-butadiene, and benzene from flow reactor experiments of methanoldegredation, and the lack of detection of 1,3-butadiene form flow reactor experiments of ethanol combustion. Possible sources for the formation of these compounds in vehicle tests are discussed.