Speciation of organic by-products from the thermal decomposition of alternative automotive fuels

The high-temperature thermal degradation of four alternative automotive fue ls (methanol, ethanol, natural gas, and liquefied petroleum (LP) gas) have been examined as a function of fuel-oxygen equivalence ratio and exposure t emperature using fused silica flow reactor instrumentation coupled to in-li ne GC-TCD and GC-MS detection. Organic speciation for methanol, natural gas , and LP gas were consistent with previous measurements. However, several p reviously undetected organic by-products were observed from ethanol oxidati on and pyrolysis. Organic speciation was found to vary significantly betwee n methanol and ethanol and less so between natural gas and LP gas. Non-meth ane organic gases (NMOG) and specific reactivities of the respective fuels were measured, and trends with respect to proposed reactivity adjustment fa ctors are discussed. A qualitative comparison of NMOG quantified in the flo w reactor tests with the results of recent vehicle tests is also reported. The most significant 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 methanol degradation, and the lack of detection of 1,3-butadiene from flow reactor experiments of ethano l combustion. Possible sources for the formation of these compounds in vehi cle tests are discussed.