The combustion of trichloroethylene studied with vacuum ultraviolet photoionization mass spectrometry

Species concentration profiles in a low-pressure premixed methane/oxygen flame, seeded with trichloroethylene (TCE), are measured with a newly developed flame sampling vacuum ultraviolet (VUV) laser photoionization mass spectrometer. The results lead to significant extensions of the kinetic mechanisms incorporated in chlorocarbon combustion models derived from previous experiments with TCE/O₂ flames at higher chlorine-to-hydrogen ratios. Sensitivity analyses reveal that the most important reaction channels in the decomposition of TCE in the CH₄/TCE/O₂/Ar flame are the displacement by H atoms of Cl atoms from TCE, 1,1-dichloroethylene, and vinyl chloride. The displacement of Cl atoms from TCE by OH, a reaction previously observed under nonflame conditions, also makes an important contribution to the decomposition of TCE and leads to the production of 2,2-dichloroethenol, a species unobserved inprevious flame studies. Other species found in large concentrations in the present CH₄/TCE/O₂/Ar flames, but not observed in earlier TCE/O₂/Ar flame studies, are ketene, chloroketene, and dichloroketene. Finally, the presence of TCE catalyzes the formation of C₃-C₆ hydrocarbons. The observation of significant concentrations of C₃H₃, C₃H ₄, and C₆H₆ suggests that these catalytic reactions may proceed by "odd carbon species" mechanisms analogous to those suggested for benzene formation in hydrocarbon flames.