TEMPERATURE DEPENDENCE OF NO TO NO_2 CONVERSION RY n-RUTANE AND n-PENTANE OXIDATION

摘要

An experimental and detailed chemical kinetic modeling investigation of the temperature-dependent role of n-butane and n-pentane oxidation on the NO to NO_2 conversion is presented. An atmospheric pressure, quartz flow reactor was used to examine the NO oxidation to NO_2 behavior for the 600 to 1100 K temperature range and residence times from 0.16 to 1.46 s. In the experiment, probe measurement of the species concentrations was performed in the flow reactor using a mixture of NO (20 ppm)/air/ hydrocarbon (10 ppm). In the chemical kinetic calculation, the time evolution of NO, NO_2, hydrocarbons, and reaction intermediates were evaluated using a n-butane oxidation model coupled with a nitrogen oxides submechanism for all temperatures. The detailed chemical kinetic model consisted of 897 reactions and 158 species. The experimental results show n-pentane promoting the NO to NO_2 conversion to a greater extent than n-butane for the entire temperature range. This may be explained by n-pentane oxidation exhibiting a vigorous chain-branched hydroperoxy-pentylperoxy radical isomerization kinetic system more so than found in n-butane. Kinetic calculations performed on the n-butane oxidation system revealed that the NO to NO_2 conversion is strongly temperature dependent. The NO + HO_2 = NO_2 + OH and alkylperoxy + NO = alkyloxy + NO_2 reactions play an important role in converting NO to NO_2 at the lower temperatures in this study. However, as the temperature increases toward 800-900K, the butyl + O_2 and hydroperoxy-butyl + O_2 network of reactions undergoes reaction reversal and allows other reaction channels to be accessed which heavily promotes NO to NO_2 conversion. Above 900 K, the decrease in NO_2 concentration is attributed to NO_2 + HO_2 = HONO + O_2, HONO( + M) = NO + OH( + M), and NO_2 + O = NO + O_2 destruction reactions. Consequently, the change of HO_2 formation with temperature plays the most important role for the temperature dependence of the NO to NO_2 conversion.