432426 Rate Coefficients for RH + NO2 and Subsequent Decomposition Kinetics on the HNO2 Potential Energy Surface

Tuesday, November 10, 2015: 9:10 AM
355F (Salt Palace Convention Center)
Claude Franklin Goldsmith III, Engineering, Brown University, Providence, RI

Alkyl nitrates are commonly added to hydrocarbon fuels to improve the combustion characteristics. The basic mechanism for RO-NO2 decomposition is relatively straightforward: The weak RO-NO2 bond cleaves, resulting in an alkyloxy radical and NO2. Although much of the improved ignition performance is due to the alkyloxy radical, the NO2 radical also participates in the oxidation of the fuel. RH + NO2 has three possible products:


RH + NO2

R + trans-HONO



R + cis-HONO



R + HNO2


Despite the prevalence of 2-ethylhexyl nitrate as a fuel additive (e.g. 100,000 tons/year), little is known about the kinetics of NO2 in the low-temperature oxidation regime (e.g. 600 to 1000 K for most transportation fuels). In this talk, we will present high-accuracy electronic structure calculations for the RH + NO2 potential energy surfaces (PES) for RH = H2, CH4, and C2H6. These benchmark calculations will be used to test compound methods for accurate determination of the PES for larger alkanes for each of the three possible product channels. Variational Transition State Theory calculations will be presented to predict the branching fraction between trans-HONO, cis-HONO, and HNO2. Contra thermodynamics, although trans-HONO is the most stable HNO2 isomer, it has the highest barrier to formation. We will also present calculations for the subsequent isomerization between the HNO2 isomers, as well as decomposition to H + NO2 and OH + NO.

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