Pressure-dependent kinetics of peroxy radicals formed in isobutanol combustion

Abstract

Bio-derived isobutanol has been approved as a gasoline additive in the U.S., but our understanding of its combustion chemistry still has significant uncertainties. Detailed quantum calculations could improve model accuracy...

Chemistry of Simple Organic Peroxy Radicals under Atmospheric through Combustion Conditions: Role of Temperature, Pressure, and NOx Level

“…Theoretical calculations and experimental data indicate that the oxygen addition to γ-QOOH followed by HO 2 elimination is likely to be faster than the direct hydrogen abstraction reaction to form HO 2 ; therefore, the latter pathway was not included in this study. The isomerization of O 2 QOOH to form a ketohydroperoxide with an additional hydroxy group (not shown in Figure ) is from analogous reactions reported in a study by Yao et al, and the isomerization to form the ketohydroperoxide is from the analogous reaction reported in a study by Goldman et al, both at the high-pressure-limit. (This contrasts with the treatment of unimolecular reactions of γBPR, which uses pressure-dependent kinetics).…”

“…To examine the behavior of RO 2 over a wide range of conditions, we combined kinetic data from a range of sources. The unimolecular reactions for n PPR and γBPR originate from recently published pressure-dependent reaction networks based on quantum chemical calculations , and are compared in Figure . Additional details of the kinetic models and simulation scripts are also available in the Supporting Information (SI).…”

“…Comparison of potential energy surfaces of n PPR (dotted lines) and γBPR (solid lines). Blue-colored pathways involve the γ-QOOH radical and red-colored pathways involve the β-QOOH radical.…”

“…The γBPR, with one hydroxyl group, is treated as a model system for investigating the impact of functional groups on RO 2 chemistry. This particular species was chosen because of the availability of an extensive pressure-dependent network for its peroxy radical . The pressure-dependent rates originate from solving a master equation with the modified strong collision approximation in the Arkane software package; , quantum chemical calculations are done using CCSD­(T)-F12a/VTZ-F12//B3LYP/CBSB7.…”

“…We start with a simple alkylperoxy radical, n -propyl peroxy radical ( n PPR), and then move to a functionalized one, γ-isobutanol peroxy radical (γBPR). These two peroxy radicals were chosen as model systems based on their relatively simple structures (3–4 carbon atoms, 0–1 functional groups) and the fact that their pressure-dependent kinetics have already been explored in detail. , By considering the full chemistry of these RO 2 radicals across a wide range of conditions (temperature, pressure, and NO mixing ratio), we are able to explore how these parameters control RO 2 branching, and hence how they control the formation of various products and the extent of radical cycling.…”