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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

From electronic structure to model application of key reactions for gasoline/alcohol combustion: Hydrogen-atom abstraction by $CH_3O\dot{O}$ radicals

Hydrogen atom abstraction by methyl peroxy ($CH_3O\dot{O}$) radicals can play an important role in gasoline/ethanol interacting chemistry for fuels that produce high concentrations of methyl radicals. Detailed kinetic reactions for hydrogen atom abstraction by $CH_3O\dot{O}$ radicals from the components of FGF-LLNL (a gasoline surrogate) including cyclopentane, toluene, 1-hexene, n -heptane, and isooctane have been systematically studied in this work. Here, the M06-2X/6-311 ++ G(d,p) level of theory was used to obtain the optimized structure and vibrational frequency for all stationary points and the low-frequency torsional modes. The 1-D hindered rotor treatment for low-frequency torsional modes was treated at M06-2X/6-31G level of theory. The UCCSD(T)-F12a/cc-pVDZ-F12 and QCISD(T)/CBS level of theory were used to calculate single point energies for all species. High pressure limiting rate constants for all hydrogen atom abstraction channels were performed using conventional transition state theory with unsymmetric tunneling corrections. Individual rate constants are reported in the temperature range from 298.15 to 2000 K. Our computed results show that the abstraction of allylic hydrogen atoms from 1-hexene is the fastest at low temperatures. When the temperature increases, the hydrogen atom abstraction reaction channel at the primary alkyl site gradually becomes dominant. Thermodynamics properties for all stable species and high-pressure limiting rate constants for each reaction pathway obtained in this work were incorporated into the latest gasoline surrogate/ethanol model to investigate the influence of the rate constants calculated here on model predicted ignition delay times.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2018

Surface Defect Chemistry and Electronic Structure of Pr 0.1 Ce 0.9 O 2-δ Revealed in Operando

Understanding the surface defect chemistry of oxides under functional operating conditions is important for providing guidelines for improving the kinetics of electrochemical reactions. Ceria-based oxides have applications in solid oxide fuel/electrolysis cells, thermo-chemical water splitting, catalytic convertors, and red-ox active memristive devices. The surface defect chemistry of doped ceria in the regime of high oxygen pressure, pO 2 , approximating the operating conditions of fuel cell cathodes at elevated temperatures, has not yet been revealed. In this paper, we investigated the Pr 0.1 Ce 0.9 O 2-δ (PCO) surface by in operando X-ray photoelectron and absorption spectroscopic methods. We quantified the concentration of reduced Pr 3+ , at the near-surface region of PCO as a function of electrochemical potential, corresponding to a wide range of effective pO 2 . We found that the Pr 3+ concentration at the surface was significantly higher than the values predicted from bulk defect chemistry. This finding indicates a lower effective defect formation energy at the surface region compared with that in the bulk. Finally, in addition, the Pr 3+ concentration has a weaker dependence on pO 2 compared to that in the bulk.

36 MATERIALS SCIENCE↗