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We carried out a theoretical study on geometries, relative energies of stationary points, and reaction rate constants for ethyl + O2, propyl + O2, and butyl + O2 reactions, which are important reactions in the low-temperature oxidation of corresponding alkanes. Geometries with CCSD­(T)/aug-cc-pVTZ for the ethyl + O2 system are adopted as the benchmark to choose a proper exchange-correlation functional for geometry optimization. Our results show that B3LYP with 6-311+G­(d,p) can provide reliable structures for this system, and structures of the other two systems are determined with this functional. The performances of the explicitly correlated CCSD­(T)-F12a and the locally correlated DLPNO-CCSD­(T) methods on barrier heights and reaction energies are evaluated by comparing their results with those of CCSD­(T)/aug-cc-pVQZ for the ethyl + O2 system. Our results indicate that reliable energy differences for this system are achieved with CCSD­(T)-F12a using the cc-pVDZ-F12 basis set, and this method is employed in calculating single-point energies for the other two systems. The single-reference equation-of-motion spin-flip coupled-cluster method is adopted to obtain the potential energy surface of the barrierless reaction C2H5· + O2 → CH3CH2OO·, and the results are compared with those using broken-symmetry density functional theory and the Morse potential. Differences between energies with these methods are <1.6 kcal/mol, but the difference in the rate constants could be sizable at temperatures <500 K, and rate constants obtained in this work are reliable only for temperatures >500 K. Pressure-dependent rate constants for these reactions are determined using the Rice–Ramsperger–Kassel–Marcus/Master equation method. The obtained reaction energies, barrier heights, and rate constants could be valuable for reactions between the large alkane radical and O2, which are important in the low-temperature combustion of fuels such as kerosene and gasoline.

Hydrogen and five short-chain hydrocarbons are mixed with RP-3 aviation kerosene (RP-3) to study their blending effects on the combustion of RP-3. Seven combustion characteristics, the ignition delay time, burnout time, adiabatic flame temperature, extinction temperature, rate of production of hydroxyl radicals, laminar flame speed, and extinction strain rate, are simulated in four different reactors. The simulated data are preprocessed to match the requirements for a variation disturbance method proposed in this paper, and then the disturbance is obtained for representing the total influence of hydrogen and five short-chain hydrocarbons blending on the combustion properties of RP-3. The results show that H2, CH4, and C2H4 have a greater degree of disturbance to RP-3. In contrast, the influence of C3H6 is the weakest. The rate of disturbance shows that H2 and C2H4 have a positive effect on each of the combustion characteristics, and especially, C2H4 plays a promoting role in the combustion performance of RP-3. The reaction paths of seven fuels are analyzed by time-integrated element flux analysis, and the viability and rationality of the variation disturbance method are supported by the calculation of branching ratios of six main reaction channels.

This paper proposes a revised variation disturbance method to provide valuable information and reference for fuel design or optimization of internal combustion engines to realize the comprehensive and quantitative evaluation of the effects of blending agents on the combustion performance of primary fuels. In this method, methanol and ethanol are blended into gasoline to form six kinds of alcohol–gasoline (E10, E20, E30, M10, M20, and M30). Then, the ignition delay, adiabatic flame temperature, component concentration, fuel-burning rate, extinction strain rate, and CO emission of gasoline and alcohol–gasoline are studied by system simulation in a wide range of operating conditions. Based on the new variation disturbance method, the effects of methanol and ethanol on the combustion performance of gasoline are next analyzed globally and characterized quantitatively. The comprehensive results of ethanol and methanol on the gasoline’s combustion are visually presented. The method proposed in this paper is preliminarily validated based on the analysis of the microscopic mechanism of combustion. The results show that the blending of ethanol and methanol has positive effects on gasoline combustion, and ethanol can rapidly ignite the gasoline in a wide range of operating conditions and is superior to methanol in terms of fuel combustion, stability, and pollutant discharge. Based on the treatment of simulated values of six combustion characteristics selected in this paper and the calculations of the variation disturbance method, the total disturbance values of ethanol and methanol to gasoline combustion are obtained as 0.8493 and 0.2605, respectively. That is, ethanol has a more significant effect on improving the combustion performance of gasoline than methanol. In addition, based on the analysis results of the combustion, it is found that the blending of ethanol enlarges the reaction of notable components in gasoline. This finding also proves the effectiveness and validity of the scientific method utilized in this paper.