Theoretical Kinetics Of Hydrogen Abstraction Reaction In Fuel Combustion

The fuel combustion reaction is very important in the global energy supply,however,the atmospheric pollutants produced by fuel combustion cause serious environmental pollution.Therefore,how to achieve efficient and clean combustion has promoted the study of combustion kinetics.With the rise of quantum chemistry,micro-combustion chemistry has developed.In this paper,three important components in fuel are selected for theoretical and computational research on combustion reaction kinetics.The specific research contents are as follows:(1)Kinetics study of the hydrogen abstraction reaction between propanol and OH radicals:we calculate the rate constants and branching ratios of the hydrogen abstraction reactions of n-propanol and i-propanol by OH radical in a broad temperature range of 63-2000 K using the competitive canonical unified statistical(CCUS)model and the multi-structural variational transition-state theory with the small-curvature tunneling approximation(MS-CVT/SCT).The results show that,in both the high-pressure and low-pressure limits,the total reaction rate constants show a significant negative dependence on temperature in the low temperature regime.Several factors,tunneling,remarkable anharmonicity of high-frequency modes of transition states,and the presence of reaction channels with a negative free energy barrier,contribute to this phenomenon.We observe pressure-dependent branching fractions at T<-400 K for n-propanol or T<200 K for i-propanol.The alpha-hydrogen(H?)abstraction with a lower barrier is not always dominant as traditionally expected.The H-abstraction from the terminal carbon(Ht)of i-propanol,with a higher barrier,is dominant above 1000 K.In the pressure-dependent ultralow temperature regime and high-pressure limit,the beta-hydrogen(H?)ion and the hydrogen abstraction from the hydroxyl group(Ho)become dominant for n-propanol and i-propanol,respectively,mainly due to the tunneling effect.(2)Hydrogen abstraction reaction kinetics of cyclopentane in a wide temperature range:we selected the seven most common radicals in the atmosphere(hydrogen radical(H),hydroxide radical(OH),hydroperoxyl radical(OOH),methyl radical(CH3),ethyl radical(CH3CH2),methoxy radical(CH3O),and formyl radical(CHO))to investigate the hydrogen ion reaction with cyclopentane.The rate constants in a broad temperature range of 150-3000 K and high-pressure and low-pressure limits were calculated by using MS-CVT/SCT method.We found that the transition state of the reaction of ethyl radical(CH3CH2)with cyclopentane shows the largest torsional anharmonicity effect.At room temperature,the rate constants of cyclopentane and the seven free radicals are kOH>kH>kCH3O>kCH3>kCH3CH2>kOOH>kCHO,where the rate constant of the OH radical hydrogen abstraction reaction is much greater than other free radicals.(3)Study on the combustion reaction kinetics of o-xylene and OH radicals:we calculate the reaction potential energy surface and rate constant of hydrogen abstraction reaction,addition reaction and dissociation reaction of o-xylene and OH radicals at 220-3000 K,1 Torr-500 atm and high-pressure limit using SS-QRRK and MS-CVT/SCT method,and the results were compared with toluene.The results show that the decay effect of the addition reaction causes a negative temperature dependence of the rate constant,and the decay effect increases with increasing temperature.At different pressures,the temperature-dependent effect transition point is between 380 and 500 K.The reaction of o-xylene with OH radicals is more pressure-dependent than the reaction of toluene with OH radicals.And its rate constant is lower than that of toluene at low and medium temperatures and at lower pressures.