Kinetic Study On The Nitrogen Dioxide And CN Related Reactions In Fuel Combustion Of Diesel Engine

Generally speaking,maritime transportation is one of the most important transportation modes against the environment of economic globalization.However,emissions from shipping have become a catchword in the discussion about environmental protection.Especially,concern is primarily about emissions in the form of Nitrogen Oxides NOX because the nitrogen-removal process is difficult and its related techniques of lowering the NOX exhaust are still under developing.Additionally,due to the fact that diesel engine has been widely used as main power source in ocean-going vessel,the researches on combustion mechanism referring to NOX are usually conducted under the high temperature environment of the cylinder.Since nitrogen dioxide(NO2)is one of the important components of NOX emissions,and nitrogen-containing small molecule CN is an important intermediate in the combustion process of nitrogen-containing fuels,it is necessary to have a deeper understanding of the reaction processes related to NO2 and CN,which is achieved through analyzing the combustion mechanism and calculating the rate constant.According to Miller-Bowman and Zeldovich combustion mechanism,this work determines the reaction systems studied.The data needed in calculating rate constant,such as the geometries of reactants,intermediates,products and transition states,are obtained by Gaussian 09 software.Then,the rate constants of each reaction at different temperatures are obtained by the YL(Yao-Lin)method.Notably,by means of Morse oscillator model,YL method considers about the anharmonic oscillator model that is close to the real situation,which breaks the limitation of traditional harmonic oscillator model.Besides,the anharmonic effect of these reactions is discussed by comparing the anharmonic rate constant with the harmonic rate constant.Also,the conclusion that the anharmonic effect of these reactions can't be ignored under high temperature is confirmed by comparing the calculating data with the rate constant fitted by the experimental data.On the other hand,based on the least-square method,this research obtains the kinetics and thermodynamic parameters of reaction mechanism through the Arrhenius and thermodynamic equations,respectively.Considering the difficulty of obtaining the mechanism parameters of complex combustion reactions experimentally,constructing the mechanism parameters by theoretical calculation means is one of the important ways to analyze the combustion process in the engineering field.With regard to the two reaction systems(NO2 and CN)studied in this paper,the harmonic and anharmonic rate constant increase with the growing temperature,respectively.When temperature is under 2000 K,the rate constant increases rapidly,nevertheless,the increment speed of rate constant tends to be gentle when temperature is above 2000 K.Furthermore,the difference between the anharmonic and harmonic rate constant becomes larger and larger as temperature increasing,and the maximum value of the difference appears at the highest calculating temperature,which indicates that the anharmonic effect of those reactions is significant.In addition,through comparing the anharmonic and harmonic rate constant under the high temperature(2800 K),which can be achieved in the cylinder of diesel engine,it is found that the anharmonic rate constant is lower than harmonic value,which suggests that the anharmonic effect of those reactions should be taken into account under the actual reaction conditions.