The Study Of Chemical Reaction Mechanism Of Sulfur And Nitrogen Containing Compound In Combustion Environment

Under the environment of energy-saving and emission-reduction of ships,the research on SO_x and NO_x emission becomes extremely important.Dimethyl sulfide(CH3SCH3)is an important sulfur compound in the fuel composition.The final oxidation products are sulfuric acid and methanesulfonic acid.They are so harmful to the marine environment.At present,the specific chemical reaction mechanism in the combustion chamber is not clear.So we choose the dimethyl sulfide system as the first study.In addition,RAPRENO_x has been widely used in view of the current situation of reducing NO_x emission.It used an important additive(HNCO).However,the study of specific reaction mechanism is not completed.Therefore,we choose the reaction system(HNCO+CN)as the second study.For these two systems,this paper calculated the rate constant of different reactions in all reaction channels by YL(Yao-Lin)method.It utilizes Morse oscillator model(MO)to simulate vibration mode.It is found that MO used in the YL method is closer to the real situation than the traditional harmonic potential.Therefore,in this paper,we analyze the anharmonic effect in the two systems by comparing the difference between the two kinds of rate constants of each reaction.In addition,by comparing the barrier heights of different reactions and the rate constants at the same temperature,the main reaction channel in each system can be obtained.For each reaction channel of the dimethyl sulfide reaction system,the rate constant increase with the increasing of temperature and energy for most of the reactions.For the main reaction channel,the anharmonic value is 1.1 times of the harmonic value when the temperature is 800 K,while the anharmonic value is 35.2 times of the harmonic value when the temperature is 3800 K.Therefore,the anharmonic effect of the main reaction channel becomes obvious with the increasing of temperature in view of the whole trend.The anharmonic rate constant is one order of magnitude larger than the harmonic value at the high-temperature combustion temperature(about 2000 K),indicating that the main reaction channel is actually more easy to occur.For each reaction channel of HNCO+CN system,rate constant increases with the increasing of temperature and energy,and the anharmonic effect is more obvious in high temperature combustion environment.The barrier height of the reaction generating HNC and NCO in the system is 6.06 kcal/mol.It is the main reaction channel.As the temperature increases from 800 K to 5000 K,the harmonic value increases from 3.34×1010 s-1 to 1.36×1012 s-1,while the anharmonic value increases from 4.03×1010 s-1 to 4.06×1012 s-1.The gap between the two values becomes larger with the increasing of temperature.That is,the anharmonic effect is most obvious in high-temperature combustion environment.In this thesis,the formation mechanism of a group of typical sulfur-containing compounds is theoretically studied.So does the removal mechanism of a group of nitrogen-containing compounds.Ranging with temperature or total energy,the rate constants of each reaction are calculated in detail.And the anharmonic effect on rate constant has also been analyzed.It provides a theoretical basis for the study of reducing SO_x and NO_x emissions from marine diesel engines.