The Research On An Adaptive Chemistry Scheme And A Multi-time Scale Method For Combustion Modeling

Combustion is the primary method of energy conversion, and the understanding ofits mechanisms is directly related to the development of different combustion devices,search for new fuel and efficient and clean combustion process management etc. whichhas become one of the most important goals for combustion. The simulation based ondetailed elementary reaction mechanism has been proved to be one of the most effectivemeans to analyze the combustion principles. However, the process of the simulationwith detailed elementary kinetic mechanisms is inevitable to face the issue of strongstiffness due to the distribution of a wide range of time scales, and the complexgoverning equations due to the large number of species and reactions. In order to solvethe contradictions between the accuracy of detailed mechanisms simulation andsimulation time, a multi time scale algorithm (MTS) and dynamic adaptive chemistry(DAC) is combined to model four kinds of fuels with detailed mechanisms in this thesis.DAC is applied to reduce chemical mechanism according to the local thermalchemical state in the combustion modeling. Based on the principle of scale separation,in this thesis, the characteristic time of each component is dynamically calculated in theprocess of combustion modeling and divided into different groups based on thecharacteristic time, and different groups using different time step. Base on the method ofMTS and DAC, the ignition process of n-heptane, n-decane, dimethyl ether and methylbutyrate is modeled. And the changes of temperature, concentrate of main component,ignition delay time in the combustion process and active species number in DAC areanalyzed.Compare the results of MTS, VODE_DAC, MTS_DAC with the results of implicitintegration algorithm VODE, which shows:1) The use range of the calculation algorithm of the MTS is expanded bycombining implicit method with MTS method, which can greatly improve its efficiency.2) It is effective to use MTS method, MTS with DAC method and VODE withDAC method. They all have a good accuracy.3) The combination with MTS and DAC method will produce significant increasesin calculation efficiency.4) According to the test results of several typical fuels under a wide range ofconditions based on MTS_DAC method, it proves that this method is of a wide range of applicability, which can be applied to study on biological diesel and surrogate fuel.To a combustion simulation method which can directly use detailed reactionmechanisms, the MTS_DAC provides a new idea to solve the conflict between theaccuracy and consumption of CPU time during the simulation process and expand theapplied range of detailed mechanism.