Skeltal Kinetic Mechanism For The Wide-Range Combustion Of Dimethyl Ether

With the rapid development of China’s economy and society,the demand for energy is increasing,and fossil energy is not only exhausted,but also triggers a severe ecological crisis.Dimethyl ether（DME）has the characteristics of high cetane number and low ignition temperature,and it has become an effective means to achieve diesel oil replacement and reduce pollutant emissions.In order to promote the efficient clean combustion of dimethyl ether and the optimal design of the engine,this thesis carried out a wide-range dynamic mechanism model construction study on the key reaction types in the dimethyl ether combustion process.The research results are as follows:Using BMK/MG3S,M06/MG3S,M06-2X/MG3S,B2PLYP/TZVP and MP2/TZVP quantum chemical calculations,as well as conventional transition state theory,variational transition state theory and improved variational transition state theory to study the reaction mechanism and kinetics of DME and molecular oxygen.The results show that the hydrogen abstraction reaction is easily carried out on out-of-plane hydrogen atoms,and it is confirmed that there is an intermediate with lower energy than the product.The tunneling effect has a small effect on the rate constant.The torsion and multi-structure non-harmonics caused by internal rotation in the transition state affect the evaluation of the thermal rate constant.That can be verified and provide some supplement to the obtained reaction kinetic models.Using B3LYP/MG3S,BB1K/MG3S,MPW1K/MG3S,M06-2X/MG3S,B2PLYP/TZVP and MP2/TZVP quantum chemical calculation methods combined with variational transition state theory,multi-structure variational transition state theory and RRKM theory to study the CH₃OCH₂ single moleculeβ-fragmentation reaction.The tunnel correction factor of the reaction was calculated using the ZCT and SCT methods.The calculation results show that the effect of tunneling on the rate constant decreases with increasing temperature.In the high pressure region,the thermal rate constant estimated using the MS-CVT/SCT theory with multi-structure and torsional anharmonic has a positive temperature dependence and is consistent with the experimental values in the existing literature.In addition,the low pressure and high pressure limit rate constants extracted from the complete attenuation analysis are consistent with the reported experimental low pressure and high pressure limit results,thus further validating the kinetic model we obtained.Using wB97XD/TZVP,M06/MG3S,M06-2X/MG3S and B2PLYP/TZVP quantum chemistry calculations combined with conventional transition state theory,variational transition state theory and RRKM theory to study the reaction of CH₃OCH₂O₂ and NO,establishing a kinetic model at a temperature of 200 to 2600 K and a pressure of 10^–6 to 10⁸ kPa.The calculation results show that the reaction rate constants of each reaction have strong dependence on temperature and pressure.It is hoped that through our precise reaction mechanism and kinetic calculations,we can provide certain kinetic theories and models for dimethyl ether as an alternative fuel for engines to reduce nitrogen oxide emissions.