Study On Chemical Reaction Mechanism Model Of Methanol/PODE Dual Fuel

Faced with the contradiction between fuel supply and demand brought by the huge car ownership in China and the atmospheric pollution problems caused by automobile exhaust emissions,the development of coal-based alternative fuels and the new combustion technologies have become hotspots in recent years.The low cetane methanol and high cetane Polyoxymethylene dimethyl ethers?PODE?are both coal-based fuels with high oxygen content.The effective combined combustion of the two is of great practical significance for energy saving and emission reduction of internal combustion engines.At present,the research on the chemical kinetic model of methanol/PODE dual fuel is still blank.Therefore,based on the idea of decoupling,a simplified chemical kinetic mechanism of methanol/PODE dual fuel was constructed,and the mechanism was optimized and verified.In this paper,using methanol and PODE₃ as the dual fuel characterization,a simplified chemical kinetic model of methanol/PODE dual fuel was constructed.Firstly,the detailed mechanism of PODE₃ reaction was simplified by combining the mechanism reduction methods such as direct relationship graph method and sensitivity analysis,and a reduced reaction model of PODE₃ comprehensive combustion consisting of 71 components and 316 reaction steps was obtained.Secondly,the detailed methanol reaction mechanism and small molecule reactions extracted from the reduced PODE₃ comprehensive reaction mechanism were used as the core part of the dual fuel mechanism.Finally,the core mechanism of the dual fuel was coupled with the reduced PODE₃ sub-mechanism,nitrogen oxides?NO_x?generation mechanism and polycyclic aromatic hydrocarbons?PAHs?generation mechanism to obtain the reduced methanol/PODE dual fuel reaction mechanism?101-component and 473-step reaction?.Simultaneously,the reaction paths of methanol and PODE₃ at low temperature and high temperature were sorted out.It was found that the oxygenation reaction is the leading factor in the consumption of methanol and PODE₃ at low temperature,while the consumption of fuel at high temperature mainly depends on the attack of active free radicals and the pyrolysis of fuel.Additionally,it was found that there is no formation path of olefins composed of C-C during the combustion process of PODE,which reveals the internal mechanism that PODE can effectively reduce diesel engine soot emissions.Based on the basic reactor experimental data and the sensitivity evaluation system of fuel ignition delay and flame velocity,the reduced chemical kinetic mechanism of the methanol/PODE dual fuel was optimized by adjusting the rate parameters of several key reactions.Different reactor models of CHEMKIN-PRO software were used to verify and analyze the fuel ignition delay,laminar flame velocity,key components concentrations and homogeneous charge compression ignition?HCCI?combustion parameters predicted by the dual fuel mechanism.The results show that the optimized methanol/PODE dual fuel reduced mechanism can accurately predict the ignition delay of PODE₃ in rapid compressors when the equivalent ratio is 0.5?1.5 and the pressure is 1.0?1.5MPa,the concentration of important substances under PODE₃ premixed laminar flames and the laminar flame propagation velocity under the standard atmospheric pressure.The ignition delay of methanol in shock tube,the oxidation process and laminar combustion speed in the flow reactor were also well reproduced.In addition,the calculation results of HCCI combustion cylinder pressure and heat release rate of PODE₃ at different fuel equivalent ratios were in good agreement with the experimental data,indicating that the reduced dual fuel mechanism has high reliability and lays a foundation for the computational fluid dynamics?CFD?simulation of dual fuel in-cylinder combustion.