Numerical Simulation Study On Combustion And Emission Characteristics Of Dual Fuel Engine

In recent years,petroleum and other fossil energy reserves are increasingly scarce,and the demand for them is increasing.IMO MEPC has formulated more and more stringent ship emission regulations.These undoubtedly put forward higher requirements for energy saving and environmental protection of marine diesel engines,and promote the development of marine diesel engines towards energy saving and low emissions.Natural gas has the characteristics of mild combustion,high calorific value and low emission.Natural gas-diesel dual-fuel engine has attracted people’s attention.Based on 4190 Z_LC-2 diesel engine experimental platform,a high-pressure cycle model of natural gas-diesel dual-fuel engine combustion in cylinder is established by using AVL-FIRE software.On the basis of verifying the accuracy of the model,the effects of the main operating parameters on the combustion and emission characteristics of the dual-fuel engine are studied.The main operation parameters are optimized and matched.Firstly,the initial and boundary conditions of the simulation model are calculated by the bench test data of 4190 Z_LC-2 diesel engine and AVL-BOOST Whole machine model,and the two-dimensional model is drawn by AUTO-CAD software according to the measured geometric dimensions of the combustion chamber of 4190 Z_LC-2 diesel engine.Three-dimensional mesh is generated by dividing,checking and generating.Chemical reaction mechanism files suitable for natural gas-diesel blend combustion are added to the FIRE gas phase reaction module.Then the cylinder pressure curves obtained from the model simulation are co mpared with those obtained from the bench test to verify the accuracy of the model,and the high-pressure cycle model of the natural gas-diesel dual-fuel engine is established.Secondly,the three-dimensional simulation model of the combustion chamber is used for numerical simulation.Five single-parameter levels of natural gas substitution rate,EGR rate,intake temperature,intake pressure and injection advance angle,which are calculated by FIRE under rated operating conditions,are studied and analyzed to study the effects of these five single-parameter levels on the combustion and emission characteristics of dual-fuel engines.The generation rates were 40%,50%,60%and 70%respectively;the EGR rates were 0,7.5%,10%and 12.5%;the inlet pressure was 0.173 MPa,、0.193 MPa、0.213 MPa、0.223 MPa;the inlet temperature was 325.15 K、335.15 K、345.15 K、355.15 K;and the injection advance angle was16.6°、18.6°、20.6°、22.6°.Finally,the orthogonal experimental design is used to arrange the simulation calculation,and the five operation parameters are optimized and matched.The range analysis of the simulation results is carried out,and the comparison with the single parameter optimization scheme is made.The interaction between the five operating parameters and their two sets of parameters was studied in the sub-regression orthogonal experiment design.The evaluation index was re-optimized and the mathematical prediction model of regression equation was established.The optimum parameters of the evaluation index were obtained by co mparing the results of orthogonal experiment design,range analysis and primary regression orthogonal design.The combination provides guidance for the design and transformation of CNG diesel dual fuel engine.