Fundamental Investigation Of Fuel Design And Premixed Low Temperature Combustion Of Wide Distillation Fuels

Wide Distillation Fuel(WDF)refers to the petroleum-based fuels with a distillation range from the initial boiling point of gasoline to the final boiling point of diesel.WDF can merge the advantages of the physical and chemical properties of conventional gasoline and diesel fuel,reduce engine-out emissions,reduce the product and usage cost of aftertreatment systems,and increase the energy conversion efficiency of petroleum-based fuels.In this paper,in order to achieve high-efficiency and clean combustion over the whole engine load range,the fuel design and combustion mode improvement of WDF Premixed Low Temperature Combustion(PLTC)were investigated by bench test.The combustion process and emission production mechanism of WDF PLTC were analyzed by simulation.The combustion and emission characteristics of WDF by blending commercial gasoline and diesel were investigated in a single-cylinder diesel engine.It is found that increasing fuel cetane number can significantly improve low-load combustion stability and both reducing cetane number and medium boiling point can reduce high-load soot emissions.Balancing the low-load combustion stability and high-load emissions,the primary fuel design principle were obtained as follow:cetane number of 39-48,medium boiling point of 155-180°C and viscosity at 20°C of 1.2-2.0 mm~2/s.Two specific fuel preparation methods were proposed according to the fuel design principle:one is blending gasoline/diesel WDF with cetane number improver,while the other is producing full distillation fuel directly.To further improve emission characteristics of WDF PLTC,Polymethoxy Dimethyl ether(PODE)with high oxygen content and high cetane number was used to temper gasoline/diesel WDF,obtaining oxygenated WDF named GDP.Compared with gasoline/diesel WDF,GDP shows better low-load stability and fuel economy,and it can also improve the NO_x and soot tradeoff at high load.After that,GDP and Multiple Premixed Compression Ignition(MPCI)was coupled to improve the tradeoff between Maximum Pressure Rise Rate(MPRR)and thermal efficiency.The results show GDP MPCI has 5-10%lower fuel consumption at the same MPRR.In order to analyze the combustion mechanism of WDF,the Converge software was coupled with reduced PRF chemical reaction kinetics to build a WDF combustion mode.It is found that large ratio of lean mixture existing in squish volume due to the long ignition delay is the reason for the inferior combustion quality at low load.The reason for low soot emissions at high load are the lower equivalence ratio downstream the spray due to the high volatility of WDF and injection ending before ignition which avoids rich spray from thrusting straight into the burned high-temperature regions.The critical parameters of PODE were estimated by Joback mothed.Based on these critical parameters,the physical properties of PODE were estimated by the group contribution mothed,and the database of PODE physical properties were established.PODE Homogeneous Charge Compression Ignition(HCCI)were investigated at various equivalence ratio and Exhaust Gas Recirculation(EGR)in the single-cylinder engine.PODE chemical reaction kinetics were established by analogy with the process of paraffin reaction kinetics establishment,and the newly-built kinetics were verified by PODE HCCI experimental data.