Numerical Simulation Of Cavitation Flow Of Nozzle Based On DME-Diesel Blends

Research on energy saving and emission reduction of diesel engine are more and more urgent,meeting the ever more stringent emission regulations,improving combustion efficiency of new alternative fuels has become a key breakthrough point.Though cavitation flow characteristics of fuel in engine injector nozzle makes metal surface withstand impact and then nozzle is wore,atomization quality and combustion efficiency can also be improving though nozzle cavitation.D40(ratio of dimethyl ether and diesel is 4:6)fuel is a promising alternative energy source,and it is of great significance to study cavitation phenomenon of D40 fuel in injector.In this paper,a three-dimensional numerical simulation of hole flow of D40 fuel in a vertical four-hole nozzle was carried out by using mixed homogeneous-flow hole model.During research,E.Winklhofer’s experiment has been simulated and results have been compared.In addition,relevant results have also been verified using relationship proposed by Nurick.Ensure accuracy and reliability of the simulation using mixed homogeneous flow model,Realizablek-εmodel and Zwart-Gerber-Belamri model.Injection pressure and backpressure,nozzle structure parameters,rounding radius,nozzle angle,elliptical orifice,and needle valve movement rule considered as prime parameters is discussed,cavitation distribution,speed distribution,vapor average volume fraction,and turbulent kinetic energy has been obtained and analyzed.Results of mass flow,velocity coefficient(C_v),cavitation number and discharge coefficient(C_d),vapor morphology are also presented and analyzed for D40 fuel nozzle.Research indicates:(1)Cavitation layer is strengthened with increase of differential pressure,and D40fuel is more prone to cavitation than ordinary diesel fuel.Average export speed of D40fuel is 5.3%higher than that of diesel(2)Rounding radius is inversely proportional to cavitation layer within nozzle and directly proportional to flow coefficient.Ratio of rounding radius and nozzle diameter is close to one-tenth,D40 fuel has better atomization quality and cycle fuel injection.(3)Under working conditions set in this simulation,when nozzle diameter is0.4mm and nozzle angle tends to be between 135°and 150°,not only can the fuel quantity of the D40 fuel be insured,but also fuel atomization quality.If circular orifice is replaced by an ellipse orifice with a minor axis of 0.15 mm and a major axis of 0.2mm,flow coefficient can be increased by 3.5%.Major axis placed horizontally,flow coefficient can be further increased.(4)Medium-expansion nozzle can not only improve the quality of atomization and flow coefficient during the cavitation stage than the conventional nozzle increased by11.5%.(5)maximum needle valve lift inhibits cavitation layer development.On the contrary,appropriate increasing needle ascending speed can effectively improve D40fuel atomization quality and circulating fuel injection amount.