Experimental Study And Numerical Simulation On Spray Characteristics Of Fuel Containing Dilute Phase Particles

Nanoparticles,as a fuel additive,have been proved to have a positive role in the field of engine combustion and emission,but the effect of nanoparticles on fuel spray characteristics is not clear.The influence of different injection pressure,ambient backpressure and mass concentration of nanoparticles on fuel spray characteristics were compared by the combination of spray visualization test and numerical simulation.The main work of this paper are as follows:（1）Preparation and stability analysis of nano-fuel.CeO₂ nanoparticles with the size of 50 nm were selected as fuel additives,Cetyltrimethyl ammonium bromide（CTAB）used as the surfactant and nano-fuel with the mass concentrations of 50/100mg·L^-1 were prepared by two-step method.After the preparation,The dispersion stability of nano fuel was investigated by the sedimentation observation method and particle size distribution method.The results show that 100 mg/L nano-fuel has no obvious precipitation after 100 hours,and the size of the agglomeration in the nano-fuel samples are all below 800nm,which meets the requirements of the test on the stability of nano-fuel.（2）Thermophysical properties of diesel and nano-fuel with different mass concentrations.The density,dynamic viscosity and surface tension of diesel,50mg/L and 100 mg/L CeO2 nano-fuel at different temperatures were measured.An Fitting formula for predicting the density,dynamic viscosity and surface tension of three fuels at different temperatures is presented.Meanwhile,the thermal conductivity of nano-fuel was estimated by Xuan model.（3）Study on macroscopic characteristics of nano-fuel spray based on fuel spray visualization platform.Through the visual experimental research,it is found that when the injection pressure of fuel increases,the spray tip penetration,spray volume and spray gas entrainment mass of nano-fuel increase remarkably,Spray cone angle is increased in the early stage of spray development and decreased gradually in the later stage.Although the increase of back pressure inhibits the development of nano-fuel spray tip penetration,it promotes the radial diffusion of nano-fuel and increases the spray cone angle.the spray volume of nano-fuel decreases slightly.With an increase of back pressure,the environmental density of the constant volume bomb increases,resulting in a slight increase in spray gas entrainment mass of nano-fuel.According to the spray test results of diesel,50mg/L and 100mg/L nano-fuel,it is found that the spray tip penetration,spray volume and spray gas entrainment mass of nano-fuel are all higher than that of diesel,while the spray cone angle is slightly smaller.At the same time,three factors（injection pressure,back pressure and nanoparticles mass concentration）of spray tip penetration and spray cone angle were evaluated by grey correlation analysis.The priority is determined as follows:injection pressure>back pressure>nanoparticles concentration.（4）The spray characteristics of nano-fuel are further explored through numerical simulation.Homogeneous model was used as physical model for nanofluid flow,the RNG6)6)-model and KH-RT model were used as the turbulence model and spray breakup model.With the rise of injection pressure,the turbulent kinetic energy of nano-fuel increases.It helps to accelerate the diffusion rate of nano-fuel.And it is conducive to the breakup of nano-fuel and reducing the SMD of nano-fuel.The increase of back pressure inhibits the spray tip velocity of nano-fuel,but it is beneficial to accelerate spray diffusion,reducing the fuel concentration near the nozzle.the SMD of nano-fuel have no remarkable change.At the same time,the increase of the mass concentration of nanoparticles raises the penetration velocity of nano-fuel,which is beneficial to reduce the fuel concentration near the nozzle.But it has weak influence on the radial diffusion and SMD of the fuel.The spray characteristics of nano-fuel under different injection pressures and back pressures are analyzed in combination with spray visualization experiments and numerical simulation.The influence of nanoparticles with different mass concentrations on spray characteristics is also explored,which provides research experience on spray characteristics of nano-fuel containing dilute-phase particles.