Molecule Dynamics Simulation Of CeO₂ Nano-fuel And It’s Single Droplet Combustion Performance

Nano-fuel is a type of nanofluid that is made by adding nanoparticles to traditional fuel.Nanoparticles have high specific surface areas and surface activity,which can greatly improve fuel’s combustion efficiency and reduce pollutant emissions.In this study,the effects of nanoparticle mass concentration and particle size on fuel properties have been examined.Cerium oxide（CeO₂）nanoparticles were used in this study due to their high surface activity and catalytic ability.A two-step method has been used to prepare different types of CeO₂ nano-fuels.The thermal properties and rate of combustion of the nano-fuel were investigated by conducting molecules dynamics simulations and analyzing single droplet rate of combustion.The following work has been carried out:（1）Preparation and suspension stability of CeO₂ nano-fuel:The use of Cetyl Trimethyl Ammonium Bromide（CTAB）as a surfactant and N-tetradecane（C14）as the base liquid fuel were allowed to prepare CeO₂ nano-fuel through a two-step method.The suspension stability of the nano-fuel was evaluated by using the sedimentation method and laser particle size analysis.The results supported that the nanoparticles could be maintained in the base liquid fuel for approximately seven days,with no observable settling during this period.These findings indicate that the prepared nano-fuel had excellent suspension stability and satisfied the requirements of subsequent testing.（2）Investigation of the thermal properties of the nano-fuel using molecules dynamics method:The molecules structure model of the nano-fuels were established to investigate its thermodynamic parameters,such as diffusion coefficient,dynamic viscosity,heat flux distribution,temperature gradient,and radial distribution function.The simulation results indicated that the thermal coefficient of nano-fuel significantly increased compared to that of the base liquid fuel,and the thermal coefficient enhancement effect of CeO₂ nanoparticles on the nano-fuel was obvious.The addition of CeO₂ nanoparticles changed the microscopic characteristics of the base liquid fuel,allowing the nano-fuel to exhibit the characteristics of both"short-range order and long-range disorder"of the base liquid fuel and the"long-range order"of the nanoparticles.The encounter probability between Ce and C atoms gradually increased with the increase of particle size and mass concentration of nanoparticles,leading to an increase in particle aggregation and moving resistance.This,in turn,improved the dynamic viscosity of the base fluid fuel to a certain extent.As the mass concentration of CeO₂ nanoparticles increased and the particle size decreased,the diffusion coefficient of C14 continuously increased.However,the nano-scale effect of CeO₂nanoparticles gradually diminished with the increase of mass concentration.The diffusion coefficient growth rate of C14 gradually slowed down with the increased nanoparticle mass concentration.（3）Experimental study on nano-fuel droplet ignition using the hanging droplet method:The single droplet visualization ignition test platform was built,and the droplet ignition process were established by using a high-speed camera.The hanging droplet method has been used and Matlab to extract pixel points and calculate the instantaneous diameter of the droplet.The ignition delay,combustion rate,and dynamic combustion process were focused in this research.The influence of particle size and mass concentration of nanoparticles have been analyzed on the ignition behavior of single droplets of nano-fuels,combined with the results of molecules dynamics.The rate of combustion process of droplets become more intense with the addition of nanoparticles,and the combustion process of nano-fuel droplets become more intense with the increased mass concentration.Micro-explosions inside the fuel droplets promote secondary atomization during the droplet combustion process,shorten the droplet combustion time,and improve the combustion rate.The mass concentration of CeO₂ nanoparticles greatly influences the ignition delay,which decreases with the increase of the mass concentration.This is due to the increased probability of encounter between Ce atoms and C atoms,higher heat transfer efficiency between molecules,faster system temperature rise,and promotion of ignition of fuel droplets.At the same mass concentration,the ignition delay of CeO₂ nano-fuel with a smaller particle size was lower.The Ce₂₀ nano-fuels have smaller agglomeration and a larger specific surface area during preparation,leading to a stronger enhancement effect on the thermal coefficient.This was more conducive to the vaporization and evaporation of the base liquid fuel,promoting the rate of combustion of CeO₂nano-fuel droplets.