Study Of Internal Flow And Deposition Characteristics Of NAl/JP-10 Nanofluid Fuel Liquid Film Evaporation

In practical engines,the jet fuel or jet fuel-based nanofluid fuel are usually sprayed onto the thermal hydrophilic walls or blades,and the fuels will spread along the hydrophilic solid surface and produce the liquid films with a small ratio of height to diameter(<0.1)and small contact angle.The evaporation characteristics of droplets/films directly affect the spray combustion performance.Therefore,this paper proposes to study the internal flow,particle deposition,and evaporation rate of films of jet fuel-based nanofluid fuels in the heating evaporation stage before internal combustion of the engine,so as to deepen the study of evaporation characteristics of liquid film.(1)A theoretical model of sessile droplet/liquid film was programmed to obtain the variation of internal flow field during evaporation with constant contact radius by using nAl/JP-10 nanofluid fuel as the research object.It is found that the capillary flow direction mainly flows from the top of the liquid film to near the contact line,and the evaporation rate reaches the maximum at the edge of the liquid film;the Marangoni flow appears as a eddy,which makes the liquid flow upward from the middle and from the sides to the bottom.With the increase of the substrate temperature,the velocity increase of the capillary flow is much smaller than that of the Marangoni flow.(2)The evaporation characteristics parameters of nAl/JP-10 nanofluid fuel liquid film fixed on hydrophilic glass substrate were tested.The results showed that there is a competitive relationship between capillary flow and Marangoni flow at different substrate temperatures.During the evaporation process,the nano-particle clusters will move back and forth at the contact line and the inner ring line,and there is a stagnation point on the surface of the liquid film with the largest difference among surface flow,surface tension gradient and surface temperature gradient.The maximum difference in surface temperature during evaporation is positively correlated with the nanoparticle concentration in the dilute phase range;the addition of nanoparticles promotes evaporation at lower temperatures,but the opposite is true at higher temperatures.(3)The changes in contact lines,contact angles,volumes and deposition patterns during evaporation of nAl/JP-10 nanofluid fuel films,with the addition of different concentrations and types of nanoparticles on substrates at lower temperatures(50 °C-100 °C)were studied.The addition of nano-aluminum improves the evaporation rate of JP-10,shortens its evaporation life and promotes the evaporation of JP-10.The contact line is repeatedly pinned and unpinned,resulting in concentric multi-loop deposition patterns;Because of the existence of energy barrier,the three-phase contact line presents discontinuous "stick-slip" behavior on the surface of hydrophilic solid,and there are many jumping stages of contact line and contact angle;There is a significant difference in the deposition mode between nano-fluid fuel with graphite or iron nanoparticles and nAl/JP-10 nanofluid fuel.The results of this paper can help to deeply analyze the competition mechanism and transformation conditions of Marangoni flow and capillary flow in sessile droplets/liquid films,and also lay the foundation for the practical application of nano-fluid fuel in engines.