Fig. 5. Dependency between the diameterdc of the drop leaving the injector and fluid’s dynamic viscosity µf at two different velocitiesv of the spray (v1 = 200 m/s,v2 = 400 m/s), for four different fuel types. Thex -axis value range 0-3600 µPa·s corresponds to typical viscosities of fuels at temperatures 40 °C and 90 °C (Table 1).
Equation 11 contains the member ΛKH , which contains the fluid’s dynamic viscosity µf . Therefore, it is possible to represent graphically the dependencydc of the drop leaving the injector and fluid’s dynamic viscosity µf for various fuels (Fig. 5). The diagrams of Fig. 5 presume that the surface tension and density of fuel does not change. The density of the gas environment is 17 kg/m3, injector’s opening’s diameter 100 µm. According to sources \cite{Chh13,Keg18,Wan06,Boh17,Mel14,Fen16,Sah17}, the physical parameters of the fuels correspond to the temperature 90 °C.
Fig. 5 shows that as the dynamic viscosity increases, the drop size in the air-fuel mixture also increases. An important factor having an effect on the drop size is the velocity of the fuel spray. The higher the velocity of the fuel spray, the smaller the diameter of the drop. Dynamic viscosity has a bigger effect on the change of fuel drop size in case of lower velocity fuel spray. For example, in case of the velocity of 400 m/s of the drop of any fuel, the change of fuel drop size is relatively smaller than compared to the speed of 200 m/s. Likewise, the physical and chemical properties of fuels have an effect on the drop size mostly at the lower velocity of the spray v1= 200 m/s. When we compare the fuel spray of gasoline and HVO fuel at spray velocity of 200 m/s, then, for example, we can see that at the dynamic viscosity’s value of 1600 µPa the difference of drop size is ~1 µm (25%). At drop velocity ofv2 = 400 m/s the change of drop size is 0.2 µm (16%).