Fig. 10. The dependency of the relative diameterdc/d of a drop that formed after the collision
and the impact parameter B at two different colliding drop
diameter ratios Δ (equation 4) (Δ1 = 0.5,Δ2 = 1.0) in case of four different fuel types.
Fig. 10 was obtained with the parameters v1 =v2 = 200 m/s and the physical parameters of the
fuels correspond to the temperature of 90 °C. Fig. 10 shows that the
drop size can differ in the air-fuel mixture at various values ofΔ . It can be concluded that the air-fuel mixture of fuels with
high viscosity (for example, HVO) contains somewhat larger drops than
the mixture of low viscosity fuel. At the same time, the drops of FAME
fuel are in the same magnitude as gasoline and diesel fuel. In addition
to viscosity, another important influencing factor is surface tension.
At low values of B , the ratio dc/d is
mostly determined by the fuel’s surface tension forces. If the value ofB is greater, then the interaction volume remains smaller, which
means that the ratio dc/d is also greater.
Table 4 was prepared to illustrate better the breakout of fuel drops.
The table gives the drop sizes of various fuels at various values of the
impact parameter B . Table 4 exemplifies also a situation in which
the colliding drops are equal. The physical parameters of fuels in Table
4 correspond to the temperature of 90 °C. In the first case (1), the
value of Cv is negative for stretching
separation, which means that the stretching separation does not occur.
The positive value of Cv shows that reflexive
separation takes place.
In the other cases (2-4) the reflexive and stretching separation of
drops occurs. The main difference between the different cases is that
when the impact parameter’s value is B = 0.1, then the drop size
of diesel fuel and gasoline is ~5 % smaller than that
of HVO and FAME fuels. It can be deduced from here that the drop size in
the air-fuel mixture of HVO and FAME fuels is somewhat greater than that
of diesel fuel. Here the air-fuel mixture corresponds to the general
knowledge, according to which the drop size in air-fuel mixtures of high
viscosity fuels is greater. At the same time, it is not sure why the
soot level of emission gas of biofuels is lower. If we presume that the
use of FAME fuels results in lower soot levels in the exhaust gas mostly
due to the oxygen content in the fuel, then what is the reason for the
lower soot level of HVO fuel? In conclusion, it can be claimed that the
drop size of biofuels in air-fuel mixture is somewhat larger. The
approach of this article does not give the answer why the soot level in
the engine’s emission gas decreases when HVO and FAME fuels are used. At
the same time, the results illustrate that there are no important
differences in the quality of air-fuel mixture. In order to account for
the reduced soot level, it is necessary to study experimentally the
breakout of drops in the fuel spray, the effect of oxygen content on the
combustion of fuel and the effect of various fuel fractions to the
combustion process.
Table 4. Drop’s diameter dc after
collision and the value of separation coefficientCv in case of a collision of two drops with equal
diameters.