Based on the problem, the method of literature overview and the modeling of the fuel drops behavior in the spray are chosen. Theoretical calculations give an opportunity to evaluate experimental results of the behavior of different biofuels in the fuel spray and explain the .reasons of the problem.
  1. Parameters describing fuel drop formation and collision
When fuel is sprayed, the fuel spray is broken down into drops. As the fuel drops move in the fuel spray, the drops are broken down by air resistance and the collision of drops occurs, which changes the drop size dc (Sauter Mean Diameter, SMD -d32 ).
Three dimensionless parameters are used for the modelling of the decomposition of fuel drops:
Weber number We
\(We=\frac{\rho\bullet\left|v_{1}+v_{2}\right|^{2}\bullet\left(D_{1}-D_{2}\right)}{\sigma}\)(1)
where ρ is the fluid’s density (kg/m3),v1 and v2 are the respective speeds of smaller and bigger drops (m/s),D1 and D2 are the respective diameters of the drops (m) and σ is the fluid’s surface tension factor (N/m).
Impact parameter B
\(B=\frac{2b}{\left(D_{1}+D_{2}\right)}\) (2)
where b is the distance from the centre of one drop to the relative velocity vector placed to the centre of the other drop (m).B = 0 corresponds to the frontal impact of the drops and B= 1 corresponds to the situation in which the drops graze each other (Fig. 1).