Fig.
3. Possible results of the collision of two drops at ambient
temperature T = 300 K and pressure p = 1 atm \cite{Qia97}.
From the point of view of biofuels, it is important the size of the drop
during spraying depends mostly on their physical and chemical
properties, density, surface tension, viscosity. These properties of
fuels are the main causes why the different fuels form different
properties of air-fuel mixtures in engine cylinder and why the
combustion properties are different. The fuel drop size is crucial
during the combustion of air-fuel mixture by affecting directly the
combustion efficiency and engine exhaust gas.