The direct use method is a method whereby crude vegetable
oil is mixed or diluted with diesel fuel in order to improve
the viscosity. For ratios of 1:10–2:10,
use of the diesel was found to be successful. However, stated that blends of oils are not practical for
direct and indirect engines. Problems related to this situation
are due to the high viscosity, acid composition, FFA content,
and gum formation.