The viscosity of a fuel depends on its hydrocarbon composition. Vegetable oil is considered an alternative to diesel fuel. Its high viscosity makes it difficult to consider as a commercial diesel fuel. Vegetable oil is lipids, fatty acid esters. They have a high calorific value and contain straight hydrocarbon chains, resulting in their relatively high cetane number. Viscosity and density determine the evaporation and mixing process in an engine, as they affect the shape and type of the fuel flame, the size of the droplets formed, and how they enter the combustion chamber. Low density and viscosity provide better fuel injection; with an increase in the diameter of the droplet, its complete combustion decreases, therefore, the specific fuel consumption increases and the smoke of the exhaust gases increases.
The viscosity of the fuel affects the pump flow and fuel leakage through the piston pair clearance. As the viscosity decreases, the amount of diesel fuel leaks between the plunger and bushing increases, resulting in a decrease in pump flow. Converting the engine to a fuel with a lower density and viscosity will result in burnout of the piston head, so the fuel equipment needs to be adjusted. Plunger wear is viscosity dependent. It fuel is in the range of 1.8-7.0 mm2/s, which practically does not affect the durability of modern high-speed diesel equipment.
Consider using vegetable rapeseed oil as an alternative to diesel fuel. Its viscosity can be reduced by chemically converting esterification to ethyl esters. When the cheese rapeseed oil is heated to 80 °C, it will give a viscosity value similar to that of commercial diesel. The mixing system will have an operating power equivalent to that of a diesel engine when heated to 40-50 °C.
Flow simulation of petroleum diesel fuel and rapeseed oil in the nozzle of a diesel injector