Petroleum Testing
Viscosity
Viscosity may be described as a measure of liquid resistance to flow. It usually is measured by recording the time required for a give volume of fuel at a constant temperature to flow through a small orifice of standard dimensions. The viscosity of diesel fuel is important primarily because of its effect on the handling of the fuel by the pump and injector system.
In diesel engines, fuel viscosity exerts a strong influence on the shape of the fuel spray. High viscosities can cause poor atomization, large droplets and high-spray jet penetration.
With high viscosities, the jet tends to be a solid stream instead of a spray of small droplets. As a result, the fuel is not distributed in, or mixed with, the air required for burning. This results in poor combustion, accompanied by loss of power and economy.