DensityThis is the mass per unit volume and is generally given as kg/m3 at 15OC and is specifcially given as that found in a vacuum. The density reduces with increasing temperature and alos reduces in air although the latter by only about 0.1%. These characteristics are important to allow proper description for commercial transactions and also for preparation ( say purifiers) and in use ( main engines). Density may also be given as specific gravity, this is a ratio of mass of the fuel to the same volume of water at the same temperature.
ViscosityThis is a measure of a fuels resistance to flow or more specifically resistance to shear of adjacent molecules. It is one of the most important characteristics of a fuel. It governs the method of handling, storage, pumping and combustion. The coefficient of viscosity is referred to as the absolute velocity and has many accepted units of value, the SI units are MPa/s and is defined as the force required to shear a set area of liquid at contant velocity.
Kinematic viscosity is this is the ratio of dynamic viscosity of a fluid over its density. The units are accepted as stokes or centistokes although the SI unit is m2/s or mm2/s. The viscosity of a fuel generally varies considerably with temperature and this is particularly the case with resif=dual fuels.