Density
This is the mass per unit volume and is generally given as kg/m³ at 15^OC 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.
Viscosity
This 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.

Flash Point
This is the temperature of a fuel at which sufficient vapour is given off that momentary ignition occurs if an external flame is introduced. This temperature si quoted as Open or Closed. The closed temperature is about 15'C lower than the open
Pour Point
This is the temperature at which and below wax crystals begin to form. This is important for pumping
Specific energy or Calorific value
This is the total energy chemically available by a unit fuel. Heavier fuels tend to have lower values.
Ignition quality
Is a property related to distillated fuel and is that quality of combustibility during combustion process in a diesel engine, which causes ignition delay. It is a relative value on a scale of 0 to 100, known as cetane number. Paraffin as non-combustible substance is taken for zero and Cetane (C₁₆H₃₄) a highly combustible substance is taken as 100.