The Calculated Ignition Index (CII) is an index of the ignition quality of residual fuel oil.
The running of all internal combustion engines is dependent on the ignition quality of the fuel. For spark-ignition engines the fuel has an octane rating. For diesel engines it depends on the type of fuel, for distillate fuels the
cetane number
Cetane number (cetane rating) is an indicator of the combustion speed of diesel fuel and compression needed for ignition. It plays a similar role for diesel as octane rating does for gasoline. The CN is an important factor in determining the quali ...
s are used. Cetane numbers are tested using a special test engine and the existing engine was not made for residual fuels. For residual fuel oil two other empirical indexes are used CII and
Calculated Carbon Aromaticity Index (CCAI). Both CII and CCAI are calculated from the
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
and
kinematic viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the int ...
of the fuel.
Definition
Formula for CII:
Where:
D = density at 15°C (kg/m
3)
V = viscosity (cST)
T = viscosity temperature (°C)
Use
CII was designed to give out numbers in the same order as the cetane index for distillate fuels.
Combustion
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