Comment:
CCAI and CII predict performance under full load conditions. However damage tends to occur at part loads and on faster running engines. BEWARE
Info Centre >> Fuel and Lube Oil Technical Manual >> 2. Fuel Oil - Characteristics >> 12.14 Ignition Quality
Calculated Carbon Aromaticity Index (CCAI) and Calculated Ignition Index (CII)
For residual fuel, there are two accepted empirical equations both based on the density and viscosity of the fuel. These are the Calculated Carbon Aromaticity Index (CCAI) and Calculated Ignition Index (CII). The CCAI gives numbers in the range 800-870, while the CII gives values in the same order as the cetane index for distillate fuels. Of the two equations, CCAI values are more frequently quoted.
The figure is a nomogram which incorporates both CII and CCAI. If the viscosity is fixed and the density is raised, the CII value falls and the CCAI value is increased. Similarly, if the density is fixed and the viscosity lowered, the CII value falls and the CCAI value is increased. In general, values less than 30 for CII and greater than 870 for CCAI are considered problematical. If required, further guidance on acceptable ignition quality values should be obtained from the engine manufacturer.
The ignition quality of a fuel is a measure of the relative ease by which it will ignite. For distillate fuels, this is measured by the cetane number. Cetane number is determined by testing in a special engine with a variable compression ratio. The higher the number, the more easily will the fuel ignite in the engine.