In the residual fuel, there are two accepted experiential equations both based on the density and viscosity of the fuel. These are the calculated carbon aromaticity index (CCAI) and calculated ignition index (CII).
ISO 8217:2010 has used the common calculation which is the CCAI and has set the maximum level for RMG/RMK grade at 870 while RME grade at 860.
The ignition and combustion quality of the residual fuel in diesel engine is dependent on the particular type, design, operation and engine condition, load profile and the chemical property of the fuel. Guidance on acceptable ignition quality values should be obtained from the engine manufacturer.
The CCAI does not provide information related to the combustion characteristics of residual fuel, it does provide an indication of ignition delay.