For residual fuel, the ignition quality is measured by the Calculated
Carbon Aromaticity Index (CCAI).
It is an empirical equation based on the density and viscosity of the fuel. CCAI is normally in the range of 800-870. The higher the CCAI, the longer fuel takes before it starts ignition in the engine. In other words, ignition delay for a fuel with low CCAI is minimal.
Changing to a fuel with a higher ignition quality or lower CCAI index means early ignition of fuel, higher peak pressures, excessive load on the bearings (especially cross head bearings) and loss of engine power. Similarly, using a fuel with higher CCAI index or lower ignition quality will cause late ignition, causing after burning which damage exhaust valve, fouling of turbocharger, burning of piston crown and liner, and loss of engine power.
It is an empirical equation based on the density and viscosity of the fuel. CCAI is normally in the range of 800-870. The higher the CCAI, the longer fuel takes before it starts ignition in the engine. In other words, ignition delay for a fuel with low CCAI is minimal.
Changing to a fuel with a higher ignition quality or lower CCAI index means early ignition of fuel, higher peak pressures, excessive load on the bearings (especially cross head bearings) and loss of engine power. Similarly, using a fuel with higher CCAI index or lower ignition quality will cause late ignition, causing after burning which damage exhaust valve, fouling of turbocharger, burning of piston crown and liner, and loss of engine power.
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