|Standard test: CCAI index using both density and viscosity|
|Measurement: Cetane Number|
With no stipulated limits under ISO 8217:1996, Annex B comments on suitable methods of calculation using density and viscosity. This is the “bang per buck” equation and unless stipulated in a separate agreement with the supplier at time of purchase cannot be claimed against. It can provide benefits with more efficient material and vice versa with poor efficiency.
Usually poor ignition quality is found in fuels of high density and low viscosity where the CCAI should be checked with either dedicated nomogramms or an electronic fuel calculator. The injection timing of engines can usually be adujsted, but still consult the manufacturer’s instructions on tolerable limits:
- Low speed marine cross-head Diesel engines run troublefree up to CCAI values of 870.
- Medium speed can get up to 860.
Towards the upper end of CCAI limits part and low load operation is more critical than full load as engines are generally more reliant on better ignition quality at this speed. Things are eased when heating the scavenge air and raising coolant temperature as the engine becomes less sensitive.
In cases where there is no ignition and the engine cannot run under low load then a change to the marine Diesel oil is unavoidable.
If there is a significant ignition delay (time between fuel injection and ignitition) it may damage the engine's working parts and thermal characteristics.