Understanding the Relation Between Cetane Number and Combustion Bomb Ignition Delay Measurements

A recently approved method for cetane determination using the Ignition -Quality Tester (IQT™) is based on an ignition delay measurement in a combustion bomb apparatus, which is empirically correlated to cetane number. The correlation assumes that all fuels will respond to the different pressure and temperature domains of the IQT™ and the cetane test engine in the same way. This assumption was investigated at a more fundamental level by conducting IQT™ measurements at different pressure and temperature points and characterising the ignition delay of the fuel in terms of an Arrhenius autoignition model. The fuel model was combined with a mathematical model of the cetane engine and the concept was evaluated using a variety of test fuels, including the diesel cetane rating reference fuels. The analysis technique was able to accurately predict the cetane number in all cases.