Cetane Scale Evaluation and Possible Modification.

An evaluation is made of the validity and accuracy of the Cetane Scale in rating fuels used in diesel engines. Six problems have been identified, analyzed and possible solutions have been proposed. Three of the problems are intrinsic to the scale and are related to its inability to rate low ignition quality fuels, instability of the ignition delay meter and the inconformity of the CFR combustion system with actual diesel systems. The other three problems are related to fuels and engines. These are the invalidity of C.N. in correlating the ignition delay data, its inaccuracy in ranking overall engine performance and emissions and its inability in rating the cold startability of engines on different fuels. The cold startability problem is investigated in two engines, under steady and actual starting conditions in a cold room. Also, a mathematical model is developed to predict the startability of the engine. These investigations indicate very clearly that the cetane rating is a hot engine, high temperature test and is unable to rate the cold startability of diesel engines. Keywords Cetane number Diesel fuels.