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Calculation Routines Supporting the use of Diesel Fuel Cetane Improver
2-ethyl hexyl nitrate.
Request file: Additives.xlsm
Cetane Improver, 2-ehn accelerates the combustion of diesel fuel as it decomposes under thermal stress on entering the engine cylinder. The effect is measured by the increase in cetane number of the fuel in a test engine or the modern IQT instrument. Refineries blending to a cetane target can predict the increase in cetane as a function of the dosage of the 2-ehn. The effect is reliable but varies with the fuel type, paraffinic diesels showing a larger boost due to the additive than aromatic. The download above is an Excel based prediction routine for the increase in cetane number as a function of dosage and fuel character.
The base cetane number is often estimated from the 2 or 4 variable cetane indices. These are calculations using the density and distillation range of the fuel to correlate to cetane number and can be determined from on-line analyzers during the blending process. The effect of dosing 2-ehn is not included in the index calculations but can be estimated as a function of dosage and fuel character and added to the index to develop a prediction of the fuel cetane number.
The availability of cetane improver can significantly change the blend character as component ratios are optimised and these changes may affect the performance of the lubricity and cold flow additives. Additives.xslm includes a prediction for the change in both lubricity and cold flow for different character blends.
Cetane Improver, 2-ehn is a strong solvent and works against the additives used to enhance lubricity in low sulphur blends. The effect is significant in fuels hydrotreated down to sulphur levels below 10 ppm but can be compensated by increasing lubricity additive dosages when using high levels of 2-ehn. Additives.xlsm correlates the wear scar with dosage and fuel analysis.
Cetane improvers can allow the blends to be broadened with kerosenes and more aromatic streams such as the FCU light cycle oils. These components may change the reaction of the cold flow additives in terms of both the dosage and effective additive type. Additives.xslm includes a routine to check the optimum dosages and additive type.