Fuel Combustion Additives:  A Study of Their Thermal Stabilities and Decomposition Pathways

The purpose of this study was to evaluate whether a relationship exists between thermal stabilities of selected fuel additives and their effectiveness as diesel fuel cetane improvers. The additives were 2-ethylhexyl nitrate, isopropyl nitrate, tetraethylene glycol dinitrate, di(tert-butyl) peroxide, and methylcyclopentadienyl manganese tricarbonyl. Rate constants and activation parameters were determined for the thermolysis of the neat additives as well as the additives dissolved in various solvents and fuels. In all cases, decomposition kinetics were first-order. Mass spectral analysis was used to identify products from the thermal decomposition of the additives in various solutions. Thermal stability, as measured by the kinetics of decomposition, was not an accurate predictor of the effectiveness of the additives as cetane improvers. The effectiveness of a given additive appeared to correlate to the degree of molecular fragmentation rather than to thermal stability.