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Diesel fuel ignition delay times were characterized in a rapid compression machine (RCM) using cylinder ambient gas temperature and pressure measurements as diagnostics. The objective of the study was to investigate the dependency of ignition delay time on: (a) cylinder ambient gas temperature, (b) cylinder ambient gas pressure, (c) injection pressure, (d) injector nozzle orifice diameter, (e) base fuel cetane number and (f) 2-ethylhexyl nitrate (2-EHN) cetane improver additive. The results presented here show that diesel ignition delay times can be shortened by increasing cylinder gas ambient temperatures and pressures, injection pressures and base fuel cetane number, either through blend components or by addition of cetane improver. Decreasing the injector nozzle orifice diameter also decreases the ignition delay time. It was also found that ignition chemistry is rate controlled by the molar concentration of the cylinder gas oxygen.

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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.

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