Duboc, B; (2014) The effect of fuel additives on diesel fuel delivery system and combustion performance. Doctoral thesis , UCL (University College London).

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Abstract

The thesis presents an investigation of several aspects of fuel additive performance, including the effects of additives on the pump torque required to deliver high pressure fuel to engine injectors, the fuel droplet size distribution at sub-zero diesel fuel temperature, when wax formation occurs, and the ignition delay of diesel fuel combustion in an engine as well as constant volume combustion vessel. Exhaust emissions due to fuel additives were also investigated in an engine. A pump torque rig was designed and commissioned to investigate fuel additive performance at various pump speeds, fuel delivery (common rail) pressures and fuel temperatures, including sub-zero temperatures at which fuel waxing occurs. An existing constant volume combustion vessel was adapted to allow observations of fuel spray with additives and it was used for spray and combustion investigations. Various components of the combustion vessel were modified to support the fuel spray instrumentation. Also, a sub-zero fuel temperature system was developed to allow fuel to be cooled down for investigations; finally, a fuel pressure intensifier was designed which allowed ease of dismantling and thorough cleaning so as to eliminate additive cross-contamination between successive tests with additives. Results have shown that in general, additives have very small effects on many aspects of the fuel delivery system performance when the primary purpose of the additive is not related to the fuel delivery system. That is, there are virtually no side effects on pumping system performance from additives not intended to affect this system. This is mainly due to the small quantity in which the fuel additives are added, which is too small to affect any of the overall fuel properties. Additionally, it was proven that a constant volume combustion vessel is unsuitable to carry out combustion performance tests on fuel with additives, due to the high error in test repeatability. In contrast, the engine tests were able to reveal the effects of several combustion modifying additives on engine combustion performance and exhaust emissions. The fuel spray analysis at sub-zero temperatures revealed that wax formation was not the likely cause of an increase in droplet size but, instead, the likely cause is an increase in fuel viscosity.

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