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1 High precision high pressure diesel common rail fuel injection systems play a key role in emission control, fuel consumption and driving performance. Deposits have been observed on internal injector components, for example in the armature assembly, in the slots of the piston and on the nozzle needle. The brownish to colourless deposits can adversely impact driveability and result in non-compliance with the Euro 4 or Euro 5 emission limits. The deposits have been extensively studied to understand their composition and their formation mechanism. Due to the location of these deposits, the influence of combustion gas can be completely ruled out. In fact, their formation can be explained by interactions of certain diesel fuel additives, including di- and mono-fatty acids. This paper describes the methodology used and the data generated that support the proposed mechanisms. Moreover, approaches to avoid such interactions are discussed.

Continued legislative pressure to reduce diesel emissions has resulted in the development of engines with advanced fuel injection equipment (FIE). These injection systems produce temperatures and pressures at the injector tips that are considerably higher than those seen in previous technologies. This environment is initiating deposit formation at and around the injector tip which is leading to significant power loss and increased smoke generation. Investigations have been carried out to understand this phenomenon. Cyclic bench engine testing has generated high levels of deposits when minimal amounts of a fuel soluble zinc salt are doped into clear fuels. The deposits are found both in and around the nozzle tips. Analysis of the deposit shows the presence of zinc. These deposits are proving to be more challenging than those previously seen with older FIE technology. Detergents that have historically been effective in resolving injector deposits are proving less effective.