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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.

Diesel engines will require new hardware to meet future emissions levels required by upcoming legislation. One of the key enablers towards meeting such legislation is the use of better fuel injection equipment (FIE). However, these systems can produce temperatures at the injector tips that are considerably higher than those seen today. This environment can exacerbate the rate of deposit formation or generate new types of deposits at and around the injector tip. Previous and ongoing investigations continue to further our understanding of this phenomenon using a modern passenger car diesel engine, various commercial 10 ppm S diesel fuels, a severe test cycle and injector nozzles representative of those likely to be in use in EURO V engines. The engine tests show good repeatability with clear and treated fuels. This supports the validity of the data generated. The test protocol used has recently been released to the industry.

Future diesel engines will require new hardware to reduce emissions to the levels required by upcoming legislation. Advances in the fuel injection equipment (FIE) of the engine are a key enabler towards meeting such legislation. These modern systems produce temperatures and pressures at the injector tips that are considerably higher than those experienced today. This environment can initiate or increase the rate of deposit formation at and around the injector tip compared with current systems. Investigations have been carried out to further the understanding of this phenomenon using experimental nozzles simulating a similar deposit build-up as expected in EU 5 engines. The investigation used a protocol that has recently been released to the industry, commercial 10 ppm S fuel and a commercial diesel fuel detergent. Testing was carried out with both clean and zinc contaminated fuel. Zinc contamination with a fuel soluble salt was used to simulate severe market conditions.

Internal Diesel Injector Deposits (IDID) in compression ignition engines have been widely studied in the past few years. Published results indicate that commonly observed IDID chemistries may be replicated using full-scale engine tests and subsequently fuel injection equipment (FIE) operated on non-fired electric motor driven test stands. Such processes are costly, complex and by nature can be difficult to repeat. The next logical simplification is to replicate IDID formation using laboratory-scale apparatus that recreate the appropriate chemical reaction process under well controlled steady state conditions. This approach is made more feasible by the fact that IDID, unlike nozzle hole coking, are not directly exposed to gasses involved in the combustion process. The present study uses an instrument designed to measure thermal oxidation stability of aviation turbine fuels to successfully replicate the deposit chemistries observed in full-scale FIE.