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Internal deposits formed within the fuel injection system have been widely reported in the literature. Several root causes exist, with many deposits consisting of more than one material. The final chemistry depends on the availability of trace fuel contaminants and additives and to a lesser extent hydrocarbon/FAME stability and operating conditions. The present paper identifies the primary deposit morphologies, along with the typical root cause. Metal carboxylate salts, also known as metal soaps are most widely reported and are easily recreated under controlled conditions using compounds present at trace concentrations in some market fuels. The salting reaction may occur at low temperatures in the fuel supply system. It is proposed that the resulting fuel insoluble salt molecules are transported as reverse micelles, occasionally plugging filters but more commonly passing to the high pressure injection system.

An increasing range of conventional and unconventional feed stocks will be used to produce fuel of varying chemical and physical properties for use in compression ignition engines. Fischer-Tropsh (F-T) technology can be used to produce fuels of consistent quality from a wide range of feed stocks. The present study evaluates the performance of F-T fuel in advanced common rail fuel injection systems. Laboratory scale tests are combined with proprietary engine and electrically driven common rail pump hydraulic rig tests to predict long-term performance. The results obtained indicate that the performance of F-T fuel is at least comparable to conventional hydrocarbon fuels and superior in a number of areas. In particular, the lubricity of F-T fuel was improved by addition of lubricity additives or FAME, with minimal wear under a wide range of operating conditions and temperatures.