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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.

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.