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The process of deposit-induced, fuel-flow reduction in multiport fuel injectors of the director-plate type was investigated both experimentally and analytically in order to understand both the flow-reduction mechanism and the non-linear variation in flow reduction with engine operating time. Injectors that had accumulated deposits in previous extended engine testing utilizing a rapid-plugging fuel were flow-tested, and the orifice plates from two of the injectors containing deposits were examined using a scanning electron microscope. A thin, carbonaceous deposit protruding into the flow paths of the orifices was found to be present on the downstream face of the orifice plate, but not present within the fuel orifices or on the upstream surface of the plate. Based upon these observations, calculations were made using a fluid flow model of an orifice plate with deposits.

An engine dynamometer test procedure was developed for evaluating fuel and fuel additive effects on the plugging of port fuel injectors. The test procedure was shown to adequately reflect the influence of fuels and additives on injector plugging in vehicles. Injector soak temperature and fuel system configuration were found to be critical factors in obtaining an acceptable engine-vehicle correlation. Injector plugging occurred in as little as 10 hours with a high-olefin base fuel; in contrast, plugging took two orders of magnitude longer with a high-quality, detergent-containing, commercial-type fuel. Furthermore, fuel additives greatly increased plugging resistance with the OEM, pintle-type injectors. Injector design alterations were also shown to be important. Pintle-type injectors with flared, aluminum caps extended plugging time considerably relative to the same injector design with plastic caps. Director plate-type injectors were much better still.