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We report on a comprehensive fuel additive study where two different detergent chemistry types, Mannichs and polyetheramines, are ranked with regard to injector deposit control in a research direct-injected gasoline (DIG) engine. The engine used was a conventional dual-sparkplug, 2.2-liter Nissan engine modified for direct injection using one of the sparkplug holes. The engine was run under 20% rich conditions to accelerate injector deposit formation. The two detergent chemistry types are shown to perform quite differently with the Mannichs showing superior performance. The Mannich detergent chemistries can reduce the DIG injector flow loss after using Howell EEE fuel from a high of 11.23% to a low of 3.14% whereas the best polyetheramine detergent chemistry tested reduced it to 8.17%. One of the Mannichs was further tested in a year 2000 specification gasoline with 150 ppm sulfur, and a North American type gasoline with 420 ppm sulfur.

Manganese oxide deposits which are exclusively in the form of Mn3O4, a benign form of manganese, are introduced in the exhaust stream from use of MMT, an octane-enhancing, emission-reducing fuel additive. The physical and chemical effect of these deposits on catalytic converters has generated some controversy in the literature. In this paper, we will focus on the effects that manganese oxide deposits have on catalytic converters. The physical effect of these deposits on the morphology of the converters was investigated by B.E.T surface area measurements, scanning electron microscopy (SEM), and x-ray fluorescence (XRF). The chemical effect was investigated with tests using both slave-engine dynamometers and a pulse-flame combustor to probe for differences in catalyst performance. Data from an extensive vehicle fleet which was tested according to a program designed in consultation with the EPA and the automobile industry will be presented.