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With the new emphasis to reduce diesel exhaust emissions, there is a greater demand for better diesel fuels. Diesel fuel qualities can be improved either by better processing of crudes, which is expensive, or with the use of additives. To develop additives which can prevent injector deposits or clean up already formed injector deposits, prechamber IDI engines are commonly used. Two direct injection (DI) engines tests have been developed in which effectiveness of additives to keep injectors clean can be evaluated. Another test has also been developed to determine clean up performance of an additive to remove already formed injector deposits in a DI engine can be assessed.

Considerable work has gone into the development of an active diesel injector additive with both deposit keep clean and clean up capabilities. TFA-4681, a high molecular weight polyisobutylene (PIB) derivative with amine functionality, was developed. In testing done with a GM 6.2 liter engine, a Daimler Benz OM-616 engine, and in testing using two 1981 Mercedes Benz 240D vehicles, the effectiveness of this additive was established. Some principals of surfactant theory as they relate to this additive development are discussed. The additive behaves as a surfactant in hydrocarbon medium. According to theory, an additve can act as a detergent (keep clean) by adsorption on a metal surface and, also, as a dispersant (clean up) by forming micelles with deposits. Usually, only high molecular additives are capable of behaving as detergent/dispersants with both keep clean and clean up activity.

A variety of diesel fuels were investigated to develop an injector test to evaluate detergent activity. In this test a 6.2 liter GM engine with indirect injector capabilities was run for either 15 or 50 hr. The injectors were then rated by air flow for plugging. Our results indicated variability due to differences in fuels. A high mercaptan content fuel increased injector plugging. On the other hand, blends of base fuel with 30 or 50% Light Cycle Gas oil (LCGO) had no effect upon injector plugging even though total aromatics, including polyaromatics, and total sulfur contents, primarily thiophenes, increased. A low sulfur content California fuel decreased injector plugging. The results suggested that mercaptans increase injector deposits while thiophenes do not. Some work was also done using two commercially available detergents. Both were effective in reducing injector plugging at proper concentrations (keep clean). Cleanup capability was noted for one of these additives.