Use of Dispersants/Detergents in Diesel Injector Keep Clean and Clean Up Studies 912330
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.
Experimental work on additive T-96A indicated that neither its clean up nor its keep clean activity increases linearly with concentration but levels off at some intermediate additive concentration. This is discussed in terms of a monolayer adsorption of the additive on the injector or deposit surface.
Based upon infrared studies, the deposit surface contains considerable oxidation products such as carboxylic acid, anhydrides, etc. In a first step, the amine function of the additive is thought to react with the acid moities on the injector deposit surface at monolayer levels. In a second step, the additive-deposit compound is believed to be washed off the injector surface by fresh fuel. This explains the absence of additive chemistries on the surface of injector deposits after contact with additized fuel, as indicated by infrared and X-Ray Surface Analysis (XPS) studies.