ABSTRACT
The purpose of this paper is to describe a new concept in the detergency phenomenon for engines. It is well known that oil detergency is associated with additive adsorption neutralisation of acid formed and insoluble encapsulation. But bibliography is poor relative to the mechanical properties of the oxidized oil film created during the coking process.
Basic experiments taking a pure base oil and an overbased additived oil show clearly two different mechanical behaviours in the burned oil film. The base oil creates a ductile film very adherent to the substrate. Conversely, the additived film can be very brittle and shows clearly cohesive cracks followed by adhesive film-substrate cracks.
A physico-mechanical model is proposed to explain the role played by the internal stress developed in the film during its gel state. This analysis leads to a very simple thermo-oxidation laboratory test, where mechanical behavior is evaluated by peeling and is correlated with engine detergency.
