Coking and microcoking: Tools for evaluating and developing lubricant additives

Abstract

AbstractTwo tests for evaluating an engine lubricant's tendency to form deposits at high temperature have been developed by a working group of the GFC,Groupement Français de Coordination (French Coordination Group). set up to establish laboratory pre‐selection tests. The first is a new static microcoking test where the oil is deposited on an aluminium alloy plate and submitted to thermal conditions similar to those found in the piston ring zone of an IC engine. The results are analysed to determine the temperature at the oil's thermal stability limit and to evaluate the quantity and nature of the deposits in the form of varnish, according to a grading system based on the CEC M‐02‐A‐78 method of gauging engine cleanliness. The second is an improved panel coking test in which a thin film of oil of a given volume is fed on to a stainless steel panel, at high temperature, and the deposits formed at the end of the test are evaluated, again using the CEC rating method, in terms of quantity and type (carbon or varnish).In addition, a video system has been designed to grade the micro‐coking panels through colour recognition. This not only allows visual grading to be faithfully reproduced but also eliminates the subjective element of colour grading. The results obtained with the ‘Video‐Rater’ constitute a first step towards computer‐assisted grading of engine parts.