IN this paper the determination of dilution of crankcase oil from Diesel engines is discussed from the standpoint of a large operator of oil-engined vehicles.
High-speed oil engines may be divided into two classes, viz. those which give rise to little or no dilution and those in which dilution gradually increases, eventually reaching very high proportions. There is considerable evidence that with either class of engine, dilution does not exhibit seasonal variation. In the case of the "non-diluting" types of engines, viscosity increase will determine when the oil must be changed; in the other class, dilution will be the determining factor.
A fundamental difficulty with crankcase oil from either class of engine (but particularly the "non-diluting" type) is that the diluent is of high boiling range and overlaps the lower fractions of the lubricating oil. A survey of methods which might be employed to determine dilution leads to the conclusion that only those based on vacuum or steam distillation are practicable. The first mentioned is rejected as unsuitable for routine purposes, the necessary apparatus being much too complicated. The objections to a steam distillation method are frankly admitted, but are regarded as counterbalanced by comparative simplicity and reasonable rapidity, whilst the degree of accuracy attainable is certainly sufficient for all practical purposes.
The standard A.S.T.M.Dilution A.S.T.M. Dilution Trap Method is shown to be inapplicable, but a suggestion is put forward that the principle might be retained were it possible to substitute a suitable highboiling liquid for the water normally employed.
A method which has been worked out for routine determinations, where both unused lubricating oil and fuel are known factors, is as follows 100 ml. crankcase oil is steam distilled at 210 C.Volume of oil distillate recovered with 200 ml. of water is recorded and converted to dilution by reference to a graph or by formula derived therefrom. Time for complete determination-46 mina. The graph was prepared by employing the method on known mixtures of lubricating oil and fuel, the relationship between oil distillate and dilution following a straight-line law up to at least 50% dilution. The "blank" of the lubricating oil (i.e. oil distillate at no dilution) is an important factor, but for a par ticular oil is allowed for in the graph or formula. Where it is not desired to construct a graph, the same method may be employed, but 400. ml. of water must be recovered. A determination is carried out on the unused oil and then on the crank case oil itself, dilution (D) being calculated by the formula 17 - bD _100b X 100, where d is volume oil distillate from crank case oil and b is volume oil, distillate (" blank ") from unused oil.
It is shown that the "blank" varies with different oils, and whilst an average "