Ideal lubrication requires that the body and the viscosity of the lubricant shall be preserved. The flash-point also must not be appreciably lowered. Contamination seriously interferes with perfect lubrication and consists of (a) fuel end-points, termed “dilution,” (b) water, (c) acid, and (d) solid matter. Each of these is discussed in turn, together with the degree to which it enters into the contamination of the lubricant and its effect in producing wear on the engine.
The average dilution obtained in more than 500 samples of oil during the winter of 1924-1925 showed 39 per cent of fuel and 1 per cent of water, the maximum being 92 per cent of fuel and 3 per cent of water. The result was a reduction of all the original lubricating properties of the oil. Water causes rust, emulsifies a poor oil, is responsible for oil-pump freezing, and combines with sulphur products to form acids. Acid corrosion is evidenced by the “etching” of the crankshaft and excessive wear or stretching of the timing-chain.
The solid matter present in used oil consists of metal particles, carbon and road dust, the effects of which are dependent upon the condition of the oil. Methods of separating out the contaminating material by filtration and evaporation are described, the effective operation of the latter being governed by four factors: (a) temperature, (b) time of application, (c) pressure, and (d) the application of heat.
The principal sources of dilution in an engine are said to be unburned gasoline and condensed vapor, which accumulate on the cylinder-wall. When the engine becomes hot, practically all dilution passes the piston-rings in the form of vapor or blow-by gas. If treated in this condition, very little heat is required to separate the dilution from the oil, but if allowed to pass the piston and enter the crankcase, it becomes cooled to the temperature of the crankcase and mixes intimately with the oil, so that the time required for the removal of liquid dilution is more than four times that required for its separation when in the vapor form obtained from behind the piston-ring. The desirability of intercepting and removing dilution near its source is therefore apparent.
The results of tests made with and without the use of a rectifier are shown in tables and curves. Prevention of dilution is said to have resulted in the elimination of all excessive engine-wear, the reduction of the up-keep expense, the doubling of the life of the engine, and improved engine-performance. The recommendation is made that all new internal-combustion engines be provided with suitable equipment for the positive prevention of dilution, for it will then be possible to maintain the viscosity, pour-test and flash-point of a crankcase oil over a greatly increased period.