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CLEANING THE OIL AND THE AIR.
Page 102
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Devices Which Reduce the Frequency of Overhauls and Lengthen the Life of the Power Unit.
TITE importance of using a good lubricating oil has been stressed so often that it is now generally recognized, but except in the case of the engines with special lubrication systems, such as that employed on the wellknown 32 ti.p. Albion, the owner of the vehicle cannot do more than drain and refill the sump occasionally, knowing that the engine will use the oil again and again in the interval. This is not of much moment if the engine be in good condition, and if it be working in districts and over roads which do not produce an exceptionally dusty atmosphere; in the ease of an old engine, however, working in dusty conditions, the oil in the sump becomes contaminated very rapidly and the rate of wear is apt to be excessive. It follows that there are many intermediate conditions where some system of rectifying the oil and cleaning the air entering the carburetter would be beneficial, if not absolutely essential.
The two things really go together, because it is only when the oil has become contaminated and thinned by mixing with a certain amount of fuel that the grit which enters the engine through the carburetter gets a real chance of doing damage to the bearings. This is because the film which a thinned oil can maintain between the bearing surfaces and the journals is not so thick as one which would be produced by fresh oil, so that grit particles are more easily able to span the gap and set up an abrasive action.
The air cleaner also serves to reduce the rate of carbon deposit, as, incidentally, do certain types of oil rectifier. The action of the air cleaner in this respect is due to the fact that quite a considerable proportion of the so-called carbon which forms on the combustion chamber and piston crown is actually composed of particles which have been sucked in with the 'air through the carburetter. Certain oil-rectifying systems, such a.s the Skinner, also tend to reduce the rate of carbon deposit because they are so arranged as to prevent the oil from working up past the pistons.
Various types of air cleaner workin"g on different principles are now on the market. One of the simplest contains a series of sheets of filtering rmaterial, through which the air passes, leaving the dust behind, and these must periodically' be replaced. Another type consItts of a casing embodying a number of fixed and inclined vanes, this casing being fitted to the air intake of the carburetter. In passing through the cleaning cylinder, the air undergoes sudden changes' in direction of flow, which causes the gritty particles to be thrown out of suspension in the air stream and trapped. In yet another device, the air entering the cleaner drives a small fan at a high speed and then passes through a D32 series of whirling vanes, driven by the fan, which produces a swirl and causes gritty particles to be thrown outwards by centrifugal action.
In considering the fitting of any type of air cleaner . it is Important to specify a size adequate to the capacity and speed of the engine, because, otherwise, the device will create a resistance to air fiow, sufficient to reduce the power output of the engine at its higher rates of revolution.
It may be argued that, at any rate in England, modern roads are so thoroughly treated that dust has been practically eliminated, so that air cleaners are 'hardly necessary. Against this may be set the fact that the mileage which vehicles are expected to cover between overhauls is getting greater and greater, so that the duration of time in which dust is continually entering the engine is much longer than was once the case, even although the actual concentration of dust in the atmosphere is much less. Again, it is, of course, easy to understand that for certain agricultural purposes and for colonial work, an air cleaner might be considered almost as an essential.
Turning to the oil rectifier, this device should really serve two purposes; first, it should remove the tiny particles of grit, metal and carbon present in the oil, and, secondly, it should subject the oil to a temperature sufficiently high to drive off in the form of vapour the fuel which it contains. Tests have shown quite conclusively that an engine fitted with an oil rectifier of this kind can be run for many thousands of miles without any attention beyond that of adding oil to make up the level from time to time, frequent drainage and re-filling being altogether unnecessary.
The problem of removing very minute particles from the oil is difficult enough in itself, and this difficulty is enhan,ced by the fact that whatever form of filter is used it must not be allowed to impose any great resistance to the flow of the lubricant. These difficulties have been very cleverly tackled by Dr. Hele Shaw, whose filter is made by Streamline Filters, Ltd. (London). This device was described in The, Comm-ercial Motor some time ago; briefly, the principle consists of using a set of specially treated paper washers packed closely together, the oil passing through the minute spaces between each washer and the next.
The particles. all cake together on the outside of the washers in the farm of a sludge, and special provision Is made for clearing this sludge away by means of a few strokes from an air pump. This filter has been built as a unit with a rectifier which heats the oil and drives off the fuel contained in it, thus making a most efficient outfit.