Why the Oil Engine Must Progress A GENERAL review of
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the development of the compression-ignition engine during 1936 was presented on Wednesday before the Diesel Engine Users Association, and has been pub lished by that -body. It deals with practically every phase of the subject, those which particularly concern readers being the position with regard to agriculture and road transport. In the introduction it is pointed out that there are some 120 concerns in Britain making oil engines of one type or another. It also mentions that it takes the best part of 250,000 to develop and get ready for the market an engine that shows merit on paper.
Theaggregate capital invested in or loaned to the British oil-engine industry and its ancillary connections is about 2'75,000,000. An entirely new and self-contained organization put down for the specific purpose of making oil engines of a novel design and versatile construction requires about 21,000,000. This is obviously an uneconomic figure, because production costs are probably not less than 23 10s, per h.p. against a current selling price of a little more than 24; moreover, oil-engine practice must remain progressive, hence experimental charges continue, although perhaps heavier than need be.
The major steps are first to ensure injection at the correct moment and to burn at the proper rate a very minute amount of oil fuel ; secondly, to change the expansive force of the gases to steady mechanical effort.
These simple facts have not prevented the Patent Office from being stocked with innumerable ideas, gadgets and devices—a drain, from every point of view, on the financial resources of the manufacturer, an addition to the selling cost, and a refmement of a value hardly commensurate to the likely improvement in the running or reliability of the engine. The solution is more co-ordination, pooling of experience, and standardization, not only of fittings and accessories, but even of cylinder dimensions and engine parts.
The total horse-power developed by liquid fuel is about 300,000,000, divided as to industrial power, 5,000,000; marine propulsion, 12,000,000; road, rail and air transport, 280,000,000; unclassified, 3,000,000.
" The capacity of the British oil-engine industry is about 10,000,000 h.p. per annum, or about one-tenth of the world's requirements, and if we assume that the major progress is due to a change-over from petrol to oil fuel (at present a ratio of 3 to 1), the era of the oil engine is only just commencing.
Oil Engine Alters Economic Outlook, For transport purposes by water, rail, road and air, the oil engine has done Much to alter the economic outlook. For road transport, commercial and pleasure, the British industry remains in the forefront of oil-engine manufacture. Whatever restrictions in legislation, burdens in the way of unstable and ever-increasing fuel costs—in fact, whatever the handicap, this type of power unit has come to stay. Home-made fuels are being marketed, although there are technological reasons for a time-lag in their commercialization; but they are bound to come and with a magnitude that must have the widest beneficial effect on our economic position, nationally and internationally.
In the sphere of design and research, there has been little development in combustion-chamber design during the past year or two, with the exception of some variations of form in that group of which the Ricardo Cornet and Oberhansli are notable examples, and in which the fuel is injected into a, separate chamber..
Considerably more research has taken place into the subjects of ignition and combustion. This work hai been of two kinds—first, with the object of laying down satisB36 factory standards of comparison between various fuels; secondly, the more fundamental question of the mechanism of ignition and the conditions which determine ignition lag and the subsequent rate of rise of pressure.
Farmers are not usually born rnechaffic.s, and the most important quality of any machinery for them is that it shall stand up to hard work without breakdown and be easily repair able.
The attention and repairs required by an oil engine of the comparatively highspeed type have. not been so well • known in country districts as they are for a petrol engine, or for its first cousin, the paraffin engine. For this reason many farmers have been shy of oil engines in spite of their great economy. This state, however, is passing. Farmers are finding in practice that oil engines are not so difficult to maintain as they thought and they obviate some of the well-known bugbears, such as crankcase dilution and ignition difficulties.
The main power requirement is the tractor, and the farmer has a choice of British-made oil-engined tractors to meet his needs. The load on a farm tractor is variable. Considerable power is needed for ploughing and cultivating, but much of the farmer's work, such as harrowing or driving barn machinery, is quite light, and here the efficiency of the oil engine on light loads is a great advantage.
Special reference should be made to one type of engine produced for tillage. These great machines, operated by contractors in various parts, have, until now, been powered by German-made engines, but a British concern has produced a special engine for the purpose to run at 900 r.p.m. Dust is very detrimental, and for agricultural work efficient air cleaners become most important.
Progress in the Sphere of Road Transport.
During 1930 the expansion in the number of oil engines in use for road transport, which has been such a noteworthy feature of recent years, was fully maintained in the case of passenger vehicles, but was less satisfactory in the goods range. The figures concerning their numbers and use have alreadybeen published' in The Commercial Motor, and it is unnecessary to repeat them.
It is pointed out, however, that the reduced risk of fire, the innocuous nature of the exhaust fumes, the greater mileage per gallon and the lower operating costs of the oiler as compared with the petrol engine; together with the great reliability and robustness which have now been attained by the oil unit, should prove overwhelming arguments to operators for the engine to be adopted for the majority of the work of public road passenger transport.
Bearing trouble is now much less than formerly. Steelbacked white-metal main bearings are widely used, with big-ends in which the upper half is made of aluminium alloy and the lower half of white metal.. A lead-bronze alloy for both main and big-end bearings gives satisfactoryperformance, and if the cost were reduced it is considered that its application could be extended. Where aluminium or lead-bronze alloys are used, the crankshaft journals should be hardened to prevent excessive wear and to avoid undue damage in case of seizure.
Little Trouble with Pistons and Cylinders.
Aluminium-alloy pistons are used practically universally and little trouble is experienced with them. Pistons have recently been tried with two scraper rings below the gudgeon pins, and excellent oil-consumption figures have resulted. The wear on pistons is found to be small, and they may run from 120,000 miles to 150,000 miles, after which there is danger of failure due to fatigue.
Excessive wear on cylinder liners has largely been overcome with the introduction of nitrogen-hardened cast-iron
types of about 950 Brinell. With these it is possible to obtain a '' wear "figure of from 20,000 miles to 25,000 miles per .001 in., which compares favourably with the figure of 6,000 miles for the same amount of wear in the case of an ordinary cast-iron liner of 450 Brinell. It is, therefore, possible to obtain 100,000 miles running from the original liner, after which it may be ground to .02 in. oversize, and a further 50,000 miles obtained. Hardened piston rings are used with such liners.
A new process known as the Listard is now available. In this chromium is electrically deposited on the cylinder bore, giving a surface of great hardness and durability. Exhaustive tests in service have not yet been made, but, so far, it would appear that an increase in cylinder life will be obtained.
With the indirect-injection engine it is necessary to change the sump oil completely once a fortnight, or after about every 2,000 miles of running, owing to thickening by carbon formation, It has now been found possible to reclaim sump oil by forcing it through filter pads of closely compressed paper, which remove the minute particles of suspended carbon.
There has been no real cpange in the methods of dealing with atomizers and fuel pumps. Treatment of the fuel by passing it through a centrifuging machine before issue to the vehicle, and then through an efficient filtering system before reaching the engine fuel pump obviates frequent trouble from atomizers. This practice is more important on a direct-injection engine, where the nozzle holes vary from .008 in. to .012 in. in diameter.
• The maintenance of oil engines has been reduced to a routine similar to that for petrol engines, and 'few difficulties are experienced, It is found that valves usually require regrinding at 15,000-mile intervals, whilst a heavy dock, including examination of bearings, pistons, etc., is necessary at 45,000 miles, and complete overhaul, includ ing crankshaft grinding, at, roughly, 90,000 miles. With the reduction in the price of spares and increased life of liners, the cost of the overhaul of an oil engine is no greater than that of a petrol unit, being about .2d per mile.
By far the most important property of an oil is its ability to effect lubrication without building up adverse decomposition, products under the influence of heat and oxidation. The greater the lubricity retained the better, but sacrifice of some degree of oiliness is justifiable if a cleaner operatini oil is thereby obtained. Generally, the more oily an oil the greater is its degree of stability. Oils compounded with a proportion of fatty lubricant are less used now than formerly, despite their higher lubricity. With high piston speeds there is a pronounced tendency to employ less viscous oils.
Improvements in Lubricants.
Big steps have been taken in the manufacture and refinement of mineral oils. These steps have consisted, chiefly, in the discovery of how to exclude from the oil the less stable parts of the crude. Thus a wider range of oils becomes available for blending purposes. The most important advance has been that of solvent refining. Briefly this consists of the removal of the least desirable substances by means of immiscible or partially miscible solvents of a non-hydrocarbon nature. In one case the extractive solvent is combined with liquid propane and removes all asphaltic materials. Solvent-refined oils are particularly stable towards heat and oxidation. They also possess high viscosity indices.
[We are afraid that the Association is somewhat on the optimistic side in its figures concerning the selling price of high-speed oil engines. We would have placed these at between £5 and £6 per h.p, although reductions will doubtless become possible with increased production.