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The Position of the Oiler is Assured
Page 84
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Already Ineradicably Established, the Compressionignition Power Unit Can Claim Many Advantages and Will Continue to Gain Ground THAT an increase in the tax upon oil fuel for road vehicles was inevitable was generally recognized long before the announcement that it was to be raised to 8d. was made. Its amount, to the majority of those affected, came rather as a surprise, and the duration of the period of freedom from handicap was largely unknown up to within a short time before the Budget proposals were published.
What the Government would judge to be an Adequate period for the establishment and development of the compression-ignition engine for the commercial motor industry would, it was assumed, be allowed to elapse before the instigation of a system of taxation that was considered to equalize the two fuels, oil and petrol.
Presumably, the Chancellor of the Exchequer has satisfied himself that this period, in the case under consideration, has now been of sufficient duration, and it remains to be seen whether oil fuel will receive acceptance as an equal or a superior on its own merits now that the advantage it has hitherto enjoyed has been removed.
We (1(.., not propose to analyse costs in this connection, as the matter was fully dealt with on Friday last. It is interesting, however, to study briefly the relative consumption rates of the two types of vehicle.
Relative Consumption Rates.
In the accompanying graph the two main curves have been plotted from m.p.g. figures extracted from The Commercial Motor road-test reports over a period of about two years, and; show what should be fairly accurate average consumption rates for various types of oil ,and petrol commercial vehicles of pay-load capacities from 1 ton to 15 tons. The shorter curves have been plotted from a different source, namely, the fuel-consumption rates given in the Armstrong-Sourer table, which was reproduced on page 384 of our issue for last week. The graph clearly reveals that the percentage advantage of the oiler increases with the load capacity of the vehicle.
Apart from matters of consumption, however, there are many other con siderations. It is, we believe, very appropriately, about 25 years since Dr. Diesel started experiments with oil engined commercial motors. Progress at first was extremely slow and, not until the present decade, was the com pression-ignition system satisfactorily employed in high-speed power units for road transport. Since the first really successful application, however, the type has advanced with rapidity.
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Whereas unreliability, only a few years ago, was a big difficulty, there are now many operators who can produce figures to show that the oilers in their fleets are cheaper to maintain and are in dock for fewer hours per year than their petrol vehicles.
Among the mechanical difficulties encountered were bearing failures, injection-system troubles, noxious exhaust gases, knock, vibration, inflexibility, and dilution or contamination of the lubricant.
A big step towards the rectification of the first fault was taken by the intro(Welkin of lead-bronze big-end bearings. At least one manufacturer, however, overcame the trouble by running its duralumin connecting rods directly on the crankshaft. Well-designed bearings, lined with suitable white metal, are, nevertheless, considered by some engineers to be the most desirable, and are used in a number of engines. There is little doubt that a proportion of the earlier troubles were caused by attempting to incorporate too much of the maker's existing petrolengine design in the new oil engine. A notable example is in the length of the crankshaft.
Many inventors directed their energies towards injection pumps and valves, but it must be admitted that there is still only one make of this equipment that is definitely in the forefront. It and a number of others which are highly efficient and completely successful in operation have been improved vastly upon earlier designs, and, apart from the development of more precise manufacturing processes, the improvement in fuel purity Pul in the precautions now taken to prevent the admission of foreign matter to the pump, have contributed to the solution of many of the injection problems, Efficient Head Design.
Combustion-chamber design has played the leading part in eliminating or diminishing practically all the remaining weaknesses mentioned above. Complete combustion of the fuel, at a controlled rate, has cleared the exhaust, so that now one can rarely detect an oiler by eye or nose, has silenced the characteristic by which it was identifiable by eat, and has done much towards reducingvibration.
The exertion of high torque over a wider range of revolutions has, in the same way, been brought about, whilst the efforts of gearbox designers in providing five, six and eightaspeed transmission systems, the development of hydraulic couplings and torque converters, have greatly aided the roadtransport application of the oil engiiie. The second and third of these, incidentally, have been notably instrumental in vibration absorption.
Dilution and sludge formation in the lubricating oil were serious hindrances to oil-engine progress, but the combined influences of better head design, improved pistons and rings, and more suitable lubricant have mitigated this evil, whilst the acquirement by users of the habit of regularly changing the crankcase oil at the appointed intervals has reduced its harmful consequences.
In this connection, it is worthy of mention that one explanation of the lack of progress made by the two-stroke oil engine is the tendency of certain types to make use of their lubricant as fuel. One would not dream, however, of predicting the complete disappearance of the two-stroke engine from the commercial-motor world.
More Pay-load and Safety.
Before concluding, two highly important points must be named. The one is the range of the oiler. When maximum weights are legally limited, fuel weight represents a financial loss. Our graph shows that the largest machines can cover, on a tank full of oil, more than twice the distance of which the petrol machine is capable on the same quantity. The other is the non-inflammability of oil fuel. Accidents too often result in fires. Petrol is a potential danger in this respect; oil is a certain safeguard against such a dire eventuality.
At the Scottish Show in November last, several promising oil engines made by prominent manufacturers were on view. Certain of these are not yet fully out of the experimental stage. We sincerely hope that those responsible will not be discouraged by the tax imposition, for the number of units of this type and of proprietary, oil, engine(' vehicles on the British market is not yet great enough for there to be no room for more, and the lead which this country holds must not be lost. ,