THE DIESEL ENGINE FOR COMMERCIAL MOTORS,
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Some Preliminary Details of Three Engines Developed in Germany to Employ Heavy Oils and Residues.
TWO references have appeared in the columns of The Commercial Motor to developments which have taken place in the design and production of heavy-oil engines for commercial vehicles. Such developments will be of enormous importance when they have been brought to the level which will permit the engines to be manufactured on a commercial scale, but they are still shrouded under a veil of secrecy, although that veil was lifted—very slightly—at the recent Berlin Show, so slightly ,indeed that no representative of a British, American or French journal seems to have lighted upon what we consider to be a very great advance. We admit that, although we knew what we were seeking and, having found it, what we were looking at, we had, the greatest difficulty in getting anything more than the barest information about the exhibits, and, as it happens, we can quite understand the reticence which is being displayed, because, in the case of one concern, very little experience of the particular size of engine operating in particular circumstances has yet been obtained, whilst, in the case of the other concern,-development has proceeded upon two different lines, and there is still indecision as to their relative merits.
Germany is the country where attention has been directed towards the production of commercial motor engines which shall burn crude and heavy oils, residues and such like, because there exists there a shortage of liquid fuels, whilst auseful potential source of such fuels is lignite, a kind of soft brown coal, of which there are very large deposits in Westphalia. It is apparently a " young " coal and not suitable for burning in open grates or furnaces, but from it can be distilled oils with a fairly wide range of specific gravity, including a light spirit which has the characteristic odour of bensole, gas oils and heavier residues. It was considered desirable first of all to make sure of the fuel, and, so, a good deal of research work was undertaken, and the distillation of these liquid fuels from lignite was brought to a commercial basis.
The importance of the subject to us in this country is that, in parts of the Empire, and particularly in Australia. there are these deposits of brown coal, and if suitable engines for burning the distillates from the coal can be provided, countries with such deposits can become self-supporting in the matter of liquid fuel, thus materially helping the fuel situation in those countries which haveto import liquid fuels.
Three of Germany's Leading Concerns.
The three concerns which set to work upon engines that could burn the heavier fractions among the distillates referred to were the Datmler Motoren Gesellschaft, Benz and Cie and the M.A.N. Masehinenfabrik Angsburg-Nurnberg. It will be remembered that there has been an amalgamation in recent months of the interests of the two firstnamed concerns and on thas taking place there was a comparison of notes and the disclosure that each concern had been working upon an engine of the Diesel type for use on heavy road vehicles, the Mercedes company having used a compressor. Ferdinand Porsche, who had come over from the Benz Co., and was now appointed technical direetor of the Mercedes company bad, however, been engaged upon the endeavour to dispense with the compressor, and naturally was biased in favour of the more simple system. It was then decided to proceed with both types and to run them in competition for some months and to come to a conclusion before the Berlin Show of last month. That a definite decision has not been reached is shown by the fact that the Benz type compressor less engine was exhibited in a chassis, whilst the • Daimler type, compressor-fed, was used for demonstration purposes on a lorry running outside. This suggests, to our mind, that the Daimler type is much the more advanced towards the production stage, but that the hopes of the technical staff are pinned to the compressorless type. The Daimler-Diesel engine was first tested quite early in the past year in
a bus chassis. The day was cold, but 7 the engine started at the very first turn under the action of ties starter. With a full load in a single-deck bus. driven by an excellent driver, a speed of 60 -miles per hour was attained, and the engine ran perfectly from
start to finish.. • The engine is on ordinary petrolengine lines except for (1) its high compression, (2) the fact that the charge is self-igniting and (3) the necessary strength in certain affected parts. There is, contrary to what one would expect, little increase in weight A steel head is employed, but the cylinder casting is of iron. There ;s call for a certain amount of stiffening up, the crankshaft is -eiy strong, and new component parts tha add to the weight.are • (1) a twostage air pump driven off the front end of the crank; shaft • (2) an air bottle to store the compressed air ; and (3) a small oil pump. As againstthese additions there is a saving in weight of the magneto, its driving mechanism, wires, switches and plugs, and the bosses in the engine head to carry the plugs ; there is no carburetter and no manifold pine. •
Starting at the First Turn from Dead Cold.
By means of the compressed air a charge of oil is injected through a selective valve into the cylinder which is in a receptive condition (that is to say, with the inlet valve open), and then with a self'. starter (which can be air-driven from the air bottle) the engine is turned until the cylinder,' with its charge, is at full compression when the charge automatically ignites and the engine then starts. Here, as will be seen, is an enormous advantage over previous attempts to run engines on heavy oil, viz, that the engine .pall start from dead cold.
The great trouble in connection with the use of paraffin in a low-compression engine is that the first charge cannot be ignited by the ordinary ignition system, and not until the engine is hot can it run oi paraffin or other heavy oil.
Two other points of advantage, considered from the commercial motor point of view, are that thao charge does not get wire-drawn at high speeds (because there is presure behind to force the oil into the cylinders) and that the mixture does not get upset when the engine turns at slow speeds, as in the case of petrol. The result is that the engine pulls to the very last revolution.
On the matter of control there is complete secrecy, because this will be the crux of patent rights on the system. The fuel consumption is, roughly, in the region of .5 lb. of fuel per b.h.p.-hour--the normal consumption of internal-combustion engines.
The Benz lorry shown at Berlin was a 5-thriller, the engine being described as Of 50 b.h.p. It will run on gas oil, tar oil, petroleum, paraffin oil or any heavy oil. It is compressorless, -with ante-chamber ignition. The fuel pumps, which have a separate piston for each cylinder, deliver the fuel first into an ante-chamber, in which early combustion takes place, and the rise of pressure forces the remainder of the fuel into the main
_ combustion Chamber through a pul Zverizer. In order to start the !'engine, the ante-chamber is heated by means of a heating spiral for a short period. 'After doing this, the engine can be started immediately on heavy oil. It runs at 1,000 r.p.m. In the case of the Benz engine it is claimed that the fuel consumption is lower than with an engine having a carburetter.
The M.A.N.-Diesel engine has apparently been developed with a view to its employment in airships and aeroplanes (where the elimination of inflammable liquid fuels is one of the greatest desiderata). It was shown at Berlin in a 2i-ton lorry chassis with cardan-shaft drive. It is compressorless, the fuel being injected (without compressed air) into the highly Compressed air in the combustion chamber, thus dispensing with any other means of ignition. So soon as we receive fuller information upon the developments of Diesel engines of the small and compact order suitable for commercial lorry and passenger vehicles we will give it immediate publicity. In the meantime we would be glad to know that British designers were at work studying the possibilities of such a system and that manufacturers were considering the advantages that such a system would open up.