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5th February 1937
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Which of the following most accurately describes the problem?

A Wide Variety of Combustibles Has Been Made Available and Engine Manufacturers Have Developed Units That Can be Readily Adapted to Run on Liquid, Gaseous or Solid Fuels

GERMANY is rather poor in fuels suitable for internal-combustion engines. The only products available in abundance are coal of different kinds and timber. Both these, however, involve more or less complicated processes to fit them for use in vehicle engines. Of the two million tons required in 1935, no less than 53 per cent. had to be imported from foreign countries, but, by intensive effort, it is expected that imports will decrease to 26-28 per cent. in 1937.

By various processes, no fewer than 980,000 tons of home-produced petrol are expected to be obtained during this year, whilst the estimated quantities of benzole and alcohol are 450,000 tons and 190,000 tons respectively. In addition to these, 5-6 per cent, of the German fuel requirements will be met by gases of different constituents, which are at present used on a small scale for transport purposes.

It is clear from the above statements that a host of new problems for engine designers has suddenly arisen, as a result of the variety of combustibles and the widely different conditions which each of them demands. The tendency to build engines capable of consuming all kinds of fuel that are available, is manifest, but a matter of considerable difficulty arises because the latter differ physically.

Before discussing details of design depending on these conditions, however, it would be as well to digress for a moment and to consider the fuels under consideration.

One must distinguish between three separate groups of combustibles— liquid, gaseous and solid. The second group has to be divided into two further classes, in accordance with their capacity for being condensed into a liquid by low pressure. Those which are liquefiable we will describe as liquid or rich gases, and the others as permanent gases.

The following is a list of combustibles that are either now used in B24

Germany, or are in the experimental stage:—

Liquid fuels—petrol, benzole, alcohol and mixtures thereof, and methanol, gas oil and lignite oil.

Gaseous fuels—liquid or rich gases: BV-treibgas, Leuna-treibgas, Deurag • (these three are mix tures of butane and propane and condense at a pressure of '6-15 atmospheres) and Ruhrgasol. Permanent gases—cokeoven gas, lighting or town gas and methane; these are compressed in gas cylinders at up to 200 atmospheres.

Solid fuels — wood, charcoal, brown-coalcoke, anthracite, etc.

" The output of these widely different fuels in an internalcombustion engine is subject to considerable variations, even when the compression ratio is altered in accordance with individual requirements. The following figures, referring to a BUssing-NAG 66 h.p. petrol engine, show clearly what might be expected from the various combustibles and what mileage might be covered with a normal supply:— It will be seen from this comparison that the rich gases marketed under the names BV-treihgas, Leuna-treibgas, Deurag, etc., give a power output practically as high as that for petrol, and at a lower consumption rate. Methane is not so effective or so valuable and the mileage from two gas cylinders of it is only some 35 per cent, of that obtainable with a rich gas. In the case of town or lighting gas, the conditions are still worse in every respect. The number of cylinders has at least to be doubled, if a reasonable mileage be desired without too frequent filling up.

Coming now to the last two columns of the table, it is clear that the additional weight of a producer-gas plant is a serious impediment to its more general adoption. Moreover, the power

loss varies between 30 per c6rt. and 40 per cent, and is, in itself, a serious matter. Attention must also be drawn to the fact that producer gas requires a compression ratio of 8-10 to 1, which is considerably more than that needed for the petrol or gaseous combustibles mentioned. •

The situation arising from these considerations may be summarized as follows:—For reasons of additional weight and space, producer-gas plants are suitable only for commereial vehicles rated at over three tons. On the other hand, they have the undoubted advantage of not being Confined to employment in specific districts, because wood or charcoal, the two chief combustibles for producer-gas plants, can be obtained at any of the 700' stations throughout the country. The loss of power, to the extent of 30-40 per cent., might, at least in new vehicles, be equalized by the choice of a larger engine.

The state grants a subsidy of 600 marks (£50) for every new producergas plant installed in a new vehicle. In addition, an allowance of 50-75 per cent. of the normal tax is granted to owners of machines equipped with such plant_ These privileges have not Jailed to cause a considerable stimulation, and on July 1, 1936, there were some 798 goods vehicles and 48 buses equipped with producer-gas plants. No new statistics have been published since this census, but it is reasonable to assume that the number has now been nearly doubled. The compressed-gas system may be expected to achieve greater popularity, although it is obvious that its use is confined to a restricted area.

The designations BV, Leuna, and Deurag are geographical rather than chemical terms and each is more or less significant of a German coal centre. Vehicles running on any of these homeproduced gases enjoy the same allowance as those with producer-gas plants, but there is another reason why this source of power is favoured, i.e., the ready adaptability of the engine for use with petrol, because no change in compression need be made.

If these fuels be classified according to compression ratios, we obtain the following arrangement: —From 5 to 6.5 to 1—petrol, benzoic, alcohol and their mixtures and all liquid and permanent gases carried in gas cylinders; from 8 to 10 to 1—all producer gases; from 12 to 19 to 1—gas oil, lignite oil and methanol.

It is clear, therefore, that, generally speaking, petrol engines will be used for the transformation to gas propulsion. However, in the case of producer-gas plants, the use of such units has not proved entirely successful, for not all petrol engines are capable of standing the higher compression. Nevertheless, conversions to producer gas have been made in hundreds of cases, the higher ratio being obtained by fitting longer pistons, mostly with domed heads. Sometimes an additional battery and a more powerful dynamo are also necessary.

Owing to the unsettled state of the German fuel market, manufacturers are developing engines that can be adapted to any kind of combustible. It is easily understood that the safest way to attain such an object is by proceeding from the engine type having the highest stresses—the compressionignition unit. The chief German makers regard this problem as an urgent one, but by no means in every case, is the existing design considered to be suitable.

The Deutz concern—a pioneer of oil and gas engines—builds a unit of the pre-combustion type with a vertical chamber to one side of the cylinder. This maker does not hold with a compromise and, for conversion, advises a change of the entire cylinder head.

• The valves and actuating gear, together with the exhaust system, are unchanged, but a head of new design, affording a compression ratio of 9 to 1, is substituted. Besides this, the filter and injection pump have to be replaced by a governor and a magneto or coil-ignition system. The cost amounts to some 18 per cent, of the complete engine. If the same power output as the engine developed on oil fuel be desired, new cylinder liners and a new set of pistons of larger diameter can be fitted.

Mercedes-Benz engines have an inclined ante-chamber placed on one side of the cylinder, and this concern claims to have designed a " universalmotor "—a unit adaptable for all kinds of fuel without change of cylinder head. Here, again, the oil engine is the basic type, and if the conversion be to producer gas, larger ante-chambers are substituted for the original ones. These afford the correct compression ratio, it being understood that the enlarged ante-chambers form part of the combustion space.

If conversion to petrol or rich gas be required, shorter pistons have to be fitted, in addition to the alterations mentioned above. In both cases a new ignition system has to be provided. the magneto or distributor unit being driven from the injection-pump drive. Sparking plugs, of course, replace the heater plugs used on the oil engine, whilst a carburetter is coupled to the inlet pipe.

In the case of the Bussing-NAG the method practised is to replace the ante-chamber by a plug, whilst the necessary compression ratio is secured by using shorter pistons. It might be mentioned, in this connection, that Bussing-NAG engines running on producer gas have a compression ratio of 8 to 1 when derived from petrol types, and 9 to 1 if they be convertedoil units.

The Lanova system is employed in the Henschel, the combustion chamber having the form of a figure 8, and the sprayer being located opposite the double air cell. For conversion to producer gas, the sprayer and cells are removed and substituted by a stopper and a plug. It is claimed that the special shape of the combustion chamber is exceptionally well suited to gas or petrol service. For producer gas, a compression ratio of 10 to 1 is secured simply by the elimination of the double cell, whilst for rich gas or petrol shorter pistons have to be installed.

These ingenious efforts are to meet a specific requirement and the alterations are made to some extent at the expense of general efficiency. They are, however, none the less interesting.


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