THE COMING OF THE LIGHT OIL ENGINE.
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Some Notes on the Progress which has Been Made During the Past Few Years and the Possibilities of the Future.
THE idea of using heavy oils in the engines of motor vehicles is as old as the motor industry itself. lip to the present, progress in this 'direction has been exceedingly slow, but changed economic conditions in certain European countries since the war have rendered economy in fuel costs of such importance that a fresh impetus has been given to the heavy-oil-engine movement. The Benz small Diesel, the French-Italian Bagnub semi-Diesel semi-Diesel and the successful Peugeot-Tartrais engine, all of which have been described in The Commercial Motor, are the forerunners of a great change in automobile engine design, particularly in connection with the industrial vehicle. It is not a rash prophecy to suggest that within the next 15 years the majority of commercial vehicles will be fitted with some form of light Diesel or other type of heavy-oil-using engine.
The problem of the successful employment of oil fuel in automobiles is a curious one. At first sight the affair would appear to be simplicity itself. With the ordinary petrol engine it is only necessary to heat up the induction piping and carburetter in some way, or fit one of the numerous " vapilrizers "which can be purchased in the open market, and the engine will run with apparent success on paraffin or other heavy fuels. In many cases the existing carbu retter can.be used, and if the engine be started up on petrol it will continue to run fairly regu larly when turned over to a heavier fuel. With a little care in the matter of carburetter adjustmeiat and correct heating, surprisingly good results may be obtained, especially on the test bench. These results, moreover, are certain and immediate. Why is it, then, that oil vaporizers and the use of heavy oils in general as fuel for automobile engines have hitherto proved almost entire failures from the commercial user's point of view? There are several reasons. The first is that, however well the particular vaporizing arrangement fitted may appear to function, a certain proportion of the fuel will refuse to burn. Returning to its liquid state, this unburnt fuel will find its way down the cylinder walls and mingle with the lubricating oil. The evil effects conseqfient upon this will extend to all the working parts of the engine.
The second trouble is found in relation to slow running and acceleration. However well the engine may behave on the test bench, it will usually refuse to run slowly under road conditions. Acceleration, moreover, will be noticeably poor, although the engin€. may pull splendidly when once it has got into its stride.
With regard to lubrication troubles, these would not occur in engines where the lubrication of the cylinder walls is independent of the main lubrication system.. In this case mingling of fuel with the main oil supply would be impossible, but we are dealing here with the ordinary type of petrol engine in general use.
As the use of paraffin or petroleum in an engine flesigned for petrol always necessitates a• preliminary warming-up process, a three-way tap is usually fitted and a supply of petrol carried on the vehicle. After a very short time it will be found in practice that this tap has a habit of remaining turned to "petrol." , The above are some of the factors which have spelt failure for the paraffin carburetter or oil vaporizer for automobile work. Hundreds of patents have been taken out for vaporizing devices, and scores upon scores of appliances have been launched upon the market with much expenditure of capital. Many of the appliances have been really good and have appeared to function splendidly. For all that, not one of them has proved a commercial success, so far as we are aware.
Now, at last, after a quarter of a century of wasted endeavour in trying to make petrol engines run on a fuel for which they were not designed, the genuine light oil engine begins to wake its appearance. A very interesting new light oil engine is now being developed in Germany ; this is the de Montazet. This engine is of French design, but the inventors, MM. Montazet and Johanson, found such a cold welcome for their offspring in the home country that after three years' work they reluctantly sold their rights to Germany.
In the latter country the engine is being successfully developed both for automobile `work and for commercial aeroplanes. The invention comprises a new system of cold vaporization, the fuel being sprayed into a very high vacuum.
The production of the said vacuum and the admission of a jet of fuel have been arrived at in a very simple and practical manner.
The cylinder of the de Montazet engine resembles the cylinder of any normal petrol engine, and may have either side valves
A diagrammatic drawing of the de or overhead valves. The piston, Montazet engine, in which the lower however, is of unusual design. part of the piston acts as a powerful From the underside of the air pump. piston a cylindrical plunger ex
tends downwards, and this works up and down in a bronze guide.
The guide completely shuts off the crankcase from the cylinder. As a result the underside of the piston functions as an exceedingly powerful air pump. The vacuum is obtained in the annular space surrounding the central plunger as it rises. At the moment when the vacuum is reaching its maximum a few drops of oil fuel are admitted at the base of the annular space by means of a mechanically operated valve, together with a very small amount of air. The fuel enters through a fine-mesh wire gauze, and immediately opposite the fuel inlet the bronze guide is scooped out and fitted with a number of small vanes to assist in breaking up the drops of oil. As the piston descends, a gas valve opens at the base of the annular chamber and allows the gas to pass out into the ordinary induction pipe of the engine. Here the main air supply is taken in the usual manner and the gas enters and leaves the combustion head exactly as in the case of a normal petrol engine.
The degree of vaporization rendered possible by spraying oil into a high vacuum is really extraordinary and the de Montazet engine would appear to have great possibilities.