Fuels for the Internal-Combustion Engine.
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A Brief Review of Possible Alternatives for Petroleum Spirit.
The steadily-increasing demand for petroleum spirit as a fuel for the internal-combustion motor so much used for selfpropelled vehicles, is prompting many men to strenuous efforts to find some fuel which will advantageously displace Or supplement it. The poesibility of a "petrol famine '' in the near future is not a pleasing prospect, either for the motor manufacturer or user ; and it is imperative that engineers should give serious thought to this question. Petrol is, in many respects, an ideal fuel. It volatilises readily, when exposed to the air, and the vapour thus given off is capable of forming a highly-explosive mixture, which is easily ignited and which, therefore, is less liable to give trouble to the engineer in such matters as carburation and ignition. It is, however, highly dangerous on account of its low flash-point, and, further, it is very necessary that it should be stored in metal vessels : wood is unsuitable, by reason of the fact that petrol does not cause it to swell, and thus ensure that the joints will remain tight, as would be the case with water. The choice of suitable fuels is, practically speaking, very limited, and, for the internal-combustion engine, the principal fuels available for experiment, or for actual use, are : petrol; paraffin ; benzol ; alcohol ; acetylene; and producer-gas. The last of these implies the use ot coal as a fuel, for the type of engine under our notice, and coal is thus brought into the field as a practical competitor of the liquid fuel's which are more generally used. We purpose briefly to discuss the' possibilities of the fuels mentioned above, as we feel convinced that, sooner or later, means will be found to render available one of which the supply is unlimited. In seeking an alternative to petroleum spirit, whether derived by distillation or decomposition, the requirements of both maker and user must be considered, and—a most important r.roperty—any new fuel must be clean and odourless. Up to the present, the one which meets these conditions is alcohol. There are indications that manufacturers are giving consideration to the fuel question, but, so far, no decided progress has been made towards placing on the market a commercially-successful, highspeed, and otherwise suitable engine to run with fuel other than petrol.
Paraffin.
In this country, many experiments with paraffin have been undertaken, and it is satisfactory to know that John I. Thornycroft and Co., Ltd., of Chiswick, will use this fuel on its 2-ton van in the forthcoming R.A.C. trials. It is a well-known fact that the actual calorific value of paraffin is much higher than petrol or alcohol, but the difficulty of vaporising it has been one of the greatest obstacles against its successful use, whilst it has a remarkable tendency to " creep," and to bring the vehicle into a " messy" state. Another unpleasant feature of this fuel is that, at high temperatures, it dissociates into less volatile and unpleasantly dirty components. A very few drops of paraffin, if they get on to Me exhaust-pipe or other hot portion of the engine, will continue to give off a most offensive odour for some time. Other, and more volatile, fuels would instantly evaporate, and leave but little indication of their presence.
Benzol.
Tests have been made with benzol, and it is said that the results obtained will cause this fuel to have an influence on the market in the near future, but we have already questioned the likelihood of any rapid increase in supplies. The qualities of benzol have been known for some time, but active experiments with it as a fuel for the motor engine have been neglected until recently on account of the low price at which petrol was obtainable. It is by no means an ideal fuel, but the possibility of using it has become of interest in view of the opinions which have been expressed by leading authorities on the fuel question, and also because it can he used in existing engines without the need for any modification other than carburetter adjustment. Benzol is one of the bv-products in the manufacture of coal gas, or of coke, but for many years the quantity produced was too small to be of actual service to the motor engineer. The ever:increasing needs of the aniline-dye industry (which uses considerable quantities of benzol) caused the demand to exceed the supply, and it was the establishing of coke " distilleries," where coke for blast furnaces is produced, that supplied the needs for the market, and offered a new method of producing coal-tar, ammonia, and benzol. In Germany, where alcohol as a fuel has been more widely used than in any other country, owing, perhaps, to favourable legislation, benzol is gradually gaining favour on account of its high calorific value and its lowness of price. From present indications, it would appear that benzol is likely to play an increasing part in the fuel question, although the supply is by no means unlimited.
Alcohol and Alcohol-Acetylene.
Alcohol appears to be the only liquid fuel of which there is potentially an unlimited supply. There are, however, many difficulties in the way of its universal adoption as a fuel for motor engines. As at present designed, such engines have not a high enough compr.ssion to use alcohol economically, and, further, they do not give as much power with alcohol as with petrol. Carburation is much more difficult with alcohol, as the fuel does not readily vaporise at atmospheric temperatures, and, therefore, requires special means for effecting this before the motor can be started. It is true that the present type of engine wilt run with alcohol, yet this fuel is not economical, because it already contains such a large quantity of oxygen, and a less quantity of carbon than petrol or paraffin ; it takes, therefore, less air to complete its combustion—in other words, much more of the liquid fuel is consumed for equal powers. The increase in the compression partly off-sets this disadvantage, and it would, perhaps, be worth while designing engines to use this fuel economically. Attempts have been made to get over the difficulties attending its use, and to obviate the necessity of changing the present engines so as to adapt them for the use of alcohol, by combining acetylene gas with the alcohol vapour : the speed of flame propagation, and the pressure generated with this combination, very nearly approach those existing in engines which use petrol as the fuel, but nothing commercial has yet been produced on these lines. The results of Barker and White, who have experimented with this combination of fuels, was given in "THE COMMERCIAL MoTon " in its issues of the t8th April and 2nd May last. The promoters of this system are working on the basis that, as engines are now built for the consumption of petrol, it is much more practical to adapt the fuel to the engine, rather than to adapt the engine to the fuel.
Producer Gas.
Producer gas may be said to be in the field as a motor fuel for the heavier types of commercial motors. Experiments have been conducted in France, with vehicles carrying threeton loads, and the results are said to have been quite satisfactory. Briefly, a gas-producer, or generator, contains a grate on which is laid a layer of coal, and, when this fuel is in an incandescent state, air and steam are drawn through it by reason of the suction which is created by the piston's movement within the engine cylinder. The air and steam corn,bine chemically with the incandescent coal, while passing through the fire, and this results in the generation of a gas which may be burnt in the cylinder of an internal-combustion engine. There are many difficulties in the way of making a satisfactory gas-producer for small-power engines, but it is not unreasonable to expect that the near future will see the introduction of such a plant for use on the heavy commercial motors, where the weights of the plant and of the water required are less important.
That the visible supplies of petrol will not long hold up to the increasing demand is generally admitted, but the question as to what will take its place has yet to be decided. Which is it to be? Paraffin, alcohol, acetylene, or producer gas? Apart from the relative advantages and disadvantages of any or all of these fuels, the question of the moment is, which fuel can be most readily made to meet the conditions demanded by the existing types of engine?