The adaptation of oil fuel to locomotives was naturally accompanied by similar experiments on steam vessels. Since 1870 steamboats on the Cas pian have used oil fuel almost entirely, and its adoption for both merchant and naval vessels has gradually spread to all the important maritime countries of the world. Two-score or more of the vessels in the fleet of the Shell Transport and Trading Company, an English concern, use petrole um exclusively with unqualified success and valua ble economies. All local vessels on the California coast, and many of the large ocean-going steamers sailing from San Francisco, burn California petro leum with the best of results ; nearly a hundred and fifty vessels of all classes from that port are now fitted with oil burners. Important steamship lines, such as the North German Lloyd, Hamburg American, and China Mutual, have already intro duced petroleum into their fleets either as an aux iliary or as the sole fuel. As an auxiliary fuel it has also been adopted in our own navy and in the navies of the principal countries of Europe, the great advantage being that, in case of emer gency, it gives a means of suddenly increasing the fires and using full steam almost immediate ly, simply by turning the oil into the injectors. Many of the newer battle ships, therefore, are fitted with furnaces to use both coal and oil. But the greatest triumph of all is in the choice of oil burning furnaces for the new English destroyer, The Swift, recently launched and claimed to be the fastest craft in the world. Believing that oil fuel is to be much more important for naval pur poses in the future, the British Government has sent two experts to examine the Canadian oil fields with reference to their capability of furnishing oil for the British navy. Great Britain desires to control her own supply of fuel oil, to guard against possible trouble in securing it in time of war.
The advantages of petroleum over coal as a fuel are almost innumerable. First, and most valuable of all, is its greater heating power, weight for weight, giving from thirty to fifty per cent more steam with the proper burners; two tons of oil are usually considered to be the equivalent of three tons of coal. For the same power oil occupies less space; thirty-six cubic feet of oil being equivalent to some sixty cubic feet of coal.
Oil is easier to handle and easier to transport ; a locomotive using oil can take on 150 gallons in a minute while making an ordinary stop at a station, and a vessel in a port or at sea can be resupplied in half the time necessary for coaling operations, without dirt or difficulty. In the use of oil there is no dirt or dust, practically no smoke, no ashes or clinkers to be removed, no big force of stokers necessary, no sparks to set fires. Oil can be lighted almost instantly and is under perfect regulation ; a simple turn of the oil valve bringing response to any demands, while as soon as power is no longer needed the oil is shut off and the expense stops. The economy in this virtue is tremendous, espe cially in locomotives where starting and stopping give constantly varying demands on the fuel re quired.
The chief difficulty in the way of the general use of oil fuel on board vessels is found in the uncer tainty of securing supplies where wanted. Coal ing stations are located in every quarter of the earth, but the places where fuel oil can be had are still few and widely scattered. Therefore, until the storage of supplies becomes general at the im portant ports of the world, the adoption of oil as the only fuel on naval stations would entail too many risks, since the supply might be cut off in time of war. In the case of merchant vessels ply ing between definite ports, this objection does not present any serious obstacle, and the many ad vantages of oil fuel are rapidly being put to practi cal use in vessels of every description.
The most widespread use of petroleum as fuel, however, is not in locomotives nor steamers, but in the gasoline engine, which, in its varying forms, has been adapted to practically every namable in dustrial process requiring mechanical power. The term "gas engine" is commonly applied indiscrimi nately to all engines which derive their power from the " explosion " of gas or oil spray when mixed with air in a cylinder. This explosion is nothing more than the very rapid burning of the fuel which may be artificial or natural gas, gasoline, naphtha, benzine, or even kerosene, but its sharp report is a familiar sound in every corner of the world. Here only those engines using petroleum products need be considered ; to this class the name gasoline en gine is generally applied from the fact that com mercial gasoline is the chief oil used. Differ ent types of engines use the oil in the form of spray, as a vapor compressed with air, or by con verting it into gas, but the underlying principle is essentially the same. In every case the power is generated by the high degree of heat created, and consequent great expansive force developed, as the mixture of oil and air is fired in the combustion cylinder. This expansive force works exactly like steam in a steam engine, in driving the piston back and forth, the power thus developed being trans mitted by rods and a crank shaft as in other en gines.
Engines depending on this principle of the ex pansive force of air and fuel undergoing com bustion in a cylinder were suggested before the days of steam power, yet the actual importance of this type dates from the perfection of the Otto Gas Engine, only about forty years ago. The last fifteen or twenty years, in fact, have marked the major part of the enormous increase in the em ployment of engines using gasoline, partly as a re sult of the greater ease in securing regular supplies of the oil, but mainly through the application of gasoline engines to automobiles and small boats. These uses suggested the great possibilities which were capable of development, and, as a result, many different engines, varying only in minor details, have been put on the market.