The first practical internal-combustion engine was that of Lenoir (186o). Two years later Beau de Rochas showed that for good efficiency it is necessary to compress the explosive mix ture before igniting it ; and in 1876 this idea was effectively realized in a successful explosion engine by Otto. The Otto cycle is the standard cycle in automobile, aeroplane and many stationary and marine engines. The fuel used by Lenoir and Otto was coal gas but in 1883 Daimler substituted volatile liquid hydro-carbon fuel (gasolene or petrol) and thereby made the engine available for automotive purposes. The use of less volatile hydro-carbon fuels (kerosene, fuel oil, etc.) was first successfully developed by Hornsby in the Hornsby-Ackroyd engine of 1894. A year later Diesel built his first engine, in which the air is brought up to the temperature of ignition of the fuel by the work of com pression alone and fuel is injected in a finely atomized state after the compression is completed. It is possible to burn in it any fuel that can be atomized by high pressure air injection, by spray ing under very high pressure through small openings, or by other means. It offers the combination of the cheapest fuel and the highest efficiency of utilization. The Diesel engine was slow in development at first because of many practical difficulties, espe cially from heat stresses. Its use in the automotive field is just beginning, particularly for trucks. In the aviation field it is par ticularly desirable in order to diminish the fire risk of the fuel.
The principal uses for power up to about 1890 were for driving shafting, pumps, compressors and hoists, for locomotives and for marine propulsion. With the improvements that had recently been made in the use of electricity the power station appeared. Elec tricity is a means for transmission of power and the only means which is economical for long distances and for complicated sys tems. The earlier power transmission systems by rope drives, compressed air and water under pressure, were too costly and cumbersome to survive. The maximum size of the electrical units installed increased rapidly from about 150 kw. in 1886 to 5,000 kw. in 1900.
The larger the engine the lower is its rotation speed. Large reciprocating engines are complex, heavy and costly, adapted only to special conditions. In 1884 Parsons had taken out a patent for a reaction steam turbine and in 1891 made it into a con densing unit and began to supply it to electric-power stations. In 1889 De Laval introduced the first practical impulse steam turbine. These turbines and those developed from them operate at high speeds of rotation, occupy little space, require no fly wheels, are exceedingly simple, and have high steam efficiencies. The largest unit built up to 1929 is of 208,000 kw. capacity. This is equivalent to 279,00o h.p. or the work of 837,000 horses,
or over 8,000,000 men working eight-hour shifts. Single power plants develop over 1,000,000 kilowatts.
In order to obtain high thermal efficiency it is desirable not only that the maximum temperature of the working substance should be high but also that the amount of thermal energy available at high temperature should be considerable. This condition exists with a saturated vapour because the abstraction of latent heat results in change of state without change in temperature. For this reason pressures of 1,400 lb. per square inch are now being used in a few plants, corresponding to a saturation temperature of nearly 600° F. At the critical pressure the temperature is only a little over 700° F, so that the limit of possible efficiency with steam is nearly reached ; higher efficiencies with external-combus tion engines can be obtained by the use of a combination of two working substances or the so-called binary-fluid system. A large scale installation of a mercury-water system has yielded a brake thermal efficiency of about 35%, which is much more than is possible with any steam plant and practically the same as for a good Diesel engine. This system is still regarded as under development. The natural line of progress in power generation would seem to be the development of an internal-combustion turbine. Unfortunately all attempts along this line appear destined to fail until progress in metallurgy has produced some metal which will maintain adequate strength at high temperatures and also until the compression of the charge can be carried out much more efficiently than is possible with present-day centrifugal com pressors.
The history of the development of power shows a constant striving for greater economy, greater compactness of the units and greater capacity of each unit. The present limits of capacity have already been indicated and they will certainly be extended. The cost of power is now becoming so low that no considerable improvement is to be anticipated. In a steam-turbine plant, with a consumption of r lb. of coal per hour per horse-power and with coal at $5 per ton, the cost of the fuel is of the cost of man-power when labour is paid $5 per eight-hour day. The total cost of power, taking all costs into consideration, is only about of the cost of man-power. In a Diesel engine plant the cost of power is still lower.
See DIESEL ENGINES ; ELECTRIC GENERATOR ; ELECTRICAL POWER IN AGRICULTURE ; ELECTRICAL POWER GENERATION ; ELECTRICAL POWER: NATIONAL AND REGIONAL SCHEMES ; ELECTRIC MOTORS ; ELECTRICAL POWER TRANSMISSION ; INTERNAL COMBUSTION ENGINES ; MOTOR CAR ; PNEUMATIC POWER TRANSMISSION; POWER TRANSMISSION: Vari able Gears; POWER TRANSMISSION: Mechanical; TURBINE: STEAM; TURBINE: WATER; WATER POWER; WINDMILLS AND WIND POWER.