The application of the Diesel, or internal-combustion, principle to mobile units in Europe, has been up to a maximum of 1,500 h.p. at 450 r.p.m., producing a draw-bar pull of about 45,000 lb., with reported overall efficiencies, when operating at between 500 and i,000 h.p. of from 21 to 27.5% thermal efficiencies. The "Diesel-Hildebrand" combination internal-combustion and steam locomotive consists of a Diesel and a steam engine, the steam being generated in a boiler utilizing the Diesel engine waste heat. It has the same inherent disadvantage as the "Still" system, for when the maximum power is required for starting and accelerating a train, no waste heat is available, and the boiler must be heated by oil or some other fuel. Likewise, when the Diesel engine is operated at moderate loading the steam engine is of little use due to the comparatively cool Diesel engine exhaust gases. The Russian State Railway Diesel locomotives, one equipped with an electric and one with a geared drive, have but partly demon strated their economic utility. The Esslingen Diesel, now under construction for the German State railways, makes use of a Diesel driven air-compressor, the air being compressed to about lb., and during the compression being cooled by injected water, after which it is heated to F by the Diesel engine waste gas, and then expanded in two ordinary air-driven locomo tive cylinders. This. system may be a step toward a satisfactory Diesel-direct drive motor car or locomotive.
For certain services and locations, the self-contained Diesel engine driven generator-storage battery (for peak loads) trolley motor generator battery charging smaller motive power units may also be useful. During recent years some of these locomo
tives have been built for switching service, as they are primarily intended for passenger and freight yard operation where locomo tives are required to operate through the city streets. The New York Central has put one of these locomotives in its New York City West Side service.
With respect to gas-electric locomotives and cars, and par ticularly the gas-direct mechanical drive equipment, these will have their place for certain classes of small unit suburban, inter urban and switching movements, but the use of gasolene will always create an undesirable hazard and expense for a service of this kind. For highway motor cars and trucks, we can look for ward to the development of a more economical fuel oil burning steam motor as a solution of the existing complicated and ineffi cient gear shifting and power transmission, and to dispense with the exhaust poisonous gas and noise. The self-contained power unit feature of the Diesel engine is an advantage over electrifica tion, but until a reliable engine of the double-acting type, with more simplified starting and reversing devices, in combination with direct drive, can be developed, its application to rail service in the United States, where adequate suitable boiler water is available, will probably be limited to the smaller and slower speed rail motive power units which should be economical where the daily average mileages will reach from 15o to 200 or more miles per day, and where the rail passenger train business will not justify the operation of steam units. (J. E. Mu.)