DIESEL ENGINE

a type of internal combustion engine using as a fuel, heavy low grade oils. This engine was first proposed by Rudolf Diesel, a German, in about 1900, its great po ibilities, however, were not realized until after the death of the inventor in 1913. Its high efficiency and simple construction have appealed greatly to engine users and have caused its rapid development and subsequent use, not only on land but also on certain cla es of sea-going ve els. While units as large as 2,400 H.P. have been used in some marine installations, the high efficiency of large steam turbines has fixed about 100 H.P. as the economical limit of size in the average land installation. The speed of a Diesel engine is inherently higher than that of most large reciprocating steam engines, which renders it better fitted for driving the present designs of electric generators. This characteristic has been utilized to advantage in some marine Diesel-Electric drives, and in many land stations, particularly in isolated locations, and where heavy oils are cheap and abundant. The Diesel engine operates on a four phase cycle (commonly called four cycle), the object being to bring about combustion of the fuel, and therefore the application of heat at or near constant temperature. The cycle is as follows: A charge of air flows into the cylinder during the aspiring stroke, where it is compre ed (without much lo of heat) to a very high pre ure, during the compre ion stroke. The inlet valve is now opened and the oil fuel is forcibly injected into the cylinder, where it immediately becomes ignited, due to the high temperature of the air, caused by the high pre compre ion. Combustion now takes place at approximately constant temperature, the piston advances, and the expansion of the gases, up to the point where the fuel is cut off is nearly isothermal. From this point up to the point where the exhaust valve opens, the temperature of the gases falls off. The exhaust valve now opens and the pre ure falls off to that of the atmosphere, the expulsion stroke takes place, and the cycle starts anew. The four phase cycle makes nece ary the use ofa relatively large and heavy flywheel to give a minimum torque and speed variation during a cycle. While the cylinders of this engine must operate at a comparatively high temperature, water cooling is resorted to, to some extent to prevent overheating of the parts. It is nece ary to start these engines by revolving them by some external source of power; when the temperature at the end of the compre ion stroke is great enough, the fuel is turned on, and the engine runs under its own power. The weak points of the engine are, its heavy flywheel, its non reversibility and the nece ity of external power for starting. Some of these objectional features are eliminated in some of the recent ‘semi-diesel’ engines.