Engineering Abstracts 1949

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Engineering Abstracts from 1949

Modern Trends in the Development of High-Powered Diesel Machinery.

CARSTENSEN, H. Trans. Institute of Naval Architects, paper read 2 Sept. 1949.

Typical examples are given of high-powered marine Diesel plants of more than 16,000 b.h.p. built between 1926 and 1939. Of these, the double-acting four-stroke engine has been abandoned, and the single-acting four-stroke engine is now used very little for larger ships, though it may be preferred under particularly difficult service conditions because of its simple and robust design, moreover, tests with high-pressure supercharge have shown that its output can be increased considerably. The remaining engine types mentioned are two-stroke engines, single-acting or double-acting, having either loop scavenging or uniflow scavenging. These two-stroke engine types and the four-stroke single-acting engine have been developed into fast-running units whereby any output desired can be furnished by geared or Diesel-electric plants.

In passenger ships the arrangement of the accommodation will determine whether steam-turbine plants, fast-running Diesel engines with geared or electric transmission, or slow-running Diesel engines coupled directly to the propeller shafts will be most advantageous. The Diesel plants, particularly the direct-coupled plants, appear to be the most economical. For cargo vessels and tankers, direct-coupled Diesel plants give the greatest advantages and economies. The possibilities of higher outputs and improved economy are discussed, and the effect of the use of heavy fuel oil in Diesel engines on the relative merits of the plants is considered briefly. Some two-stroke engines of the single-acting crosshead and the double-acting types with uniflow scavenging, and examples of high-powered marine Diesel plants with these engine types for a tanker, an intermediate cargo and passenger ship, and a passenger liner are described and illustrated.

Volume XII, No. 5, June 1949

Crankshaft Damping

The author attempts to give a correct physical explanation of natural damping by torsional vibrations, and also to obtain approximate formulae for pre-calculation of the damping in any given case. The paper describes experimental work with a single-cylinder engine driven by external power, and excited to torsional vibrations by a spring- loaded cam disk. In this way the damping from the moving parts could be investigated separately, and it was found that the damping was almost entirely due to hysteresis in the crankshaft, and oil damp­ ing, due to lateral shaft movements in the main and crankpin bearings, which was directly proportional to the bearing clearance. The paper also gives a simple and practical method for the calculation of damped vibrations in arbitrary elastic systems, and the calculation of hysteresis and bearing damping in a single-cylinder engine. Formulas are given for the total damping in multi-cylinder engines, with or without heavy flywheels, and the results are compared with the measured damping in a number of oil engines in service.—Paper P. Draminsky, read

In this paper the subject of "engine wear” has been limited to