Large Oil Engines, With Special Reference to the Double-Acting Two-Cycle Type

Abstract

Efforts to build large oil engines have been growing in number and in variety of means selected to meet marine requirements, stimulated by the success of motorships and the desire to increase their size or utility in prevailing sizes. Possible stationary applications of larger oil engines have also contributed additional motives and other solutions. Much of this work has not been published and is therefore not as well known to the engineering profession as it deserves by reason of its high quality and the foundation it lays for the future. This paper is concerned with a review of some of this work, with special reference to double-acting engines.

One of the problems considered is that of the possibility of raising the mean pressure in the cylinder to get high horsepower per cubic foot of displacement and without rise of maximum pressure to thereby reduce the weight per horsepower. High injection-air pressures, extra injection air, and supercharging of cylinders are included here in addition to studies of shape of combustion chamber, position of sprayer, and design of spray valve. A second one is that of determining the maximum diameter of cylinder that can be operated at very high or at moderate mean pressures without injury to the metal of cylinder, piston, or cylinder head, with particular reference to the effect of special designs of these parts for resisting heat damage at a given heat-generation rate or the corresponding relation of diameter and mean indicated pressure.

A third problem is that of securing results in two-cycle cylinders as nearly as possible equal to those of the earlier developed and more widely standard four-cycle, to determine how close the former can be brought to half the weight per horsepower of the latter on the one hand, and on the other, for the same size of cylinder and similar engine structures, how close to twice the maximum horsepower of a four-cycle engine it may be possible to build the two-cycle. Still another, from the standpoint of double action of the piston, assuming a given diameter and mean pressure or heat-generation rate established in four- or two-cycle single-acting cylinders, and a construction of cylinder, piston and cylinder head not injured for these values, is that of determining the practicability of making both ends develop the same power in both four-cycle and two-cycle engines. This includes the determination of how close to half the weight per horsepower of the single-acting it may be possible to build the double-acting engine or how close to twice the maximum horsepower of the single-acting it may be possible to make the maximum horsepower of the double-acting engine. Some of the double-acting designs published are reviewed, including the rodless piston and the double opposed pistons.