| April/May 1997

Stroke Cycle Engine

Fig. 2Clerk Two-stroke Cycle Engine

The following begins a series of articles from the 1923 edition of Modern Mechanical Engineering, on the subject of gas engines. The original articles were sent to us by Jan van der Gugten, 2633 Ware Street, Abbotsford, B.C., Canada V2S 3E2, who thought our readers would find them of interest.

CHAPTER 1: Introduction

Historical Summary.Space permits of a very brief reference only to the early history of the internal-combustion engine; for a full account the reader may consult Vol. I of Sir D. Clerk's The Gas, Petrol, and Oil Engine. Probably the earliest instance of the use in Britain of an explosion to obtain mechanical effect is that of the primitive cannon used by Edward III about A.D. 1327. Three hundred and fifty years later C. Huygens, followed by Papin and d' Hauteville, endeavored to obtain continuous motion from successive explosions of gunpowder in a cylinder fitted with a piston; and much later still, viz. in 1820, Farish of Cambridge constructed a small engine intended to be driven by gunpowder; this explosive is, however, quite unsuited for use in internal-combustion engines for both thermal and practical reasons.

In 1820 Cecil, also of Cambridge, made what was probably the first actually working gas-engine, using as his fuel an explosive mixture of hydrogen and air; thereafter appeared in succession Brown's 'gas-vacuum' engine, Wright's engine, Barnett's engines, and the very singular 'free-piston' engines of Barsanti and Matteucci and of Otto and Langen; and in 1860 the once popular, though very uneconomical, Lenoir engine, which may be fairly described as a double-acting steam-engine using a mixture of coal-gas and air in lieu of steam; Hugon (1865) effected improvements in the details of Lenoir, but its still high fuel consumption caused its abandonment in favour of the much more economical, though mechanically objectionable, Otto and Langen free-piston type. It should be mentioned also here that in 1873 there appeared in America the theoretically efficient 'constant pressure' Brayton gas-engine, whose success was prevented by practical difficulties; the modern highly economical Diesel oil-engine illustrates the principle embodied in the Brayton of burning fuel at (approximately) constant pressure during its admission to the combustion chamber.

The final step in the evolution of the modern four-stroke cycle internal-combustion engine was made in 1862 when de Rochas first laid down explicitly the procedure to be adopted to obtain maximum economy in the working of gas-engines, comprising suction, compression, explosion and expansion, and exhaustall performed within the working cylinder.

A four-stroke single-acting engine of the simplest type is illustrated diagrammatically in Fig. 1. It includes an open ended cylinder fitted with a closely fitting piston which drives a crank by means of the usual type of connecting-rod; in the upper end, or 'combustion chamber', of the cylinder a pocket is formed containing the inlet valve A, and exhaust valve B, the latter being forcibly raised at suitable intervals by a cam C and roller-ended tappet-rod D. Suppose the engine to be turning, and the suction stroke about to commence. The piston in its descent creates a partial vacuum above it, the inlet valve A accordingly opens and fresh mixture passes into the cylinder; this is the suction stroke. When the piston has reached the bottom of its stroke and commenced to return the inlet automatically closes, and the upper charge is compressed into the upper part of the cylinder and valve pocket; this is the compression stroke. The mixture is exploded by the ignition plug at, or near, the instant of greatest compression, and the piston is next driven downwards, thus performing the expansion or working stroke. Near the bottom of this stroke the cam C lifts the exhaust valve B, and the burnt gases escape into the atmosphere; B remains open throughout the whole of the succeeding or exhaust stroke; this cycle is repeated indefinitely so long as the engine continues running. The cam-shaft is driven by gearing at half the crank-shaft speed, and is accordingly frequently referred to as the 'half-time' shaft. In all modern engines the inlet valve is also cam-operated, an increased volumetric efficiency and increased speed being thus obtained.

The Otto Silent Gas-Engine.It was not, however, until 1876 that Dr. Otto produced his world-famous 'silent' gas-engine, working exactly upon the four-stroke cycle as laid down by de Rochas fourteen years earlier. Otto realized the de Rochas cycle in a practical and most successful manner and employed flame ignition. The gas consumption of his engines was at once found to be much lower than had ever previously been attained, averaging only from about 24 to 30 c. ft. of coal-gas per brake horse-power hour. The introduction of the 'Otto silent gas-engine' marked the beginning of the era of the internal-combustion engine as a prime mover of world-wide importance.