HISTOPIGAL DEVELOPMENT. In 1078 the Abb6 d'Hantefeuille invented an engine in which the explosive power of gunpowder was employed to drive a piston in a cylinder. This was the pro totype of the modern gas-engine. Two years later the eminent Dutch physicist Christian Huygens devised a similar gunpowder engine. No further development of the internal-combus tion engine occurred until 1791, when John Bar ber, an Englishman, specified in a patent the use of a mixture of a hydrocarbon gas and air and its explosion in a vessel which he called an ex ploder. Some years later a fellow countryman of Barber's, John Street, took out a patent for the production of an explosive vapor by means of a liquid and air, ignited by a flame, in a suit able cylinder so as to drive machinery. In 1709 Philip Tehon, a Frenchman, took out a patent in which was described the construction and prin ciple of operation of an engine using coal-gas as the explosive, and two years later he secured a second patent on an improved form of the same engine. Several inventors followed Tebon with designs for gas-engines, some of which were highly ingenious machines, but none of which attained any practical utility. Indeed, up to 1860 no internal-combustion engine had appeared which was capable of regular and comparatively efficient work.
In 1860 Lenoir, a Frenchman, invented the first practical gas-engine. This engine re sembled in external appearance a simple-cyl inder horizontal steam-engine, and was double acting. Gas was drawn into the engine during the first half of the forward stroke, and ex ploded by an electric spark from a Ruhmkorf coil when the piston was commencing the second half of the forward stroke. The exploding gases, after having done their work, were drawn out through the exhaust on the return stroke, during which work was being done by a similar explo sion on the other side of the piston. A water jacket prevented the cylinder walls from becom ing overheated. The engine ran smoothly and regularly, and its development raised high hopes that the successful substitute for the steam engine had appeared. The machine, however, was enormously expensive in its consumption of gas, and had so many other defects that it soon dis appeared. The principal good accomplished by Lenoir's work was to direct attention again to the gas-engine, which had been lost sight of in the labors of developing the steam-engine. Not much importance came of this renewed study until 1862, when M. Beau de Rochas took out a patent for the working principles of an inter nal-combustion motor. These principles were set forth as follows: During the forward stroke of the piston the explosive mixture was to be drawn into the cylinder, and during the return stroke this volume of gas was to be compressed ; at the beginning of the second forward stroke the ex plosion was to take place, driving the piston for ward, the gases being expelled during the second return stroke. As will he observed, the invention called for an engine with a cycle of four distinct operations for each impulse. No engine was built by Beau de Rochas, and for sixteen years the existence of his invention remained practical ly unnoticed. Meanwhile, in 1867, two Germans, Otto and Langen, patented an engine in which the explosion of gases in the cylinder served only to obtain a partial vacuum underneath the piston, which was, therefore, forced down by the excess of atmospheric pressure above it. This engine was very crude mechanically, but it con sumed about one-half the gas consumed by the Lenoir engine, and large numbers were sold. This was the first atmospheric engine to attain commercial importance.
In 1878 Dr. Otto, encouraged by his previous success, brought out his gas-engine. In this
engine the German engineer reinvented the Beau de Rochas cycle, and applied it in the construc tion of an actual engine. In the Otto engine the cylinder was continued back beyond the stroke of the piston to form a compression chamber into which the mixture of air and gas was drawn dur ing the forward stroke of the piston. The mix ture was compressed in this chamber during the return stroke, the pressure rising at the end of the stroke to from 45 to 60 pounds per square inch. At this point in the cycle of movements a flame was brought into contact with the com pressed gases, and they were ignited. This ig nition or explosion raised the temperature of the gases to 1500° Centigrade, and drove for ward the piston under a pressure of about 150 pounds per square inch. During the second return stroke the piston drove out the products of combustion. The heating of the cylinder was prevented by a water-jacket. Special attention was paid by the inventor to the efficiency of his engine, and in order to increase it he diluted e alr an gas drawn into the cyl inder with a portion of the gases already burnt in the pre vious stroke. This caused a less violent explosion, the gases continuing to burn during the entire stroke of the piston. As the piston re ceived a driving im pulse only once in every four strokes, or two revolutions, regularity of motion had to be secured by heavy fly-wheels. Otto's engine was a marked improvement over any previous in ternal-combustion engine. It consumed only 915 liters of gas per horse-power per hour, as compared with a consumption of 1380 liters by the Otto and Langen engine, and 2700 liters of the Lenoir engine. After the expiration of Otto's patents various other inventors began turning out four-stroke cycle engines, and some of them have succeeded, by improvements in mechanical details, and by using gas at higher initial temperatures, in reducing the consump tion of fuel and increasing the efficiency of the motor generally. Another 'set of inventors de voted themselves to the devising of different cycles. Of these only Dugald-Clerk and Griffin will be referred to at present.
In the ideal internal-combustion motor we should have at least one explosion or impulse for every revolution, instead of one every two revo lutions, as in the Otto engine. For this reason inventors have tried to construct gas-engines with a two-stroke cycle. One of the most notable of these will be described, but it may be re marked at the beginning that no motor of this type has been able to compete with those of the Otto type. The two-stroke cycle engine was invented by Dugald-Clerk. There were tuo cylinders of equal diameter placed side by side; the first of these was the power-cylinder, in which the explosion took place; the other was used for compressing the explosion mixture, and also for supplying at each revolution a volume of fresh air for blowing out the products of com bustion in the power-cylinder. The Clerk engine had the advantage of giving an impulse every revolution, and thus permitted the use of a lighter fly-wheel ; its great disadvantage was that, owing to the sudden combustion, it was less efficient than the Otto engine. Clerk's two stroke cycle engine was followed by several others of the same type, but of different con struction. Griffin's engine had two explosions for every three revolutions, or six strokes of the piston, and was double-acting. The cycle of operation was as follows: (1) Gases drawn into the cylinder; (2) compression of gases; (3) ignition and expansion; (4) products of combus tion expelled; (5) volume of fresh air drawn into cylinder to expel products of combustion; (6) this volume of fresh air expelled.