Excerpted from Gas & Oil Engines by D. Clerk, 1908 Edition
1772 Conrad Avenue, San Jose, California 95124-4501
In external appearance this engine, illustrated in Fig. 320, bore a marked resemblance to the ordinary type of double-acting horizontal steam engine with flywheel and connecting rod, with which designers were already very familiar. Gas was merely substituted for steam, with very few alterations of the parts, and the distribution was effected by ordinary slide valves operated by two eccentrics. For the ignition of the mixture an electric spark was passed between two points inside the cylinder when the piston reached its mid-stroke position, and for the production of the high-tension spark a Ruhmkorff coil and batteries were supplied. During the latter portion of the forward stroke the drive took place, and on the return stroke the exhaust gases were driven out, while the other face of the piston was acted upon by the driving force. Around the cylinder walls cold water was circulated to prevent the temperature from becoming abnormal. This double-acting arrangement, which does not permit of initial compression of the mixture, has been abandoned by all de signers, because the regularity of the action is obtained at the expense of the economy, and owing to the successive actions on the two sides of the piston, the quantity of gas burned is out of all proportion to the power developed.
Fig. 321 illustrates this engine, which works on the mixed principle of the Otto and Langen atmospheric engine. Expansion of the exploded gases raises the piston, which is then driven, during the working stroke, by the pressure of the atmosphere. Very successful results were obtained from the first engines, which were well designed and constructed, but very few examples now exist. As will be seen from the illustration, the engine, which was of small power, was of a vertical type, with the piston crosshead guide surmounting the cylinder. On the outside of the cylinder were cast numerous ribs of metal, which, by providing a large air-cooling surface, served the same purpose as a water jacket.
In 1880 the inventor was awarded a prize of 1000 francs for his engine, which was considered the best low-power engine suited to the requirements of small users.
This simple engine was the first one made by the designers of the Benier producer engine. As will be seen from the illustration (Fig. 322), the cylinder A was inverted, and the crank was driven through a connecting rod coupled to a side lever, the end B of which received its motion from the piston rod. A cam G on the shaft operated a single slide valve E, controlling admission and ignition, and side springs r, r were provided to keep the cam and slide always in contact. Air and gas in the proper proportions were drawn in by the piston until the middle of the stroke, when the mixture was ignited by the exposure of a flame at the admission port, and the explosion took place. A pilot flame-was provided for the relighting of the ignition jet after each explosion. A second cam on the shaft opened a separate exhaust valve at the proper moment. Water-cooling jackets kept the heat of the cylinder within reasonable limits, and the economy obtained in actual practice was quite satisfactory, the consumption being about 50 cubic feet per horsepower hour. Towards the year 1880 the system received a certain amount of attention, owing to the simplicity of the design and the relatively small cost.
The Economic motor, which was first constructed in New York about the year 1883, was a small type of engine rarely exceeding Vi HP and working on the non-compression system. Its arrangement was ingenious but somewhat complicated, as will be seen from the illustration, Fig. 323. A is the cylinder, provided with external air-cooling ribs, and G E is the rocking lever from which the crank O C received its motion through the connecting rod B. Regulation of the speed was effected by means of a centrifugal governor throttling the gas admission, as in the other engines of the same class. It is understood that the results obtained in practice were satisfactory.
In the design of a gas engine the ideal arrangement is to have an explosion, that is, an impulse, every stroke, and for many purposes the very usual Otto cycle having one impulse every four strokes is not sufficiently good. Many attempts have been made to devise a satisfactory two-cycle engine, but the experimenters have, in general, found that the problem is more difficult in practice than in theory. Dugald Clerk's engine, which first appeared in 1881, was the earliest of the two-cycle types, and his name is generally associated with such engines. It was of the simplest possible design, the use of gear wheels being avoided, and in actual use the working was very regular and noiseless (see Fig. 324). Two cylinders were arranged side by side on the overhanging end of the bed plate; the one serving as a single-acting engine, and the other as a compressor for the explosive mixture; that is, the mixture was compressed in a separate cylinder instead of in the working cylinder, as in engines of the four cycle type. After the transfer of the compressed charge into the working cylinder, the compressor was arranged to entrap and compress a quantity of air, which was later used for sweeping out of the cylinder the exhaust gases resulting from the previous explosion. By the use of the second cylinder it is possible to dispense with half the strokes of the Beau de Rochas cycle, and to have one impulse for each revolution of the crank. Combustion which takes place at constant volume is more complete and instantaneous, but the expansion is greater, notwithstanding that the out put is increased. It should be mentioned that the ignition is effected by the carriage of a flame from the ignition jet to the combustion chamber by means of a slide valve provided with suitable pas sages. A water jacket round the cylinder keeps the temperature from becoming excessive, and by a special arrangement the two cylinders could be made to work on the compound principle by allowing the gases, after their expansion in the working cylinder, to act on the forward face of the second (compressor) piston. Exhaust then took place in the ordinary way, but from the compressor instead of from the working cylinder. In spite of its many excellent features the engine never competed successfully with the somewhat more economical engines of the Otto type, and at the present time the system has been almost wholly abandoned.
As will be seen from Fig. 328, this double-acting engine comprised two equal cylinders arranged side by side, with a pair of connecting rods driving two cranks set at an angle of 65 degrees to one another. One of the cylinders acted solely as a compressor for the ex plosive mixture, which was transferred at the proper moment to the other cylinder, in which the exploded mixture exerted its driving force.
There are many other types of two-cycle engines, but space forbids further reference to them here. Description of these engines are given in considerable detail in the treatise by M. Witz on The Theory and Practice of Gas and Oil Engines, already referred to. The Benier two-cycle producer-gas engine will, however, be dealt with later, when treating of engines driven with poor gases, as certain novel and interesting features are involved in it. The following section deals with four-cycle engines introduced by Beau de Rochas, but first practically realized by Dr. Otto in 1887.
A general description now of the principles upon which the Otto engine is based will save further repetition when dealing with the engines built by other makers, which work on the Otto cycle, or on some very analogous system. From the first introduction of the Otto engine the successful results obtained ensured its very general adoption, and on the expiry of the patents many imitations and improvements of more or less value were introduced by other manufacturers.
A partial section through the cylinder, compression chamber, and slide valve of a vertical engine of the Otto type is given in Fig. 329. An enlargement I of the cylinder bottom serves as a chamber for the compression of the explosive mixture of gas and air, which is sucked in during the upward stroke of the piston and compressed on the return to a pressure of from three to four atmospheres. At this pressure, when the piston has reached the end of its stroke, the gas jet b is exposed to the explosive charge in the cylinder by the movement of the slide valve operated by the connecting rod t. Explosion then takes place, and the temperature rises to about 1500 C, the driving pressure being about 185 lb. per square inch of the piston area. On the return of the piston to the bottom of the cylinder, that is, during the fourth stroke corresponding to the final half of the second revolution of the crank, the burnt gases are expelled to the atmosphere under a pressure of from 2 lb. to 4 lb. Water jackets are fitted around all portions of the engine that are subjected to the high temperature of the exploded gases. Attention was particularly directed by the designer to the question of the reduction of the gas consumption, and good results were obtained by diluting the mixture with a proportion of the waste gases resulting from the previous explosion. By diluting the mixture in this way the charge was consumed more gradually instead of explosively. It was found that the low consumption was not wholly due, as claimed, to the super posed arrangement of layers of gas and air in the cylinder, but to a certain action of the walls.
Mechanically, the Otto was an excellent example of good design and simplicity of arrangement. Admission and exhaust were controlled by means of cams, and ignition of the charge was effected by the transport of a flame under pressure. When the speed exceeded a certain fixed limit, a governor acting on the 'hit &. miss', or, as it is called by French engineers, 'the all or nothing', system, suppressed the admission until the speed again became normal. Motion was transmitted to the crank in the usual way by means of a connecting rod, and a specially heavy flywheel was employed for the storage of sufficient energy during the working stroke to ensure some regularity of running during the three remaining idle strokes of the cycle. The consumption was about 28 cu. ft. of gas per horsepower hour.
Fig 330 is an end view in partial section showing the arrangement of the valves adopted by Dr. Otto in his early engines and the arrangement of the levers for operating them. A section through the mixture admission valve M and the ignition slide and port I is also given in Fig. 331.
Gas enters through the valve G, which is opened at the correct moment by a system of levers operated from a cam on the half-speed shaft at the right side of the engine, and the mixture of gas and air is sucked as shown by the arrows into the chamber M and thence through the valve M' into the cylinder. An external view of an Otto engine is given in Fig. 332.
To Dr. Otto belongs the credit of having first introduced the gas engine in a really practical form, and of indicating the direction of future developments. Other engineers, following the lead of Otto, have improved the details of construction, and the consumption of gas, to a very considerable extent by reducing heat losses and increasing the expansion until at the present time the gas engine is able to compete with steam under most industrial conditions.
A few of the more remarkable types introduced during the last twenty-five years will be now briefly described, in order to illustrate the development of four-cycle engines that has taken place.
In this engine, which first appeared in 1883, the inventor introduced the experience of twenty-five years of continuous experiment and work. The cylinder which overhung the base was provided externally with air-cooling vanes, as illustrated in Fig. 333, and the crosshead was guided in a bored out trunk in line with the cylinder. Electric ignition was adopted, the spark being produced by a battery in conjunction with a Ruhmkorff coil. About 28 cu. ft. of gas were consumed per horse-power hour. Two other Lenoir engines burning petroleum vapor have been introduced, one of them being specially arranged for motor-car work. These will be described later when dealing with oil engines.
These engines were originally made by Andrew & Company, and were known in France as the Triomphe engine. Two modern examples of Hornsby-Stockport engines are given in Figs. 335 [not shown here] and 336. The latter has a specially heavy flywheel for direct electric lighting, and the outer ' end of the shaft is supported on an extra bearing. Governors of a special vibrating weight type are fitted to the small engines of about 6 HP, Fig. 335, but centrifugal-ball governors are used for all larger sizes, which are also provided with self-starters of a compressed-air type. Small engines may be readily started by hand, and for the intermediate sizes a simple pump arrangement is recommended. Either tube or electric ignition may be provided, but magneto-electric ignition is supplied in all cases where suction gas is used.
To start an engine provided with a self-starting gear, care must be taken to stop the engine with the connecting rod just above the centre and with the piston near the end of its stroke at the position of ignition. Gas is then admitted to the cylinder through a small valve held open by a light spring, and entering as it does, under some pressure, a portion of the air in the cylinder is driven through another small spring controlled valve into a chamber communicating directly with the incandescent ignition tube. After a few moments some of the entering gas also passes through the up per valve into the ignition space, and when sufficient has passed to make an explosive mixture, ignition of the small charge takes place in contact with the tube or the electric spark. The flame of the small charge in turn explodes the mixture in the cylinder, and the piston moves forward, driven by the force of the expanding gases. After the first stroke the working of the engine be comes automatic, the gas and air valves being controlled in the usual way from the cam shaft driven from the engine itself. Producer gas may also be used, in which case the consumption of anthracite is about 1 to 1 lb. per horse power hour.
Editor's Note: We'll be continuing with more 'Typical Gas Engines' in a future issue.