Gas engines, at the present day, are common enough, the past ten or twelve years having witnessed the production of a host of designs, although of these probably by far the larger number have gained little more publicity than that afforded by the patent office records of different countries. But the more fortunate ones,—those that have been put into marketable shape and sold for a variety of motive power purposes,—have been sufficient to amply advertise this type of motor and to practically demonstrate its applicability to many, if not all, the uses to which the steam engine has hitherto been put. It would, therefore, seem almost unnecessary to more specifically define it as an engine in which the working fluid is an inflammable gas, or, more correctly, a mixture of atmospheric air and inflammable gas, introduced directly into the engine cylinder and there ignited and burned. All gas engines, while they may differ widely in theory of action and mechanical construction, possess in common this one feature of heating the working fluid in their cylinders proper. Compared with the steam engine as a familiar example, and with most hot air engines, we thus find in the gas engine relative simplicity in so far as no separate furnace is necessary in which to burn the fuel from which the energy is primarily derived; furthermore, the energy is available at exactly the moment needed, and there is no storing up of heat in the same sense as in the steam engine and boiler combination. Hence, it will be seen that the gas engine also has a special applicability in all cases where continuous work is not required.
Concerning the origin of the gas engine there is no definite information. By some it has been dated as far back as the latter part of the seventeenth century when gunpowder was proposed and used for obtaining motive power in special apparatus. These early engines, however, can scarcely be properly classed as gas engines. The first gas engine, in the now accepted sense of the term, was probably that patented in the year 1791, in England, by one John Barber. It provided for the use of coal, wood, oil or any combustible in a retort, the generation of vapor or gas from such combustible, and the collection and cooling of the gas in a reservoir. Thence the gas was taken to a compressor which supplied the motor cylinder, and in this latter the gas was mixed with atmospheric air in proper proportion, and exploded by a light. This engine embodied, in the main, the principle of the modern gas engine. Three years later, in 1794, Thomas Mead and Robert Street both obtained patents in England for gas or vapor engines, Mead proposing to raise the piston in his engine cylinder by the ignition of a gaseous, explosive mixture and to utilize for the down-stroke both the weight of the piston and the partial vacuum formed underneath it. This was, in part, the principle of the much later Otto and Langen engine. Street's engine, on the other hand, partly anticipated the also much later hydrocarbon engine of George Brayton, providing, as it did, for the production of motive power by introducing a few drops of spirits of turpentine into the heated bottom of a cylinder. The turpentine was vaporized by the heat, air was mixed with it in sufficient quantity to produce an explosive compound, and a flame was applied to ignite it. The next patents for gas engines were not issued until nearly thirty years later (1823). From that time on they appeared at shorter intervals until more recently, when design crowded design in rapid succession, so that now the gas engine patents are numbered by the hundreds. The essential differences between the inventions, however, are not very great. In many cases, in fact, it seems sadly true that the inventors have been satisfied with producing simply some detail by which the original patents could be avoided, rather than anything which really marked a step in advance.
It would be impracticable to here follow the history of the gas engine in anything like detail from its earliest days to the time when it became justly looked upon as a distinctly practical and useful source of power. A few of the types, however, which, though comparatively crude and more or less imperfect, still came into somewhat extended use and practically opened up the era of commercially successful gas engines, deserve mention. The first of these was the Lenoir engine, made even at this date in a modified form, a machine of simple construction and very similar in appearance to an ordinary horizontal steam engine. The piston moving, say, from the right to the left drew in a mixture of illuminating gas, or of hydrogen, and air through a slide valve worked by the engine. When a certain quantity of this mixture had entered the cylinder, the slide valve shut off the supply and an electric spark from an induction coil kindled the gas and caused an explosion which drove the piston to the other end of its stroke. Arrived there, at the left end, a second slide allowed the products of combustion to escape while the fly wheel, by reason of its momentum, went on and moved the piston in the opposite direction, from left to right. While it moved in this direction, the explosive mixture again entered and was ignited as before, and the piston completed its travel to the right under the impulse of this second explosion. The action, it will be seen, was thus very similar to that of the ordinary, familiar steam engine. To prevent overheating of the cylinder and piston, the former was surrounded with a jacket filled with cold water.
Following the Lenoir engine came that of Hugon, in which the tendency to become overheated was counteracted by introducing into the cylinder, together with the gas and air mixture, a quantity of water which, in vaporizing, absorbed considerable heat and thus kept the temperature within a reasonable limit. The expansive force of the gases was in this way, it is true, somewhat diminished, but the moving parts suffered less, and the engine required less repair and was more durable. Ignition of the explosive charge was effected by a gas jet.
A number of years after the bringing out of both these engines, Otto and Langen together entered the gas engine field with what they termed their atmospheric or free piston engine for which they were awarded a gold medal at the Paris Exposition in 1867. The main features of this engine are briefly referred to further on.
The Brayton engine, an American invention, was first brought out in 1872. It had two cylinders, or in some cases a single cylinder with a double acting piston. Brayton engines were made in many different configurations but the operation performed was that One side of the piston or one of the cylinders being a compressor and the other side of the piston or cylinder acted as an expander. Brayton's early engines operated on town gas or on benzine with a vapor carburetor. The charge of gas and air was first drawn into the compressor cylinder on the out-stroke, and on the back-stroke was compressed into a receiver at about 70 psi. At or near the top of the stroke the pressurized air/ fuel mixture was admitted into the expander cylinder where it passed through a pilot flame and was ignited as it entered the expansion cylinder. A series of screens prevented the flame from passing back into the reciever . The mixture proper, in fact, did not enter the motor cylinder at all; what entered it was a continuous flame and the action, therefore, was not explosive in character. At a certain point the supply was cut off (determined by the governor) , and the piston moved on to the end of its stroke under the influence of the expansion of the hot gases. The flame grating / screens in this engine, however, was a weak point. If by any accident the grating or wire gauze was pierced, in cleaning for example, the flame went back into the receiver and exploded the whole stored-up mixture. Such accidents became so troublesome that Mr. Brayton in 1874 discontinued the use of gas and modified his engine into a oil motor. Light oil was pumped onto a felt pad using a very precise adjustable metered pump and the compressing cylinder charged the receiver with air alone. The air, in subsequently passing through the felt, carried the petroleum along with it, partly in vapor, and partly in spray form. This oil vapor and air mixture was then ignited just like the previous version. The arrangements in fact, were precisely similar to those of the gas engine, except in the addition of a small oil pump and a slight alteration in the valve disposition. The engine, was made in both single and double acting versions. The Brayton engine had 4 distinct cycles which were intake, compression, expansion, and exhaust but unlike a 4 stroke engine it accomplished a 4 cycles in one rotation of the crankshaft. Brayton engines were some of the first internal combustion engines used for motive power. Several were used to power boats, two were used to power submarines (Holland boat #1 and the Fenian Ram) , one was installed in a rail car and one was installed in a bus (unsuccessful though)
Right here it should be pointed out that the similarity between the original Brayton gas engine and the converted Brayton engine using oil is typical, also, of all gas and oil engines of the present day. All the oil engines follow the lines of the gas engines very closely; in fact, in some of the gas engines now on the market gas or oil mixtures can be used indiscriminately, the engines working well with either, and without modifications of designs to suit the particular kind of fluid used. A distinct classification into oil motors and gas motors cannot, therefore, be well made, and both may be, very appropriately, considered together under practically one head. Broadly speaking, however, the various engines, early and modern, and using either gas or oil mixtures, may be divided into a few, well-defined types:
- 1. Engines drawing into the working cylinder gas or oil vapor and air at atmospheric pressure for a portion of the piston stroke, cutting of communication with the outer air, and igniting the mixture. The pressure of the ignited gases pushes the piston forward during the remainder of the stroke, and the in-stroke of the
piston expels the products of combustion from the cylinder.
- 2. Engines in which a mixture of gas or oil vapor and air is drawn into a pump forming part of the engine proper, and discharging the gas mixture into a receiver or reservoir in a state of compression. From this receiver the mixture enters the motor cylinder, being ignited as it enters. The ignition here does not increase the pressure, but increases the volume. The pump, say, puts one volume or cubic foot into the receiver; ignition causes it to expand, while entering the cylinder, to two cubic feet. It does the work of two cubic feet in the motor cylinder, so that though there is no increase of pressure, there is nevertheless an excess of power over that spent in compression. The return stroke of the piston again expels the products of combustion.
- 3. Engines in which a mixture of gas or oil vapor and air is compressed, or introduced under compression, into the cylinder or space at the end of the cylinder, and is then ignited, the volume remaining constant and the pressure rising. Under this pressure the piston moves forward, and on its return as in the previous types, discharges the waste gases from the cylinder.
Types 1 and 3 are explosive engines, the volume of the gas remaining constant while the pressure increases. Type 2, on the other hand, is a gradual combustion engine in which the pressure is constant while the volume increases. The third type is generally regarded as the best kind of compression gas engine yet introduced, and by far the largest number of gas engines now in every day use are made in accordance with its requirements. The leading idea, compression and ignition at constant volume, was first proposed by Barnett in 1838, and later by several others, but Otto was the first to successfully apply it in 1876, in the now well known engine bearing his name.
There still remains one important type of gas engine not included in this classification. It is the kind of engine known as the free piston or atmospheric gas engine already referred to above, and may be regarded as a modification of the first type. The first part of its action is precisely similar; the latter part differs considerably from it. In this engine the piston on moving forward, takes in its charge of gas and air from without at atmospheric pressure and temperature. When cut off it is ignited instantaneously, the volume being constant and the pressure increasing. The piston is not connected directly to the motor shaft, but is perfectly free to move under the influence of the explosion, like a projectile in a cannon, for example. It is thus shot forward in the cylinder, which is purposely made very long. The energy of the explosion gives the piston velocity, and the piston therefore continues to move considerably after the pressure has fallen by expansion down to atmospheric pressure. Owing to this and to the cooling of the gaseous products a partial vacuum is formed behind the piston till its whole energy of motion is absorbed in doing work against the pressure of the outside air. It then stops and the external pressure causes it to perform its return stroke, during which a clutch arrangement connects it with the motor shaft, giving the latter rotary motion. The piston during its return stroke proceeds completely to the bottom of the cylinder, expelling the products of combustion. This kind of engine was first proposed in 1854 by Barsanti and Matteucci, but Otto and Langen, as previously mentioned, in 1866, were first successful in overcoming the practical difficulties in its way, and many engines were built by them for practical uses. The engine though cumbersome and noisy, was a good and economical worker, and many are probably still in operation today.
It is scarcely within the province of this article to take up the theoretical considerations presented by these representative types of gas engines. Suffice it to say that the causes of the comparative efficiency of the modern gas engine over the older forms, such as the Lenoir and the Hugon engines may be summed up in the one word "compression." Without compression before ignition an engine could not be produced which would furnish power economically and with small bulk.
To the prospective user of a gas engine, the question of cost of operation, or more specifically the cost of fuel used for a given amount of power is, as might naturally be expected, one of the first to present itself. That the fuel or gas cost is unduly great has been, and is still, a more or less prevalent impression and the fact seems to have been largely lost sight of by many power users that the development of the gas engine from what was at first perhaps little more than an interesting novelty to a source of even large powers at the present day has naturally brought with it much increased efficiency and correspondingly reduced running expenses. Just what these expenses are, so far as they are affected by the items of gas quality and cost, of course depends much upon special circumstances. The price of gas as well as its quality varies with locality and time, and definite statements of cost can therefore not easily be given.
Professor Ayrton, in England, several years ago, in comparing the fuel costs of gas engines and of portable and semi-portable steam engines to determine the relative expenses in driving electric light dynamos, estimated that the steam engines in question would, in a competition, consume about four pounds of coal per indicated horse-power per hour, but that in ordinary work their consumption would run up to six and seven pounds. Assuming a four-pound basis, however, which seems pretty fair, and taking, for the sake of illustration, the price of coal as $5 per ton, we get for the cost of a horse-power for fuel in these engines one cent per hour. At the rate for gas, paid in London at the time,—three shillings, or about seventy-five cents per thousand cubic feet,—the cost of one horse-power in the gas engine would amount to one and one-half cents per hour. Taking the highest prices paid in London for gas,—four shillings, or about one dollar per thousand,—the gas would cost two cents per horse-power per hour. This makes a very favorable showing for the gas engine, which has so many advantages and economies, as compared with the steam engine, as to easily overbalance its slightly higher fuel cost. In the United States, where the prices for gas are considerably higher, the comparison of the fuel costs would, of course, be somewhat; less favorable to the gas engine. Much, however, is to be expected both here and abroad, in the direction of cheaper heating gas, and there seems little reasonable doubt that such a gas can be made and will probably be made in the near future, and will render the ordinary gas engine up to a certain size, much more economical in running expenses than an equal sized steam engine. Even as it is, however, with gas at the current rates, the gas engine in a great many cases foots up a smaller expenditure for a given horse-power than the steam engine. There is always a very considerable saving when standing still, and this, when the stoppages are frequent, may amount to a most appreciable total.
As a sample of what may be accomplished with a cheap heating gas we call to mind a low cost gas enterprise, started a number of years ago in the vicinity of New York City, by which heating gas was made on a large scale under the Strong patents. From figures that were received at the time it appeared that this gas had been used in an Otto engine at the rate of thirty-five cubic feet per hour for each horse-power. As the gas was produced at the rate of about twenty-seven cubic feet per pound of coal, it is easily seen that the engine was running on an equivalent of a little less that one and one-third pounds of coal per horse-power per hour. At the common retail price, the gas was worth fifty cents per 1,000 cubic feet and there was every reason to suppose that the price could be reduced by a large percentage in the case of a larger plant. Ample evidence was given, however, to show that with the plant in question a great saving over coal gas effected, even though it did not produce the gas at the lowest possible rate.
In several other cases in England where Otto gas engines were supplied with cheap Dowson gas from Dowson producers specially erected for the purpose, it was found on test that the engines consumed on an average the equivalent of 1.2 pounds of coal per indicated horse-power per hour. These results at the time had not a little to do with the subsequent building in England of gas engines of comparatively high powers,—double-cylinder engines indicating in the neighborhood of seventy horse-power.
As to the possibilities of the uses of gas and its future as a source of power, it may not be amiss here to refer finally to one of C. William Siemens' addresses to the British Association for the Advancement of Science in which he expressed the conclusion that if a temperature of about 2,732 degrees Fahrenheit and a pressure of four atmospheres could be obtained in an explosive gas engine, a theoretical efficiency of about one-half could be obtained, while with a good expansive steam engine the theoretical efficiency would be about two-sevenths. Deducting the losses by friction and by radiation in both kinds of engine, he held that the best steam engine would yield in mechanical effect about one-seventh of the heat energy, while with the gas engine one-fourth could be easily obtained. As a prediction he finally remarked that "before many years we shall find, both in factories and on board ships, engines with a fuel consumption not to exceed one pound of coal per effective horsepower per hour, and with these engines the gas producer will take the place of the steam boiler." This prediction, made a little more than ten years ago, has, as we all know, scarcely yet been fully realized though much progress has been made in the direction outlined,— how much, it is, in a measure, our object to show here by an exposition of the various gas and oil engines now in current use, doing a large variety of work.
THE OTTO GAS ENGINE
It seems but rational and proper that we should begin our series of descriptions with an account of the Otto engine, or Otto "Silent" engine as it was called in its earlier days, since Mr. Otto, the first to succeed with the free-piston engine, was also the first to succeed in adapting compression in a reliable form, and since, further, it is to the utilization of this compression principle that the gas engine owes its present advanced state of development. The Otto engine belongs to the third type previously referred to, using a gaseous explosive mixture, compressed before ignition, and ignited in a body, so that the pressure increases while the volume remains constant. The power is obtained by expansion after the increase of pressure. It is interesting to note that the Lenoir and the Hugon engines were practically double-acting, there being two explosions for every revolution ; the Brayton engine is single-acting, there being one ignition of a charge for every revolution; the Otto engine, however, is what may be termed only half single-acting, there being one explosion for every two revolutions of the engine.
The first of several designs of the engine, and one, which is still looked upon as the standard form, has a single horizontal, open-ended cylinder. In this' works a long trunk piston the front end of which serves as a guide. The cylinder is appreciably longer than the piston stroke, so that the piston, when full in, leaves a considerable space at the end of the cylinder into which it does not enter and which forms a compression chamber. Across the back end of the cylinder works a slide valve, controlling the admission and explosion of the charge, and held in place by a cover plate and strong, spiral springs. The valve is worked back and forth by a small crank on the end of a shaft parallel to the cylinder axis, and rotating at half the speed of the main crankshaft from which it receives its motion by bevel gearing. An exhaust valve and governing gear are also worked from this secondary shaft.
The engine cylinder serves alternately the purposes of motor and pump. During the first forward stroke of the piston, the admission valve is in such position that the gas and air mixture streams into the cylinder from the beginning to the end of the stroke; the return stroke then compresses the mixture into the space at the back end of the cylinder. Meantime the slide valve has moved to another position, first closing the admission port to permit the compression of the charge, and then exposing a cavity in the valve in which there is a gas flame when the compression stroke is completed. The compressed charge is then ignited and under the influence of the resulting explosion the piston again moves forward. This constitutes the motive stroke. At the end of it the exhaust valve opens, and the return stroke drives out the burnt gases. The piston is then again in the position to take in a new charge for the next explosion. The cylinder is water-jacketed.
/fig. 1.jpg) Fig. 1—Plan View of the Original Otto Slide-Valve Engine |
A sectional plan of the original Otto engine is given in Fig. 1. In this
A is the cylinder;
B, the piston;
C, the compression chamber; the admission port shown extending through the cylinder head communicates alternately with the gas and air admission port
E, and the flame port
F, both of which are in the slide valve
G. The latter, as already explained, is held in place by the cover
J in which is carried the igniting jet
R. The exhaust valve, which is a lift valve with a conical seat, is at
K and is driven by the geared shaft
M through a cam and lever,
N and
P. The main slide valve is also driven from this shaft in the manner clearly shown in the illustration. The governor with which the engine is provided is so arranged that when the speed goes above the normal rate it acts on a cam controlling the main gas supply valve and prevents its opening when the piston is drawing in air. To start the engine the igniting jet at
R should be lighted, the gas supply turned on, and a few turns be given to the fly-wheel by hand.
/fig. 2.jpg) Fig. 2—The Otto Gas Engine |
In some of the later types of Otto engines the admission slide valve
G is replaced by a poppet valve design, Fig. 2 showing one of the modern styles of larger size, indicating about sixty-five horse-power. In this later design, the igniting jet used in the earlier form of engine for exploding the gas charge has also given way to what is known as a tube igniter, or hot tube. This, as its name implies, is simply a wrought iron tube of small diameter, closed at one end. The open end is made to communicate with the engine cylinder by the valve arrangement. The tube is heated by a Bunsen gas flame within a non-conducting casing to prevent loss of heat, and the explosive gas mixture from the cylinder, entering the heated tube under pressure, becomes ignited. This method of ignition is at once simple and effective. The tube, moreover, is inexpensive and can be easily renewed when necessary.
/fig. 3.jpg) Fig. 3—Otto Gas Engine and Dynamo for House Lighting |
The almost infinite variety of uses to which the engine may be put, and for some of which special designs are turned out, will not admit detailing here and we must content ourselves with the few examples shown. Thus, Fig. 3 shows a modern Otto engine applied to electric lighting, the sizes for this work ranging from fifty to 100 horse-power. Fig. 4 shows an engine and pump combination of the latest design in which gear wheels for driving the pump, as first used, have been entirely displaced by belting and correspondingly quiet running has been secured. Double cylinder and vertical Otto engines are also on the market, all having their legitimate field of use.
THE OTTO GASOLINE ENGINE
The poppet valve design has been adopted also in the Otto gasoline engine which has been on the market only a few years. This engine, like all oil engines, can be used where gas is not available, an advantage which has much to commend it and which in a measure explains the impulse which has been given to the oil engine industry during the past few years. In appearance and action the Otto gasoline engine is practically similar to the Otto gas engine, embodying as it does, only some minor valve modifications, and Fig. 2 may, therefore, be taken to represent it as well as its gas ally.
In this engine the gasoline is supplied from a tank which may be located outside the building, through a galvanized iron pipe with soldered joints, and provisions are made against any possible leak of the oil between engine and tank, or after it has reached the engine. The gasoline flows to the admission valve on the engine cylinder by gravity, and on being atomized or sprayed within the cylinder by a current of air, is at once fired either by an electric spark or by a tube igniter. Safety considerations may make the electric ignition method the preferable one, and this is therefore generally used.
/fig. 4.jpg) Fig. 4—Otto Gas Engine and Pump Combined |
While the gasoline engine can be used everywhere, and is not limited to exclusive use outside of cities because of possible gasoline vapor dangers, still the largest number of these engines have been placed in manufacturing suburbs not reached by city gas, and in the country. Like the gas engines, they are turned out in various designs for various kinds of work, and gasoline mining engines, electric light engines, portable engines mounted on trucks, etc., are now not uncommon.
Messrs. Schleicher, Schumm & Co., of Philadelphia, Pa., are the builders of both the Otto gas and the gasoline engines in the United States, the sizes of both types ranging from one-third horse-power upward. In England the Otto engine is made by
Messrs. Crossley Bros., of Manchester, to whose design reference will be made in a future issue.
THE FIELDING GAS ENGINE
/fig. 5.jpg) Fig. 5—Fielding’s Gas Engine |
/fig. 6.jpg) Fig. 6—Fielding’s Gas Engine, Side Elevation |
/fig. 7.jpg) Fig. 7—Fielding’s Gas Engine, Plan View |
The Fielding engine is made by an English firm,
Messrs. Fielding & Platt, of Gloucester, the accompanying illustrations, Figs. 5, 6 and 7, showing one recently built and capable of indicating 100 horse-power at a speed of 160 revolutions per minute. The engine works upon what has become generally known as the Otto cycle referred to in the just given description of the Otto engine as well as somewhat earlier in this article; but the arrangement of the valve gear embodies some new features. Fig. 5 gives a general view of the engine, while Figs. 6 and 7 show an elevation and a plan respectively.
The working charge is admitted and the waste products exhausted by means of a simple mitre-seated valve, through inlet and outlet ports controlled by the movements of a piston valve which receives independent motion from an eccentric, which also operates the timed ignition valve. The valves are placed horizontally by the side of the cylinder, an arrangement, which permits of very straight and direct pipe connections for gas and exhaust, the air being drawn through the cylinder base, which acts as a muffle. The main mitre-valve is worked from a cam by a rod leading direct to the valve. The governor is of the high-speed, ball type acting upon a hit-and-miss gear interposed between the gas valve and its cam.
The importance of a starting gear for engines of such large size which cannot easily be turned over by hand is at once apparent, and due account has been taken of it in this engine by the provision of a new form of such gear patented by Mr. Fielding. This gear comprises a small reservoir of about the size of the cylinder jacket, which, after the engine has once been started, is charged with compressed air at a pressure of about fifty pounds per square inch by the engine itself when being stopped, thus utilizing the power stored up in the fly-wheels for use when re-starting the engine. The action of starting is as follows: The engine crank being placed slightly in advance of the dead centre nearest to the cylinder, gas is admitted by a small cock to the combustion chamber, from which the air is allowed to escape at a small pipe provided with a stop-cock and terminating in a jet near the top of the tube igniter.
When the air has been driven out and the gas begins to escape at the jet, it becomes ignited, and as soon as it burns with a steady flame, showing that an ample supply of gas is present in the cylinder, the outlet and inlet cocks are closed. Compressed air is then turned into the cylinder, and the igniting valve being open, as soon as an explosive mixture is formed and sufficient pressure attained, the charge is ignited by the igniting tube, and the piston is driven forward with a powerful impulse, the ordinary cycle at once coming into operation. This method of starting is claimed by the builders to be so powerful that an engine can be started with partial load on, and any arrangement of fast and loose pulleys or friction clutch is thus entirely dispensed with.
THE DAY ENGINE
/fig. 8.jpg) Fig. 8— The Day Gas Engine |
/fig. 9.jpg) Fig. 9— The Day Gas Engine, Front Sectional View |
/fig. 10.jpg) Fig. 10— The Day Gas Engine, Side Sectional View |
The Day engine, shown in perspective and sectional elevations in Figs. 8, 9 and 10, is built by
Messrs. Llewellin & James, of Bristol, England, and appears to have been designed with special reference to adaptability to domestic or other uses where the utmost simplicity and consequent ease of management by unskilled attendants are primary considerations. Few moving parts and an entire absence of what may properly be considered valve gearing are therefore the leading features of this engine. What moving parts there are besides the piston and fly-wheel are, moreover, completely hidden by a casing, so that the engine is simple in appearance as well as in fact. The crank chamber, as shown, is closed in and as the piston
A rises a partial vacuum is formed underneath, and gas and air in proper proportion are drawn in through the passages
D. These are controlled by a flap valve on the inside of the crank casing, and when the piston, after having reached the upper end of its stroke, begins to descend, this flap valve closes the gas and air inlets, and the completion of the down-stroke causes a slight compression of the explosive mixture in the crank chamber. At the end of the down-stroke a port opening at the side of the cylinder is uncovered by die upper end of the piston and through this the explosive mixture rushes into the cylinder proper above. In passing into the cylinder the gases impinge on the fin
B on top of the piston and are thus deflected upward, displacing the products of combustion of the previously exploded charge, which pass out through the exhaust opening
K (Fig. 10). The cylinder how is practically filled with an explosive mixture at atmospheric pressure. The piston, now again rising, cuts off both the supply and exhaust openings, and the mixture in the cylinder is compressed. When the piston reaches the upper end of its stroke, it drives the gas mixture into an ignition tube,
F, and an explosion results.
It will be understood from this that there is one explosion for every double stroke or every revolution. A water-jacket keeps the cylinder cool. To start the engine, which obviously is made only in small sizes, it is simply necessary to give a few turns to the flywheel by hand.
THE GRIFFIN OIL ENGINE
/fig. 11.jpg) Fig. 11—The Griffin Oil Engine, Front ¾ View |
/fig. 12.jpg) Fig. 12—The Griffin Oil Engine, Rear ¾ View |
The Griffin oil engine, made by
Messrs. Griffin & Co., of Bath, England, works with ordinary petroleum, either such as is used in domestic lamps, or with the cheaper and heavier varieties. This engine, too, works on the four-stroke or Otto cycle.
The points of novelty lie principally in the vaporizer, and in the burner for keeping the incandescent firing tube red-hot. The vaporizer lies athwart the bed under the cylinder. It is a cast-iron vessel, surrounded with a passage for the emission of hot exhaust products from the cylinder, and provided internally with ribs to increase the heating surface. The oil enters it at one end, that shown in Fig.11, in the form of fine spray, and is drawn out through the curved neck at the opposite end, Fig. 12, into the cylinder. In their passage the vesicles of oil become converted into vapor by the heat of the walls, and shortly before the cylinder is reached they are mixed with additional air entering through the box to be seen below the bed. This air also has its temperature somewhat raised, as the inlet and exhaust passages run side by side in the curved end of the vaporizer leading to the cylinder. The spraying of the oil is effected by air compressed to twelve pounds on the square inch by a pump worked off the side shaft. The oil runs by gravity out of a reservoir in the bed, and is emitted through a fine tube into the air delivery nozzle. The blast picks it up, and, driving it forward, atomizes it at once. The flow of oil is regulated by the air jet itself; when the jet is cut off by the governor, the oil ceases to flow. This result is attained by means of a valve on the oil pipe. This valve closes naturally and is only opened by the air pressure: immediately this is admitted to the pipe the valve lifts and the air flows. The heating of the incandescent tube is accomplished simply and ingeniously. The oil trickles into a tiny box and flows over a weir, which keeps it at a constant height. Two little wire pins stand in the oil at such a distance apart that the liquid creeps up between them by capillary attraction. On to the head of the column so raised, there impinges a fine air blast, which sprays the oil and carries it forward through a pipe to a Bunsen burner playing on the ignition tube. The pipe rapidly becomes heated by conduction from the burner and effects the vaporization of the oil, which burns like a gas jet, without odor.
The governor is of the centrifugal type and controls a hit-and-miss device. From this there is worked the admission valve, the exhaust valve, and the air inlet to the vaporizer, all being thrown in and out of action simultaneously. It is claimed as a feature of importance in the engine that all the valves are at rest when running light and operate only in direct proportion to the work being done, thus saving wear and tear.
The vaporizer needs to be heated before the engine is started. A hand lever is supplied by which the air-pump is worked for ten minutes. The air is used to spray the oil, as if the engine were at work, but the jet is ignited as it enters the vaporizer and fills the latter with a powerful flame. A door is opened at the further end of the vaporizer and a temporary deflector fixed on to direct the flame under the passage leading to the cylinder. Ten minutes suffice to raise the temperature to the required extent. Up to the present time only small sizes of the engine have been built, but larger designs are under way.
Information Sources
- Cassier's Magazine, V3, Mar 1893 pgs. 341-356