If the oil be fed under pressure the cylinder is more constantly lubricated. Pressure-lubricators are nowadays widely used on large engines. It is advisable to add a little salt to the water contained in sight-feed lubricators so that the drop of oil is easily freed.
These oil-pumps are provided with small check-valves at their outlets as well as at the inlets of cylinders. In order that pressure-lubricators may operate perfectly they should be regularly inspected and the check-valves ground from time to time.
The lubrication of the crank-shaft and of the two connecting-rod heads should receive every attention.
Lubricating devices should be employed which, besides being efficient, do not necessitate the stopping of the engine in order to oil the bearings. The foot of the connecting-rod at the point where it is pivoted to the piston is generally lubricated with cylinder-oil which is supplied by a tube mounted in the proper place across the piston-wall (Fig. 69). This arrangement may be adequate enough for small engines; but it is not sufficiently sure for engines of considerable size. An independent lubricating system should be employed, lubrication being effected either by a splasher mounted in front of the cylinder or by a lubricator secured to the connecting-rod by which the pivot is lubricated through the medium of a small tube supplying special oil (Fig. 21). The head of the connecting-rod where it meets the crank, must also be carefully lubricated because of the important nature of the work which it must perform, and because of the shocks to which it is subjected at each explosion. For motors of high power the system which seems to give most satisfactory results is that illustrated in Fig. 70. The arrangement there shown consists of an annular vessel secured at one side of the crank and turning concentrically on its axis; the vessel being connected with a long tube extending into a channel formed in the crank and discharging at the surface of the crank-pin within the bearing at the head of the connecting-rod. An adjustable sight-feed lubricator conducts the oil along a pipe to the vessel. Turning with the shaft, the vessel retains the oil in the periphery so that the feed in the previously mentioned channel in the connecting-rod head, is constant.
The main crank-shaft bearings are more easily lubricated. Among the systems commonly used with good results may be mentioned that shown in Fig. 71, in which the half section represents a small tube starting from the bearing and terminating in the interior of an oil recess or reservoir cast integrally with the bearing-cap. This reservoir is filled up to the level of the tube opening. A piece of cotton waste held on a small iron wire is inserted in the tube, part of the cotton being allowed to hang down in the reservoir. This cotton serves as a kind of siphon and feeds the bearing by capillary attraction with a constant quantity of oil, the supply being regulated by varying the thickness of the cotton. When the motor is stopped, the cotton should be removed in order that oil-feeding may not uselessly continue. Glass, sight-feed lubricators with stop-cocks, are very often used on crank-shafts. They are cleaner and much more easily regulated. Of all shaft-bearing lubricators, those which are most to be recommended are of the revolving-ring type (Fig. 72). They presuppose, however, bearings of large size and a special arrangement of bushings which renders their application somewhat expensive. Furthermore, the revolving-ring system can hardly be used in connection with engines of less than 20 horse-power. Since the system is applied almost exclusively to dynamo-shafts, it need not here be described in detail. As its name indicates, it consists of a metal ring having a diameter larger than that part of the shaft from which it is suspended and by which it is rotated. The lower part of the ring is immersed in an oil bath so that a certain quantity of lubricant is continually transferred to the shaft.
The revolving ring bearing should be fitted with a drain-cock and a glass tube in order to control the level of the oil in the bearing.
Many manufacturers have adopted lubricating devices for valve-stems, and especially for exhaust-valves. The system adopted consists of a small tube curved in any convenient direction and discharging in the stem-guide. The free end is provided with a plug. A few drops of petroleum are introduced once or twice a day.
The lubrication of an engine entails certain difficulties which are easily overcome. One of these is the splashing of oil by the connecting-rod head. In order that this splashed oil may be collected in the base of the engine a suitably curved sheet-metal guard is mounted over the crank. A more serious difficulty is presented when the oil from a crank-bearing finds its way to the hub of the fly-wheel, whence it is driven by the centrifugal force to the rim. The oil is not only splashed against the walls of the engine-room, but it also destroys the adhesion of the belt if the fly-wheel be employed as a pulley. In order to overcome this objection the oil is prevented from spreading along the shaft by means of a circular guard (Fig. 73) mounted on that portion of the shaft toward the interior of the bearing.
The problem of lubrication is of particular importance if the engine is driven for several days at a time without a stop. This happens in the case of mill and shop engines. Lubricators of large volume or lubricators which can be readily filled without stopping the engine should be employed.
CHAPTER VII
General Care.—Gas-engines, as well as most machines in general, should be kept in perfect condition. Cleanliness, even in the case of parts of secondary importance, is indispensable. Unpainted and polished surfaces such as the shaft of the engine, the distributing cam-shafts, the levers, the connecting-rod and the like, should be kept in a condition equal to that when they were new. The absence of all traces of rust or corrosion in these parts affords sufficient evidence of the care taken of the invisible members such as the piston, the valves, ignition devices, and the like.
Lubrication.—The rubbing surfaces of a gas-engine should be regularly and perfectly lubricated. The absence of lost motion and backlash in the bearings, guides, and joints is of particular importance not only because of its influence on steady and silent running, but also on the power developed and on the consumption. As we have already seen in the chapter on lubrication, a special quality of oil should be employed for the lubrication of the cylinder. The feed of the lubricator supplying this most vital part of the engine is so regulated that it meets the actual requirements with the utmost nicety possible. In a subsequent chapter, in which faulty operation will be discussed, it will be shown how too much and too little oil may cause serious trouble.
Tightness of the Cylinder.—The amount of power developed depends principally on the degree of compression to which the explosive mixture is subjected. The economical operation of the engine depends in general upon perfect compression. It is, therefore, necessary to keep those parts in good order upon which the tightness of the cylinder depends. These parts are the piston, the valves, and their joints, and the ignition devices whether they be of the hot-tube or electrical variety. In order to prevent leakage at the piston, the rings should be protected from all wear. It is of the utmost importance that the surfaces both of the piston and of the cylinder, be highly polished so that binding cannot occur. In cleansing the cylinder, emery paper or abrasive powder should not be employed; for the slightest particle of abrasive between the surfaces in contact will surely cause leakage. The oil and dirt, which is turned black by friction and which may adhere to the piston rings, should be washed away with petroleum. Similarly the other parts of the cylinder should be cleaned to which burnt oil tends to adhere.
Valve-Regrinding.—The valves should be regularly ground. Even in special cases where they may show no trace of rapid wear they should be removed at least every month. In order to avoid any accident, care should be taken in adjusting the valves after the cap has been unbolted not to introduce a candle or a lighted match either in the valve-chambers or in the cylinder, without first closing the gas-cock. Furthermore, a few turns should be given to the engine, in order to drive out any explosive mixture that may still remain in the cylinder or the connected passages. The exhaust-valve, by reason of the high temperature to which the disk and the seat are subjected, should receive special attention. The valve should be ground on its seat every two or three months at least, depending upon the load of the engine.
Bearings and Crosshead.—The bushings of the engine shaft should always be held tightly in place. The looseness to which they are liable, particularly in gas-engines on account of the sharp explosions, tends to unscrew the nuts and to hasten the wear of the brass, which is the result of frequent tightening. The slightest play in the bearings of the engine-shaft as well as in the bearings of connecting-rods increases the sound that engines naturally produce.
Governor.—The governor should receive careful attention so far as its cleanliness is concerned; for if its operation is not easy it is apt to become "lazy" and to lose its sensitiveness. If the governor be of the ball type, or of the conical pendulum type operated by centrifugal force, it is well to lubricate each joint without excess of oil. In order to prevent the accumulation and the solidification of oil, the governor should be lubricated from time to time with petroleum. If the governor is actuated by inertia, which is the case in most engines of the hit-and-miss variety, it needs less care; still, it is advisable to keep the contact at which the thrust takes place well oiled.
The operation of any of these governors is usually controlled by the tension of a spring, or by a counterweight. In order to increase the speed of the engine, or in other words, to increase the number of admissions of gas in a given time, all that is usually necessary is to tighten up the spring, or to change the position of the counterweight. It should be possible to effect this adjustment while the engine is running in such a manner that the speed can be easily changed.
Joints.—In most well-built engines the caps of the valve-chests and other removable parts are secured "metal on metal" without interposing special joints. In other words, the surfaces are themselves sufficiently cohesive to insure perfect tightness. In engines which are not of this class, asbestos joints are very frequently employed, particularly at the exhaust-valve cap and the suction-valve.
In some engines, where for any reason it is necessary frequently to detach the caps, certain precautions should be taken to protect the joints so that they may not be exposed to deterioration whenever they are removed. For this purpose, they are first immersed in water in order to be softened, then dried and washed with olive or linseed oil on the side upon which they rest in the engine. On the cap side they are dusted with talcum or with graphite. Treated in this manner, the joint will adhere on one side and will be easily released on the other. Joints that are liable to come in contact with the gases in the explosion-chamber should be free from all projections toward the interior of the cylinder; for during compression these uncooled projections may become incandescent and may thus cause premature ignition. As a general rule when the cap is placed in position the joint should be retightened after a certain time, when the surfaces have become sufficiently heated. In order to tighten the joints the bolts and nuts should not be oiled; otherwise the removal of the cap becomes difficult.
Water Circulation.—In a previous chapter, the importance of the water circulation and the necessity of keeping the cylinder-jacket hot, have been sufficiently dwelt upon. As the cylinder tends to become hotter with an increase in the load, because of the greater frequency of explosions, it is advisable to regulate the flow of the water in order to prevent its becoming more than sufficient in quantity when the engine is lightly loaded; for under these conditions the cylinder will be cold and the explosive mixture will be badly utilized. A suitable temperature of 140 to 158 degrees F. is easily maintained by adjusting the circulation of the water. This can be accomplished by providing the water-inlet pipe leading to the cylinder with a cock which can be opened more or less, as may be necessary. The temperature of 140 to 158 degrees F., which has been mentioned, may, at first blush, seem rather high because it would be impossible to keep the hand on the outlet-pipe. The cylinder, however, will not become overheated so long as it is possible to hold the hand beneath the jacket near the water-inlet. This relates only to engines having a compression of 50 to 100 lbs. per square inch. For engines of higher compression, a lower running temperature will be safer. On this matter the instructions of the engine maker should be carried out.
Adjustment.—Gas-engines, at least those which are built by trustworthy firms, are always put to the brake test before they are sent from the shops, and are adjusted to meet the requirements of maximum efficiency. But since the nature and quality of gas necessarily vary with each city, it is evident that an engine adjusted to develop a certain horse-power with a gas of a certain richness, may not fulfil all expectations if it is fed with a gas less rich, less pure, hotter, and the like. The altitude also has some influence on the efficiency of the engine. As it increases, the density of the mixture diminishes; that is to say, for the same volume the engine is using a smaller amount. From this it follows that a gas-engine ought to be adjusted as a general rule on the spot where it is to be used.
The fulfilment of this condition is particularly important in the case of explosion-engines, because an advancement or retardation of only one-half a second in igniting the explosive mixture will cause a considerable loss in useful work. From this it would follow that gas-engines should be periodically inspected in order that they may operate with the highest efficiency and economy. As in the case of steam-engines, it is advisable to take indicator records which afford conclusive evidence of the perturbations to which every engine is subject after having run for some time.
Most gas-engine users either have no indicating instruments at their disposal or else are not sufficiently versed in their employment and the interpretation of their records to study perturbations by their means. For this reason the advice of experts should be sought,—men who understand the meaning of the diagrams taken and who are able by their means to effect a considerable saving in gas.
CHAPTER VIII
The first step which is taken in starting an engine driven by street-gas is, naturally, the opening of the meter-cock and the valves between the meter and the engine. When the gas has reached the engine, the rubber bags will swell up and the anti-pulsator diaphragm will be forced out. The drain-cock of the gas-pipe is then opened. In order to ascertain whether the flow of gas is pure, a match is applied to the outlet of the cock. The flame is allowed to burn until it changes from its original blue color to a brilliant yellow.
If the hot-tube system of ignition be employed, the Bunsen burner is ignited, care being taken that the flame emerging from the tube is blue in color. If necessary the admission of air to the burner is regulated by the usual adjusting-sleeve. A white or smoky flame indicates an insufficient supply of air to the burner. A characteristic sooty odor is still other evidence of the same fact. Sometimes a white flame may be produced by the ignition of the gas at the opening of the adjusting-sleeve. A blue or greenish flame is that which has the highest temperature and is the one which should, therefore, be obtained. About five or ten minutes are required to heat up the tube, owing to the material of which it is made. When the proper temperature has been attained the tube becomes a dazzling cherry red in color. While the tube is being heated up, it is well to determine whether the engine is properly lubricated and all the cups and oil reservoirs are duly filled up. The cotton waste of the lubricators should be properly immersed, and the drip lubricators examined to determine whether they are supplying their normal quantity of oil.
The regulating-levers of the valves should be operated in order to ascertain whether the valves drop upon their seats as they should. The stem of the exhaust-valve should be lubricated with a few drops of petroleum.
If the ignition system employed be of the electric type, with batteries and coils, tests should be made to determine whether the current passes at the proper time on completing the circuit with the contact mounted on the intermediary shaft. This contact should produce the characteristic hum caused by the operation of the coil.
If a magneto be used in connection with the ignition apparatus, its inspection need not be undertaken whenever the engine is started, because it is not so likely to be deranged. Still, it is advisable, as in the case of ignition by induction-coils, to set in position the device which retards the production of the spark. This precaution is necessary in order to avoid a premature explosion, liable to cause a sharp backward revolution of the fly-wheel.
After the ignition apparatus and the lubricators have been thus inspected, the engine is adjusted with the piston at the starting position, which is generally indicated by a mark on the cam-shaft. The starting position corresponds with the explosion cycle and is generally at an angle of 40 to 60 degrees formed by the crank above the horizontal and toward the rear of the engine. The gas-cock is opened to the proper mark, usually shown on a small dial. If there be no mark, the cock is slowly opened in order that no premature explosion may be caused by an excess of gas.
The steps outlined in the foregoing are those which must be taken with all motors. Each system, however, necessitates peculiar precautions, which are usually given in detailed directions furnished by the builder.
As a general rule the engines are provided on their intermediary shafts with a "relief" or "half-compression" cam. By means of this cam the fly-wheel can be turned several times without the necessity of overcoming the resistance due to complete compression. Care should be taken, however, not to release the cam until the engine has reached a speed sufficient to overcome this resistance.
Engines of considerable size are commonly provided with an automatic starting appliance. In order to manipulate the parts of which this appliance is composed, the directions furnished by the manufacturer must be followed. Particularly is this true of automatic starters comprising a hand-pump by means of which an explosive mixture is compressed,—true because in the interests of safety great care must be taken.
The tightness and free operation of the valves or clacks which are intended to prevent back firing toward the pump should be made the subject of careful investigation. Otherwise, the piston of the pump is likely to receive a sudden shock when back firing occurs.
When the engine has been idle for several days, it is advisable, before starting, to give it several turns (without gas) in order to be sure that all its parts operate normally. The same precaution should be taken in starting an engine, if a first attempt has failed, in order to evacuate imperfect mixtures that may be left in the cylinder. Before this test is made, the gas-cock should, of course, be closed in order to prevent an untimely explosion. It is advisable in starting an engine not to bend the body over the ignition-tube, because the tube is likely to break and to scatter dangerous fragments.
Under no condition whatever should the fly-wheel be turned by placing the foot upon the spokes. All that should be done is to set it in motion by applying the hand to the rim.
Care During Operation.—When the engine has acquired its normal speed, the governor should be looked after in order that its free operation may be assured and that all possibility of racing may be prevented. After the engine has been running normally for a time, the cocks of the water circulation system should be manipulated in order to adjust the supply of water to the work performed by the engine. In other words the cylinder should be kept hot, but not burning, as previously explained in the paragraph in which the water-jacket is discussed. The maintenance of a suitable temperature is extremely important so far as economy is concerned. All the bearings should be inspected in order that hot boxes may be obviated.
Stopping the Engine.—The steps to be taken in stopping the engine are the following:
1. Stopping the various machines driven by the engine,—a practice which is followed in the case of all motors;
2. Throwing out the driving-pulley of the engine itself, if there be one;
3. Closing the cock between the meter and the gas-bags in order to prevent the escape of gas and the useless stretching of the rubber of the bags or of the anti-pulsating devices;
4. Actuating the half-compression or relief cam as the motor slows down, in order to prevent the recoil due to the compression;
5. Closing the gas-admission cock;
6. Shutting off the supply of oil of free flowing lubricators, and lifting out the cotton from the others.
If the engine be used to drive a dynamo, particularly a dynamo provided with metal brushes, the precaution should be taken of lifting the brushes before the engine is stopped in order to prevent their injury by a return movement of the armature-shaft;
7. Shutting off the cooling-water cock if running water is used.
If the engine is exposed to great cold, the freezing of the water in the jacket is prevented while the engine is at rest, either by draining the jacket entirely, or by arranging a gas jet or a burner beneath the cylinder for the purpose of causing the water to circulate. If such a burner be used the cocks of the water supply pipe should, of course, be left open.
CHAPTER IX
In this chapter will be discussed certain perturbations which affect the operations of gas-engines to a more marked degree than lack of care in their construction. In previous chapters defects in operation due to various causes have been dwelt upon, such as objectionable methods in the construction of an engine, ill-advised combination of parts, defects of installation, and the like; and an attempt has been made to determine in each case the conditions which must be fulfilled by the engine in order to secure efficiency and economy at a normal load.
Difficulties in Starting.—The preliminary precautions to be taken in starting an engine having been indicated, it is to be assumed that the advice given has been followed. Nevertheless various causes may prevent the starting of the engine.
Faulty Compression.—Defective compression, as a general rule, prevents the ignition of the explosive mixture. Whether or not the compression be imperfect can be ascertained by moving the piston back to the period corresponding with compression, in other words, that position in which all valves are closed. If no resistance be encountered, it is evident that the air or the gaseous mixture is escaping from the cylinder by way of the admission-valve, the exhaust-valve, or the piston. The valves, ordinarily seated by springs, may remain open because their stems have become bound, or because some obstruction has dropped in between the disk and the seat. In a worn-out or badly kept engine the valves are likely to leak. If that be the case grinding is the only remedy. If a valve be clogged, which becomes sufficiently evident by manipulating the controlling levers, it is necessary simply to clean the stem and its guides in order to remove the caked oil which accumulates in time. If the engine be new, the binding of the valve-stems is often caused by insufficient play between the stems and their guides. Should this prove to be the case, the defect is remedied by rubbing the frictional surface of the stem with fine emery paper and by lubricating it with cylinder-oil. The exhaust-valve, however, should be lubricated only with petroleum.
It is not unlikely that the exhaust-valve may leak for two other reasons. In the first place, the tension of the spring which serves to return the valve may have lessened and may be insufficient to prevent the valve from being unseated during suction. Again, the screw or roller serving as a contact between the lever and the valve-stem, may not have sufficient play, so that the lengthening of the stem on account of its expansion may prevent the valve from falling back on its seat. The first-mentioned defect is remedied by renewing the spring, or by the provision of an additional spring or of a counterweight in order to prevent the stoppage of the motor. The second defect can be remedied by regulating the contact.
Leakage past the piston may be caused by the breaking of one or more rings, by wear or binding of the rings, or by wear or binding of the cylinder. The whistling caused by the air or the mixture as it passes back proves the existence of this fault.
Presence of Water in the Cylinder.—It may sometimes happen that water may find its way into the cylinder with the gas by reason of the bad arrangement of the piping. It may also happen that water may enter the cylinder through the water-jacket joint. Again, the presence of water in the cylinder may be due to condensation of the steam formed by the chemical union of the hydrogen of the gas and the oxygen of the air, which condensation is caused by the cool walls of the cylinder. The water may sometimes accumulate in the exhaust pipe and box, when they have been improperly drained, and may thus return to the cylinder. Whatever may be its cause, however, the presence of water in the cylinder impedes the starting of the engine, because the gases resulting from the explosion are almost spontaneously chilled, thereby diminishing the working pressure.
If electric ignition be employed, drops of water may be deposited between the contacts, thereby causing short circuits which prevent the passing of the spark.
If there be no drain-cock on the cylinder, the difficulty of starting the engine can be overcome only by ceaseless attempts to set it in motion. The leaky condition of a joint as well as the presence of a particle of gravel in the cylinder-casting, through which the water can pass from the jacket, is attested by the bubbling up of gas in the water-tank at the opening of the supply tube. These bubbles are caused by the passage of the gas through the jacket after the explosion. If such bubbles be detected, the cylinder should be renewed or the defect remedied. In order to obviate any danger, the stop-cocks of the water-jacket, which have already been described in a previous chapter, should be closed while the engine is idle.
Imperfect Ignition.—The difficulties encountered in starting an engine, and caused by imperfect ignition, vary in their nature with the character of the ignition system employed, whether that system, for example, be of the electric, or of the incandescent or hot tube type. Frequently it happens that in starting an engine a hot tube may break. If the tube be of porcelain the accident may usually be traced to improper fitting or to the presence of water in the cylinder. If the tube be of metal, its breaking is caused usually by a weakening of the metal through long use—an accident that occurs more often in starting the engine than in normal operation, because the explosions at starting are more violent, owing to the tendency of the supply-pipes to admit an excess of gas at the beginning.
A misfire arising from a faulty tube in starting may be caused by an obstruction or by leaks at the joints or in the body of the tube itself, thereby allowing a certain quantity of the mixture to escape before ignition. This defect in the tube is usually disclosed by a characteristic whistling sound.
A tube may leak either at the bottom or at the top. In the first case, starting is very difficult, because the part of the mixture compressed toward the tube will escape through the opening before it reaches the incandescent zone. In the second case, ignition may be simply retarded to so marked an extent that a sufficient motive effect cannot be produced. An example of this retardation, artificially produced to facilitate the starting and to obviate premature explosions, is found in a system of ignition-tubes provided with a small cock or variable valve (Figs. 74 and 75).
The mere enumeration of defects caused by leakage is sufficient to indicate the remedy to be adopted. It may be well to recall in this connection the important part played by the ignition-valve. If it be leaky, or if its free operation be impeded, starting will always be difficult.
Electric Ignition by Battery or Magneto.—If the electric ignition apparatus, whatever may be the method by which the spark is produced, be imperfect in operation, the first step to be taken is to ascertain whether the spark is produced at the proper time, in other words, slightly after the dead center in the particular position given to the admission device at starting. If a coil and a battery be employed, it is advisable to remove the plug and to place it with its armature upon a well-polished metal surface to produce an electrical contact, preventing, however, the contact of the binding post with this metallic surface. The same method of inspection is adopted with the make-and-break apparatus of an electric magneto. In both cases it should be ascertained whether or not there is any short-circuiting. The contacts should be cleaned with a little benzine if they are covered with oil or caked grease.
If no spark is produced at the plug or at the make-and-break device it may be inferred that the wires are broken or that the generating apparatus is out of order. A careful examination will indicate what measures are to be taken to cure the defects.
Premature Ignition.—It has several times been stated that the moment of ignition of the gaseous mixture has a pronounced influence on the operation of gas-engines and upon their economy.
Premature ignition takes place when there is a violent shock at the moment when the piston leaps from the rear dead center to the end of the compression stroke. The violent effects produced are all the more harmful because they tend to overheat the interior of the engine and thereby to increase in intensity.
Premature ignition may be due to several causes. If a valveless hot tube be employed it may happen that the incandescent zone is too near the base. If the tube be provided with a valve, it very frequently happens that the valve leaks or that it opens too soon. In the case of electric ignition, the circuit may be completed before the proper time, because of faulty regulation. The suggestions made in the preceding chapters indicate the method of remedying these defects.
Faulty ignition may have its origin not only in the method of ignition employed, but also in excessive heating of the internal parts of the engine, caused by continual overloading or by inadequate circulation of water.
Passing to those cases of premature ignition of a special nature which are not due to any functional defect in the engine, but which are purely accidental in origin, such as the uncleanliness of the parts within the cylinder or the presence of some projecting part which becomes heated to incandescence during compression, it should first be stated that these ignitions, usually termed spontaneous, often occur well in advance of the end of the compression stroke. They are characterized by a more marked shock than that caused by ordinary premature ignition and usually result in bringing the engine to a complete stop in a very short time. These spontaneous explosions counteract to such an extent the impulse of the compression period, during which the piston is moving back, that they have a tendency to reverse the direction in which the engine is running. In such cases a careful inspection and a scrupulous cleaning of the cylinder and of the piston should be undertaken.
The bottom of the piston is particularly likely to retain grease which has become caked, and which is likely to become heated to incandescence and spontaneously to ignite the explosive mixture.
Untimely Detonations.—The sound produced by the explosions of a normally operating engine can hardly be heard in the engine-room. Untimely detonations are produced either at the exhaust, or in the suction apparatus, near the engine itself. These detonations are noisier than they are dangerous; still, they afford evidence of some fault in the operation which should be remedied.
Detonations produced at the exhaust are caused by the burning of a charge of the explosive mixture in the exhaust-pipe, which charge, for some reason, has not been ignited in the cylinder, and has been driven into the exhaust-pipe, where it catches fire on coming into contact with the incandescent gases discharged from the cylinder after the following explosion.
Detonations produced in the suction apparatus of the engine, which apparatus is either arranged in the base itself or in a separate chest, are often noisier than the foregoing. They are caused by the accidental backward flowing of the explosive mixture, and by its ignition outside of the cylinder. The accident may be traced to three causes:
1. The suction-valve of the mixture may not be tight and may leak during the period of compression, allowing a certain quantity of the mixture to pass into the suction-chest or into the frame. When the explosion takes place in the cylinder that part of the mixture which has passed back is ignited, as we have just seen, thereby producing a very loud deflagration. The obvious remedy consists in making the suction-valve tight by carefully grinding it.
2. It may happen that at the end of the exhaust stroke incandescent particles may remain in the cylinder, which particles may consist of caked oil or may be retained by poorly cooled projections. The result is that the mixture is prematurely ignited during the suction period.
3. The engine is so regulated, particularly in the case of English-built engines, as to effect what is technically called "scavenging" the products of combustion. In order to obtain this result, the mixture-valve is opened before the end of the exhaust stroke of the piston and the closing of the exhaust-valve. Owing to the inertia and the speed acquired by the products of combustion shot into the exhaust-pipe after explosion, a lowering of the pressure is produced in the cylinder toward the end of the stroke, causing the entrance of air by the open admission-valve and consequently effecting the scavenging of the burnt gases, part of which would otherwise remain in the cylinder. It is evident that if a charge of the mixture has not been normally exploded, either because its constituents have not been mingled in the proper proportion, or because the ignition apparatus has missed fire, this charge at the moment of exhausting will pass out of the cylinder without any acquired speed, and will flow back in part at the end of the exhaust stroke past the prematurely opened admission-valve, thereby lodging in the air suction apparatus. Despite the suction which takes place immediately following the re-entrance of the gas into the cylinder, a certain quantity of the mixture is still confined in the suction-pipe and its branches, where it will catch fire at the end of the exhaust stroke after the opening of the mixture-valve.
In order to avoid these detonations it is necessary simply to see to it that the mixture is regularly ignited. This is accomplished by mixing the gas and air in proper proportions or by correcting the ignition time.
Retarded Explosions.—Retarded explosions considerably reduce the power which an engine should normally yield, and sensibly increase the consumption. They are due to three chief causes: (1), faulty ignition; (2), the poor quality of the mixture; (3), compression losses. The existence of the defect cannot be ascertained with any certainty without the use of an indicator or of some registering device which gives graphic records. Nevertheless, it is possible in some degree to detect retarded explosions, simply by observing whether there is a diminution in the power or an excessive consumption, despite the perfect operation and good condition of all the engine parts.
In order to remedy the defect it should be ascertained if the compression is good, if the supply of gas is normal, and if the conditions under which the mixture of air and gas is produced have not been changed. Lastly, the ignition apparatus is gradually adjusted to accelerate its operation until a point is reached when, after explosion, shocks are produced which indicate an excessive advance. The ignition apparatus is then adjusted to a point slightly ahead of the corresponding position. Recalling the descriptions already given of the various systems of ignition, the manner of regulating the moment of ignition in each case may be summarized as follows:
1. For the valveless incandescent tube, provided with a burner the position of which can be varied, ignition can be accelerated by bringing the burner nearer to the base. Retardation is effected by moving the burner away from the base.
2. In the case of the incandescent tube of the fixed burner type, the moment of ignition will depend upon the length of the tube. The retardation will be greater as the tube is shorter, and vice versa.
3. If the tube be provided with an ignition-valve, the time of ignition having been regulated by the maker, regulation need not be undertaken except if the valve-stem be worn or the controlling-cam be distorted. If these defects should be noted, the imperfect parts should be repaired or renewed.
4. In electric igniters the controlling apparatus is generally provided with a regulating device which may be manipulated during the operation of the motor. If the manual adjustment of the regulating apparatus be unproductive of satisfactory results, it is advisable to ascertain whether the spark is being produced normally. Before the engine has come to a stop, one of the valve-casings is raised, and through the opening thus produced it is easily seen whether the spark is of sufficient strength, the engine in the meanwhile being turned by hand. Care should always be taken to purge the cylinder of the gas that it may contain, in order to prevent dangerous explosions. If the spark should prove to be too feeble, or if there be no spark at all, despite the fact that every part of the mechanism is properly adjusted, it may be inferred that the fault lies with the current and is caused by
1. Imperfect contact with the binding-posts, with the conducting wire, or with the contact-breaking members;
2. A short circuit in one of the dismembered pieces;
3. The presence of a layer of oil or of caked grease forming an insulator, injurious to induction, between the armature and the magnets;
4. A deposit of oil or moisture on the contact-breaking parts;
5. The exhaustion of the magnets, which, however, occurs only after several years of use, except when the magneto has been subjected for a long time to a high temperature.
The mere discovery of any of these defects sufficiently indicates the means to be adopted in remedying them.
Lost Motion in Moving Parts.—Lost motion of the moving parts is due to structural errors. Its cause is to be found in the insufficient size of the frictional bearing surfaces, and improper proportioning of shafts, pins, and the like. The result is a premature wear which cannot be remedied. Imperfect adjustment, lack of care, and bad lubrication, may also hasten the wear of certain parts. This wear is manifested in shocks, occurring during the operation of the engine,—shocks which are particularly noticeable at the moment of explosion.
Besides the inconveniences mentioned, wearing of the gears and of the moving parts leads to derangement of the power-transmitting members.
So far as the admission and exhaust valves are concerned, the wearing of the cams, rollers, and lever-pivots is evidenced by a retardation in the opening of these valves and an acceleration in their closing.
The ignition, whatever may be the system employed, is affected by lost motion and is retarded. The engine appreciably loses in power, and its consumption becomes excessive.
Overheated Bearings.—Apart from the imperfect adjustment of a member, it may happen that the bushings of the main bearings of the ends of the connecting-rod, and of the piston-pivot, may become heated because of excessive play, or of too much tightening, or of a lack of oil, or of the employment of oil of bad quality. The overheating may lead to the binding of frictional surfaces and even to the fusion of bushings if they be lined with anti-friction metal. In order to avoid the overheating of parts, it is advisable, while the engine is running, to touch them from time to time with the back of the hand. As soon as the slightest overheating is felt, the temperature may be lowered often by liberal oiling. If this be inadequate and if for special reasons it is impossible to stop the engine, the overheated part may be cooled by spraying it with soapy water.
If the overheating has not been detected or reduced in time, a characteristic odor of burnt oil will be perceived, accompanied by smoke. The part overheated will then have attained a temperature so high that it cannot be touched with the hand. Should this occur, it is inadvisable to employ oil, because it would immediately burn up and would only aggravate the conditions. Cotton waste should be carefully applied to the overheated member, and gradual spraying with soapy water begun.
In special cases where the lubricating openings or channels are not likely to be obstructed, a little flowers of sulphur may be added to the oil, if this be very fluid. Castor oil may also be successfully employed.
If the binding of the rubbing surfaces should prevent the reduction of the overheated member's temperature, the engine must necessarily be stopped, and the parts affected detached. All causes of binding are removed by means of a steel scraper. The surfaces of the bushings and of the shaft which they receive are smoothed with a soft file and then polished with fine emery paper. Before the parts are replaced, the precaution of ascertaining whether they touch at all points should be taken. Careful inspection and copious lubrication should, of course, be undertaken when the engine is again started.
Overheating of the Cylinder.—The overheating of the cylinder may be due to a complete lack of water in the jacket or to an accidental diminution in the quantity of water supplied. If this discovery is made too late, and if the cylinder has reached a very high temperature, the circulation of the water should not be suddenly re-established, because of the liability of breaking the casting. It is best to stop the engine and to restore the parts to their normal condition.
It is well to recall at this point that if the calcareous incrustation of the water-jacket or the branch pipes should hinder the free circulation of water, cleaning is, of course, necessary. The jacket may be washed several times with a twenty per cent. solution of hydrochloric acid. After this treatment the jacket should, of course, be rinsed with fresh water before the piping of the water-circulating apparatus is again connected.
Overheating of the Piston.—If the overheating of the piston is not due to faulty adjustment, it may be caused by lack of oil or to the employment of a lubricant not suitable for the purpose. In a previous chapter the importance of using a special oil for cylinder lubrication has been insisted upon. The overheating of the piston can also result from that of the piston-pin. Should this be the case it is advisable to stop the engine, to ascertain the condition and the degree of lubrication of this member and its bearing. Overheating of the piston is manifested by an increase of the temperature of the cylinder at the forward end. If this overheating be not checked, binding of the piston in the cylinder is likely to result.
Smoke Arising from the Cylinder.—This is generally a sign either of overheating, which causes the oil to evaporate, or of an abnormal passage of gas, caused by the explosion. Abnormal passage of gas may result from wear or from distortion of the cylinder, or from wear or breakage of the piston-rings. The result is always the overheating of the cylinder and a reduction in compression and power.
If the engine is well kept and shows no sign of wear, leakage may be caused simply by the fouling of the piston-rings, which then adhere in their grooves and have but insufficient play. This defect is obviated by cleaning the rings in the manner explained in Chapter VII.
Lubrication is faulty when the quantity of lubricant supplied is either insufficient or too abundant, or when the oils employed are of bad quality. It has already been shown that insufficient lubrication and the utilization of bad oils leads to the overheating of the moving parts.
Insufficient lubrication may be caused by imperfect operation of the lubricators, or, particularly during cold weather, by too great a viscosity or congelation of the oil. If a lubricator be imperfect in its operation, the condition of its regulating mechanism should be ascertained, if it has any, and an examination made to discover any obstruction in the oil-ducts. Such obstructions are very likely to occur in new devices which have been packed in cotton waste or excelsior, with the result that the particles of the packing material often find their way into openings.
An oil may be bad in quality because of its very nature, or because of the presence of foreign bodies. In either case an oil of better quality should be substituted.
The freezing of oil by intense cold may be retarded by the addition of ordinary petroleum to the amount of 10 to 20 per cent.
An excess of oil in the bearings results simply in an unnecessary waste of lubricant, and the splashing of oil on the engine and about the room. If too much oil be used in the cylinder, grave consequences may be the result; for a certain quantity of the oil is likely to accumulate within the cylinder, where it burns and forms a caky mass that may be heated to incandescence and prematurely ignite the explosive mixture. Especially in producer-gas engines is an excess of cylinder-lubricant likely to cause such accidents. Indeed, the temperature of explosion not being as high as in street-gas engines, the excess oil cannot be so readily removed with certainty by evaporation or combustion. On the other hand, the compression of the mixture being generally higher, premature ignition is very likely to occur.
Back Pressure to the Exhaust.—How the pipes and chests for the exhaust should be arranged in order not to exert a harmful influence on the motor has already been explained. Even if the directions given have been followed, however, the exhaust may not operate properly from accidental causes. Among these causes may be mentioned obstructions in the form of foreign bodies, such as particles of rust, which drop from the interior of the pipes after the engine has been running for some time and which, accumulating at any place in the pipe, are likely to clog the passage. Furthermore, the products of combustion may contain atomized cylinder oil which finds its way into the exhaust-pipe. This oil condenses on the walls of the elbows and bends of the pipe in a deposit which, as it carbonizes, is converted into a hard cake and which reduces the cross-section of the passage, thereby constituting a true obstacle to the free exhaust of the gases.
These various defects are manifested in a loss in engine power as well as in an abnormal elevation of the temperature of the parts surrounding the exhaust opening.
Sudden Stops.—Sudden stops are occasioned by faulty operation of the engine, and by imperfect fuel supply. Among the first class the chief causes to be mentioned are the following:
1. Overheating, which has already been discussed and which may block a moving part.
2. Defective ignition.
3. Binding of the admission-valve or of the exhaust-valve, preventing respectively suction or compression.
4. The breaking or derangement of a member of the distributing mechanism.
5. A weakening of the exhaust-valve spring, so that the valve is opened by the suction of fresh quantities of mixture.
These faults are due to carelessness and improper inspection of the engine.
So far as the fuel supply of the engine is concerned, the causes of stoppage will vary if street-gas or producer-gas be employed. In the former case the difficulty may be occasioned by the improper operation of the meter, by the formation of a water-pocket in the piping, by the binding of an anti-pulsator valve, by the derangement of a pressure-regulator, or by a sudden change in the gas pressure when no pressure-regulator is employed. If producer-gas be used, stoppages may be occasioned by a sudden change in the quality, quantity, or temperature of the gas. These defects will be examined in detail in the chapter on Gas-Producers.