The methods of igniting the working charges in gas and oil engines are details of design to which considerable study has been given without, however, having brought about anything like uniformity of practice. No one particular device, as was to be expected, has been centered upon as the best or most desirable one, and recurrence to the descriptions of engines already given in the preceding papers will show that electric ignition, flame ignition and ignition by incandescence all have found a share of favor in the eyes of gas engine builders. Electric ignition has been practiced either by the spark method, as in the early Lenoir engine, in which, at the proper times, an electric spark was made to pass between two electrodes within the cylinder, or by the incandescent wire method, in which an electric current was applied directly to heat a thin platinum wire. This latter method would appear to have been used only in an experimental way. Still another electric arrangement has been suggested a number of times, by which an electric arc was to be maintained in the cylinder of the engine, between two heavy platinum points, but this device, so far as can be found, simply figured in patent specifications, and never came into actual use. The flame method is currently employed in many good engines of the present day, and was put into its first practical shape more than fifty years ago, since which time it has undergone a variety of modifications. With the early non-compression engines, in which the pressure in the cylinder before explosion of the charge was the same as, or even less than, the pressure of the atmosphere, flame ignition was a comparatively simple thing, and it was easy enough to transfer a flame from the outer air into the interior of the cylinder with little, if any, trouble from extinction. In the early flame-ignition experiments the very simple expedient was adopted of providing a hole in the cylinder wall, which hole was uncovered by the piston after a portion of the stroke had been passed over, and the flame was sucked through it into the cylinder. The hole was either so small that no appreciable loss of pressure occurred upon explosion of the charge, or it was covered by a small valve which closed automatically as soon as the pressure in the cylinder rose. When the gases to which the flame was to be communicated, however, were under a pressure of some magnitude, as is the case in nearly all the gas engines of the present time, the difficulties of the ignition problem were at once increased. The method just referred to, and not ineptly termed the "touch-hole" method, obviously became inapplicable, and special valve devices had to be designed to meet the new conditions, a good example of one of them being that of the earlier Otto engine, as illustrated in the first paper of this series.
Ignition of explosive gas and air mixtures by contact with more or less highly heated metallic surfaces, or the hot-tube method, as it is now generally termed, was suggested independently by several investigators a number of years ago. The general scheme proposed was to ignite the gas and air charge by passing it through a metal tube heated to redness by a flame outside of it, and this method is in successful use to-day in a large number of engines. Wrought iron is generally employed for the tubes, though in a few engines platinum has been pressed into service, its higher cost being counter-balanced, in a measure, by its greater durability. A difficulty with the iron tubes is found in their rapid oxidation and furring, necessitating their more or less frequent renewal, but with their cheapness and the ease with which an old and worn-out one may be replaced by a new one, this objection is not so serious as might be supposed. In some engines the tubes are so screwed into the cylinders as to be constantly in communication with them, while in others, valves are arranged which admit the compressed air and gas charge to the tubes at the proper moment. The flame method and the hot-tube method just mentioned are the ones which seem to have secured the greater measure of popularity, being claimed, by their advocates, to be more certain in action and cheaper and simpler in arrangement than the electric devices. The latter, however, are by no means allowed to rest under any such imputations of comparative inefficiency. A number of engine builders have devoted much energy to their development and as a result, this type of ignition device is now used with much satisfaction in some of the best engines on the market. A flexible electrode arrangement, which is employed in several of these devices, affording absolute certainty of contact in completing the electric battery circuit, is one of the most important improvements that has been made in connection with them, and to it is mainly due their present satisfactory action.
/fig. 98.jpg) Fig. 98— Marine Type of Pacific Gas Engine |
One of the forms of gas and oil engines, in which this arrangement is in use, and which has attained much popularity, especially for boat propulsion, is the Pacific engine, built both by the
Union Gas Engine Company, of San Francisco, Cal., and the
Globe Gas Engine Company, of Philadelphia. One of the earlier designs of this engine, arranged as a launch motor, with reversing gear and circulating pump for the cylinder water jackets, is shown in Fig. 98. In this A represents a relief valve, through which part of the compressed vapor may be allowed to escape to facilitate starting up the engine. The throttle valve is marked
B, while
C and
D are gas and air regulating cocks;
E is the reversing lever which, by being shifted from the upper to the lower position, brings a back gear into operation and causes the propeller shaft to run in a reverse direction;
G is a clutch lever for stopping and starting the propeller shaft. The circulating pump
H takes water through the bottom of the boat, and discharges it into the lower part of the water jacket around the cylinder, while the overflow pipe
L from the upper part of the jacket is led out through the side of the boat above the water line. Water from the jacket may be drained off through the cock
K. The coupling for connecting the engine with the propeller shaft is placed at the end of the secondary shaft
I, The exhaust valve is marked
J. The engine works according to the Otto cycle, and the charge, as previously intimated, is fired by an electric spark,
F and
M being the wires from the battery, the former connecting with an interrupting device, so that a spark is produced only at the beginning of every second down stroke of the piston. It will be understood that, like in the several other launch outfits, described in some of the preceding papers, the engine itself is never reversed, but runs continuously in one direction, and the direction of motion of the propeller shaft and the secondary engine shaft alone is changed, when desired, by the lever arrangement already mentioned.
/fig. 99.jpg) Fig. 99— Section of Pacific Gas Engine |
The valve gearing of the engine, which is one of its special features, and entirely unlike that of any other engine in the market, is illustrated more clearly in the sectional view, Fig. 99. It will be noticed that on the crank-shaft is a cam,
P, having two grooves which run parallel part of the way around, and then intersect each other. A segment shaped finger, 5", rests in one of these grooves, and as the engine shaft revolves the finger is guided through the intersection from one groove to the other, and carries a swinging arm,
T, under the exhaust valve stem once in every two revolutions. The cam
O at those periods lifts the arm
T, and with it the exhaust valve rod, opening the valve and permitting the escape of the waste gases from the cylinder. The governor acts directly on the exhaust valve rod, holding it up, with the valve open, whenever the speed of the engine rises above the normal. The effect of this, to begin with, is that neither back pressure nor partial vacuum are created in the cylinder when running without working explosions, air from without being alternately drawn into the cylinder and expelled from it through the exhaust pipe. Admission of fresh gas and air mixture into the cylinder is, at such times, prevented simply by the fact that the exhaust passages are very large as compared with the gas and air inlet, and the exhaust valve, as stated, is held wide open, and there is thus less resistance to the flow of air through them than there is to the flow of gas and air mixture through its regular admission port and valve. The latter will, therefore, not open, and, consequently, no working charge can enter the cylinder until the governor catch on the exhaust valve rod is released by a falling off in the engine speed and the exhaust valve is allowed to close.
/fig. 101.jpg) Fig. 101— Double Cylinder Pacific Gas Engine |
The design of the engine has latterly been somewhat modified, but only in details which but slightly change its appearance, the manner of operation remaining exactly the same. A double cylinder engine is built on essentially the same lines as the one just described, and is shown in Fig. 101. This illustration also shows the improved form of vaporizer with which the engine is fitted when using gasoline, and which takes the place of the various forms of carburetors employed in connection with most other engines.
/fig. 100.jpg) Fig. 100— Vaporizer for Pacific Gas Engine |
The vaporizer is shown attached to the lower right hand part of the engine, at the side of the base near the fly-wheel, a detail view being given in Fig. 100. It consists of either a glass or metal body
E, glass being used in the one shown attached to the engine, and inside of this is a ball-shaped valve,
N, seated on the end of a tube connected with the air inlet pipe
G. Connection from the vaporizer to the engine cylinders is made at
M. A casing around the exhaust pipe of the engine affords an annular space through which the air is drawn on its way to the vaporizer inlet
G, and is heated by contact with the hot exhaust pipe. As the air enters the vaporizer body, it lifts the ball valve
N, and the latter strikes against the spindle
O of the gasoline valve, raising it and permitting a small quantity of gasoline to flow into the vaporizer through the cock A, from a conveniently placed tank at a higher level. The gasoline so admitted is at once turned into vapor by the heated air and is drawn off on its way to the engine through the connection
M.
The lower end of the valve
N is shown at
H where a leather washer,
I is provided on a collar,
J, the latter preventing the valve from lifting too high. The upper part
X X of the vaporizer proper is arranged so that it may be revolved by loosening the screw
D, enabling the attendant to observe the flow of gasoline through the opening,
C, if desired, when starting the engine. The gasoline and air inlet valves
O and
N, of course, open only during the suction strokes of the pistons, remaining shut during the remainder of the working cycles. In actual practice this vaporizer has been found to perform admirably, and some preliminary trials made even with ordinary oils have been found to give promising results. The vaporizer being directly attached to the engine, and not a separate addition like the several currently used carburetors, makes the whole outfit comparatively simple and self-contained. The stationary Pacific engine is, in all essential details, the same as the marine type except that the reversing and clutch gears are omitted.
/fig. 104.jpg) Fig. 104— Union Gas Engine |
Another engine, of the horizontal type, however, made by the same builders, and known as the Union engine, is shown in Fig. 104.
/fig. 102.jpg) Fig. 102—Valve Gear of Union Gas Engine |
| /fig. 103.jpg) Fig. 103— Vertical Section Through Valve Chambers of Union Gas Engine |
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Details of the valve gear and igniting device are shown in Figs. 102 and 103, the former representing an arrangement slightly different in appearance from that seen in the general view of the engine in Fig. 104, but exactly the same so far as the manner of operation is concerned. Motion from the crank shaft
C of the engine is reduced and transmitted to the cam shaft
A through a series of intervening gear wheels not shown in the illustration, and the several cams on this shaft A operate on the cam rollers
B and
D, the former being on a rocker arm which works both the inlet and exhaust valves at the same time through a bell crank,
E, while the latter is on another rocker arm controlling an electrode disc,
F. The inlet and exhaust valves are designated by the letters
G and
H, respectively, and it will be easily seen that when one of these valves is closed, the other is opened, and vice versa, a small rocking beam,
Y, being interposed for this purpose.
Mounted on the engine crank shaft is also the governor with its restraining spring and weight,
K, which latter, under the influence of excessive speed, moves outwards and, in the course of its revolution, depresses the catch lever
L. The latter when so depressed hooks on to the upper end of the rocker arm
B when the latter reaches its extreme right hand position, and keeps it there, with the inlet valve
G closed and the exhaust valve
H wide open, until the speed becomes slower and the governor weight again moves inward and no longer presses down the lever
L.
As in the case of the Pacific engine, previously described, the exhaust valve, in virtue of this arrangement, is held open constantly while the idle strokes of the piston are being made, air being freely drawn into and expelled from the engine cylinder through the exhaust pipe during this period, so that there is no possibility of a partial vacuum being formed in the cylinder, or of back pressure being created.
The current interrupter for the electric igniting device is shown at M, and requires no special explanation as its manner of working is quite clear from the illustration. There is, it will be noticed, a flexible contact strip carried by a collar on the rod operating the bell crank
E, and this strip, in moving back and forth with the rod in question, makes and breaks the electric contact at
M at the proper periods which are determined both by the governor and by the nature of the reducing gearing between the crank shaft
C and the cam shaft
A. A vertical section through the exhaust and inlet valve chambers, showing also the nature of the igniting electrode arrangement which is somewhat different from that used in the Pacific engine, is given in Fig. 103. The rod
R, in Fig. 102, connects by means of the pin
P, with the electrode disc
F, seen in both views, and gives it an oscillating motion which, of course, is imparted also to the electrode
K, carried on the end of the electrode disc spindle. This electrode
K, as will be at once understood, is thus made to alternately strike and clear the flexible electrode
S, which is connected with one of the battery wires, and when contact is thus made and broken at this point, contact also being made at the interrupter
M, in Fig. 102, a spark is produced which fires the explosive charge in the inlet valve chamber and cylinder. A four cylinder engine of this type, with the cylinders placed opposite one another in two pairs, and with a modified form of valve gear has been built and has given particularly good results in point of steadiness of speed. The igniting devices described form subjects of several patents.
/fig. 105.jpg) Fig. 105— Stockport Gas Engine |
| /fig. 106.jpg) Fig. 106— Vertical Hoisting Stockport Gas Engine |
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An English engine, which has achieved considerable prominence, is the Stockport engine, built by Messrs.
J. E. H. Andrew & Co., Limited, of Stockport. In its early form it was of the double-end design—that is to say, there were two horizontal cylinders placed opposite each other, one being the motor cylinder proper, and the other, the compressor cylinder, and the crank was placed midway between the two. A number of modifications have, however, of recent years, been instituted in the design, so that, in one of its latest shapes, the engine is substantially like that shown in Fig. 105. In this, it will be observed, there is no separate compressor cylinder, and the engine works according to the regular Otto cycle, with, normally, one explosion in every two revolutions. The valve gearing and governor are operated from a secondary shaft running along the side of the cylinder, and driven from the main shaft through intervening bevel gears. Firing of the working charge is accomplished by a tube igniter, and the valves all are of the poppet type.
/fig. 111.jpg) Fig. 111— Vibrating Stockport Governor |
On the larger engines the type of governor shown in Fig. 105 is used, while the smaller sizes are provided with a vibrating governor shown on page 375, in which a weight, riding on a spring, is moved by a vibrating lever. So long as the engine runs at a certain speed the weight keeps in position a small hit-and-miss lever, and gas enters the cylinder of the engine. With any variation of speed above the normal, however, the position of the weight changes, moving the valve operating lever out of gear and cutting off the gas supply. For electric lighting and other work requiring very steady motion, a special governor is used for varying the explosive mixture, so that the speed may be controlled without missing explosions in the cylinder.
Messrs.
Andrew & Co., who, by the way, are, next to Messrs.
Crossley Bros., of Manchester, England, probably the oldest firm of gas engine builders, are the makers also of the Bisschop engine—an engine which will probably appeal only to the smaller power users, being a surviving form of the early non-compression type of motor which has been almost completely driven out of the commercial gas engine field by the developments of recent years. In this engine the principal end aimed at is to get a small, workable engine with the least possible complication, economy of gas being a secondary consideration. Instead of having a water jacket, the cylinder has cast on it a number of radiating ribs, which carry away the heat of the explosions and keep the temperature of the cylinder walls at a reasonable point. The cylinder is vertical, the piston rod and its connections extending upward, and motion from the crosshead being imparted to the crank by a vibrating lever arrangement. In order to prevent sticking of the piston in the cylinder owing to the rather high temperature which it attains, it is fitted quite loosely without rings, and the pressure from the gas explosions is so slight that the leakage past the piston is not serious. The flame ignition method is used to fire the charge, the flame being drawn into the cylinder through an opening in its walls on the already mentioned
touch-hole principle.
In the matter of size of engines it is interesting to note that Messrs.
Andrew & Co. are now building Stockport engines indicating as high as 150 horse-power in a single cylinder. One of the largest gas-driven electric light installations in England, at More cam be, was equipped with eng1nes by them, the plant comprising three Stockport engines of sixteen horse-power each, a Dowson gas plant, and three dynamos of 300 lights each, besides a storage battery outfit.
/fig. 107.jpg) Fig. 107— 100 H.P. Tangye Gas Engine |
Messrs.
Tangye, Limited , of Birmingham, and Messrs. Crossley Bros., Limited, of Manchester, England, also have turned out noteworthy engines of large size, developing from eighty-five to 100 actual horse-power. One of the Tangye engines, rated at 115 indicated horse-power, furnishes power for fine weaving machinery in a Belfast mill, and is stated to give eminent satisfaction, both in point of economy and steady running.
/fig. 110.jpg) Fig. 110— 100 H.P. Crossley Gas Engine |
The Crossley-Otto engine is, in the main, similar to the Otto engine made in the United States, and already described in the first paper of this series, so that it is not necessary to enter into its details here. In nearly all the larger sizes of gas engines some form of starting device is now used which dispenses with the necessity of turning the fly wheels by hand —a proceeding which is not only difficult, but, in some cases, would be quite impossible.
/fig. 108.jpg) Fig. 108— Cylinder End Section of Stockport Gas Engine |
| /fig. 109.jpg) Fig. 109— Side View of Stockport Gas Engine Starting Gear |
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Of these starting gears that used by Messrs.
Andrew & Co. on their engines is shown in Figs. 108 and 109, the former representing a side view, and the latter a sectional view of the end of the cylinder. At
A is a Bunsen burner for heating the ignition tube
B. At
C is the exhaust valve, and above it a gas admission valve
E. Above, and at the outer end of the ignition tube
B, is an air outlet valve, with handle
D. At
F is a timing valve for fixing the period at which the gaseous mixture shall be admitted to the ignition tube. When it is desired to start the engine, the gas admission valve
E—over the exhaust valve
C—is opened. Gas commences to flow into the cylinder, which then contains only air at atmospheric pressure. This air is allowed to escape in quantity equal to that of the gas admitted by the valve at the end of and above the horizontal part of the ignition tube
B. As soon as sufficient gas has in this way flown into the cylinder to produce an explosive mixture where it enters into the ignition tube, ignition takes place and the engine starts. The valve
E and the air outlet valve are then closed, and the gas main, which had been previously closed, is opened and gas allowed to flow into the gas bag.
Messrs.
Tangye’s self-starter consists mainly of an air pump worked by hand, by means of which the space behind the piston may be filled with gas and air under a slight pressure. Some of this mixture enters the ignition tube and is fired, giving the initial impulse, after which the engine continues running in the regular way.
/fig. 112.jpg) Fig. 112— Clerk-Lanchester Starting Gear |
Messrs.
Robey & Co., of Lincoln, England, to whose engines reference was made in the July number of this magazine, use on their large engines what is known as the Clerk-Lanchester starter, illustrated in Fig. 112. It consists of a chamber
A, outside and separate from the engine, and of a capacity rather greater than that of the cylinder, with which it is connected by a pipe
E, and check valve
W. The crank being set at about fifteen degrees, gas is turned on by a tap
X, from the gas main
G, and it flows into the chamber by the pipe
J, mingling with the air therein and forming an explosive mixture. At the same time gas flows into the cylinder by the pipe shown. When the mixture is so far formed as to be flammable, it lights at the jet
Y, and a little later becomes of sufficient explosive strength. The tap
X is then closed, and the ejecting pressure ceasing, the flame at Y shoots back, ignites the gaseous mixture in the chamber, and this forces the gas in
E into the cylinder under a pressure of about fifty pounds per square inch, and forms there a compressed mixture which, on ignition, gives an average pressure in the cylinder of about eighty-five pounds per square inch, and starts the engine and its load.
In the line of petroleum motors, Germany would appear to have kept well abreast of other countries, and a number of German makers have established agencies outside of their own domain, notably in England, for the sale and general advertisement of their product, competing, thus, directly with a host of other engines in their own territory. Among these is the firm of
J. M. Grob & Co., of Leipsic-Eutritzsch, who are building an engine which in Germany, at least, seems to be well known, and to have found considerable favor for all kinds of work—marine, stationary and portable. It appears, in fact, to be a modification of the Capitaine engine, already described in one of the earlier papers of this series.
/fig. 113.jpg) Fig. 113— Grob’s Oil Engine |
| /fig. 114.jpg) Fig. 114— Vertical Section of Grob’s Oil Engine |
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Though on the market for only about two years and a half, something like 1400 of these engines are said to be now in use. The sectional view clearly explains the working mechanism. The engine belongs to that class of petroleum motors in which the oil is vaporized in a heated chamber before being drawn into the working cylinder, the vaporizing chamber being marked V in the illustration. Working, as the engine does, on the Otto cycle, it draws in air on its first down-stroke through the valve
A, and petroleum through the atomizer
S, the petroleum spray being vaporized in
V before it mixes with the fresh air and enters the working cylinder. The vapor and air mixture is compressed on the next up-stroke of the piston, the air and atomizer valves closing automatically, and explosion of the charge at the beginning of the second down-stroke of the cycle is produced by some of the mixture having been forced into hot vaporizer, which serves the purpose of an ignition tube. The working stroke having been performed, exhaust during the second up-stroke of the piston takes place through the valve E, which is worked by a long shaft receiving motion from the crank shaft of the engine through intervening gear wheels. The valve rod is not connected to the exhaust valve, but simply strikes against the valve spindle and pushes it upward, the seating of the valve being effected by a spring. The valve is opened only once in every two revolutions of the main shaft. Heating of the vaporizing chamber is effected by the lamp
L, and cooling water for the cylinder jackets enters and escapes through the connections
WW.
The oil pump
P, which supplies oil to the vaporizing chamber, is controlled by the governor in such a way that the amount is varied in accordance with the demand for power. The oil used is of the ordinary kind burned in lamps for illuminating purposes.
Information Sources
- Cassier's Magazine, V4, Sep 1893 pgs. 363-377