One source of criticism is the thermal loss occasioned in this type of engine at low load factors. Using the class of governors just referred to, the injection point must be placed early enough in the cycle to enable all the fuel required at full load to be in jected before dead-center is reached. Indeed, the entire fuel charge must be injected sufficiently early to allow it to be com pletely vaporized by the time the, piston reaches dead-center. It follows, then, that even at low loads the fuel is introduced early in the stroke. This oil, on vaporizing, adds to the existing pressure in the cylinder against which the advancing piston must do work to overcome this resistance. This work is not given back during the expansion stroke since the cooling water has partially or totally absorbed the heat produced by the work performed during the compression stroke. With the variable governor, on light loads, since the admission is later, this loss is not so great. Under full-load conditions, the losses with each type are equal.
Another disadvantage lies in the inability of the engine to carry as great an overload as is possible with the variable injec tion engine. The reason for this is that the builders arrange the injection point to allow the full-load charge to be injected and vaporized before dead-center. The beginning of the injection is made as late as it is possible, while giving a sufficient time in terval for vaporization before dead-center. The result is that when an overload is experienced, the engine cannot obtain enough vaporized fuel before dead-center to enable it to carry.this addi tional load. If such an engine does display an ability to handle a large overload, it naturally follows that the normal injection point is too early for economical operation at partial loads. Another element that must be taken into consideration is the liability of preignition with early injection, but this can be con trolled by the use of water injection.
Bessemer Oil Engine Governor.—The governor used on this engine is decidedly novel in design. The governor proper, as shown in Fig. 310, is of the inertia type, the governor weight being in the form of a ring A. This ring is pivoted on one of the wheel arms B, and its movement following a change in speed is opposed by a tension spring C. The eccentric E is carried on an arm which is pivoted on the wheel at D and which has one end en gaged in a slide F on the weight circle. The eccentric drives the fuel pump through an eccentric strap and reach-rod G. It is evident that the governor circle will move outward when the engine speed increases. This shifts the eccentric E toward the shaft center, shortening the pump stroke; the reverse occurs on an increased load when the speed drops.
In order to limit the movement of the weight, an inner and outer stop is employed. The inner stop, which is the one ad jacent to the tension spring, limits the movement of the ring toward the spring. This stop, then, controls the maximum stroke which the pump plunger can take. On starting the engine, the inertia of the ring causes it to move more slowly than the wheel, and if there were no stop the pump stroke would be excessive.
To prevent the eccentric, at an increase of the engine speed, from moving across the shaft center, an outer stop is provided. This is adjusted to allow the eccentric sheave to throw central with the shaft at no load. This, then, is the minimum position of the eccentric, and, being central, no stroke of the plunger occurs. With this arrangement, if the spring breaks, there can be no run-away since the eccentric throw would be reduced to zero. To steady the governor and prevent hunting, a dashpot H is supplied. The eccentric rod is adjustable but, when shipped, is usually regulated to give the proper maximum pump stroke.
Bessemer Fuel Pump.—This governor is used in conjunction with the fuel pump in Fig. 312. The eccentric, through the agency of the eccentric rod, actuates the pump plunger a. The oil enters the pump body through the suction opening b and the suction valve F. The discharge valve is spring-loaded while the suction valve F is mechanically operated by means of a bell crank N and rod driven by the cam M, Fig. 311, which is keyed to the engine shaft. During the suction stroke of the pump the suction valve is held open by the bell-crank N and cam M. When the governor reaches its dead-center and begins its return or deliv ery stroke, the suction valve F is still held open. The oil then merely passes back through the suction passage. At the proper moment the flat spot 0 on the cam comes under the cam roller P. This allows the valve plunger spring, Fig. 312, to force the suction valve closed. The oil raises the discharge valve and enters the cylinder through the injection nozzle. After the crank turns 12 to 15 degrees, the roller leaves the flat surface of the cam, Fig. 311, and the suction valve is reopened. In actual operation the suction valve is not open longer than 3 degrees. This, of course, is due to the fact that the tappet does, not completely close the valve until_the roller has traveled several degrees on the flat spot. This valve-opening action prevents any further injection into the engine cylinder. The cam now holds the suction valve open for approximately 345 degrees.