It remains here during the entire compression stroke. If the oil varies in character, it will ignite earlier or later as the case may be. There is, then, a danger of pre ignition. Figure 221 is an in dicator card taken from an engine equipped with this device. The primary explosion occurred when the piston was approximately 20 degrees ahead of dead-center. The injection of the oil from the cup into the cylinder and the igni tion of this charge took place some 15 degrees after dead center had been passed. The burning of this main charge is shown in the horizontal line. Apparently the combustion of part of the heavy particles was somewhat delayed, the burning taking place at the point C.
It is to be expected that this cup will require the same care as the one previously described. Since the injection is not posi tively controlled, the openings H must be altered in size to regu late the flow of oil through them. On a light oil, if the openings are large, the injection will be early, causing preignition. The compression carried, averaging 450 pounds, requires a sturdiness of construction approaching the Diesel. The cup and fuel valve must be maintained in the best of shape. The smallest leak will lower the cup compression. Since the explosive pressure ap proximates 600 pounds, it is evident that the valve must be ground often and with the utmost intelligence. As there is no water cooling of this valve and seat, it will corrode and pit if it does not receive attention. This device is found on the horizontal Atlas Lyons (now Midwest) V.D.H. engines, as well as on the Burnoil engine. An illustration of the V.D.H. engine appears in Fig. 222. The governor, which is of the spring-loaded type, is driven off the layshaft and controls the fuel needle valve E in Fig. 220.
Lyons-Atlas Vertical V.D.H. Engines.—On their vertical V.D.H. engine the Lyons-Atlas Co. has eliminated the governor controlled needle valve and uses a fuel pump for each engine cyl inder, the fuel pump being under governor control.
The vertical engine is illustrated in Fig. 223. The cylinders, which are 9-inch bore by 13-inch stroke, are mounted on A-frames. On one side the frames are open, being supported by tension rods. The openings are covered by steel oil guards that are removable. The cylinder construction is quite unusual. Each cylinder is provided with a removable skirt. This skirt can be unbolted, allowing the piston to be swung out to the side without unship ping the connecting-rod from the crank. The engine is built
for both stationary and marine service.
Fuel Consumption. Hvid Engines.—The fuel consumptions of the various engines employing the Hvid principle are prac tically the same. Table XVI covers tests on a three-cylinder vertical engine, 9;-inch bore by 10;-inch stroke, and is quite representative of this type.
Nordberg Ignition . Device.—Another form of ignition cup, adopted by the Nordberg Manufacturing Co. for their two-stroke cycle semi-Diesel (or high-compression, as the manufacturers call it) engine, appears in Fig. 224. The fuel oil is injected into the cup A through the atomizing nozzle B, by the action of the fuel pump, a few degrees before mid-point in the compression stroke. This fuel, as it leaves the injection nozzle, mixes with the air which has been forced into the cup by the advancing engine piston. As with the devices already discussed, the lighter con stituents ignite as soon as the oil enters the hot cup and mingles with the air. The combustion of this part of the oil charge creates, within the cup, an extremely high pressure, which is much greater than the engine compression pressure. This dif ference in the two pressures causes the remainder of the fuel charge to be forced out through the ports marked C. The high velocity of the fuel passing through the ports C atomizes it suffi ciently to produce ignition when mixed with the air charge in the cylindei.
In this engine the point of injection of the fuel into the cup is about mid-stroke of the piston. Since the timing of the injection of the main charge from the cup into the cylinder is not under positive control, with certain oils preignition may occur. If the oil is of light gravity, the high compression pressure carried will cause it to ignite very early. This primary explosion forces the main charge into the cylinder before dead-center, causing preignition and bearing pounding. To avoid premature combus tion, the cup is designed with a water-cooled space; this assists in keeping down the temperature of the cup and delays combus tion.
Figure 225 is a later design of cup. In this the water-cooling is discarded. The injection nozzle is provided with a spring loaded check valve and is held in position by a screwed lock bushing instead of a locking bar as was used on the former design. The bowl of the cup is bolted to the body of the igniter; this eliminates the difficulty experienced with the screwed ring collar of the previous cup.