Figure 235 shows a card where such a heavy oil was used. The compression reached 275 pounds while the maximum cylinder pressure approximated 600 pounds. Since with light oils the combustion is in the nature of an explosion, preignitions will be present if the injection opening is not delayed. Tp allow necessary adjustments of the fuel in jection timing, the needle valve rocker arm is provided with a screw arrangement whereby the moving of the roller alters the timing. This is plainly seen in Fig. 234, a cross-section of a single-cylinder F.H. engine.
It is problematical whether the vaporizer is actually required after the engine is in operation and has become warmed. The compression pressure of 280 to 300 pounds should be sufficient to vaporize and ignite all save the heaviest of crude oils. That none of the light fuel oils ever reach the vaporizer is conclusively proven by the absence of soot or carbon. When heavy crude is burned, there is some carbon deposit, but not more than is usually found on the piston heads of Diesel engines when supplied with similar oils. Furthermore, true Diesel engines have been ob served operating with a compression as.low as 300 to 350 lbs. per sq. inch, in cases where piston rings leaked or where the engine was turning over very slowly. Under such conditions the Diesel would ignite every charge although the exhaust was somewhat cloudy. After an engine is warmed up, a compression of 275 to 300 lbs. per sq. inch will ignite any fuel above 28° Baume gravity.
Fuel Consumption. F.H. Oil fuel consumption this engine approaches the Diesel engine. Figure 236 shows the results of a test on one of these engines. It must be understood that such low fuel consumptions are not usually secured in opera tion. If a full-load consumption of .55 lb. per brake horsepower is obtained, the engine can be considered in excellent condition.
The indicator card, Fig. 235, is somewhat like a Diesel card, though the combustion line is not a constant-pressure one. The major part of the fuel charge explodes almost instantaneously, the slow combustion occurring with the heavier parts only.
Fuel Specifications. F.H. to the use of the vaporizer, practically all fuels above 16° Bamme.can be consumed with success. If the cylinder temperature is inadequate for the combustion of the heavy oils, the hot surface of the vaporizer will "crack" the oils and complete the ignition. With the
asphaltum-base heavy crude oils, a deposit of carbon Will usually be found in the vaporizer. This deposit is not as serious nor as extensive as in the low-pressure engine, and the cleaning need be performed only every month or so.
De La Vergne Fuel the F.H. engines the De La Vergne Co. employs the same fuel pump and governor as shown in Fig. 143. On the single-cylinder units the governor is the same while the operation of the pump is slightly different.
Valve Timing.—Figure 237 shows the valve timing for the F.H. engine. The timing of the valves does not differ materially from standard Diesel practice. The period of fuel injection varies with the fuel charge, although the period of fuel valve opening is constant.
Price Ignition System.—During the past year several American engine builders have begun the manufacture of semi-Diesel engines with the Price ignition system or principle. The theory of operation contemplates the use of a compression pressure of 200 lbs. per sq. inch. Into this combustion chamber two streams of oil are injected. These two streams meet and com bustion ensues due to the thorough breaking up of the oil charges.
The combustion chamber, which is located in the head or separately, as the builder chooses, is along the lines of Fig. 238. The two injection nozzles, a cross-section of which appears in Fig. 239, are placed in opposite sides of the chamber in an in clined position.
The cycle of events is as follows: The engine, which so far has been built on the four-stroke-cycle • plan, during the suction stroke draws in a cylinder charge of pure air. On the compression stroke this air is compressed to a final pressure of 200 lbs. per sq. inch. Six degrees before dead-center is reached the fueil pump injects an oil stream through the two nozzles. As a consequence of the excellent nozzle design, the two oil streams enter the combustion chamber in a highly divided con dition. These two jets of oil particles, traveling at a high velocity, meet at the center of the combustion space and ignite. The entire combustion is instantaneous, and the engine may be said to operate on the "constant-volume" or Otto cycle. The remainder of the engine's events are such as is usual in a four stroke-cycle engine.