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50 Improved Marine Diesel (Continued from Page 20) design of this type which will be used for illustration purposes. Referring to the cross section view of this engine, the first thing which will be noticed is the absence of com- plicated parts. In the two cycle en- gine there are no inlet or exhaust valves, as the piston performs these functions. It will be noticed in the illustration that the piston is in the lower dead center position. On _ its way down to this position the air en- trapped in the crank case, which has come through the grid valve is slight- ly compressed and when the air in- let port is uncovered by the piston this air flows up through the passageway MARINE REVIEW only small remnants of fuel oil va- por. As the piston moves on the downward stroke the burning gases rush through the neck into the cyl- inder space and complete combustion of the charge to carbon dioxide takes place. Expansion Source of Power It can be seen from this that no ignition devices are required, as the heat of compression fires the charge. There is no explosion in any sense of the word as the fuel burns at a con- stant pressure due to the fact that it expands into the cylinder and the pis- ton is beginning to move on its down- ward stroke. As the piston moves on its downward stroke, it first uncovers the edge of the exhaust port and the CONTROL SIDE OF FOUR CYLINDER UNIT LOOKING FORWARD—TWO CYLINDER SIZES ARE BUILT FOR THE 4 CYLINDER UNIT, GIVING ‘RATINGS OF 240 AND 120 BRAKE HORSEPOWER and clears the cylinder of the gases due to the combustion. On its return stroke, the piston covers both the air inlet and exhaust ports and the charge of fresh air is compressed in the cylinder. As the piston approaches the top of the cyl- inder, the injection of the fuel oil takes place through the nozzle into the auxiliary combustion chamber. The air which is being compressed rushes through the neck of this chamber and meets the spray from the fuel nozzle and aids in breaking the fuel up into a finely atomized state. In the mean- time, the piston has been moving up and the compression pressure has reached about 500 pounds per square inch which raises the temperature of the charge to practically 1000 de- grees Fahr. and combustion begins. Slow combustion which now takes place burns the fuel charge to the gas carbon monoxide. All of the liquid fuel is converted into this gas with burned gases pass out through this port and the pressure of the cylinder is lowered to practically that of the atmosphere. When the piston moves slightly farther it uncovers the air inlet port and the air which has again been slightly compressed in the crank case flows through the cylinder, thus clearing out the gases of combustion. It will be noted from this brief de- scription of the operation that the two cycle engine receives a power stroke at every revolution of the crankshaft. In the four cycle’ engine, there is a power stroke at every other revolution since the piston on its upward travel must force out the exhaust gases through an exhaust valve which is timed to open at the proper mo- ment. On the downward stroke the piston in the four cycle engine pulls in a fresh air charge through the air inlet valve, which is also timed to open at the beginning of the downward stroke. On the next revolution the February, 1926 charge of air is compressed and the fuel is injected, combustion occurs and the piston again travels down on the expansion or power stroke. Another imortant feature of marine diesels which must be given careful consideration is the arrangement which is provided for controlling the speed and for reversing. If a boat is to maneuver well the engine must respond quickly to speed changes and reversals of direction which are called for. Here also the modern trend has been for simplification and in the case of the engine under discussion the cen- tralized control has been so perfected that it is a comparatively simple mat- ter to start the engine or to reverse it. This is accomplished by the use of two hand wheels, one of which takes care of the starting and reversing and the other, the variation in speed. All that is necessary in starting the engine is to give the starting hand wheel a turn to the right or left, according to whether the boat is to be driven astern or ahead. Speed control is taken care of by a small hand wheel which changes the setting of the governor springs. An indicator in connection with this gov- ernor shows the change in speed as the hand wheel is turned. The simplicity of this control scheme is due mainly to the simplicity of the airless injection of fuel. A simple fuel pump is required for each cylinder and it has been possible in this engine to so arrange the mechanism that the fuel injection is cut off at the time the control wheel is thrown to the starting position. During this starting period the engine operates by means of com- pressed air and as soon as it turns over the control is thrown to the run position and injection of the fuel and firing begins. The whole opera- tion takes only a few seconds. Lubrication Is Automatic Another detail which has an impor- tant bearing on diesel engine depend- ability is in the arrangement which is provided for lubrication. In the early days entire dependence was placed on the use of oil cups and oil holes and the oil can which was an important part of the operation equip- ment of the engineer. In the modern diesel engine, however, the operator is relieved of any such duties as the lubrication is entirely automatic and is not dependent on the personal effi- ciency of the operating forces. Mech- anical lubricators are driven by the engine and every bearing surface is lubricated with just the proper amount of oil. In addition to the fact that the engine is properly lubricated, in- suring dependability in operation, the | SSS Ea eae