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5
DIESEL ENGINE FUEL SYSTEMS
 
A. DIESEL FUELS
 
5A1. General. Normally, diesel fuel oils for use in the Submarine Service are purchased by the Bureau of Supplies and Accounts. At the time of delivery, the diesel fuel oils are inspected to make sure that they meet the specifications set up by the Bureau of Ships. However, emergencies occasionally arise both in the supply and in the handling of diesel fuels that make it imperative for operating engineering personnel to have at least a fundamental knowledge of the requirements for diesel fuel oil.

5A2. Cleanliness. One of the most important properties necessary in a diesel fuel oil is cleanliness. Impurities are the prime sources of fuel pump and injection system trouble. Foreign substances such as sediment and water cause wear, gumming, corrosion, and rust in the fuel system. Diesel fuel oil should be delivered clean from the refinery. However, the transfer and handling of the oil increase the chance of its picking up impurities. The necessity for periodic inspection, cleaning, and care of fuel oil handling and filtering equipment is emphasized under the subject of maintenance for each system.

5A3. Chemistry of diesel fuel oil. Diesel fuel oils are derived from petroleum, more generally known as crude oil. All crude oils are composed of compounds of carbon and hydrogen known as hydrocarbons. The structure of the oil is made up of tiny particles called molecules. In crude oil, a molecule consists of a certain number of atoms of carbon and a certain number of atoms of hydrogen. The ratio between carbon and hydrogen atoms in a molecule determines the nature of the crude oil.

Crude oil is separated into various products by a process known as fractional distillation. In general, each product is obtained at its particular boiling point in the distillation process. The relative order of products obtained, with their distillation temperature is:

Gasoline-100 degrees to 430 degrees F
Kerosene-300 degrees to 500 degrees F
Fuel oil-400 degrees to 700 degrees F
Lubrication oil-650 degrees F

The fractional distillation process may be

  stopped at any point, leaving a residue of a heavier viscous liquid. This residue may be cracked in cracking stills by the application of heat and pressure in the presence of a catalyst. This cracking process may be controlled so as to get products of almost any given type of hydrocarbon molecular structure. The products mostly desired are those that can be used as gasoline and fuel oil blends.

Fuel oils that meet the specifications for high-speed diesel engine operation are of two types, distillate and blended. The distillate type is obtained by the direct distillation of crude oil only. Blended type is obtained by blending the distillate with the residual products from the cracking stills. As a general rule, distillate fuel oil is superior to blended fuel oil for high-speed diesel operation because it possesses better ignition quality, has a lower carbon content, and contains fewer impurities.

American crude oils are classified into three types: paraffin base, asphalt base, and mixed base. These three classifications depend upon whether paraffin waxes, asphalt, or both remain after all the removable hydrocarbons have been distilled from the petroleum.

5A4. Differences in internal combustion fuels. The two principal types of internal combustion fuels are gasoline and diesel fuel oil. Both types are hydrocarbons, but the hydrocarbons differ radically in their chemical composition.

Gasoline is a fuel adapted to spark ignition, while diesel fuel oil is adapted to compression ignition. In spark ignition, the fuel is mixed with combustion air before the compression stroke. In compression ignition, the fuel is injected into the combustion air near the end of the compression stroke. Thus a spark-ignition fuel must have a certain amount of resistance to spontaneous ignition from compression heat. The opposite holds true for diesel fuel oils. Entirely different ignition properties are required of the two fuels.

5A5. Properties of diesel fuel oils. The following are the chief properties required of diesel fuel oils. With the definition of each

 
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property is an explanation of its application to engine operation.

a. The ignition quality of a diesel fuel oil is the ease or rapidity with which it will ignite.

A diesel fuel with good ignition quality will auto-ignite (self-ignite) at a relatively low temperature. In simple language the fuel will ignite quickly and easily under relatively adverse conditions. Thus, where diesel engines must be started at low temperatures, good ignition quality makes starting easier.

Poor ignition quality will cause an engine to smoke when operating under a light load at a low temperature. It will also often cause the engine to knock and overheat due to the accumulation of fuel in the cylinder between the injection and ignition period. The sudden ignition of accumulated fuel causes the knock.

There are two widely accepted methods of determining the ignition quality of a diesel fuel oil

1. Cetane number test. In this method a standard reference fuel is used in a test cylinder. The most widely used reference fuel is a mixture of cetane and alpha-methyl-naphthalene. Cetane has an extremely high ignition quality (ignites quickly) and is rated for the test at 100. Alpha methyl-naphthalene has a very low ignition quality (is difficult to ignite) and is rated for the test at 0.

The single-cylinder test engine used is like any diesel engine cylinder, except that the compression ratio of the cylinder is adjustable. Other cylinder conditions, including the delay period, that is, the interval between injection and ignition, are held constant. This delay period is measured by electrical equipment. The fuel to be tested is used in the test cylinder and the compression ratio is adjusted until the standard length delay period is reached. Fuel with high ignition quality requires a low compression ratio. Fuel with low ignition quality requires a high compression ratio.

Next the reference fuel is used in the cylinder. Using the same compression ratio, various mixtures or proportions of cetane to alpha-methyl-naphthalene are used until the standard length delay period is attained. The cetane number of the diesel fuel oil tested is then equal to the percentage of cetane in the

  reference fuel that produced the same standard delay period with the same compression ratio. For example: if the reference fuel required 60 percent cetane and 40 percent alpha-methyl naphthalene to produce the same standard delay period at the same compression ratio as the diesel fuel oil tested, then the cetane rating of the diesel fuel oil is 60.

NOTE. The cetane rating for gasoline indicates low ignition quality while cetane rating for diesel fuel oil indicates relatively high ignition quality. Cetane numbers of diesel fuels in use today range from about 30 for engines least critical to fuel to over 60 for the highest ignition quality fuels.

2. Diesel index. This method of determining ignition quality is obtained by a simple laboratory test. This test takes into account the fact that there is a definite relationship between the physical and chemical properties of diesel fuel oils and their ignition quality. The diesel index number method is based on the relation between the specific gravity of the fuel oil and the aniline point, which is the temperature in degrees Fahrenheit at which equal quantities of the fuel oil and aniline (a chemical derived from coal tar) will dissolve in each other. To obtain the diesel index number, the gravity of the fuel oil, in degrees API, is multiplied by the aniline point and divided by 100. The result is the diesel index number of the fuel.

While the diesel index method is accepted as a fairly reliable method of determining the ignition quality, the cetane number test is considered more accurate. Hence it is preferable to use the cetane number test where possible. It must be remembered, however, that the diesel index test possesses the advantage of simplicity and low cost. The normal range of diesel index is from below 20 to about 60 for diesel fuels in use.

b. Specific gravity. The specific gravity of a diesel fuel oil is the ratio of its weight to the weight of an equal volume of water, both having the same temperature of 60 degrees F. The specific gravity of the majority of diesel fuel oils ranges from 0.852 to 0.934. As a matter of convenience and to standardize reference, the American Petroleum Institute has established the API gravity scale calibrated in degrees for diesel fuel oil

 
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gravities. Lighter weight fuel oils have high numbers (about 20 degrees to 40 degrees) and heavier weight fuel oils have low numbers (from 10 degrees up to about 20 degrees).

Diesel fuel oils are generally sold by volume. Hence the specific gravity of a fuel oil plays an important part commercially. Knowing the specific gravity, temperature, and quantity of a fuel oil, the volume can easily be computed from standard tables. The specific gravity of a diesel fuel oil is often referred to, but its significance is frequently overestimated. Efforts have been made at various times, but with little success, to establish a definite relationship between gravity and other characteristics such as viscosity, boiling point, and ignition quality.

c. Viscosity. The viscosity of a fluid is the internal resistance of the fluid to flow. The viscosity of a fuel oil is determined by the Saybolt Universal Viscosimeter test. In this test, a measured quantity of the fuel oil is allowed to pour by gravity through an opening of established diameter and with the fuel oil at an established temperature, usually 100 degrees F. The length of time in seconds required for the given quantity of fuel oil to pass through the opening determines its viscosity.

Viscosity is important in diesel fuels because of its effect on the handling and pumping of the fuel, and on the injection of the fuel. Viscosity, together with the rate of fuel consumption, determines the size of fuel lines, filters, and fuel pumps. The efficiency of filtering is greatly increased in a fuel oil of lower viscosity. In the injection system viscosity affects the characteristics of the fuel spray at the injection nozzles. It also affects the amount of leakage past pump plungers and valve stems, and therefore the lubrication of the various types of valves and pumps.

d. Heating value. The heating value of a diesel fuel oil is its ability to produce a specific Btu output of heat per unit of weight or volume. There is a definite relation between the gravity of a diesel fuel oil and the Btu content. The relationship is approximately:

Btu per pound of fuel = 17,680 + 60 x API gravity.

It is well to remember that although a pound of the lighter grades of oils has a higher

  heat value than a pound of the heavy oils, a gallon of the former is generally lower in heat value than a gallon of the latter. The difference, however, in the normal range of diesel fuels is relatively small. For example, a 24 degrees API diesel fuel has approximately 3 percent greater heating value per gallon than a 34 degrees API fuel. Considering the many factors related to gravity which may affect over-all thermal efficiency, the effect of this difference on fuel economy is usually negligible.

e. Flash point. The flash point of an oil is the lowest temperature at which a flash appears on the oil surface when a test flame is applied under specified test conditions. It is a rough indication of the tendency of the product to vaporize as it is heated. The flash point is important primarily with relation to regulations covering handling and storing of inflammable liquids. It is of little importance to diesel fuel oil performance. Most diesel fuels have a flash point well above 180 degrees F. The minimum flash point required by Navy specifications is 150 degrees F.

f. Pour point. The pour point of a diesel fuel is the temperature at which the fuel congeals and will no longer flow freely. This is usually due to the presence of paraffin wax, which crystallizes out of the fuel at low temperatures. Pour point usually determines the minimum temperature at which the fuel can be handled, although in some cases, where there is considerable agitation preventing the crystallization of wax, the fuel will usually flow at temperatures below the pour point.

g. Carbon residue. The carbon residue of diesel fuels is usually determined by the Conradson test, in which the fuel is burned in a covered dish. The carbon remaining is weighed and expressed as a percentage of the fuel. The test provides a rough indication of the amount of high-boiling heavy materials in the fuel, and is particularly useful where, because of high boiling points, distillation data cannot be obtained. Carbon residue is sometimes taken as an indication of the tendency of the fuel to form carbon in the combustion chamber and on the injection nozzles, although there is a little basis for using the test for this purpose due to the difference in the method of combustion used in the test and that actually encountered in an engine.

 
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h. Sulphur content. The sulphur content of a diesel fuel includes both noncorrosive and corrosive forms of sulphur. If the sulphur content is high, the copper strip corrosion test should be made to determine whether or not the sulphur is in corrosive form. If sulphur in corrosive form is present, a sample of the oil should be sent to the nearest laboratory facility for a test to determine the percentage present. Sulphur in excess of Navy maximum specifications is likely to damage the engine. When the fuel is burned, the sulphur is combined with oxygen to form sulphur dioxide which may react with water produced by combustion to form sulphuric acid and cause excessive cylinder wear. It will also act to corrode other internal engine parts.

i. Ash content. The ash content of a diesel fuel oil is the percent by weight of the noncombustible material present. This is determined by burning a quantity of fuel of known weight and weighing the ash residue. Ash is an abrasive material and the presence of ash above the maximum amount allowed by Navy specifications will have an obvious wearing effect on engine parts.

j. Water and sediment. The percent by volume of water and precipitable sediment present in the fuel oil is determined by diluting a quantity of fuel oil with an equal quantity of benzol, which is then centrifuged, causing water and

  sediment to separate. The percentage by volume is then determined.

The presence of water and sediment is generally an indication of contamination during transit and while handling. Fuel containing water and sediment causes corrosion and rapid wear in fuel pumps and injectors.

5A6. Engine troubles caused by fuel. As indicated in the discussion of diesel fuel oil properties, any number of engine troubles may be caused by unclean or poor fuel oil. Some of the more common troubles are:

a. Carbon deposits at injection nozzles may be due to excess carbon residue or excessive idling of engine.

b. Excess wear of injection pumps and nozzles may be due to too low a viscosity, excess ash content, or corrosion from water or sulphur content in the fuel oil.

c. Exhaust smoke may result when a fuel with too high an auto-ignition temperature is used. This is particularly true at light loads when engine temperatures are low.

d. Combustion knock in a diesel engine is believed to be due to the rapid burning of a large charge of fuel accumulated in the cylinder. This accumulation is the result of nonignition of fuel when it is first injected into the cylinder, a condition usually caused by fuel oil of poor ignition quality.

 
B. SHIPS FUEL SYSTEM
 
5B1. General. The engineering installation on present fleet type submarines consists of four main engines and one auxiliary engine. These are divided between two engine rooms, with two main engines in the forward engine room, and two main engines and the auxiliary engine in the after engine room. The function of the ship's fuel oil system is to supply clean fuel oil to each engine from the ship's storage tanks. The system may be divided into two parts: 1) the tanks and their arrangement, and 2) the different piping systems.

The tanks include normal fuel oil tanks, fuel ballast tanks, clean fuel oil tanks, expansion tank, and collecting tank. All of these tanks are in the spaces between the inner pressure hull and the outer hull of the submarine with the

  exception of the clean fuel oil tanks which are inside the pressure hull.

The two main piping systems found in the main fuel-oil system are the fuel oil filling and transfer line and the fuel oil compensating water line. These lines connect to the various tanks and give the fuel oil system a flexibility which it otherwise would not have.

5B2. The compensating principle. In order to understand the operation of a submarine fuel system, it is important to know the basic fuel oil compensating principle. In a submarine, to assist in maintaining trim it is necessary to have as little weight change as possible when fuel is being used m a fuel tank. Therefore, a compensating system is used which allows salt water to replace fuel oil as the fuel oil is taken from a tank. Let us assume that the weight of fuel

 
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used is 7.13 pounds per gallon and the weight of salt water is 8.56 pounds per gallon. Therefore, when one gallon of fuel is used from a fuel tank, instead of the submarine-becoming light by 7.13 pounds, it becomes heavy by 8.56 - 7.13 or 1.43 pounds. The submarine, then, becomes heavy as fuel oil is used. This compensating principle is used in the normal fuel oil tanks, fuel ballast tanks, expansion tank, and collecting tank. These tanks must at all times be filled with a liquid, either fuel oil, sea water, or a combination of both. The compensating principle is not used in the clean fuel oil tanks.

5B3. Fuel oil tanks. a. Normal fuel tanks. The normal fuel tanks are used only for the storage of fuel oil. They are usually located toward the extremities of the boat rather than close to amidships. They vary in size, but normally have capacities of from 10,000 to 20,000 gallons each. Most modern submarines have four of these tanks. In a typical installation (Figure 5-1) they are numbered No. 1, No. 2, No. 6, and No. 7.

b. Fuel ballast tanks. Fuel ballast tanks are large tanks, amidships, between the pressure hull and the outer hull, which may be used either as fuel storage tanks or as main ballast tanks. They are connected to the fuel oil system in the same manner as the normal fuel oil tanks, but in addition, they have main vents, main flood valves, and high-pressure air and low-pressure blower connections which are necessary when the tank is in use as a main ballast tank. When rigged as a main ballast tank, all connections to the fuel oil system are secured.

Most fleet type submarines have three fuel ballast tanks varying in capacity from about 19,000 to 25,000 gallons. On a typical installation (Figure 5-1), the fuel ballast tanks are numbered No. 3, No. 4, and No. 5. Current practice is to depart on war patrol with all fuel ballast tanks filled with fuel oil. Fuel is used first from No. 4 fuel ballast tank, and as soon as that tank is empty of fuel (filled with salt water) it is converted to a main ballast tank. Upon conversion, the tank is flushed out several times to insure that all fuel oil is out of the tank. The conversion of No. 4 FBT to a main ballast tank increases the stability of the submarine and decreases the amount of wetter surface of the hull when on the surface.

  c. Collecting tank. The collecting tank is one side of a section of tank space between the inner and outer hulls, the other side being the expansion tank. This tank has a connection to the fuel oil filling and transfer line. All of the fuel used by the engines normally passes through the collecting tank. A connection from the top of the collecting tank leads to the fuel oil meters, fuel oil purifiers, clean fuel oil tanks, and eventually to the attached fuel oil pumps on the engines. This tank has a capacity of about 3,000 gallons, and on submarines is located outboard of the forward engine room. The main function of the collecting tank is to insure that no large amount of water gets to the purifiers, clean fuel oil tanks and engine until all the fuel in normal fuel oil tanks, fuel ballast tanks, expansion tank, and collecting tank has been used.

d. Expansion tank. The expansion tank is alongside and on the opposite side of the ship from the collecting tank. It is connected to the fuel oil compensating water line. It serves two important functions: first, as a tank to prevent oil from being blown over the side through the compensating water line in case of small air leaks in either the fuel ballast tanks or the normal fuel oil tanks; and second, as a tank to which oily bilge water may be pumped without danger of leaving a slick. This tank has a capacity of about 3,000 gallons.

e. Clean fuel oil tanks. The clean fuel oil tanks, two in number, are used to store oil prior to its use in the engine and after it has been purified. These tanks are not compensated with compensating water. They have capacities of approximately 600 gallons each.

5B4. Fuel oil piping systems. a. Fuel oil filling and transfer line. The fuel oil filling and transfer line extends the length of the ship and is used for filling the fuel system and transferring the fuel from the various fuel oil tanks to the collecting tank where it can be piped off, purified, and used in the engine. There is a connection from the fuel oil filling and transfer line to the top of each side of each normal fuel oil and fuel oil ballast tank. This may be a direct connection or through a manifold, as shown in Figure 5-1 for normal fuel oil tanks No. 1 and No. 2. There is also a connection from the fuel

 
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Figure 5-1. TYPICAL INSTALLATION OF SHIP'S FUEL OIL AND COMPENSATING WATER SYSTEMS.

oil transfer line to the bottom of the collecting tank. This is the line through which passes all of the fuel from the main fuel oil tanks. At the forward and after end of the transfer line is a fuel filling line that connects the forward and after fuel filling connections on the main deck with the fuel oil filling and transfer line.

When the fuel system is in use, only one of the normal fuel or fuel ballast tanks is in service at a time. This is made possible by a stop valve in the fuel oil transfer line to the top of each side of each tank. This valve permits all tanks except the one in service to be secured on the fuel transfer line.

b.Fuel oil compensating water line. This line runs the length of the ship and has a connection to the bottom of each normal fuel oil and fuel oil ballast tank. The salt water that replaces the fuel oil in the fuel tanks comes from the main engine circulating salt water discharge to the compensating water line or, if all engines are secured, from the main motor cooling circulating salt water discharge to the compensating line. Most of this water goes over the side by

  way of a header box in the conning tower shears, but the amount of water needed to replace the fuel oil used goes down into the compensating water line by way of a four-valve manifold. The header box serves to keep a head of water on the system, insuring that the entire system is completely filled at all times.

The four-valve manifold is really a bypass manifold for the expansion tank. The four valves on the manifold (see Figure 5-2) are used as follows:

Valve A cuts off the four-valve manifold from the header box.

Valve B closes the line from the manifold to the bottom of the expansion tank.

Valve C is the bypass valve for expansion. If this valve is open, the compensating water an go directly into the compensating water line without going through the expansion tank. If the valve is closed, the compensating water must go into the compensating water line through the expansion tank. During normal operation this valve is closed.

Valve D closes the line from the manifold to the top of the expansion tank.

Figure 5-2. Four-valve manifold.
Figure 5-2. Four-valve manifold.
 
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Under ordinary operating conditions, all the valves on the compensating water line to the individual tanks are locked open and valve C is locked closed. This is necessary because sea pressure must be maintained on the inside of the fuel ballast tanks, normal fuel tanks, expansion tank, and collecting tank, when the submarine is submerged. If this were not done, the sea pressure on a deep dive would become so great as to cause a rupture of the relatively weak outer hull. Therefore, it is vital that all the valves mentioned above be open or closed as indicated. If these valves are properly rigged when the submarine is submerged, sea pressure can enter the system through the header box and then go to the inside of every fuel oil tank except the clean fuel oil tanks, if the valves on the compensating water branch lines to each tank are open. These valves on the individual branch lines are also normally locked open. This maintains the same pressure on each side of the submarine outer hull, insuring that it will not rupture. The valves are always locked to prevent accidental closing or opening.

5B5. Operation of the system. When the submarine is departing on war patrol, all tanks in the fuel oil system are completely filled with fuel. Upon departure, one of the normal fuel oil or fuel ballast tanks will be on service. As soon as fuel is drawn from the top of the collecting tank by means of the fuel oil transfer pump, salt water comes into the bottom of the expansion tank, keeping the system completely filled with liquid.

The path of the water can be traced by referring to Figure 5-1: Assume that No. 4 FBT is in service. As fuel is taken off the top of the collecting tank, fuel comes from the top of No. 4 FBT through the fuel oil filling and transfer line into the bottom of the collecting tank, replacing the fuel taken from the top of that tank. At the same time the fuel taken from the top of No. 4 FBT is replaced by the fuel from the top of the expansion tank by way of the four-valve manifold, the compensating water line, and the compensating water branch line to the bottom of No. 4 FBT. The fuel oil drawn from the top of the expansion tank is replaced by salt water entering the bottom of the expansion tank by way of the four-valve manifold and the line to

  the header box. It must be emphasized that all the above operations are taking place concurrently and that the entire movement of the liquids is caused by the head of water on the system from the header box.

As soon as the expansion tank is filled with salt water, the salt water comes up to the four-valve manifold through valve D into the compensating water line, and thence into the bottom of No. 4 FBT. As soon as No. 4 FBT is empty of fuel, salt water rises into the fuel oil transfer line and then into the bottom of the collecting tank. This is a positive indication that the No. 4 FBT has no more fuel in it. In order to tell when the salt water reaches the collecting tank, a liquidometer age which reads directly the amount of fuel in the tank is placed on the collecting tank. As soon as this gage reads less than completely filled, it is evident (in this case) that No. 4 FBT has no more fuel. No. 4 FBT is then secured on the fuel transfer line and another fuel tank is placed on service. The small amount of water may be left in the bottom of the collecting tank, as fuel oil that comes into the tank will rise through the water to the top of the tank. The water normally is left in the bottom of the collecting tank until the ship is refueled. At that time the water is withdrawn by pumping it out with the drain pump through the drain line to the bottom of the collecting tank.

5B6. Blowing and venting of fuel tanks. Each side of each tank is provided with blow connections which connect to the ship's low-pressure 225-pound air line. In an emergency or to effect repairs, it is often necessary to blow a fuel tank completely clear of all liquids. This is done by closing the tank's stop valves to the fuel oil transfer line and blowing the fuel or water over the side or to another tank (through the compensating water line).

The air line from the blow valve to the tank also has a connection to permit venting of the tank if some air has accumulated in its top or if it is desired to fill a completely empty tank with oil or water. All fuel tanks are equipped with either liquidometer gages or sampling cocks. These sampling cocks are used to take samples of liquid at various fixed levels in the, tank in order to ascertain approximately the

 
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amount of fuel in the tank. The liquidometer gages are adjusted so as to read directly the number of gallons of fuel in the tank.

5B7. Liquidometers. In submarine fuel systems, liquidometers are used to determine:

1) the level of oil in partially filled tanks, such as clean fuel oil tanks, and

2) the level between fuel oil and salt water in completely filled tanks such as normal fuel tanks, fuel ballast tanks, collecting tank, and expansion tank.

The liquidometer is equipped with a float mechanism, the movement of which activates a double-acting opposed hydraulic mechanism which registers upon a properly calibrated dial the volume of oil in a tank in gallons.

The float of a liquidometer used in compensated fuel tanks is usually filled with kerosene to a point where it will float in water but sink in fuel oil. Since the water is below the oil, the float will sink through the oil and stop at the compensating water level.

The instrument consists essentially of two

  units, a tank unit located in the tank whose capacity is to be measured, and a dial unit located at some distant point away from the tank (such as in the control room of a submarine). Operation of the instrument is dependent upon the movement of the float in the tank which is mechanically connected to an upper and lower bellows of the tank unit. These two bellows are rigidly supported at one end by a bracket, and both are connected by tubing to two similar bellows in the dial unit. The dial unit bellows are each supported at one end by a bracket which also provides a bearing connection for the indicator pointer. The free ends of the bellows, facing the pointer, are connected to a link which actuates the pointer. When the float moves down, the mechanical linkage between the float arm and the upper and lower tank bellows compresses the lower bellows, forcing a portion of the liquid from it into the interconnected dial unit bellows, causing it to expand. At the same time, the upper bellows in the tank unit is being elongated through the mechanical
Figure 5-3. Schematic diagram of liquidometer.
Figure 5-3. Schematic diagram of liquidometer.
 
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connection to the float arm and takes in a portion of the liquid from the other dial unit bellows, which is then caused to contract. Reverse action takes place if the tank float moves upward.

5B8. Maintenance of ship's fuel system. All fuel storage tanks should be periodically inspected and cleaned. This is usually done during submarine overhauls at naval shipyards.

All screen strainers used in connection with the fuel oil system should be periodically removed and cleaned.

The valve seat gaskets used in the fuel ballast tanks are made of special, oil-resisting rubber. These gaskets should be inspected at each filling and replaced if deteriorated or damaged.

In the fuel ballast tanks, all valves are enclosed in galvanized wire mesh screens. These wire mesh screens should be cleaned whenever inspection indicates that it is necessary. On some

  submarines, the connection between the compensating water line and the four-valve manifold is provided with a plug protected sight glass to check the pipe's contents. This glass should be kept in clean and readable condition at all times. In most modern fleet type submarines this sight glass has been blanked off because of possible breakage during depth charge attack.

It is essential that all air be excluded from the fuel system, or the system may become air-bound, thus preventing proper flow of oil to the engines and also disturbing the trim of the submarine. This may be done by venting the system through the vent facilities provided.

In venting fuel tanks in use, the following order should be observed: first, the expansion tank, then the fuel tank on service, then the collecting tank. The remaining fuel tanks may then be vented in any order. The discharge line from the collecting tank to the clean fuel oil tank should be closed during venting operations.

 
C. SUPPLY FROM SHIP'S FUEL SYSTEM TO ENGINE FUEL SYSTEMS
 
5C1. General. After leaving the collecting tank, fuel is piped through a system comprised of strainers, fuel meters, fuel oil transfer pumps, purifiers, and clean fuel oil tanks before reaching the engine. This section of the fuel oil system is divided into two parts. One part serves the forward engine room, the other the after engine room. The two are interconnected to provide flexibility of operation.

5C2. Strainers and meters. Fuel oil to be used in the engine is normally taken from the top of the collecting tank. It may, however, in some installations, be drawn directly from the fuel oil filling and transfer line. In either case, the oil should go through a wire mesh type strainer and fuel meter before entering the suction side of the fuel oil transfer pump. Both strainer and meter are fitted with bypass connections by means of which a strainer, or meter, or both may be bypassed.

5C3. Fuel oil transfer and purifier pumps. Located in each engine room is a positive displacement type fuel oil transfer and purifier pump, driven by an electric motor. The primary function of this pump is to transfer fuel oil from the collecting tank to the clean fuel oil tank

  through the purifier. It may also be used for priming purposes by taking a suction from the clean fuel oil tank and delivering the priming oil to the individual engine fuel system. An engine normally is primed before starting, particularly if it has been secured for some time.

Under normal operating conditions this pump is operated until the clean fuel oil tanks are full. It is then secured until the level of oil in the clean fuel oil tanks becomes such as to indicate need for replenishment.

5C4. Pure oil purifiers. a. General. The fuel oil purifiers are Sharples centrifuge units which operate on the principle of centrifugal force.

Centrifugal force is the force exerted upon a body or substance by rotation that impels that body or substance outward from the axis of rotation. When a mixture of liquids is revolved at high speed in a container, the centrifugal force causes the components of the liquid to separate. The component with the greatest specific gravity will assume the outermost position, and the lightest component, the innermost position. Thus, if a mixture of water and oil is revolved, the water, being the heavier component, will separate from the lighter oil and form

 
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Figure 5-4. Fuel oil supply from ship's fuel system to engine fuel system in one engine room.
Figure 5-4. Fuel oil supply from ship's fuel system to engine fuel system in one engine room.
a layer around the wall of the container, while the oil remains near the center of the container. The Sharples fuel oil purifier operates on this principle.

The Sharples purifier can be used as a separator or a clarifier. When used as a separator, the purifier separates oil from water and solid sediment. When used as a clarifier, it separates oil from solid sediment only. The unit is usually set up as a separator in fuel oil systems and a clarifier in lube oil systems. (See Section 7B7.)

b. Operation. The fuel oil transfer and purifier pump forces fuel oil through a short connecting line at the bottom of the purifier bowl. The purifier bowl is revolved by an attached electric motor at about 15,000 rpm. A three-wing partition extends the full length of the bowl on the inside. The purpose of this partition is to keep the liquid in the bowl revolving with the bowl. Otherwise there would be slippage of the liquid column which would

  reduce the effect of the centrifugal force.

When the machine is operated as a separator, the bowl is primed with fresh water until an effective water seal is created at the water discharge outlet. The water priming line is sealed off from the fuel inlet line by means of a check valve which prevents water from finding its way into the fuel system. Then the fuel oil supply is forced into the swiftly revolving bowl. The centrifugal force throws the water, which has a heavier specific gravity than the oil, to the outside wall of the bowl and creates a vertical layer of water at this outer extremity. The fuel oil, which has a lighter specific gravity, forms a layer next to the water. Any particles of sediment in the fuel oil have a heavier specific gravity than either the water or oil and are drawn and held against the wall of the bowl by the centrifugal force. Dirt and sediment are cleaned out of the bowl when necessary.

At the top of the purifier bowl is a barrier called a ring dam, which covers the top of the

 
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Figure 5-5. Fuel oil transfer and purifier pump.
Figure 5-5. Fuel oil transfer and purifier pump.

vertical column of water and fuel oil. There is an opening at the outer diameter of the ring dam through which only excess water is discharged. At the inner diameter of the ring dam is another opening through which only purified fuel oil discharges. Thus, as long as the centrifugal force and the effective water seal are maintained, it is impossible for fuel oil to displace the water and get out through the water discharge opening. It is just as impossible for water to get out through the fuel oil discharge opening as long as the centrifugal force is in effect.

5C5. Clean fuel oil tanks. All fuel oil supplied to the engines is normally drawn from the clean fuel oil tanks. There are two clean fuel oil tanks, one in the forward engine room and one in the after engine room. Under normal operating conditions, the engines in each compartment draw their supply from the clean fuel oil tank in that compartment.

Each tank averages about 600 gallons capacity in fleet type submarine installations. By means of a system of valves and piping, fuel

  Figure 5-6. Attached fuel oil supply pump, F-M.
Figure 5-6. Attached fuel oil supply pump, F-M.

oil can be pumped to either fuel oil purifier by means of the transfer and purifier pumps and discharged to either clean fuel oil tank. Also, the transfer and purifier pump may be used to draw fuel oil from either clean fuel oil tank and supply any engine directly, during priming operation.

A hand pump is connected to the clean fuel oil tanks to provide a means of checking the contents of the tank for water, for testing the quality of the oil, and for removing residual oil in the tank when it is desired to clean it.

Each engine in a compartment is connected to the clean fuel oil tank in the same compartment by a fuel line which goes from the bottom of the clean fuel oil tank up to the attached fuel oil pump on the engine. The attached fuel oil pump takes a suction from the clean fuel oil tank and delivers the oil to-the engine fuel system. If the attached fuel oil pump on one engine should become inoperative, it is possible to connect the fuel oil transfer and purifier pump so as to supply fuel up to the engine, thereby preventing a shutdown of the engine.

 
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Figure 5-7. Exploded view of attached fuel all supply pump, F-M.
Figure 5-7. Exploded view of attached fuel all supply pump, F-M.
 
Figure 5-8. Exploded view of attached fuel oil supply pump, GM.
Figure 5-8. Exploded view of attached fuel oil supply pump, GM.
 
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Each clean fuel oil tank is equipped with a liquidometer to measure the quantity of fuel oil in the tanks at all times.

5C6. Attached fuel oil supply pump, F-M. The attached fuel oil supply pump (Figures 5-6 and 5-7) draws fuel by suction from the clean fuel oil tank and delivers it through the strainer and filter units to the engine main fuel oil header.

The pump is a positive displacement type gear pump and is driven directly from the lower crankshaft of the engine through a flexible gear drive. A packing gland is provided on the fuel oil pump drive gear shaft to prevent fuel oil from leaking out around the shaft.

5C7. Attached fuel oil supply pump, GM. The function of the GM attached fuel oil supply pump is the same as that of the pump described in section 5C6 above. This pump is also of the positive displacement type, but it is driven directly from one of the engine camshafts instead of the crankshaft as on the F-M engine. The pump drive shaft is provided with a packing gland to prevent fuel oil from leaking around the shaft.

Fuel oil is drawn from the clean fuel oil tank by suction created by the pump and fed into the pump housing through an inlet at the top of the pump. Oil is forced from the outlet at the bottom of the pump into the engine supply line. A pressure regulating valve in connection with the pump may be set to maintain a pressure of 40-50 psi in the engine fuel system. A pressure relief valve may be set at slightly above the desired pressure to bleed off excess fuel oil when the pressure exceeds the maximum setting. This oil returns to the clean fuel oil tank.

5C8. Duplex fuel oil strainer. All fuel oil delivered to the engine fuel header by pressure from the attached pump must pass through a duplex type strainer. This strainer actually consists of two strainer elements which may be used either individually or in pairs. The flow of fuel oil through either or both strainers is controlled by a manually operated valve. When the valve is set to bypass one strainer, the bypassed element may be removed and cleaned without disturbing the flow of fuel oil to the engine.

  Figure 5-9. Fuel oil filter.
Figure 5-9. Fuel oil filter.

Each strainer consists of a body or case which is fitted with a metal ribbon wound element. A scraper device with long blades that contact the inside surface of the element is fitted into each strainer. A handle for turning the element extends through the top of the strainer so that the operator may occasionally turn the element, thereby cleaning accumulated dirt from the surface of the element. Dirt and sediment drop to the bottom of the case and should be removed at regular cleaning periods.

Each duplex strainer is equipped with a duplex pressure gage which measures the pressures of the fuel oil fed into the strainer and of the oil leaving the strainer. A drop of 10 psi between the inlet pressure and the outlet pressure indicates that the element or elements of the strainer needs cleaning. Each strainer has a small valve at the top of the case for venting air from the unit.

5C9. Duplex fuel oil filter. Most installations are equipped with duplex fuel oil filters as well as strainers. In function and operation the

 
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filters are similar to the strainers. In the duplex filter, the element is a removable absorbent type cartridge which is removed and thrown away when it becomes dirty. The absorbent type filter cartridge is a denser element than the strainer element and consequently filters out finer   particles of dirt and foreign matter. The filter elements are not equipped with scrapers. They should be examined when the pressure registered by the duplex pressure gage drops a specified value. If found dirty, they must be removed and replaced by a new element.
 
D. FUEL INJECTION SYSTEMS
 

5D1. Basic requirements of a fuel injection system. The primary function of a fuel injection system is to measure accurately, vaporize, and inject the fuel at the proper time according to the power requirements of the engine.

In order to accomplish this there are certain basic requirements that any fuel injection system must fulfill.

a. It must measure or meter the fuel. The quantity of fuel injected determines the amount of energy available to the engine through combustion. The brake mean effective pressure and hence, economy, are dependent to a great extent upon the air to fuel ratio. Thus, it is important that the fuel injection system accurately measure the correct quantity of fuel according to engine requirements.

b. It must time the injection. The injection timing has a pronounced effect on engine performance. Early injection tends to develop high cylinder pressures, because the fuel is injected during the part of the cycle when the piston is traveling slowly and therefore the combustion takes place at nearly constant volume. Extremely early injection will cause knocking. Late rejection tends toward decreasing the mean effective pressure of the engine and consequently lowering the power output. Extremely late injection tends toward incomplete combustion resulting in a smoky exhaust.

A more complete description of these fuel injection systems is contained in the Bureau of Ships publications entitled: Fairbanks-Morse Fuel Injection Systems Maintenance Manual, NavShips 341-5019; and General Motors Diesel Fuel Injector Maintenance Manual, NavShips 341-5018.

c. It must control the rate of feed during injection. The rate of injection is important because it determines the rate of combustion and influences the engine efficiency. Injection should

  start slowly so that a limited amount of fuel will accumulate in the cylinder during the initial ignition lag before combustion commences. It should proceed at such a rate that-the maximum rise in cylinder pressure is moderate, but it must introduce the fuel as rapidly as permissible in order to obtain complete combustion and maximum expansion of the combustion product.

d. It must properly atomize the injected fuel. The fuel must be injected into compressed air in the combustion chamber with sufficient force to accomplish thorough atomization. Atomization reduces the fuel to minute particles or globules. In general, the smaller the particles of fuel the shorter will be the delay period, that is, the interval between injection and ignition.

Opposed to this requirement is the fact that the smallest particles of fuel have a low penetrating quality. Therefore, with very fine atomization there is a tendency toward incomplete mixing of the fuel and air which leads to incomplete combustion.

e. It must inject fuel with sufficient force for effective penetration and distribution. Fuel must be atomized into sufficiently small particles to produce a satisfactory delay period. However, if the atomization process reduces the fuel to too small particles, they will lack penetration. This lack of penetration results in igniting of the small particles before they can be injected far enough into the area of the combustion chamber. Consequently, injection pressure must be of sufficient force and the orifice properly proportioned to effect good penetration.

The fuel spray must also be directed by the spray tip to secure a uniform distribution of the spray charge over the entire combustion area.

High turbulence in the combustion chamber causes a more thorough mixing of the fuel and air and aids in complete combustion.

 
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5D2. Types of fuel injection systems. The earlier diesel engine fuel systems utilized the air injection principle in their design. This method of injection consisted of furnishing both fuel oil and air to an injector valve. The high-pressure air carried the fuel into the cylinder where it was burned. Engines using air injection usually developed a high combustion efficiency because of the efficient mixing of fuel and air possible in such a system. However, a considerable amount of high-pressure air was necessary to inject the mixture into the cylinder against the compression pressure present in the cylinder. The necessary air pressure was usually supplied by an attached air compressor. These air compressors used a large percentage (10 to 15 percent) of the power developed by the engine, and, in addition, it was difficult to maintain them in proper operating condition.

In order to increase the reliability and compactness of these older engines, it became necessary to do away with the attached air compressor and shift to the solid injection system in which the fuel alone was injected into the cylinder in a fine atomized spray. This type of injection requires a higher grade fuel than did the air injection system. Solid injection engines are in general more powerful for their size, more simple in construction, and more reliable than their air injection predecessors. Also the total weight per horsepower of the engine is much less. All of our present modern submarine engines operate on the solid injection principle.

5D3. Components of the solid fuel injection system. The solid fuel injection systems under discussion may wary in design but they are alike in principle. The components of the mechanical fuel injection system are:

a. The fuel measuring or injection pump. These pumps are usually of the plunger type and are operated from cams on the engine camshafts through a rocker lever or push rod assembly.

A separate pump (or pumps) is used for each cylinder of the engine. In the Fairbanks Morse OP engines each pump is a separate unit connected to the fuel injection nozzle by a

  branch line. In the General Motors engines each pump is an integral part of the unit injector which includes, the injection nozzle. In both engines the injection pump meters the fuel, delivers it to the injection nozzle, and supplies the energy through hydraulic pressure of the fuel oil for the injection and atomization of fuel at the injection nozzle.

b. The fuel injection nozzle. The fuel injection nozzle contains a check valve which may be either needle type or spherical head type. The valve is opened for injection by hydraulic pressure from the injection pump which acts on the differential area of the valve. The pump plunger forces fuel oil through the orifices of the spray tip, atomizing the fuel delivered into the combustion chamber. The injection is timed at the pump, not at the injection nozzle.

c. High-pressure fuel oil lines. Valve opening pressures up to 3,000 psi are encountered in many fuel injection systems, necessitating the use of high-pressure lines. Such tubing should meet the following requirements:

1. It should be of uniform inside diameter, otherwise the injection characteristics will be seriously impaired. For example, if the inside diameter of the tubing should occasionally run smaller than that specified, excessive pressures are likely to result. Where inside diameters exceed specifications, the pressures will drop and there is the possibility that the tubing will develop structural weakness.

2. It should possess sufficient and uniform strength to withstand pressures up to 9,000 psi without yielding.

3. It should have high ductility to permit easy bending to the desired shape and cold swaging without cracking. Bending of the tubing does not affect the injection characteristics as long as the bends do not have a radius of less than 1 1/2 inches.

4. It should have a smooth, accurate bore, absolutely free from scale, seams, laps, laminations, deep pits, or other serious defects which would weaken the structure of the metal or cause restrictions to the flow of the fluid.

 
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E. GENERAL MOTORS ENGINE FUEL OIL SYSTEM
 
5E1. General. The attached fuel oil pump draws fuel oil from the supply tank and forces it through the fuel metering block, the strainer, and the filter. From the filter, the fuel oil flows to the fuel supply manifold, which is the bottom tube of the multiple manifold assembly on each cylinder bank, through a tube to a single jet filter on each cylinder head. This filter is a metal ribbon wound type with passages of approximately 0.001 inch in the element. From the filter, the fuel flows through the jumper tube that supplies the injector. The injector inlet contains a filter to further prevent solid matter from reaching the spray valve.

Two relief valves in the fuel metering block limit the fuel oil pressure in the system. Any excess oil is bypassed back to the clean fuel oil tank.

Surplus fuel from the injector flows through a filter in the outlet passage so that any reverse flow of fuel cannot carry dirt into the injector. The surplus fuel passes from the injector through a jumper tube to the bleed manifold which is the middle tube in the multiple manifold assembly on each cylinder bank. The fuel from the bleed manifold on each bank flows through a metering valve in the metering block, then back to the clean fuel oil tank.

5E2. The unit injector. a. Description. On the GM engine the fuel injection pump and spray valve are combined into a single compact unit called the unit injector, which meters the fuel and also atomizes and sprays it into the cylinder. The unit injector is held in position in a water-cooled jacket in the center of the cylinder head. At the lower end, the injector forms a gastight seal with the tapered seat in the cylinder head. All injectors in the engine are alike and interchangeable. Fuel is supplied through jumper tubes with spherical type gasketless connections.

The pumping function of the injector is accomplished by the reciprocating motion of the constant stroke injection plunger which is actuated by the injector cam on the engine camshaft through the injector rocker lever. The position of the plunger, and thereby the timing, is adjusted by means of the ball stud and lock nut

  at the injector end of the rocker lever. The quantity of the fuel injected into each cylinder (and therefore the power developed in that cylinder) is varied by rotating the plunger by means of the injector control rack. A rack adjustment, called the micro-adjustment and located on the control linkage, permits balancing the load of each cylinder while the engine is running.

The unit injector is comprised of the various parts illustrated in Figure 5-11. Of these, the principal parts are the body, spray valve nut, bushing, plunger, needle valve or spherical type check valve (depending on the type of injector), valve spring, and the spray tip.

The injector body is a heat-treated, alloy steel forging with two flat surfaces extending on opposite sides for holding the injector in a vise when necessary. These surfaces are drilled in line to support a part of the injector control linkage. A small vent, just below the holding down clamp seat, allows leakage fuel which serves as the lubricant for the plunger and bushing to escape from the plunger spring chamber. This hole also serves as a breather opening to prevent pumping action by the plunger follower. On some injectors, plunger pump fuel leakage flows through a hollow drain dowel, then through a drilled passage in the cylinder head and back to the clean fuel oil tank.

The bushing is the cylinder for the plunger pumping unit of the injector. It is located and held against turning in the body by a guide pin that fits into a groove at the upper end of the bushing. Two openings in the bushing wall, on opposite sides, serve as the inlet and bypass ports for the fuel oil. The bottom surface of the bushing is lapped to form an oiltight seal against the full injection pressure.

The unit injector pump plunger is made of a special steel, lapped to a close fit in the bore of the bushing. The clearance between the surface of the plunger and bushing is so fine that it is usually measured by forcing a specific amount of oil of a fixed viscosity between the surfaces and measuring the time consumed.

The lower end of the plunger is cut away to form a recess with an upper and a lower helical lip. These helical lips cover and uncover the

 
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Figure 5-10. Isometric view of fuel injection system, GM.
Figure 5-10. Isometric view of fuel injection system, GM.
 
108

Figure 5-11. Relative arrangement of parts, spherical check valve type unit injector, GM.
Figure 5-11. Relative arrangement of parts, spherical check valve type unit injector, GM.
 
109

inlet and bypass ports in the bushing to control the beginning and ending of the pumping part of the plunger stroke. An oil hole, drilled horizontally from one side of the recess, through the plunger to the other side, connects with a central oil hole extending vertically from the bottom of the plunger.

The plunger stroke remains constant at about 3/4 of an inch. However, the pump plunger does not pump fuel oil for the entire length of the stroke. The effective pumping stroke begins when the upper helical lip covers the upper port and ends when the lower helical lip uncovers the lower or bypass port. The upper part of the plunger extends into the hub of the control gear. When this gear is turned, through the rack and linkage, the plunger rotates and changes the angular position of the helical lips with respect to the bushing ports, thereby changing the quantity of fuel injected and the timing of the injection.

In the two types of unit injectors used, one is equipped with a spherical check valve, the other with a needle valve. In the spherical check type valve, fuel, forced down by the pump plunger, passes through a drilled passage in the check valve seat and comes in contact with the spherical check valve. Pressure of the fuel acts on the differential area of the spherical check valve, forcing it off its seat against the check valve spring tension. The oil then goes past the spring and around the check valve stop, through the check valve spacer, around the flat check valve, and out through the openings in the spray tip.

In the needle valve type injector, fuel is forced through drilled passages in the spacer, down through a passage in the needle valve spring cage and needle valve seat, and into an annular groove at the bottom of this seat. It then is forced up through a short inclined passage leading to the needle valve against which the fuel pressure acts. When the fuel pressure is built up high enough to open the valve, the fuel passes around the flat check valve and out through the spray tip.

NOTE. On some injectors the spacer has been eliminated and the fuel passes directly from the pump plunger into the needle valve spring cage.

  Figure 5-12. Unit Injector plunger
and bushing, GM.
Figure 5-12. Unit Injector plunger and bushing, GM.

The needle valve or spherical check valve spring, as well as the spray tip, are made of hardened, chrome-vanadium steel. The spring tension is such that it holds the valve on its seat to insure quick opening and cutoff until the fuel pressure is built up high enough to produce a fine spray when the oil is forced through the spray tip. The upper surface of the spray tip is lapped to affect a seal against this pressure.

b. Operation. Fuel oil enters the unit injector body through a filter and passes around the outside of the plunger bushing. From this supply chamber around the outside of the plunger bushing, the oil goes through the upper and lower ports of the bushing and into the pump chamber.

As the plunger is moved downward by the rocker lever, fuel in the pump chamber is first displaced through both ports into the supply chamber around the bushing, until the lower edge of the plunger closes the lower port. Fuel

 
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Figure 5-13. Cross sections of needle valve and spherical check valve type unit injectors, GM.
Figure 5-13. Cross sections of needle valve and spherical check valve type unit injectors, GM.
 
Figure 5-14. Plunger position at no Injection, idling, half load, and full load.
Figure 5-14. Plunger position at no Injection, idling, half load, and full load.
 
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in the pump chamber is then displaced through connecting central and transverse holes in the lower port of the plunger and through the upper port into the supply chamber. Further downward movement of the plunger causes the upper lip to cover the upper port at which point the effective pumping stroke begins and the fuel in the pump chamber is then forced down through the spray valve. Injection continues until the lower lip on the plunger uncovers the lower port in the bushing at which point the effective pumping stroke ends. The fuel then bypasses upward through the holes in the plunger and through the lower port into the supply chamber. This immediately lowers the pressure of the fuel remaining in the pump chamber so that the valve snaps shut to prevent dribble. On the return stroke, the upward movement of the plunger uncovers the ports and allows fuel to enter the chamber.

The cylinder load, that is, the amount of fuel sprayed into the cylinder, is controlled by the rotation of the pump plunger. Rotating the

  plunger locates the helical plunger lips with respect to the port openings in the plunger bushing and thereby controls the amount of fuel injected into the cylinder. Figure 5-14 illustrates the plunger position and effective stroke for no injection, idling load, half load, and full load.

In addition to measuring the amount of fuel, the injector pump plunger varies the timing of injection. This is accomplished by means of the upper helix on the pump plunger. The angularity of this helix causes injection to be advanced for a longer effective stroke of the plunger (more fuel) and retarded for a shorter effective stroke of the plunger (less fuel).

In the pressure chamber, fuel oil under pressure works on the differential area of the needle valve. The pump plunger creates a hydraulic pressure on the fuel oil in the pressure chamber that is greater than the pressure of the needle valve spring. This pressure working on the differential area of the needle valve overcomes the spring tension and raises the needle valve, opening the passage to the spray tip.

Figure 5-15. Fuel oil supply system, F-M.
Figure 5-15. Fuel oil supply system, F-M.
 
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Figure 5-16. Isometric view of fuel injection system, F-M.
Figure 5-16. Isometric view of fuel injection system, F-M.
 
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Fuel oil enters the spray tip and the force of the hydraulic pressure sprays the fuel oil through the orifices of the spray tip at a 75-degree angle with the centerline of the cylinder. Spray tips normally are marked to indicate   number and diameter of orifices and angle of spray. For example: A spray tip marked 6-006-155 has 6 orifices, each measuring .006 inch, directing the spray at a 155-degree included angle.
 
F. FAIRBANKS-MORSE ENGINE FUEL OIL SYSTEM
 
5F1. General.The attached fuel oil pump draws fuel by suction from the clean fuel oil tank and delivers it through the strainer and filter units to the engine main fuel oil header. The pump has a greater capacity than is required to furnish fuel oil to the engine at maximum speed, therefore a pressure is built up in the supply line to the engine. A relief valve in the engine supply header prevents this pressure from being built up above a certain desired pressure, usually 15 psi. Pressure in excess of this amount is relieved by the relief valve which returns the excess oil to the clean fuel oil tank by gravity.

Fuel oil delivered to the engine inlet is piped along both sides of the engine through the supply header which in turn is connected to the fuel inlet ports of each injection pump.

Two injection pumps serve each cylinder, one from the left side, the other from the right. The pumps are actuated in proper sequence by the cams on the camshafts. Each injection pump delivers fuel oil to one of the injection nozzles, which, like the pumps, are arranged two to a cylinder, one on each side. The amount of fuel the pumps deliver to the nozzles is regulated by movement of the injection pump control racks which are actuated, through plungers and guides, by an injection pump control rod on each side of the engine.

A drip pan under each injection pump collects any fuel oil that drains from the top of the pump body. This oil is sent to the clean fuel oil tank through tubes extending from the drip pan at each end of the engine. Oil collecting on the bottom of the injection nozzle compartments is also drained into the clean fuel oil tank.

5F2. Fuel injection pump. a. Description. The injection pumps receive fuel oil at low-pressure, measure it into correct amounts for injection, build up a high pressure, and deliver

  it to the injection nozzles at the proper time. Each of the fuel injection pumps consists primarily of a tappet assembly, pump barrel, plunger return spring, discharge valve with its seat and spring, and the control rack.

A tappet assembly attached to the top of the pump body, transforms the rotary motion of the camshaft into up-and-down motion of the pump plunger. The assembly is comprised of a cam roller, a push rod, and a push rod spring. The push rod spring holds the push rod and cam roller against the camshaft cam. As the camshaft rotates, the cam acts against the cam roller to force the push rod down against the spring tension to actuate the injection pump plunger.

Figure 5-17. Arrangement of injection nozzles
in F-M cylinder.
Figure 5-17. Arrangement of injection nozzles in F-M cylinder.

 
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Figure 5-18. Cross section of fuel injection pump, F-M.
Figure 5-18. Cross section of fuel injection pump, F-M.
  The injector pump plunger moves vertically in the pump barrel, delivering fuel to the injection nozzle by way of a discharge valve and the injection tube connecting the pump and the nozzle. At the base of the plunger is an annular recess. The lip formed between the annular recess and the bottom of the plunger has a slanting, or helical, edge. A vertical slot extends from the annular recess to the bottom of the plunger. It should be noted that, except at the slot, the edge of the helical lip at the bottom of the plunger is constant or even. Hence it is referred to as the constant beginning helical lip. The edge of the helical lip toward the recess in the plunger is helical, or slanting, and is referred to as the variable ending helical lip.

The plunger is lapped to an extremely close fit in the bore of the pump barrel. These two parts are always provided in pairs and should not be separated.

The pump barrel is positioned in the pump body by a setscrew which extends into an elongated slot at the lower part of the barrel. Fuel is delivered to the pump chamber of the barrel through a single inlet port which is also the bypass port.

The plunger spring returns the plunger to the starting position when the high point on the cam passes. The spring is held in position at the upper part of the pump body by a snap ring.

The pump discharge valve is held in its seat by a pump discharge valve spring. The spring returns the valve to its seat at the end of an effective pumping stroke.

The amount of fuel delivered by the injection pump is controlled by rotating the pump plunger. The mechanism by which this is accomplished is known as the fuel injection pump control rack and the control gear. The control gear is splined to the pump plunger and meshes with teeth in the control rack. Any lateral movement of the rack is transmitted to the control gear, causing the pump plunger to rotate. The control racks have calibration scales for reference in checking operating conditions under various engine loads. Normally the control racks are set at the 0 marking, as indicated by a pointer, when in the no fuel position. Each of the control racks is adjustable to the correct calibration by means of the control rack adjusting screw.

The control racks are connected to the control rod at the control rack collar. The control

 
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Figure 5-19. Cutaway of fuel injection pump, F-M.
Figure 5-19. Cutaway of fuel injection pump, F-M.
 
Figure 5-20. Fuel injection pump parts, F-M.
Figure 5-20. Fuel injection pump parts, F-M.
 
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Figure 5-21. Details of injection pump plunger
and barrel, F-M.
Figure 5-21. Details of injection pump plunger and barrel, F-M.
  Figure 5-22. Cross section through control
rack, F-M.
Figure 5-22. Cross section through control rack, F-M.
Figure 5-23. Position of GM fuel injection pump plunger at no injection, idling half load, and full load.
Figure 5-23. Position of GM fuel injection pump plunger at no injection, idling half load, and full load.
 
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rod is connected to the engine governor by a linkage. Thus the rotary position of the pump plungers, and hence, the amount of fuel delivered, can be directly controlled by the governor.

It should be noted that there is no means provided for advancing or retarding the time of injection in the cylinder for a change in fuel supply as there is in the unit injector pump of the GM engine.

b. Operation. Figure 5-23 shows how the amount of fuel delivered through the discharge valve is varied by rotating the pump plunger. The plunger stroke remains constant at about 5/8 of an inch The effective pumping stroke begins when the constant beginning edge of the helical lip covers the fuel port. The pumping stroke ends when the variable ending edge of the helical lip uncovers the port, allowing the fuel oil remaining in the chamber to flow through the bypass area in the pump plunger.

The first picture in Figure 5-23 shows the pump plunger in a position in which the vertical slot is aligned with the fuel port. This is the no fuel position. Any downward movement of the pump plunger in this position allows the fuel to pass from the chamber beneath the pump plunger, through the slot and out through the inlet port. Thus no fuel is delivered through the discharge valve.

When the pump plunger is rotated slightly, a relatively shallow depth of the helical lip is aligned with the fuel inlet port. The effective pumping stroke is short, and only a small amount of fuel is delivered through the discharge valve such as is required for an idling engine.

The third and fourth pictures in Figure 5-23 shows the rotary position of the pump plunger at half load and full load fuel delivery.

Fuel oil is supplied to the fuel injection pump through a line from the engine main fuel oil header. The fuel oil enters the fuel port in the pump bushing at approximately 15 pounds' pressure and fills the chamber below the pump plunger. At the proper time the pump plunger is actuated by the cam on the engine camshaft through the tappet mechanism on the pump. The force exerted on the fuel oil in the chamber beneath the pump plunger overcomes the spring tension on the discharge valve and opens the valve. The oil then passes through holes below

  the discharge valve seat, through the discharge valve cage, and into the high-pressure line to the injection nozzle.

Fuel enters the annular groove in the injection nozzle and is directed down through longitudinal grooves comprising the edge type filter. The clearance between the grooves of the filter and the injector nozzle body is approximately 0.0015 inch. The fuel oil is forced from the filter, down through flutes on the outside of the needle sleeve, then through needle sleeve holes at the bottom of the flutes to enter a fuel chamber in the needle sleeve. In this chamber, the hydraulic pressure of the fuel, acting on the differential area of the valve, lifts the valve from the needle valve seat. The oil is then discharged into the combustion chamber through the nozzle tip. As soon as the pressure from the fuel injection pump diminishes, the spring in the nozzle forces the needle valve closed.

The three orifices in the nozzle tip are 0.0225 of an inch in diameter and are positioned to direct the spray at a 15-degree angle for thorough distribution in the combustion chamber.

Figure 5-24. Cutaway of Injection nozzle. F-M.
Figure 5-24. Cutaway of injection nozzle. F-M.

 
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