ML20043F655
| ML20043F655 | |
| Person / Time | |
|---|---|
| Issue date: | 02/12/2020 |
| From: | Office of the Chief Human Capital Officer, Woodard Corp |
| To: | |
| Gary Callaway | |
| Shared Package | |
| ML20043F634 | List:
|
| References | |
| Download: ML20043F655 (48) | |
Text
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems 4.0 COMBUSTION AIR, FUEL, AND NOTE: Text, illustrations, and examples in EXHAUST SYSTEMS this chapter are based on typical nuclear plant applications and, therefore, may not This chapter presents the basic principles of apply to a specific system or design.
combustion air, diesel fuel, and exhaust systems, and their inter-relationship. 4.1 Introduction to the Air and Fuel Systems Learning Objectives:
In Chapter 2, we discussed the three As a result of this lesson, you will be able to: elements of combustion: fuel, oxygen, and heat. The power developed by the diesel
- 1. Describe the relationship between the engine is directly related to the amount of intake air charge and fuel delivery in fuel it can burn efficiently. In this chapter, development of power in a diesel engine. we discuss the inter-relationship of these elements in the development of power and
- 2. Identify major components of the diesel the manufacturers rating of a diesel engine.
engine air intake and fuel systems, and state the purpose of each. 4.1.1 Air and Fuel for Combustion
- 3. Identify major components of a diesel 4.1.1.1 Composition of Air engine fuel system and understand the purpose of each. Air is composed primarily of nitrogen and oxygen. By weight, 76% of the air is
- 4. List the functions that must be performed nitrogen (N2) while 23% is oxygen (02). The by the components of a diesel engine remaining 1% is made up of other fuel injection system. substances such as carbon dioxide, carbon monoxide, water vapor, dust, and other
- 5. Describe the construction and operation materials and gases. Of this mixture, only of a typical diesel engine fuel injection the oxygen is required for combustion.
pump.
4.1.1.2 Composition of Fuel
- 6. Describe the construction and operation of a typical diesel engine fuel injection Fuel oil is mostly two elements, hydrogen nozzle. and carbon and, therefore, is classified as a hydrocarbon fuel. Its composition by weight
- 7. Describe the construction and operation is approximately 15 % hydrogen (H2) and 85 of a unit type diesel engine fuel injector. % carbon (C). Fuel oil also contains trace amounts of sulfur, organic compounds, and
- 8. Describe how the governor operates to other substances. Paraffin-based fuel oil control fuel delivery to each cylinder. has the empirical chemical formula CnH2n+ 2
- 9. Describe the exhaust system functions, Fuel oil specifications are normally construction, and operation. established by the engine manufacturer, Rev 3/16 4-1 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems and incorporated into plant Technical 2CnH2n + 2 + (3n + 1)O2 Specifications (TS). Generic fuel oil specifications include the following: 2nCO2 + (2n + 2)H20
- Cetane Number: 40 (Minimum) Actually, not every atom of fuel mixes with exactly the correct number of oxygen atoms.
- Total Sulfur: 15ppm (Maximum) This is the result of incomplete mixing, residual exhaust gases in the cylinder, and
- Organic Chlorides: 20ppm (Total, Max) the presence of various contaminants in the air. Under these imperfect conditions,
- Viscosity: 32- 40SUS @ 100ºF complete combustion cannot occur.
- Ash Content: 0.02% (by Weight) 4.1.2.2 Combustion with Excess Air
- Heating Value: 18,190 BTU/lb Minimum In order to compensate for these less than perfect conditions, and to ensure that nearly
- Cloud Point: above 40oF complete combustion does occur, diesel engines are designed to operate with 15 to NOTE: EPA lowered the maximum Sulfur 25 % excess air.
content of Diesel Fuels in steps, from 3000ppm (0.3%) to 500ppm (0.05%), then 4.1.2.3 Air to Power Relationship 15ppm (0.0015%). Chapter 13 will cover some potential issues associated with Ultra- Assuming all other factors are equal, the Low Sulfur (ULS) fuel, all of which appear to relationship of air flow to the power be readily manageable by NPP licensees. developed by a diesel engine is as follows:
4.1.2 Combustion Chemistry
- The greater the mass of air entering the engine, the more oxygen will be 4.1.2.1 Combustion with Theoretical Air available to support combustion.
Assume we mix a specific amount of fuel
- More oxygen available for combustion, with exactly the amount of air required for means more fuel can be injected into the complete combustion (theoretical air). This cylinder and still burn efficiently.
is based on the diesel engine operating at full load for optimum combustion heat. In
- The more fuel which can be burned this mixture, each carbon (C) atom and each efficiently, the more usable power the hydrogen (H) atom will be in contact with the engine can develop.
required number of oxygen (O) atoms for complete combustion. Then, the maximum 4.1.3 The Combustion Process conversion of chemical energy to thermal energy would occur. Under these ideal We will begin this section by examining the conditions, the following stoichiometric series of events which occur in the cylinder (chemically correct) reaction will occur. as the fuel oil is sprayed into the heated air Rev 3/16 4-2 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems charge. This fuel charge goes through the 4.2 The Intake Air System four phases listed below as combustion occurs. 4.2.1 Intake Air System Requirements Refer to Figure 4-1 and points C, D, and E In order for the engine to operate efficiently on Figure 4-2 for the following discussion. and reliably, the intake air system must provide the following:
4.1.3.1 Delay Period 4.2.1.1 Sufficient Air Quantity A delay period occurs from the time of initial fuel injection to when actual ignition takes The system must supply a sufficient quantity place. The delay period consists of two of air to each cylinder to support complete parts. First, the physical delay, which is the combustion under maximum load. This time it takes the fuel to atomize, mix with the typically means 15 25% excess air.
air charge, and vaporize, thereby creating a combustible mixture of air and fuel. Second, For 2-stroke cycle engines, additional air the chemical delay is the localized pre-flame must also be provided to ensure proper oxidation caused by the catalytic effect of scavenging of exhaust gases from cylinders.
high temperature wall surfaces and hot residual exhaust particles. These localized 4.2.1.2 Clean Air regions can reach 1000ºF to 2000ºF.
The incoming air charge must be clean.
4.1.3.2 Rapid Combustion That is, it must be free of abrasive particles which would damage the engines internal After the delay period, there is rapid parts. Another type of contamination would combustion of the fuel which entered the be engine exhaust recirculation to the air cylinder during the delay period. intake, which would lower Oxygen content.
4.1.3.3 Continued Combustion 4.2.1.3 Cool Air As fuel continues to be injected, normal The mass of air which can be contained in a combustion occurs, increasing the specific volume is dependent on air density.
temperature and pressure of the heated As air temperature increases its density gases within the cylinder. Normal peak decreases (if pressure remains constant).
temperatures for such combustion range Air that is too warm will not provide sufficient from 3500ºF to 4500ºF. oxygen to support complete combustion.
Potential causes of that are recirculation of 4.1.3.4 After-burning EDG room cooling air to the engine intake or, if the engine normally draws its air from After the injection is completed, there is an the EDG room, failure of room cooling fans.
after-burning period where any remaining fuel combines with the remaining oxygen to 4.2.1.4 Reduced Noise Levels essentially complete the burning process.
Rev 3/16 4-3 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Due to the cyclical action of the engine,
- Oil Bath Air Filters are very effective at pressure pulsations tend to develop in the removing particulate from the incoming flow of the incoming air charge. These air charge. The oil bath air filter shown pressure pulsations cause an increased in Figure 4-5 consists of a cylindrical noise level within the diesel space. They housing, internal air piping, an oil also create vibrations in the intake air piping, reservoir, a wire mesh filter, and various which can lead to damage and component baffles.
or system failure. Flexible connections are usually provided to permit thermal Incoming air enters the housing and travels expansion and isolate engine vibrations downward toward the oil reservoir. As the from the piping. air reaches the oil pool its forced to change direction 180o. This sharp change in 4.2.2 The Typical Intake Air System direction causes the heavier particles to sling out from the air and become trapped The intake air system shown in Figure 4-3 by the oil. The air and lighter particles pick (the right hand section) displays the up some of the oil and carry it upward into components which would be found in a the wire mesh. The oil and lighter particulate typical nuclear plant application. become trapped by the wire mesh allowing only clean air to pass through to the engine.
4.2.2.1 Intake Air Filter Periodic cleaning of the oil reservoir and wire mesh is the only maintenance needed.
The intake air filter removes particulate suspended in the air prior to entering the 4.2.2.2 Intake Air Silencer system. It also helps to remove any excess moisture in the air and may reduce the noise The intake air silencer consists of a plenum level of the incoming air charge. type housing which may include chambers and baffles to reduce or dampen the Various types of air filters are used. pulsations which have developed in the Sometimes, two types will be combined for incoming air flow. Often, some form of a single application. The two most common sound deadening material may be included.
types, dry and oil bath, are discussed in In some installations, the intake air silencer detail below. is incorporated into the intake air filter.
- Dry Type Filters (Figure 4-4) use a 4.2.2.3 Intake Air Piping porous, fibrous cloth or paper type media. As air passes through the media The intake air piping makes the physical airborne particulates are captured and connection between the intake air filter and held, allowing only clean air to reach the silencer. This piping should be as short as engine. Periodically the media becomes possible and as large in diameter as restricted due to a buildup of the practical so as to provide a minimal particulate. Since this restriction then resistance to the air flow. Sharp bends and reduces the air flow to the engine, the fittings should be kept to a minimum to media or elements must be replaced. ensure free air flow to the engine.
Rev 3/16 4-4 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems 4.2.3 Blowers and Turbochargers the compressor housing by the bearing housing. The inlet of the turbine housing is As discussed previously, the power an connected to the outlet of the engine engine can develop depends on the amount exhaust manifold.
of air available for combustion. By mechanically increasing the air flow into the Hot exhaust gases, which contain a engine, the power produced by that engine substantial amount of thermal energy, enter will be increased. Two devices are the turbine housing, pass through a set of commonly used on diesel engines to stationary blades, and are directed against increase the quantity of air into the cylinders. blades of the turbine wheel. As these gases pass through the turbine wheel, they expand 4.2.3.1 Blower/Supercharger and cool, thereby releasing energy to rotate the turbine wheel and its shaft, which also The blower (Figure 4-6), sometimes called a rotates the compressor connected to it.
supercharger, is a positive displacement air pump which delivers air to the engine. It Air is drawn into the center (inducer) of the consists of a pair of helical rotors inside a compressor wheel. Rotation of the housing. As the rotors turn they draw air in compressor wheel throws the air radially, by through the intake air piping, force it through centrifugal force, increasing its velocity the blower housing and discharge it under (kinetic energy). As the air exits the pressure into the intake air manifold. compressor wheel at high velocity, it enters the plenum-like compressor housing. The The blower is mechanically driven by the velocity of the air is suddenly decreased engine accessory drive gear train, so the resulting in a sharp increase in the pressure quantity of air delivered by the blower is a in the compressor housing. This increase in function of engine rpm. These units require pressure increases the density of the air flow power to operate but the power gained from entering the engine cylinders.
increased air flow more than offsets the power needed to operate the blower. 4.2.3.3 Blower vs Turbocharger 4.2.3.2 Turbocharger (Figure 4-7) There are significant advantages in using a turbocharger rather than or in addition to a The turbocharger also provides an increase mechanically driven blower.
in intake air flow to the engine with a corresponding increase in power output. 1. Since the turbocharger is powered by the Unlike the blower, the turbocharger uses a heat of the exhaust gases, it does not centrifugal compressor. The impeller is require power directly from the engine. It surrounded by a scroll-shaped compressor does present a restriction to exhaust gas housing, much like a centrifugal pump. The flow and so creates a back-pressure in impeller is attached to the turbine shaft. A the exhaust manifold. However, the turbine wheel is attached to the other end of overall result is a greater increase in the turbine shaft. This turbine wheel is engine power output than would be encased in a turbine housing connected to attained with an engine driven blower.
Rev 3/16 4-5 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems
- 2. The increased mass of intake air aftercoolers. These are air-to-jacket-water provided by the turbocharger is heat exchangers located between the determined by the heat energy of the discharge of the turbocharger and the air exhaust gases leaving the engine. The intake manifold. They reduce the temperature and mass flow of the temperature of the intake air charge by exhaust gases are functions of the transferring excess heat from the air charge quantity of fuel being burned in the to the engine jacket water cooling system.
cylinders, which is in turn a function of the load applied to the engine. As the The water for cooling the Intercooler-load on the engine increases, the aftercooler will be discussed further in quantity of fuel burned increases. This Chapter 6, Engine Cooling Systems.
increase in heat input to the engine increases the heat energy of the exhaust 4.2.3.5 Diesel Engine Ratings and therefore the amount of energy driving the turbocharger. The result is an The quantity, quality, and temperature of increase in the mass of air entering the ambient and combustion air directly affect cylinders and a subsequent increase in engine performance. Therefore, engine engine power which gives the manufacturers rate and de-rate their engine turbocharger a unique load-following based upon a set of standard conditions. A ability not available with a blower. typical basis for ratings for one manufacturer is illustrated by Figure 4-9.
Some engines, such as the Fairbanks-Morse opposed piston engine, efficiently 4.3 The Diesel Engine Fuel System combine a turbocharger and a blower. See Figure 4-8. Once the cylinder has been charged with air and the air compressed, raising its The EMD engine turbocharger is initially temperature above the ignition point for the engine-gear driven during startup to provide fuel oil, a metered quantity of fuel is sprayed exhaust scavenging until hot exhaust gases into the cylinder and combustion occurs.
drive the turbocharger faster than the gear. The diesel engine fuel system can be divided into three separate but 4.2.3.4 Intercoolers - Aftercoolers interdependent subsystems. Each system must perform reliably and efficiently in order Turbochargers, while increasing the flow of to support the operation of the engine.
intake air to the cylinders, also increase the temperature of the air. This increase in air 4.3.1 Fuel Oil Storage and Transfer temperature reduces the density of the air System (Figure 4-11) charge and therefore the amount of oxygen available for combustion. 4.3.1.1 Fuel Oil Storage Tank To compensate for this reduction in density, Typically the fuel oil storage tank is sized to most turbocharged diesel engines utilize provide the engine with a specified (e.g. 5-heat exchangers known as intercoolers or or 7-day) fuel supply when operating at full Rev 3/16 4-6 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems power. The required size of the tank
- A better approach involves placing the depends on the rate of fuel consumption for pumps in the diesel room at floor level the engine, at the specified heat value of the while placing jet pumps (ejectors) inside fuel. EMD and OP engines consume the fuel oil storage tank (as shown in approximately 4,500 gallons per day. Figure 4-11). These pumps do not draw Larger Cooper and Pielstick engines may suction directly from the storage tank but consume around 10,000 gallons per day! from the fuel oil day tank and they discharge to the nozzle of the jet pumps.
Fuel oil storage tanks usually incorporate a The venturi action of the jet pumps low point or sump for the collection and transfers the fuel oil into the fuel oil day removal of water and sediment. This low tank. This method allows for easy point can be pumped out periodically to maintenance of the transfer pumps, and remove moisture and heavy contaminants. the jet pumps require no maintenance as they have no moving parts to wear out.
In determining fuel available and accessible in a tank, consideration must be given to the 4.3.2 Fuel Oil Supply System (Figure 4-12) amount of fuel between the pump suction level and the lowest level before tank refill. 4.3.2.1 Fuel Oil Day Tank 4.3.1.2 Fuel Oil Transfer Pumps The day tank stores a limited amount of fuel at a location near the diesel engine. It may Fuel oil transfer pumps are fractional be located in the diesel room itself or in a horsepower pumps that supply fuel to room adjacent to the diesel room. The size elevated day tanks that supply a positive of the tank depends on its location and on pressure fuel head in sufficient quantity for any governing codes or standards, including initial starting and operation of the EDG. applicable technical specifications.
Fuel oil transfer pumps may be placed in The tank is usually positioned so the fuel one of three locations, depending on the level is above the suction of the fuel oil site-specific design. supply pumps, to ensure a positive flow into the pumps. Automatic level switches in the
- The pumps may be submerged below day tank activate the fuel oil transfer pumps the fuel oil level in the fuel oil storage to ensure the level of the fuel in the tank is tank. While ensuring a positive suction kept above a specified minimum.
head for the pumps, this configuration makes pump maintenance somewhat 4.3.3.2 Fuel Oil Strainers (Figure 4-13) difficult.
These strainers, located between the fuel oil
- A second option involves locating the day tank and the suction of the fuel oil supply pumps in a pit, placing the suction pumps, remove large particulate, sediment, connection below the fuel level in the and moisture from the fuel. They are usually storage tank. Pump access is improved of the duplex type incorporating a three-way but still less than ideal. valve which allows one strainer element to Rev 3/16 4-7 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems be taken out of service for cleaning while the 4.4 Fuel Injection Systems EDG remains operational. The strainer element is usually a fine wire mesh which The fuel injection system has the most can be removed periodically for cleaning. precise and demanding job of the three Valves on duplex type strainers should be systems. Regardless design used, the fuel left in a position that uses only one of the injection system must perform each of the strainer elements. That makes the other following functions:
immediately available if needed (rather than both being plugged in case of a problem).
- The quantity of fuel delivered to each cylinder is metered to control the power 4.3.3.3 Fuel Oil Supply Pumps (Fig.4-14) produced by the engine.
Two fuel oil supply pumps are normally
- Inject the fuel into the heated air charge provided. One is engine driven and is at a time relative to the rotation of the functions whenever the engine is running. crankshaft, which produces the desired An electric-driven supply pump is also combustion characteristics.
provided to ensure positive fuel flow during startup, before the engine-driven pump can
- Inject the fuel at a rate which will ensure provide sufficient pressure for engine run. smooth, complete, efficient combustion.
These pumps are usually positive
- The injection must begin and end displacement gear type pumps though some quickly. This is to prevent uncontrolled applications use screw type pumps. They distribution and poorly atomized fuel supply fuel oil to the fuel header under a from entering the cylinder. Under these fairly low pressure (e.g. 45 psig). conditions, the fuel would not mix adequately with the oxygen in the 4.3.3.4 Fuel Oil Filters (Figure 4-15) cylinder which would waste fuel and produce soot and cause engine These filters, located between the problems.
discharge of the fuel oil supply pumps and the fuel oil manifold or header, remove any
- The fuel must be sufficiently atomized to minute particles (e.g. 5 micron or as the provide optimum mixing of the fuel with engine manufacturer specifies) that may be the compressed air charge. The more in the diesel fuel. effective the atomization, the more complete the combustion.
These filters are normally of the duplex type with a three-way valve to allow for
- The fuel spray must be distributed evenly replacement of the elements while the throughout the combustion space. This engine remains in operation. The elements helps to ensure effective mixing and use a paper or fabric like media to trap these complete combustion.
extremely small particles. Again, the valve handle should be in a position to use only Two basic types of fuel injection systems are one of the filter elements at a time. commonly used on diesel engines. The Rev 3/16 4-8 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems pump and nozzle type is a two-part system The return spring and spring retainer return with an injection pump and a separate the plunger to the non-delivery position, nozzle. The unit injector type combines the while keeping the cam follower in contact injection pump and nozzle into a single unit. with the injection cam.
4.4.1 Fuel Injection Pump and Nozzle A delivery valve assembly at the discharge System (Figure 4-16) of the plunger acts as a spring-loaded check valve which prevents the back flow of fuel In the pump and nozzle system, a fuel during non-delivery.
injection pump, operated by the engine camshaft, injects the fuel at the proper time 4.4.1.2 Injection Pump Operation and proper rate, and stops the delivery quickly to ensure clean, efficient Refer to the injection pump in Figure 4-17.
combustion. The injection nozzle, mounted Though there are different pump designs, all in each cylinder head (on 4-stroke and 2- of them are constant stroke, variable volume stroke conventional engines) or through the (as dictated by governor demand for more, wall of the cylinder liner (on opposed piston or less, fuel). And they all depend on the engines), atomizes the fuel while distributing fact liquids are nearly incompressible.
it evenly throughout the combustion space.
- Principle of Operation - The plunger is 4.4.1.1 Injection Pump Construction precision-fitted to the barrel which has (Figure 4-17) separate fill and spill ports. A single or double helix is cut into the end of the The main components of the injection pump plunger. A slot/drilled passage connects are the plunger and barrel. These two items the plungers delivery end to the helix.
are precision machined and fitted to ensure precise delivery of the fuel. Together, the The plunger has a mechanically constant plunger and barrel regulate the quantity of stroke length established by the lift of the fuel entering the cylinder while establishing injection cam lobe. The fuel delivery is other key injection characteristics such as determined by "effective" stroke length, injection timing and injection rate. which is created by the indexing of fill and spill ports with the plunger helix. The The pump body is the main structural and effective stroke is that portion of the pressure-retaining component of the pump. mechanical stroke where both the fill and It houses the plunger and barrel assembly. spill ports are simultaneously blocked.
Whenever both ports are closed at the A spur gear keyed to the plunger allows the same time, fuel pressure builds up within plunger and its helix to be rotated for the the barrel and is then directed to the purpose of metering the fuel. A fuel control nozzle assembly. Rotation of the rack, positioned by the engine governor, plunger within the barrel changes the engages with the spur gear to provide a relationship of the helix to the ports. This means for rotating the plunger from outside changes the length of the effective stroke the body, thereby metering the fuel. and, thereby, the fuel quantity delivered.
Rev 3/16 4-9 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems
- Zero Fuel Delivery (Figure 4-18)- At Upward movement of the plunger blocks zero delivery, the slot aligns with one of off both ports and begins the delivery of the ports so there is no time when both fuel into the combustion chamber. With ports are covered simultaneously. Fuel the plunger in the full fuel position, the moves back and forth through the slot ports are covered for the greatest and in and out of the spill port. amount of time with the maximum amount of fuel entering the cylinder.
- Engine Idling - With the plunger at the bottom of its stroke, fuel enters through As the helix uncovers the spill port, fuel the fill port to fill the barrel. As the delivery stops just as before. The plunger moves upward, both ports plunger then completes its stroke and become blocked and fuel is delivered to returns to bottom position to be refilled.
the injection nozzle where it is sprayed into the cylinder. 4.4.2 Fuel Injection Nozzles (Figure 4-21)
Continued upward movement of the The fuel injection nozzle has the job of plunger delivers fuel until the helix atomizing the fuel as it enters the uncovers the spill port at which time the combustion space and distributing the fuel injection ceases, and fuel passes evenly for efficient combustion.
through the slot and out the spill port.
4.4.2.1 Nozzle Body or Housing The plunger completes its strokes, returning to the bottom of its stroke The housing or body is the main structural where it is again filled with fuel. and pressure retaining component of the assembly. Fuel supply and return lines
- Low Power - At low power, the plunger connect to the upper end of the nozzle body is rotated as shown in Figure 4-19. With while at the lower end is the nozzle spray tip.
the plunger at the bottom of its stroke, the barrel again fills with fuel. Upward 4.4.2.2 Nozzle Spray Tip (Figure 4-22) movement of the plunger closes off both ports. Fuel continues to be delivered The spray tip actually enters the combustion until the helix uncovers the spill port, space. A series of small holes in the tip stopping the fuel injection. Rotation of atomize the fuel as it passes through. The the plunger has increased the effective size of the holes determines the degree of length of the stroke and therefore the atomization while the number of holes and amount of fuel injected into the cylinder. their angle distribute the fuel evenly and correctly throughout the combustion
- Full Power - At full load, maximum fuel chamber.
delivery is required. The plunger is now rotated as shown in Figure 4-20. With 4.4.2.3 Pintle Nozzle (Figure 4-23) the plunger at the bottom of its stroke, the barrel is again filled with fuel. Some engines, such as the Fairbanks-Morse opposed piston, use a single-hole, Rev 3/16 4-10 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems "pintle" type nozzle. Here, a small plunger 4.4.4 Unit Type Fuel Injectors or pintle passes through the single hole. As fuel is delivered, the pintle lifts up creating a The unit type injectors used on the EMD 2-cone- shaped fuel spray which atomizes and stroke cycle engine combine the injection distributes the fuel for efficient combustion. pump and injection nozzle into a single unit installed in each cylinder head. With this 4.4.2.4 Nozzle Valve Assembly type injector, high pressure fuel lines and their potential for leakage are eliminated.
The nozzle valve assembly consists of a needle valve in a fitted, lapped cylinder. It The main components of the unit type may be part of the spray tip, or a separate injector are the matched and lapped plunger unit. Its function is to prevent combustion and bushing assembly as shown in Figure gases from entering the nozzle assembly. 4-24. This plunger uses an upper and lower The nozzle valve is held in the seated helix to control injection timing and duration position by the nozzle spring assembly. with a T-shaped drilled passage to bypass the fuel. The bushing has an upper port and 4.4.2.5 Nozzle Spring Assembly a lower port positioned 180 to each other.
A spring seat directs the force of the spring The body and nut form the structural portion against the upper tip of the nozzle valve. of the injector. The rack gear engages with The force of the spring acting on the nozzle the spur gear, which is indexed to the valve sets the pressure of the fuel being plunger. The spur gear causes the plunger injected into the cylinder. The spring force to rotate while allowing it to move freely up is adjustable by either adjusting a screw or and down.
changing the thickness of the shim pack at the upper end of the spring. A follower, actuated by the injector lobe on the engine cam lift, connects to the end of 4.4.3 Injection Nozzle Operation (Fig. 4-21) the plunger. The follower spring returns the plunger to its upper most position when the The fuel delivered by the injection pump cam in on its base circle. A check valve passes through a heavy walled fuel pipe to located below the plunger and bushing the nozzle assembly. This fuel is directed prevents the back flow of fuel during the through internal passages in the nozzle upward stroke of the plunger.
body to the nozzle valve near its seat.
A spring-loaded needle valve is located in The high pressure fuel creates an upward the injector spray tip. The spring holds the force against the needle valve. When the valve seated while establishing the injection force of the fuel is sufficient to overcome the pressure.
spring force, the nozzle valve unseats, and fuel is injected into the combustion space. 4.4.5 Injector Operation (Figure 4-25)
As soon as fuel delivery stops, the sudden drop in pressure allows the nozzle valve to The fuel pump supplies fuel to the unit quickly seat, stopping the injection. injector at low pressure, about 50 psi.
Rev 3/16 4-11 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems As with the injection pump discussed 4.4.5.2 Low Power (Figure 4-27) previously, fuel injection occurs whenever both ports (upper and lower for unit At idle or low power, the bushing is filled injectors) are closed simultaneously. while the plunger is at its upper most point of travel. Downward movement of the Figure 4-25 illustrates the following. With plunger blocks off the lower port, and the the plunger at the top of its stroke, fuel fuel bypasses the plunger and exits through enters through the lower port to fill the cavity the upper port until the upper helix closes below the plunger. The fuel also travels the upper port. Injection begins as soon as upward through a drilled passage in the the upper port is covered and continues until plunger and bypasses out the upper port. the lower helix passes the lower port allowing the fuel to bypass into the return Downward plunger movement closes the passages of the injector body.
lower port but allows fuel to bypass out the upper port. As soon as the upper port is The beginning of the injection is determined closed by the helix on the plunger, injection by the upper helix while the ending of the begins. Fuel is delivered as long as both injection is regulated by the lower helix. As ports are closed. in the other injectors, the effective stroke is the distance the plunger travels when both Injection stops when the lower helix ports are blocked.
uncovers the lower port and fuel begins to bypass the plunger and out the lower port 4.5.5.3 Full Fuel (Figure 4-28) into the fuel return passages of the injector body. The plunger continues downward to For maximum fuel delivery, the plunger is the end of its mechanical stroke. indexed as shown in Figure 4-28. With the bushing full, injection begins as the upper 4.4.5.1 Zero Fuel Delivery (Figure 4-26) helix blocks the upper port. Downward movement of the plunger delivers fuel until With the plunger in its upper-most position, the lower helix uncovers the lower port.
fuel passes through the lower port to fill the bushing. As the plunger moves downward, In this orientation, the effective stroke length the plunger blocks off the lower port, and is at its maximum. Maximum fuel is fuel bypasses through the drilled passage. delivered leading to maximum power output for the engine.
When the engine is to be shut down, the fuel control racks are moved to the zero fuel 4.4.5.4 Needle Valve Action (Figure 4-24) position. This indexes the plunger helix to the ports as shown in Figure 4-26. In this The high pressure fuel is directed through position, there is no time during the stroke internal passages to the needle valve. The when both ports are simultaneously force of fuel acting on the needle valve blocked. Fuel simply bypasses into the causes the valve to overcome the spring return passages in the body of the injector, force and inject fuel into the combustion and none is delivered to the cylinder. space.
Rev 3/16 4-12 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems 4.4.5.5 Injector Timing 4.5.1.2 Reduce Noise Levels Static injector timing is established by the The high energy level and large volume of relationship between the injector plunger exhaust gas flow can create a substantial and the fuel injection lobe on the engine noise problem. The exhaust system must camshaft. During engine operation, timing include some form of noise suppression must change slightly according to the load device to reduce the noise level of the on the engine. This incremental timing is exhaust gases to an acceptable level.
accomplished by the shape of the helix on the plunger. As the engine load increases, 4.5.1.3 Direct Exhaust Gas Flow the helix closes off the upper port earlier in The system must be designed and the timing sequence which gives the constructed in a manner which will direct the cylinder more time to complete the exhaust gases far enough away from the combustion process. Helix design is very combustion air intake to prevent the cross-important and will vary for different engines, over of exhaust gases into the air intake, as well as for different applications of the thereby contaminating the intake air and same engine (e.g., nuclear, rail, marine). reducing the effectiveness of the combustion process.
4.5 The Exhaust System 4.5.2 Exhaust System Components Just as the intake air system is designed to efficiently supply fresh air to the cylinders, 4.5.2.1 Exhaust Manifold or Header the exhaust system is designed to efficiently remove burned gases out of the cylinders. The exhaust manifold or header collects the To maximize the amount of air available for exhaust gases at the cylinder heads or combustion, the exhaust system must exhaust ports and directs the gas flow to the minimize the amount of exhaust gases inlet of the turbocharger. Some exhaust remaining in the cylinders. The basic manifolds or headers are water cooled configuration of a diesel engine exhaust which reduces the buildup of heat in the system is shown in Figure 4-3 (the left half). diesel engine space.
4.5.1 Exhaust System Requirements 4.5.2.2 Exhaust Gas Muffler Following are the fundamental requirements The exhaust muffler (Figure 4-10), reduces of the engine exhaust system: exhaust noise by dampening the pulsations resulting from the cyclical action of the 4.5.1.1 Minimal Resistance to Flow engine. This is accomplished by passing the gases through a series of chambers and The exhaust system must be designed and baffles causing a gradual expansion of the constructed so that it presents a minimum gases and a reduction in noise emission.
resistance to flow. Engine horsepower The chamber dimensions and shape may be ratings are based upon not exceeding a tuned for anti-resonant action at engine specified exhaust back pressure. pulse frequencies, further reducing noise.
Rev 3/16 4-13 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems 4.5.2.3 Exhaust Relief Valve In nuclear applications where the exhaust gas silencer and / or piping are exposed to the atmosphere and unprotected, an automatic relief valve may be installed. This device functions similarly to a conventional safety valve. It may be either spring-loaded or weight loaded in the closed position; however, some are simply a thin sheet of metal (such as heavy aluminum foil) which will rupture at an excessive pressure.
Should the exhaust system downstream of the valve become damaged or clogged, the back-pressure in the exhaust will increase.
When the back pressure in the exhaust system exceeds a specified value, the relief valve will automatically open, or rupture, discharging the gases to the atmosphere and allowing the engine to continue to operate normally.
Rev 3/16 4-14 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-1 Combustion Activity Rev 3/16 4-15 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-2 Diesel Cycle - Pressure vs Stroke Rev 3/16 4-16 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-3 Basic Intake and Exhaust System Rev 3/16 4-17 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-4 Dry Type Air Filter Rev 3/16 4-18 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-5 Oil Bath Air Filter Rev 3/16 4-19 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-6 Blower/Supercharger Rev 3/16 4-20 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-7 Exhaust Driven Turbocharger Rev 3/16 4-21 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-8 Intake Air and Exhaust Flow Rev 3/16 4-22 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-9 Typical Diesel Generator Basis for Ratings/DEMA Ratings Rev 3/16 4-23 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-10 Exhaust Gas Muffler Rev 3/16 4-24 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-11 Fuel Oil Storage and Transfer System Rev 3/16 4-25 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-12 Fuel Oil Supply to Engine Fuel Header Rev 3/16 4-26 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-13 Fuel Oil Strainer Rev 3/16 4-27 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-15 Fuel Oil Filter Figure 4-14 Fuel Oil Supply Pump Rev 3/16 4-28 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-16 Pump and Nozzle System Rev 3/16 4-29 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-17 FM OP Engine Injection Pump Construction Rev 3/16 4-30 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-18 Zero Fuel Delivery Rev 3/16 4-31 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-20 Full Power Figure 4-19 Low Power Rev 3/16 4-32 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-21 Injection Nozzle Rev 3/16 4-33 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-22 Injection Nozzle Spray Pattern Rev 3/16 4-34 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-23 Pintle Nozzle Rev 3/16 4-35 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-24 Unit Type Fuel Injector Rev 3/16 4-36 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-25 Injector Operation Rev 3/16 4-37 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-26 Zero Fuel Delivery Rev 3/16 4-38 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-27 Low Power Rev 3/16 4-39 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-28 Full Power Rev 3/16 4-40 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-29 Turbocharger Cutaway Section Rev 3/16 4-41 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-30 Casing Assemblies Rev 3/16 4-42 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems Figure 4-31 Brown and Boveri Turbocharger Rev 3/16 4-43 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems WALKAROUND SESSION 4 temperature exhaust gases into pressurized engine intake combustion air.
4.0 COMBUSTION AIR, FUEL, AND EXHAUST SYSTEMS The instructor will use the cutaway dry air filter and its components, as well as the Purpose cutaway oil bath air filter and its components, to illustrate their features and This session's purpose is to complement the functions.
classroom instruction of Chapter 4.
4.2 Fuel Oil System Learning Objectives The OP engine cutaway will be used to illustrate the flow path of fuel oil in the Upon completion of this lesson you will engine.
become familiar with:
The instructor will use the cutaway fuel oil
- 1. The appearance and function of the transfer pump to illustrate its component air combustion system and its parts and their functions.
components.
The cutaway fuel supply pump will be used
- 2. The appearance and function of the to illustrate component parts and their fuel oil system and its components. functions.
- 3. The appearance and function of the exhaust system and its components. The instructor will use the ALCO engine to illustrate the following:
4.1 Combustion Air System
- The governor-to-fuel-rack linkage including the individual adjustable The instructor will use the OP engine linkage to each engine cylinder fuel cutaway to illustrate and explain the injection pump fuel metering gear.
combustion air system and the combustion air intake manifold that would connect to the
- How each cylinder fuel injection supercharger, turbocharger, intake air pump stroke is controlled by a cam piping, filters, and silencers. He will explain on the engine camshaft.
the flow of combustion air into each engine cylinder. The instructor will use the dual cutaway fuel oil filter and the cutaway fuel oil strainer to The instructor will use cutaway blower and illustrate the component parts of each and its component parts to illustrate how they their functions.
function to pressurize combustion air and scavenge exhaust gases. The instructor will use a cutaway fuel injection pump to illustrate component parts The instructor will use the cutaway and their functions in metering and turbocharger and its component parts to supplying fuel to the injection nozzle.
illustrate their function in converting high Rev 3/16 4-44 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems The instructor will use the cutaway fuel injection nozzle to illustrate component parts and their function in the injection process.
4.3 Exhaust System The instructor will use the OP engine cutaway to illustrate:
- The flow path of exhaust gases from each cylinders exhaust ports to exhaust manifold.
- The Exhaust manifold that would connect to the turbocharger, exhaust piping, & muffler.
The instructor will use the turbocharger cutaway to illustrate how hot exhaust gases drive the turbine to produce pressurized intake combustion air.
The instructor will use the muffler cutaway to illustrate how its baffles reduce noise.
Rev 3/16 4-45 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems HANDS-ON SESSION 4A The same general principle applies to the 2-stroke cycle engine as well. The normal 4A.0 COMBUSTION AIR, scavenging air blower output capacity was TURBOCHARGERS, AND restricted by the engine output horsepower SCAVENGING BLOWERS to drive it. Turbocharging a 2-stroke cycle engine considerably increases the power Purpose output capability without an increase in the horsepower to drive the blower since the This session's purpose is to complement the energy to drive the turbocharger is derived classroom instruction of Chapter 4. from waste energy in the engine exhaust.
Learning Objectives While it does cost some energy for the engine to overcome the increased exhaust Upon completion of this lesson you will be back pressure required to drive the able to: turbocharger, the net effect of the increased combustion air supply to the engine far
- Understand the basic components that outweighs the slight increase in the make up the engine turbocharger, their horsepower required to overcome the assembly, and their functions. increase in exhaust back pressure.
Turbocharged engines are more efficient
- Better understand instructor presentation than blower-scavenged or naturally-of the cutaway scavenging air blower. aspirated engines, thus proving that turbo-charging assists the engines power output.
4A.1 Turbochargers The turbocharger consists of five basic The purpose of the turbocharger is to parts. See Figures 4-29 and 4-30.
provide air to the engine for combustion.
Before turbocharging became common, 1. The rotating assembly consisting of the most engines of the 4-stroke cycle design turbine and the compressor mounted on were naturally aspirated. That is, the air was a common shaft.
breathed into the cylinder by the action of 2. A center housing that holds the bearings the piston sucking the air into the engine. that support the rotating assembly.
This resulted in the air in the cylinder being 3. The compressor housing with its diffuser slightly below atmospheric pressure and as ring.
a result, the air was less dense and
- 4. The exhaust casing which surrounds the contained less oxygen than normal air.
turbine end of the rotating assembly.
Because the engine is dependent on the amount of oxygen to burn the fuel, the 5. The exhaust inlet casing with its nozzle engines output was restricted. By using a ring to direct flow to the turbine blades.
turbocharger, more air (oxygen) is pumped On most of the turbochargers made by into the cylinder at positive pressure. American manufacturers, the bearings are Therefore, the engine is capable of burning within the center housing and the lube oil more fuel and putting out more power. supply is from the engine lube oil system. In Rev 3/16 4-46 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems most turbochargers of European the presence of piston ring parts or other manufacture, the bearings are outboard of debris. Also inspect compressor wheel for the turbine and compressor wheels and the damage, particularly the leading edges of oil is supplied from sumps within the the blades where air enters the compressor.
turbocharger assembly and there is a self-contained lube oil pump. See Figure 4-31. The turbocharger is reassembled in reverse There are examples of these differing order to that given above for disassembly.
constructions available for students to study. However, it is necessary in the process to add or subtract shims to obtain the correct With directions from the instructor, students end clearance in the rotating assembly.
will disassemble a typical OP turbocharger Also, take care in replacing the exhaust inlet by using the following procedure: casing and compressor inlet casing, to not damage the compressor wheel or the
- 1. Remove the bolts holding the exhaust turbine wheel and nozzle ring.
inlet casing to the exhaust housing and remove the exhaust inlet casing.
Most turbocharged FM engines have an
- 2. Remove the bolts holding the exhaust adapter section in the exhaust piping, just housing to the center (bearing) housing prior to the turbos exhaust inlet connection.
and remove the exhaust housing This section contains a conically shaped section. screen to keep engine parts from entering
- 3. Remove the bolts holding the air inlet the turbocharger. Clearances between the casing to the air compressor housing end of the nozzle ring and the turbine blades and remove the inlet casing. are such that parts of piston rings that may have failed, for instance, will not pass
- 4. Remove the bolts holding the air through the turbine and may machine the compressor housing to the center turbine blades. The screens purpose is to housing and remove the compressor trap these parts and prevent them from casing. entering the turbocharger. There are small
- 5. This leaves the rotating assembly boxes attached to these transition sections supported by the center (bearing) in which this debris is collected. These housing. Remove the nut at the should be inspected periodically to see that compressor end of the rotating assembly they are clear. If debris is found, the engine and use a puller for removing the should be inspected to determine the source compressor wheel from the rotating of the debris. The most likely source is shaft. When the compressor wheel has pieces of broken piston rings so this section been removed, then pull the shaft with is often referred to as a ring catcher.
the turbine wheel, from the bearing housing. 4A.2 Scavenging Air Blower
- 6. Inspect the bearings, including the thrust Using the cutaway blower, the instructor will bearing surfaces.
discuss its construction and operation. Its gear drive from the engine and mounting on While the turbocharger is disassembled, the engine will be shown.
inspect nozzle ring for signs of damage and Rev 3/16 4-47 of 48 USNRC HRTD
Emergency Diesel Generator Combustion Air, Fuel, and Exhaust Systems HANDS-ON SESSION 4B The nozzle should open sharply when the fuel pressure reaches the specified point to 4B.0 FUEL INJECTION PUMPS, FUEL open the nozzle and spray fuel. The nozzle INJECTION NOZZLES should also close sharply, with no dribbling or leaking from the nozzle. Once it closes.
Purpose it should open at a specific pressure.
This session's purpose is to complement the The purpose of this exercise is to classroom instruction of Chapter 4. disassemble several injection nozzles of various types, and inspect their parts. The Learning Objectives nozzles are then reassembled and tested to see that they operate properly. The testing Upon completion of this lesson you will be process is generally referred to as pop able to understand: testing. Refer to nozzle illustrations, Figures 3-39 and 4-21 through 4-28.
- Disassembly / assembly and test of fuel injection pumps, and how they operate. At the instructors direction, disassemble assigned injector nozzle(s). The instructor
- Disassembly / assembly and test of fuel will direct which parts are to be inspected injection nozzles, and how they operate. and how an inspection is carried out.
4B.1 Injection Pumps and Nozzles Instruction will be given on reassembling the nozzles. Some nozzle assemblies have The students, with the assistance and copper gaskets which must be annealed directions of the instructor, will dissemble a before being installed. Annealing is carried PC engine injection pump. After out by heating the gaskets until cherry red disassembly, the pump parts will be and quenching in water. The gasket must examined and explained. This injection then be inspected to see that it was not pump is similar to the OP engine injection damaged in the annealing process.
pump, but much larger. The relationship of the injection pump to the cam shaft and After nozzles are reassembled, attach the tappet assembly will be explained and assembly to a nozzle test stand and pump demonstrated. fuel pressure up until the nozzle pops open.
It should open at or slightly above specified 4B.2 Injection Nozzle Assemblies pressure and spray fuel in the form of a fine mist. The nozzle should not leak after it The injection nozzle is a very important part pops shut, nor while subsequently being of the engine. If the injection nozzle does pumped up again to recheck pop pressure.
not function properly, the fuel in not properly atomized into the cylinder and the fuel may CAUTION: Keep hands away from the not burn properly. This affects the operation nozzle tip when pop testing the nozzle. The of the engine by making exhaust fuel comes out of the nozzle at a high temperatures higher than normal and fuel enough pressure to cause injury to hand or consumption higher than it ought to be. fingers in the spray path.
Rev 3/16 4-48 of 48 USNRC HRTD