ML20043F653
| ML20043F653 | |
| 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: ML20043F653 (52) | |
Text
Emergency Diesel Generator Introduction to Diesel Engines
2.0 INTRODUCTION
TO DIESEL ENGINES signal. They may also be started manually when the plant operators determine a This chapter presents the basic theory and threatening or potentially hazardous principles of design which show how the condition exists. Once on line, these diesel chemical energy in fuel oil is converted into generators must be able to supply the rotational shaft output horsepower by plant's dedicated electrical needs for as long means of the diesel engine. as necessary to allow the plant operators to reach a safe shutdown condition and Learning Objectives maintain that condition until the offsite electrical supply is re-established.
As a result of this lesson, you will be able to:
2.2 Energy Conversion
- 1. Explain the basic energy conversion process resulting from the operation of a Fundamentally, diesel engines are just diesel engine. energy conversion devices. In a nuclear application, the energy contained in the fuel
- 2. Differentiate between the operating supplied to the engine is converted into principles of 4-stroke cycle and 2-stroke electrical energy needed to accomplish a cycle diesel engines. safe shutdown of the plant. This process requires three steps:
- 3. Identify selected basic terms applicable to the design and operation of a diesel First, the chemical energy contained in the engine. fuel oil is converted into thermal energy by the process of combustion.
- 4. Describe the basic heat / power balance which exists during the operation of a Second, this thermal energy, in the form of diesel engine. heated gases, is converted into mechanical energy by expansion-cooling of the gases.
2.1 Introduction to Emergency Diesel This creates the forces on the pistons, Generators connecting rods and crankshaft. Those key components convert the linear back and Electrical power is normally supplied to the forth motion of pistons into rotational output nuclear utility by the power grid to which the shaft horsepower.
plant is connected. Should this source of power become unavailable, known as a Third, the output shaft drives a generator Loss Of Offsite Power (LOOP), some that, through electro-magnetic induction, alternate power source must be available to converts the mechanical energy supplied by power the essential electrical loads. This the engine into electrical energy used to run alternate power is provided by the plant key nuclear plant systems. This process will Emergency Diesel Generators (EDGs). be discussed in more detail in Chapter 9.
EDGs are designed to start automatically in 2.2.1 Combustion the event of a LOOP or other emergency Rev 3/16 2-1 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Combustion is defined as: The chemical understanding of the combustion process as reaction between the elements of hydrogen it occurs within the diesel engine.
and carbon (supplied by the fuel) and oxygen (supplied by free air), resulting in the 2.2.2.1 Closed Container (Figures 2-1, 2-2) release of energy in the form of heat and light. We will begin with the closed container shown in Figure 2-1. It has been charged For combustion to occur, three (3) key with a mixture of fuel and air in the proper elements must be present. Elimination of proportions for combustion to take place.
any one of the three will prevent combustion The pressure and temperature of the from occurring. contents of the container are at equilibrium with its surroundings.
Fuel, which is comprised primarily of carbon and hydrogen, supplies the energy to be With the addition of heat, ignition of the fuel converted. Within the engine cylinders, the and air occurs as shown in Figure 2-2. The chemical energy of the fuel is converted into combustion causes a sharp rise in both thermal energy. On average, diesel fuel oil temperature and pressure within the contains energy of approximately 140,000 container. Since the volume of the container Btu's per gallon. is fixed, no movement can occur and therefore no work is accomplished.
Oxygen is the second key element of the combustion process. It combines with the 2.2.2.2 Addition of Piston (Figures 2-3, 2-4) carbon and hydrogen of the fuel to produce heat, and light. Diesel engines obtain their By adding a movable piston to the bottom of oxygen from the intake of atmospheric air, the container, we still have a confined which contains about 21% O2. space, but the volume is now variable. A charge of fuel and air is placed above the Heat of sufficient value is required to cause piston as before. With the addition of heat ignition of the fuel and air mixture. This heat to ignite the air fuel mixture, combustion comes from rapid compression of the air occurs causing the temperature and charge confined within the cylinder, an effect pressure to rise sharply. This rise in described in Charles law. pressure causes the piston to move downward rapidly, forcing it out of the The combustion process will be discussed in bottom of the container. No useful work is more detail in Chapter 4, "Fuel, Air, and provided, but there is movement.
Engine Governing."
2.2.2.3 Connecting Rod and Crankshaft 2.2.2 Cylinder Activity (Figures 2-5, 2-6)
In order to fully comprehend the operation of The problem we face is how to convert the a diesel engine and how each of the thermal energy of combustion into the components is necessary to support that mechanical energy required to operate the operation, we must have a solid generator. We know from the fundamentals Rev 3/16 2-2 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines of mechanical design that by adding a
- Once heated above the ignition crankshaft and connecting rod to the piston temperature, a specific quantity of fuel and cylinder, we can convert the linear must enter the combustion chamber and motion of the piston into rotary motion of the mix with the air charge in such a manner crankshaft. that combustion will occur.
We now have a configuration as shown in
- The mechanical components of the Figure 2-5. The connecting rod makes the engine will then convert the resulting physical connection between the piston and thermal energy into the mechanical the crankshaft. The area above the piston, energy desired.
the combustion chamber, is charged with an air fuel mixture.
- The spent gases must be removed to allow for a fresh air charge to enter the By adding the heat needed to ignite the air cylinder.
fuel mixture, combustion will occur causing a rapid increase in temperature and 2.2.3.2 Cylinder Configuration (Figure 2-7) pressure above the piston. This pressure then forces the piston downward. The To fulfill these requirements, a cylinder connecting rod transmits the force of the arrangement as shown in Figure 2-7 is piston to the crankshaft causing it to rotate constructed. This configuration is typical of 180 degrees as shown in Figure 2-6. 4-stroke cycle diesel engine. (We will cover 2-stroke cycle diesel engines later in this 2.2.3 Four-stroke Cycle Operation chapter.)
The activity up to this point is limited to only
- A cylinder, or cylindrical volume is 180o of crankshaft rotation, so the useful created with a fixed upper closure work output of the engine is also limited. (cylinder head).
The problem now is to find a way to make this process repeatable for each cylinder.
- A piston forms the closure at the lower end of the cylinder and transmits the 2.2.3.1 Operational Requirements forces of combustion through the connecting rod to the crankshaft.
To make this process repeat, creating a continuous rotation of the crankshaft the
- A crankshaft works in conjunction with following series of events must take place. the connecting rod and piston to convert the linear motion of the piston to the
- A fresh charge of air must be supplied to required rotary motion.
each cylinder in preparation for the next combustion cycle.
- An exhaust valve is placed in the upper closure of the cylinder to provide a path
- This fresh air charge must be heated for removal of spent gases from the above the ignition temperature for the combustion space.
fuel oil supplied.
Rev 3/16 2-3 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines
- An intake valve is also added to the 2.2.3.3 Intake of Air Charge (Figure 2-8) upper closure. It provides a means for directing a fresh air charge into the We begin the 4-stroke cycle process with cylinder. the cylinder in the configuration as shown in Figure 2-8. The piston is at the top of its
- A fuel injector is added to provide a stroke and the intake valve is open.
method for delivering fuel to the air Rotation of the crankshaft causes the piston charge once the air charge has been to move downward. This downward sufficiently heated. movement of the piston causes a negative pressure to develop within the cylinder. This
- The heat required to ignite the fuel is is shown between points A and B on the obtained by rapidly compressing the air graph provided in Figure 2-14.
charge. This will be detailed in the following paragraphs. Atmospheric pressure, being higher than that in the cylinder, pushes a charge of air Diesel engine operation is based on the air into the cylinder. Once the piston has standard Diesel cycle shown in Figure 2-12. reached the bottom of its stroke, the cylinder The graph plots the pressure in the cylinder should be fully charged with fresh air.
against the volume of the cylinder as the piston moves through its cycle. Beginning 2.2.3.4 Compression of the Air Charge at point 1, the piston is at the bottom of its (Figure 2-9) stroke with the cylinder volume the greatest.
Once the piston has reached the bottom of As the air charge is compressed, the its stroke (point B), the intake valve closes.
pressure increases as the volume This traps the air charge in the cylinder.
decreases from point 1 to point 2. Point 2 Further rotation of the crankshaft moves the represents the highest pressure at which piston upward, thereby compressing the air time fuel is injected into the cylinder. With charge, which sharply increases both its this ideal cycle, combustion occurs at a pressure and temperature. As the piston constant pressure while the cylinder volume approaches the top of its stroke the air has increases from point 2 to point 3. been heated above the temperature Combustion is complete at point 3 where the required to ignite the fuel oil.
gas pressure decreases as the volume increases from point 3 to point 4. 2.2.3.5 Injection of Fuel (Figure 2-10)
At point 4, the volume is at its maximum, A short distance before the piston reaches exhausting the spent gases and refilling the the top of its stroke, a specific quantity of fuel cylinder with a fresh air charge. is injected into the heated air charge, in the form of a fine mist (to promote complete, Figure 2-14 represents the actual pressure efficient mixing and combustion). The fuel versus stroke activity in the cylinder of a 4- mixes with the heated air in the cylinder and stroke cycle diesel engine. This graph will ignition occurs. This results in very rapid be referenced in sections 2.2.3.3 2.2.3.7. combustion.
Rev 3/16 2-4 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines This occurs at point C on the graph of Figure 2.2.3.8 Four-stroke Cycle Operation 2-14. As a result of combustion, pressure in the cylinder increases sharply as the piston The process just described required four moves past its uppermost point of travel strokes of the piston or two revolutions of the (point D). crankshaft (720 degrees) to complete one power event. This process is therefore 2.2.3.6 Development of Power (Figure 2-11) referred to as the 4-stroke cycle of operation and the engines using it are called 4-stroke The injection of fuel continues past the cycle diesel engine.
uppermost point of piston travel, causing the combustion process to be extended. The 2.2.4 Two-stroke Cycle Operation -
pressure in the cylinder continues to Conventional increase, reaching its peak (point E of Figure 2-14) shortly after the piston has During the development of the diesel passed its uppermost point of travel. engine, a means was discovered that allowed an engine to provide one power The piston is now being forced downward by event for each revolution (360 degrees) of the expanding gases, delivering power to the crankshaft, or two strokes of the piston.
the crankshaft. The power being delivered As would be expected, this process became to the crankshaft is indicated by the line D- known as the 2-stroke cycle of operation.
E-F on the graph of Figure 2-14.
The following information is representative 2.2.3.7 Exhaust of Spent Gases (Fig. 2-12) of the General Motors, Electro-Motive Division (EMD), Series 567, 645 and/or 710 Several degrees before the piston reaches diesel engines, widely used in Emergency the bottom of its stroke, the exhaust valve Diesel Generator systems at US nuclear opens (point F of Figure 2-14). With the power plants.
pressure in the cylinder still above atmospheric, the spent or burned gases 2.2.4.1 Cylinder Configuration (Figure 2-15) begin to exhaust to the atmosphere. After reaching the bottom of its stroke, the piston The 2-stroke cycle cylinder configuration again moves upward. This upward motion shown in Figure 2-15 varies somewhat from of the piston forces most of the remaining that of the 4-stroke cycle discussed above.
gases from the cylinder. It retains the exhaust valves and fuel injector mounted in the cylinder head as found in the As the piston reaches the top of its stroke, 4-stroke cycle engines. However, the intake represented by point A of Figure 2-14, the valves have been replaced by ports cut exhaust valve closes and the intake valve through the wall of the cylinder as shown.
opens. This returns the cycle to its starting point and the engine is again ready to take Intake of the air charge will only occur when in a fresh charge of air so that its operation the top of the piston is below the intake ports may continue. in the cylinder wall. And, as we will now see, piston action cannot draw in air on its own.
Rev 3/16 2-5 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines One problem associated with the 2-stroke As the piston passes its uppermost point of cycle of operation is that during the intake travel, the expanding gases of combustion and exhaust events, the air must be pumped force it downward delivering power to the into the cylinder. Generally, these engines crankshaft. Power continues to be delivered use a mechanically driven blower and/or to the crankshaft until shortly before the exhaust driven turbocharger to force the air piston reaches the intake air ports. At this into the cylinder for combustion and removal point the exhaust valves open, ending the of the spent gases. We will cover blowers power event.
and turbochargers in detail in Chapter 4, "Fuel, Air and Engine Governing." 2.2.4.5 Exhaust Event 2.2.4.2 Intake Event (Figure 2-16) Once the exhaust valves have opened, the spent gases, having a pressure greater than The 2-stroke cycle begins with the piston at atmospheric pressure, begin to exhaust the bottom of its stroke with the intake ports from the cylinder. Continued downward uncovered and the exhaust valves open. movement of the piston opens the intake Air, supplied by the blower, is forced through ports allowing the intake air, under pressure the intake ports into the cylinder. Some of from the blower, to enter the cylinder, this air is used to push the remaining spent scavenging (removing) the remaining spent gases out of the cylinder past the exhaust or burned gases.
valves.
The piston has now reached the bottom of As the piston begins to move upward, the its stroke, and with both the exhaust valves exhaust valve closes. The blower continues open and the intake ports uncovered, the to provide pressurized air to the cylinder cycle is ready to repeat as the piston moves until the piston has moved up sufficiently to upward. This cycle of events has occurred close off the intake ports. This completes in only two strokes of the piston or 360 the intake event. degrees of crankshaft rotation.
2.2.4.3 Compression (Figure 2-17) 2.2.5 Two-stroke Cycle Operation --
Opposed Piston Once the piston has closed off the intake ports, the upward movement of the piston A variation of the 2-stroke cycle of operation, compresses the air charge, raising its which has been in commercial use since temperature above that needed to cause before World War II, is the opposed piston ignition of the fuel. As with the 4-stroke engine. This unique design shown in Figure cycle engines, as the piston approaches the 2-19 uses two pistons (upper and lower) per top of its stroke, fuel is injected into the cylinder. There are also two connecting heated air charge. The resulting ignition of rods and two crankshafts. The engine uses the fuel begins the combustion process. no valves. Both the intake air and exhaust gases flow through ports in the cylinder wall.
2.2.4.4 Combustion and Power The fuel injection nozzles are placed (Figure 2-18) through the cylinder wall near the center.
Rev 3/16 2-6 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines 2.2.5.1 Intake Event (Figure 2-20) metered quantity of fuel is then precisely injected into the heated air mass and The process begins with both pistons near combustion occurs. The FM OP engine their outermost points of travel. Both the fuel injectors are angled to promote mixing intake and exhaust ports are uncovered. (the tornado effect again). As the The incoming air charge, being forced in by combustion gases expand, they force the a blower and / or turbocharger, fills the pistons away from each other, transmitting combustion space while pushing the power to both crankshafts.
remaining spent gases from the cylinder through the exhaust ports. The Fairbanks 2.2.5.4 Exhaust Event (Figure 2-20)
Morse OP engine intake ports are angled, producing a tornado effect (swirl) that Downward motion of the lower piston, with makes this action more efficient (complete). its lead, uncovers the exhaust ports allowing the exhaust gases to begin to escape. The It should be noted that the lower upper piston then uncovers the intake ports piston/crankshaft leads the upper by allowing the incoming air charge to help approximately 15o of crankshaft rotation. push the spent gases from the cylinder.
This is done to ensure that the exhaust ports are closed before the intake ports during With both pistons near the outermost points inward movement of the piston. With the of their travel, the cycle is ready to be exhaust ports closed and the intake ports repeated for continuous operation of the still open, the incoming air slightly engine. As with the 2-stroke conventional pressurizes the cylinder. As the upper engine, the opposed piston engine also piston closes the intake ports, the intake delivers one power event for every two event is completed. strokes of the piston, or 360 degrees of crankshaft rotation.
2.2.5.2 Compression (Figure 2-21) 2.2.6 Two-stroke vs Four-stroke Cycles With both ports closed, the air charge is captured and compression of the air charge Theoretically, for two engines of similar begins. Compression continues until both configuration and size, one a 4-stroke cycle pistons are near their innermost points of and the other a 2-stroke, the 2-stroke engine travel. With the 12 to 15 lead between the should be able to develop twice the power of lower and upper crankshafts, both pistons the 4-stroke. However, the 2-stroke engine will not reach their innermost points of travel requires horsepower to drive the blower, at the same time. reducing the HP available for work. Further, incomplete scavenging and a reduced 2.2.5.3 Combustion and Power (Figure 2-22) effective stroke length as the piston passes the intake ports of a 2-stroke cycle engine As the pistons approach their innermost limits the power output of the engine.
points of their travel, the air charge is fully compressed and its temperature has If one looks at Figure 2-14 again and applies reached the ignition point for the fuel. A it to the 2-stroke cycle engines, it is basically Rev 3/16 2-7 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines the same from point B (at the point the 2.3.1.2 Stroke Intake Valve/port closes) to point F (the point that the exhaust valve/port) opens, and This dimension represents the total distance substitutes another means of charging the traversed by the piston as it moves from the cylinder with air between those two points top of its stroke to the bottom and vice versa.
(B-valve closed to F), then the diagram Specified in inches and fractions, it is equal applies to the 2-stoke cycle engine just as to twice the length of the crankshaft throw.
well. Combining the bore and the stroke gives the cylinder displacement as described in Selection of an engine type, 2-stroke or 4- section 2.3.1.7.
stroke, for a particular application becomes a decision based on engineering data, 2.3.1.3 Top Dead Center (TDC) economics, and personal preference. Both types of engine perform satisfactorily and This term is applicable to 4-stroke cycle and reliably when proper maintenance and 2-stroke cycle conventional engines. Rather operating procedures are followed. than a dimension, it represents the position of the piston when it is at the top or 2.2.7 Typical Times for All Events uppermost point of its stroke. References to (Figures 2-26 and 2-27) injection timing or crankshaft position are termed as degrees before or after TDC. For Each event must occur smoothly, within a example, injector timing may be set to 23o few milliseconds, and at precisely the right before TDC, while exhaust valve closure time for satisfactory engine operation. may be 15o after TDC.
2.3 Diesel Engine Terminology 2.3.1.4 Bottom Dead Center (BDC) 2.3.1 Dimensional Specifications As would be expected, this term is the (Figure 2-23) opposite of Top Dead Center, the lowermost point of piston travel. Some specifications 2.3.1.1 Cylinder Bore are given relative to BDC. For example, inlet valve closure would normally be given as 7o This is the specified inside diameter of the after BDC.
engine cylinder. Its nominal size is given in inches and fractions. For example, the 2.3.1.5 Inner Dead Center (IDC) nominal bore of a Fairbanks Morse, Model 38TD8-1/8 opposed piston engine is 8 and This term, similar to TDC for 4-stroke and 2-1/8 inches. stroke conventional engines, is uniquely applicable to 2-stroke cycle opposed piston Actual bore, for manufacturing and (OP) engines. It represents the piston maintenance purposes, will be specified in position at its innermost point of travel. Keep inches and decimals. For the same engine, in mind, however, that both pistons do not the bore indicated in the maintenance reach IDC at the same time due to the lead manual is 8.125 to 8.129 inches. of the lower crankshaft.
Rev 3/16 2-8 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines 2.3.1.6 Outer Dead Center (ODC) 2.3.1.8 Clearance Volume (Figure 2-24)
This term references the piston position at Clearance Volume (CV) represents the total the outermost point of its stroke. It is here volume of the cylinder when the piston is at that intake ports and the exhaust ports are Top Dead Center. This volume includes the fully open (uncovered). Due to crankshaft cylindrical volume between the piston and lead, the pistons do not reach ODC at the the cylinder head including any volume same time. created by the shape of the top of the piston and/or cylinder head combustion space.
2.3.1.7 Cylinder Displacement 2.3.1.9 Compression Ratio (Figure 2-24)
The power an engine is capable of developing is relative to the amount of fuel The compression ratio (CR) of an engine is the engine can burn efficiently. In turn, the the ratio of the volume of the cylinder with amount of fuel which can be burned the piston at BDC (D+CV) to the volume of depends on the volume of the air charge or the cylinder with the piston at TDC (CV). It displacement of the cylinder. can be represented numerically as follows.
Cylinder displacement (D) is the volume +
displaced by the piston as it moves from = = +1 TDC to BDC or BDC to TDC.
This can be simplified as follows.
Numerically, this is calculated by multiplying the cross-sectional area of the cylinder by the length of the stroke (L). The following () +
formula will determine the displacement of a single cylinder.
Where C represents the clearance distance 2 between the piston and cylinder head. This
= method gives only an approximation when 4
the actual clearance volume is not known.
(All in inches or same dimensional units)
Compression ratios for diesel engines can To determine the total displacement (TD) of run from as low as 8:1 for large, low speed an engine, simply multiply the displacement units to 21:1 for smaller, high speed of 1 cylinder by the number of cylinders (N). automotive types. It should be recognized that on a turbocharged engine the actual compression ratio in the cylinder is the 2 product of the swept volume compression
=
4 ratio (from the piston motion), and the pressure ratio of the turbocharger Hereafter, the total engine displacement will compressor, and may approach 20-30 to 1.
be referred to as DISP.
Rev 3/16 2-9 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines 2.3.2 Engine Performance NOTE: If the stroke (L) is given in inches, then the constant in the above formula for 2.3.2.1 Horsepower IHP becomes 396,000 instead of 33,000.
The term Horsepower used alone usually If LA is for a cylinder, then the IHP is that of represents the power output of the unit. a single cylinder. If DISP is substituted for However, there are different types of LA, then the IHP is that for the whole engine.
horsepower which must be considered when discussing diesel engines Frictional Horsepower (FHP) - represents the power required to operate the engine. It Brake Horsepower (BHP) - represents the is used to overcome friction, operate engine net power output of the engine at the components and move air into and gases crankshaft. The term "brake" indicates that out of the engine.
the power was measured by applying a braking device, sometimes called a "prony" The relationship between these three types brake, to the unit to measure its output in of horsepower is as follows:
terms of torque per unit of time. With the diesel engine operating at a specific speed BHP = IHP FHP (RPM), the brake is applied until the engine can no longer maintain its set RPM. At this 2.3.2.2 Torque (T) point, the torque is measured and converted into horsepower using the following Torque represents a twisting or turning equation. effort. Torque may involve rotary motion or no motion at all. For diesel engines, torque is the turning effort exhibited by the
=
5252 crankshaft. Since there is rotary motion of the crankshaft, there is a definite T = torque in foot-pound relationship between this torque and the N = engine speed in RPM brake horsepower produced by the engine.
Indicated Horsepower (IHP) - is the total 5252
=
power developed by the engine. It is a function of the mean indicated pressure applied to the top of the piston. The Brake Torque can also be determined by the following formula:
=
33,000 =
75.4 Pi = indicated mean effective pressure (psi)
L = length of stroke (ft.) 2.3.2.3 Brake Mean Effective Pressure (BMEP)
A = area of piston (in2) n = number of power strokes per minute This is a purely theoretical term but it does Rev 3/16 2-10 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines have significance for the engine, as it relates For example: What is the thermal efficiency to the stress placed on key engine parts of an engine which produces 1000 BHP when operating at rated continuous power. while consuming 50 gallons of fuel per hour?
(It could also be a measure of the nerve of Assume fuel with a heat value of 140,000 the manufacturers chief engine designer!) BTU per gallon.
BMEP is obtained from the equation below Heat input of the fuel:
as Pb, representing mean effective pressure for each power stroke when the engine is 50 gal / hr x 140,000 BTU / gal =
producing rated brake horsepower. 7,000,000 BTU / hr Numerically for 4-stroke cycle engines; Engine power output:
1000 hp x 2545 BTU / hr. hp. =
792,000
= 2,545,000 BTU / hour Thermal efficiency then becomes:
Numerically for 2-stroke cycle engines; 2,545,000 = 0.364 = 36.4%
396,000 7,000,000
=
For this example, the remaining 63.6% of D = DISP (displacement of the engine) heat energy is rejected to the environment:
N = Number of revolutions per minute 2.3.3.3 Heat Balance Pb = Brake mean effective pressure in psi, often represented as BMEP This shows the approximate heat balance for a typical turbocharged diesel engine and 2.3.3 Engine Efficiency accounts for all the heat input from its fuel:
2.3.3.1 Mechanical Efficiency (em)
- Power output (BHP): 33 40%
Mechanical efficiency is the ratio of the
- Exhaust and radiation: 30 33%
power output of the engine (BHP) to the indicated power input (IHP). Numerically;
- Jacket water cooling: 10 15%
- Lube oil cooler: 4 8%
=
- Turbocharger aftercooler: 5 10%
- Generator Inefficiency: 3 5%
2.3.3.2 Thermal Efficiency (et)
- Radiation (engine to room): 2%
This ratio of the engines energy output to the heat input of the fuel, over a period of Heat balances are performed by measuring time. One horsepower is equal to 2545 the temperatures of the fluids entering and BTUs per hour. leaving the engine, and by knowing the fluid Rev 3/16 2-11 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines flows. This allows computation of the heat horsepower hour. For electric generation, it being rejected to a system such as the lube may be given as pounds or gallons of fuel oil, the jacket water, or the air system. The per kilowatt hour.
exhaust system figure is generally found by subtracting all of the other known systems 2.3.4 Additional Terminology from the total heat computed from the heat input of the fuel. See BSFC below. 2.3.4.1 Supercharging 2.3.3.4 Volumetric Efficiency During operation of a diesel engine, atmospheric pressure provides the force This term is normally applied to non- needed to cause the intake air charge to turbocharged 4-stroke cycle engines. It is enter the engine cylinder. Engines which an indication of the engines ability to rely on atmospheric pressure for their intake breathe. Numerically, it is the ratio of the air charge are referred to as "naturally volume of fresh air taken into the cylinder to aspirated. By providing an air pumping a volume of air equal to the displacement of device to the engines intake air system, it is the cylinder. A volumetric efficiency of 1 possible to increase the pressure and indicates the cylinder has taken in a full subsequently the mass flow of air entering charge of fresh air. the cylinder. Whenever the mass of air entering the cylinder is greater than that 2.3.3.5 Scavenging Efficiency which would be attained by atmospheric conditions, the engine is said to be This term, applicable to 2-stroke cycle supercharged.
engines, is the ratio of the new air charge trapped in the cylinder compared to the total When an engine is supercharged, a greater volume of air and exhaust gases in the mass of air enters the cylinder, providing an cylinder at the time of port closing. increased quantity of oxygen to support combustion. With this increase in available 2.3.3.6 Brake Specific Fuel Consumption oxygen, the engine can burn more fuel and, (bsfc) therefore, develop more horsepower (BHP).
BSFC is an indication of the engines fuel 2.3.4.2 Blower / Supercharger efficiency. It is based on the rate of fuel consumption per hour per horsepower These terms, often used interchangeably, output of the engine. apply to the mechanical devices used to increase the mass of air entering the engine cylinder. They are usually mechanically
()/ driven by the engine and, therefore, require
= horsepower from the engine to operate, in contrast with Turbocharger (defined below).
The results are normally given on the basis Their output, expressed in mass of air, is a of pounds of fuel per horsepower hour, but function of the engines speed (RPM).
may also be on the basis of gallons per Rev 3/16 2-12 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines 2.3.4.3 Turbocharger of key engine parts), its usually necessary to either reduce the compression ratio of the This is another device used to increase the engine and / or retard the timing, to limit the intake air mass for a diesel engine and, pressure at point E.
therefore, increase its power output. The key difference between a Turbocharger and 2.4 Typical Engine Design Criteria a Blower / Supercharger is the turbocharger is powered by the energy of the heated There are some limits imposed by physical exhaust gases leaving the engine. It does forces that limit the power output of an not require horsepower directly from the engine to ensure reliability and longevity.
engine, making the overall process more They are as follows:
efficient. It does, however, represent a restriction to the flow of exhaust gas BMEP Typical BMEP values (limits):
producing an increased back-pressure in 2-stroke cycle engines 150 160 the exhaust system. The power increase 4-stroke cycle engines 300 320 resulting from the addition of the turbocharger more than offsets the slight Peak Firing Pressure Typically limited to power lost due to increased back pressure.
1200 to 1500 psi.
Additionally, since the volume of air Piston Speed 1500 to 2000 fpm (feet per discharged by the turbocharger is a function minute). Piston speed = piston stroke of the heat energy of the exhaust gases, the turbocharger tends to respond to the load (inches) 2 rpm / 12. An OP engine with imposed on the engine. The greater the 10-inch stroke at 900 rpm has a piston engine load, the greater the heat energy in speed of 1500 fpm.
the exhaust. With the increased heat energy, the turbocharger produces an These limits advance slowly as engine increased boost to the intake air charge. technological and metallurgical improvements Initially, the process was described as being are made over time.
Turbo-supercharged. But over time, it has been simplified to Turbocharged. 2.5 Chapter Summary Blowers and turbochargers will be To summarize what we have learned in this discussed in greater detail in Chapter 4, lesson, let us look at Figure 2-27. This figure "Fuel, Air and Engine Governing." shows the timing diagrams for the typical 2-and 4-stroke engine cycles. The upper Another look at Figure 2-14 is warranted. diagram shows the timing of the events in The effect of turbocharging on this diagram the 4- stroke cycle engine in a circular is to raise the line at 14.7 (standard diagram. Remember that this engine atmospheric pressure) to a higher line, say requires two complete rotations in order to to 28 psia. This also raises the peak firing complete the events of the cycle.
pressure point at E. To compensate for this (as pressure may be limited by the strength There is a bar diagram in the center of this figure that shows the timing events along a Rev 3/16 2-13 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines line extending from 0 degrees to 720 cylinder. Then the upper piston covers the degrees - two revolutions. The valve timing air ports, and compression begins.
for the intake valves usually starts before the top of piston motion, and overlaps the As the pistons approach inner dead center, exhaust valve opening. One reason is to the exhaust piston arriving there first, the better scavenge the cylinder. The other is fuel is injected. As the fuel burns, pressure that it takes time, from the beginning of valve is created in the cylinder and the pistons are opening, to get it fully open and obtain full air now moving apart. This is the power stroke.
flow into the cylinder. When the exhaust piston approaches outer dead center, it uncovers the exhaust ports Once the intake valve closes, shortly after and the expended gases are allowed to the piston is past Bottom Dead Center, the leave the cylinder. A few degrees later, the trapped air is compressed. Near top dead air ports also open and the fresh air charge center, the fuel is injected and shortly begins enters the cylinder and purges the exhaust to burn, creating pressure in the cylinder. gases. The cycle then begins again.
Note that while the injection is shown as a fixed length, in reality it varies in length Only one revolution was required. Note that proportional to the load requirement. On the exhaust ports are centered on the outer stationary engines, the start of injection is dead center of the lower piston stroke, while normally constant, always starting at the the air ports are centered above the upper same crankshaft position. After injection, piston outer dead center. If there were no the piston moves down in the cylinder on the crank-lead, then the exhaust ports would power stroke. always be open when the air ports were also open, and there would be no opportunity to Near the end of the power stroke, the pack air into the cylinder before exhaust valve is opened so expended gases compression started.
can be removed. The exhaust valve then stays open until slightly after the piston gets The EMD 2-cycle engine would be similar to back to top dead center, allowing some the OP diagram except there would be no overlap with the air valve for scavenging the upper piston, with its offset lead. The air cylinder. Then the cycle begins again. ports would be opened by the motion of the piston, similar to the exhaust ports on the The lower circle diagram shows the 2-stroke OP engine. The exhaust valves would be cycle opposed piston timing cycle. All opened at the correct point in the cycle, events occur within one revolution. The before the air ports opened to allow the cycle starts with the piston at outer dead cylinder to blow down. They would then center and the blower / turbocharger putting close just after bottom dead center, in order air into the cylinder. This not only fills the to trap air in the cylinder before compression cylinder with air but, due to overlap (exhaust starts when the air ports close.
ports and air ports both open), allows the cylinder to be scavenged of exhaust from These relationships will be discussed again the last cycle. Exhaust ports are covered in Chapter 4, when fuel injection is covered.
first, as the lower piston moves up the Rev 3/16 2-14 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-2 Fixed Volume Plus Heat Figure 2-1 Fixed Volume Rev 3/16 2-15 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-4 Addition of Piston Plus Heat Figure 2-3 Addition of Piston Rev 3/16 2-16 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-6 Addition of Crankshaft Plus Heat Figure 2-5 Addition of Crankshaft Rev 3/16 2-17 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-8 Intake Air Charge Figure 2-7 Cycle Configuration Rev 3/16 2-18 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-10 Injection of Fuel Figure 2-9 Compression of Air Charge Rev 3/16 2-19 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-12 Exhaust of Spent Gases Figure 2-11 Development of Power Rev 3/16 2-20 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-13 Air Standard Diesel Cycle Rev 3/16 2-21 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-14 Pressure vs Stroke Diagram Rev 3/16 2-22 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-15 Cylinder Configuration Stroke Cycle EMD Engine Rev 3/16 2-23 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-16 Intake Event Rev 3/16 2-24 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-17 Compression Event Rev 3/16 2-25 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-18 Combustion and Power Stroke Rev 3/16 2-26 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-19 Cylinder Configuration Stroke Cycle OP Engine Rev 3/16 2-27 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-22 Combustion & Power Figure 2-21 Compression Event Figure 2-20 Intake Event Rev 3/16 2-28 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-23 Bore & Stroke Rev 3/16 2-29 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-24 Clearance Volume Rev 3/16 2-30 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-25 Compression Ratio Rev 3/16 2-31 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-26 Typical Times for Events 900 rpm Diesel Engine Rev 3/16 2-32 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-27A Typical Timing Diagram 4-Stroke Cycle Rev 3/16 2-33 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-27B Typical Timing Diagram 2-Stroke Cycle Rev 3/16 2-34 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-28 OP Engine Cross Section Rev 3/16 2-35 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-29 ALCO Engine Cross Section Rev 3/16 2-36 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-30 OP Engine Crankshaft Rev 3/16 2-37 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-31 OP Engine Vertical Drive Rev 3/16 2-38 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-32 Cylinder Liner Jacket Water Cooling Rev 3/16 2-39 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-33 OP Engine Cylinder Rev 3/16 2-40 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-34 OP Piston and Con-Rod Assembly Rev 3/16 2-41 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-35 OP Injection Nozzle Mounting Rev 3/16 2-42 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-36 OP Fuel Injection Pump Rev 3/16 2-43 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-37 Chain Type Drive Mechanism Rev 3/16 2-44 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-38 Camshaft Control End Rev 3/16 2-45 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-39 Fuel Injection Assembly Rev 3/16 2-46 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Figure 2-40 Injection Pump Plunger Positions Rev 3/16 2-47 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines WALKAROUND SESSION 2 and supported in the lower end of the cylinder block-in the crankcase. See Figure 2.0 DETAILED PRESENTATION OF THE 2-30. The two crankshafts are joined 2-STROKE CYCLE OP AND 4- together at the back (power) end of the STROKE CYCLE ALCO ENGINES engine by a vertical drive shaft which is connected to the two crankshafts by bevel Purpose (miter) gear sets. See Figure 2-31.
The overall purpose of this Walkaround The crankshafts rotate at the same speed session is for the students to identify engine but in opposite directions, and they are components, engine systems, and how they offset by a number of rotational degrees.
function as the diesel engine goes through The lower shaft leads the upper shaft a few all of its cycles of operation. degrees. This difference in angular position is called the crank lead. As the crankshafts Leaning Objectives rotate, the pistons travel up and down in the engine cylinders. The cylinder walls have As a result of this lesson, you will be able to: intake air and exhaust ports. The combustion chamber is formed by the walls
- 1. Identify the major features of the 2- of the cylinder and the crowns (tops) of the stroke cycle OP engine and of the 4- pistons. See Figures 2-32 and 2-33.
stroke cycle ALCO engine. Neither conventional cylinder heads nor valves are used in this engine.
- 2. Identify the primary systems and components of the OP and ALCO Refer to Figure 2-33 for this discussion:
engines.
The two cycles of this engine begin when air
- 3. Understand the functions of the major features, primary systems, and major is admitted to the cylinders through their components of the OP and ALCO ports when the upper piston nears outer engines. dead center (ODC). Air is supplied to the area around the intake ports by pressurized
- 4. Operate the rotatable cutaways for self- air supplied either by the scavenging air learning. blower (non-turbo engines) or by the turbocharger and blower on turbo-charged 2.1 OP Engine Rotatable Cutaway engines. At the very outward position of the Explanation upper piston, the exhaust ports are also open. Fresh intake air is forced down The OP Cutaway engine will be used to through the cylinder and out the exhaust demonstrate features and characteristics of ports. This scavenges the exhaust gases this 2-stroke cycle engine. Figure 2-28 from the last cycle. Because the air and shows a cross sectional view of this engine exhaust ports are open simultaneously, the design. It has two crankshafts-an upper fresh air blows completely through the crankshaft housed and supported in the top cylinder in one direction. This is called of the engine and a lower crankshaft housed uniflow scavenging.
Rev 3/16 2-48 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines In a few more degrees of crankshaft As the pistons travel toward (ODC), the rotation, the exhaust ports are covered by pressure and temperature in the cylinders the lower piston, and the fresh air super decrease as the pistons are driven apart and charges the cylinder space to inlet air cylinder volume increases. When the manifold pressure. As the crankshaft pistons approach ODC, the lower piston continues to rotate, the air ports also close. uncovers the exhaust ports. The cylinder From this point on, the air is compressed as pressure is further reduced as the exhaust the two pistons approach each other. As the gases leave the cylinder. If the engine is air is compressed, its pressure and turbocharged, the pressurized high temperature increase. temperature exhaust gases provide the power to drive the turbocharger.
A few degrees before the lower piston arrives at its inner dead center (IDC) As the crankshaft continues its rotation, the position, fuel is injected into the cylinder air ports are uncovered, allowing air to enter through the two injection nozzles. The the cylinder and scavenge exhaust gases injection nozzles spray fuel under high from the cylinder. At this point, the engine pressure into the cylinder through holes in has made one complete revolution of the the side wall of the cylinder liner assembly. crankshaft; each piston has made 2 strokes.
The fuel heated by the hot air in the cylinder For further information on the engine cycle, gets to its ignition temperature of about 450 see Figures 2-14 and 2-19 through 2-23.
to 550oF. Some of the fuel ignites and begins to burn. This raises the temperature 2.1.1 Pistons and Piston Rings further until soon all of the fuel is burning as it mixes with oxygen from air in the cylinder. The piston must have enough clearance to move freely up and down the cylinder bore, By the time the fuel is burning well and the both when its hot and when it is cold. So pistons have traveled beyond their IDC there is clearance between the piston and positions, combustion pressure on the the cylinder liner. Piston rings are provided pistons and connecting rods create the force to seal off the piston-to-liner space, to rotate the crankshafts. This is the power thereby creating a combustion chamber stroke of the engine. In order for the engine without excessive blow-by. This is the to run smoothly, there must be several purpose of the rings at the top of the piston, cylinders that fire in sequence and are timed and they are called the compression rings.
throughout a revolution of the crankshaft. They are made slightly larger in diameter than the bore of the cylinder but have a gap Each cylinder contributes to generating to accommodate the expansion due to power that is used for first, producing the temperature changes. Usually there are power necessary for the compression taking multiple rings (3 or 4) as some combustion place in other cylinders, second, to gasses will always bypass a single ring.
overcome the friction within the engine, and With several rings, it is possible to get an lastly, to produce power to drive the almost perfect seal.
generator.
Rev 3/16 2-49 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines Another set of rings on the piston is for cocktail shaker cavities to cool the piston controlling the amount of lubrication that crowns. Lube oil from these cavities returns gets to the cylinder liner. In most engines, to the crankcase. Refer to Figure 2-28.
there is no specific supply of oil to the cylinder surface. The oil gets to the cylinder On a 900 rpm OP engine, the piston makes surface by being splashed or flailed there its journey from ODC to IDC and back 15 from the crankshaft and other times a second. The oil in the connecting rotating / oscillating parts. There is generally rod drilling, the wrist pin area, and the piston too much oil supplied by that means; so it is crown space develops momentum which necessary to have piston rings to control the causes it to be propelled against the amount of oil getting up into the space underside of the piston crown. A moment between the piston and the cylinder bore. later, this same oil is sent to the other end of Oil control rings generally have drain the piston as the piston arrives at the ODC holes / slots. The piston is provided with position. A drain hole in the piston insert drain holes in the control oil ring area to allows this oil to escape and the next time drain the excess oil back into the crankcase. the piston arrives at the IDC position, a fresh charge of lube oil comes up the rod to impact On 2-stroke cycle engines, particularly again on the underside of the piston crown.
ported engines, it is necessary to also seal The oil is alternately driven against the the crankcase from the lower end of the piston crown, pulled away and drained, and piston. This is done by putting the oil rings replenished again on the next stroke.
at the lower / upper end of the pistons shown in Figure 2-34. This is referred to as the cocktail shaker action of oil cooling of the piston. The lube The piston crowns on most large diesel oil cooling of the engine is important, but it engines are chrome plated. This protects alone will not keep the piston adequately the cast iron or steel piston crown material cooled. In fact, the primary means of from the extreme heat of combustion. keeping the piston from becoming over heated is the next charge of scavenging and 2.1.2 Lube Oil Supply to the Piston combustion air entering the cylinder on the next intake event.
Lube oil from the crankcase is pumped through or around lube oil coolers to 2.1.3 Injection of Fuel into the Cylinder strainers / filters and then into the engine oil headers. On the OP engine, separate There are four holes around the center of the headers supply oil to the main bearings on cylinder liner. (See Figure 2-32) Two of the upper and lower crankshafts. Drilled these holes are for the injection nozzles passages from the main bearings feed the which spray fuel into the cylinder at the lube oil from the main bearings to the proper time in the cycle. See Figure 2-35.
connecting rod bearings. Drilled holes in the The injection nozzles are connected through connecting rods feed oil to the wrist pin high pressure steel tubing to the delivery bearings. Oil from the wrist pin bearings valve of their injection pump. The injection flows through a drilled hole into the piston pump and injection nozzle assemblies will Rev 3/16 2-50 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines be covered in more detail in a future session. service, the fourth opening is used for a However, while at the model, note the cylinder cock which can be used to relieve camshafts and how they are driven from the cylinder pressure and permit engine barring upper crankshaft with a chain drive setup. to check for hydraulic lock from water / oil.
See Figures 2-36 through 2-39.
2.1.4 Engine Cooling (See Figure 2-32).
As the cams rotate, they press down on a plunger in the tappet assembly. The plunger There was a discussion above on the is held against the cam surface by the force cooling of the piston by the lube oil system.
of a spring. The cam lobe overcomes the It is also necessary to cool the cylinder liners force of the spring and pushes the tappet and this is done with water. A jacket plunger down as it rotates through the surrounds the cylinder liner to provide a injection cycle for that pump. The tappet space for the cooling water to pass up along plunger in turn, presses down on the the cylinder. Usually water is supplied by an injection pump plunger. When the injection engine-driven pump. The water enters the plunger is all the way up, fuel fills the space engine at one end into the exhaust manifold in the injection pump barrel. Then the jacket (on non-turbo engines) or through the injection pump plunger moves; it first covers exhaust deck bridges (on turbo engines).
a port and traps the fuel sending it out through the delivery valve to the injection At each cylinder, a pair of pipes duct the nozzle and into the cylinder. When the water into the lower end of the cylinder injection pump plunger moves a little further, jacket. It passes up alongside the cylinder it uncovers the spill port and injection ends. liners as well as going around the 4 ports at the liners center. Water exits the liner at the The injection pump plunger has a helical top, on one side, and a header carries the cutout that is positioned by means of a gear water from the engine, Usually it passes and rack assembly. By rotating the plunger, through a temperature control valve to the the amount of fuel injected is controlled. A heat exchanger or radiator.
system of levers and rods connects the injection pump rack gear to the governor 2.2 ALCO Engine Cut-Away Model output shaft in such a way that the governor Demonstration (See Figure 2-29.)
can control the amount of fuel injected as the load or speed changes. See Figure 2-40. Many features of the ALCO engine are very similar to those of the OP engine just Two other ports or openings are provided at discussed. Emphasis will be made of the the center of the cylinder. One is used on primary differences - that of a 4-stroke cycle OP engines to house the air start check versus the OP 2-stroke cycle.
valve, a part of the starting system. The other port is used variously for either a The ALCO unit has only one crankshaft and dummy plug, a pressure adapter is a V configuration engine. It is really two connection, a cylinder pressure relief cock, 8-cylinder engines joined at the crankshaft or on OP commercial engines, for the gas with each bank of the engine tilted away admission valve. On OP units in nuclear from the other.
Rev 3/16 2-51 of 52 USNRC HRTD
Emergency Diesel Generator Introduction to Diesel Engines The cycle of this engine begins when the In order for the engine to run smoothly, there pistons are at top dead center (TDC) with must be a number of cylinders, timed both inlet air valves open. As the crankshaft throughout a revolution of the crankshaft, rotates, the piston is moved from the TDC which fire in sequence. Each cylinder position to the bottom dead center (BDC) contributes to generating power that is used position with inlet air valves open. As the first, to produce the power necessary for the piston moves, air is admitted to the cylinders compression taking place in other cylinders, through the intake valves. second, to overcome the friction within the engine, and lastly, to produce power to drive Air is supplied to the area around the valves the engine load-in our case, a generator.
from the intake manifold by suction (non-turbo engines) or by pressure for the As the piston travels toward BDC, the turbocharged engines. At the very outward pressure and temperature in the cylinder is position of the piston, or slightly after BDC, falling due to the increasing volume. When the intake valves close and the cylinder is the piston arrives near BDC, the exhaust isolated. valves are opened, and the cylinder pressure is further reduced as the exhaust From this point on, the air is compressed as gases escape from the cylinder. In the case the piston approaches TDC. As the air is of the turbocharged engine, this exhaust compressed, its pressure and temperature pressure drives the turbocharger turbine.
rise - the air has become heated.
As the crankshaft continues its rotation, the A few degrees before the point that the piston travels back to TDC, expelling the piston arrives at its (TDC) position, fuel is exhaust gases. Near TDC, the intake valves injected into the cylinder through the open, allowing air to enter the cylinder and injection nozzle in the cylinder head. The scavenge the exhaust gases from the injection nozzle sprays fuel under high cylinder. There is an overlap between the pressure into the cylinder combustion space air intake valve opening and the exhaust beneath the cylinder head. The fuel is first valve closing that allows for scavenging and heated by the hot air in the cylinder. When cooling. Since the valves are usually both it reaches ignition temperature of about 450 on the same end of the cylinder, there is no to 550oF, some of the fuel ignites and begins uniflow, but a loop or cross-flow performs to burn. This raises the temperature further the scavenging process. At this point, the until soon all of the fuel is burned as it mixes crankshaft has made two complete with the oxygen in the air in the cylinder. revolutions, and the piston has made four strokes.
By the time the fuel is burning well, the piston has traveled beyond TDC. The For further information on the 4-stroke cycle pressure in the cylinder is now acting on the engine, see Figures 2-7 through 2-13.
piston, which in turn is acting on the connecting rod to create a force that causes the crankshaft to rotate. This is the power stroke of the engine.
Rev 3/16 2-52 of 52 USNRC HRTD