ML20043F657
| ML20043F657 | |
| Person / Time | |
|---|---|
| Issue date: | 02/12/2020 |
| From: | Office of the Chief Human Capital Officer, Woodard Corp |
| To: | |
| Gary Callaway | |
| Shared Package | |
| ML20043F634 | List:
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| References | |
| Download: ML20043F657 (11) | |
Text
Emergency Diesel Generator Engine Cooling Systems 6.0 ENGINE COOLING SYSTEMS this heat is not removed, engine internal temperatures would soon reach a point of This chapter identifies the major component damage and engine failure. All components of the diesel engine cooling commercial diesel engines use some form systems and explains how each system is of cooling system to absorb this heat and necessary for reliable operation of the transfer it to a heat absorbing medium engine. outside of the engine.
Learning Objectives Many modern engines are equipped with turbocharging systems to provide enough As a result of this lesson, you will be able to: air to allow the burning of the fuel required to produce the required power. The
- 1. State the purpose of a diesel engine turbocharging system adds heat to the jacket water cooling system. combustion air. In order to ensure that sufficient pounds of air are provided for the
- 2. Identify the major components of a combustion of the fuel, it is necessary to cool typical diesel engine jacket water cooling the combustion air before it goes into the system and describe the operation of engine cylinders (to maintain air density).
each. This is done by means of a radiator-like heat exchanger called the air intercooler, or
- 3. State the purpose and describe the aftercooler, mounted in the piping between operation of the jacket water keepwarm the turbocharger compressor outlet and the and circulation system as is commonly engine air manifold.
used on nuclear application diesel engines. This radiator removes excess heat from the combustion air. Water from either the jacket
- 4. State the purpose of a diesel engine water system or the service water system intercooler (aftercooler) water cooling (the ultimate heat sink) may be used in this system. heat exchanger. When service water is used, there may be an additional heat
- 5. Identify the major components of a exchanger between the service water typical diesel engine intercooler water system and the intercooler water system so system and describe the operation of the water in the intercooler system can be each. treated and maintained in a state that will not contribute to the deterioration of the air
- 6. Identify other cooling requirements, such intercooler.
as engine room cooling.
6.1.1 Cooling System Basics 6.1 Engine Cooling Most diesel engines use a closed loop jacket Approximately 25 to 30 percent of the total type cooling system. Coolant flows through heat input to the engine supplied by the fuel the engine absorbing heat from the cylinder is absorbed by the engine cooling system. If liners, heads, and other components.
Rev 3/16 6-1 of 11 USNRC HRTD
Emergency Diesel Generator Engine Cooling Systems 6.1.1.1 Coolant Temperature - As a De-mineralized water is most frequently general rule, the higher the temperature of used. The water should be slightly alkaline, the coolant leaving the engine, the more specifically meaning a pH of 8 to 9.5.
efficiently the engine will operate. On the other hand, extremely high coolant Addition of a corrosion inhibitor such as temperatures can allow overheating of Nalco 2000 is recommended to prevent the engine components which could cause build-up of scale on cylinder liners and structural damage. Jacket water may also cylinder heads. One sixteenth inch of scale be used to cool the lubricating oil through a is like adding one inch of steel with respect heat exchanger. For most diesel engines, a to the resistance to heat transfer from the jacket water discharge temperature of about engine. Periodic chemical analysis of the 180oF is preferred, with a temperature rise coolant is performed and corrective through the engine in the range of 8 15oF. amounts of corrosion inhibitor added to maintain proper water chemistry.
6.1.1.2 Engine Coolant - Water is the most common coolant used in diesel engines. 6.1.2 Engine Cooling Systems However, water alone presents the possibility of corrosion, mineral deposits, A typical closed loop cooling system for a and freezing. turbocharged diesel engine, equipped with a keepwarm system, is shown in Figure 6-1.
Where engines could be subjected to temperatures near or below freezing, an In the following discussion, the word antifreeze such as ethylene glycol or 'radiator' could be substituted for 'heat propylene glycol must be added. The most exchanger' on engines equipped with a common solution is a 50:50 mix of radiator. On some units, there are separate antifreeze and water, which is good for radiator sections for cooling the intercooler temperatures down to -40oF. Commercial water and the jacket water. In such cases, antifreeze includes corrosion inhibitor the lube oil is typically cooled from the jacket additives. However, adding antifreeze does water circuit.
negatively affect heat transfer.
Coolant is stored in the engine system itself Diesel engines used for emergency service with the assistance of an expansion tank at nuclear facilities are not generally (head or make-up tank) which is mounted at subjected to temperatures where freezing is a point above the engine to maintain a head a possibility. Under these conditions, use of on the system. The engine-driven pump antifreeze is not required. However, the draws suction on the system and delivers corrosion inhibitor additives can be mixed the coolant to the engine. In most systems, with demineralized water to provide the water exits the engine and goes through corrosion protection. a thermostatically controlled valve. From the valve, the water either goes through the 6.1.1.3 Water Chemistry - The water used heat exchanger, if the water is hot, or for engine coolant should be clean and free through a bypass line around the heat of deposits or scale forming substances. exchanger when the water is too cold.
Rev 3/16 6-2 of 11 USNRC HRTD
Emergency Diesel Generator Engine Cooling Systems The thermostatic control valve (TCV) intercooler water to a temperature below senses and reacts to coolant temperature. that of the jacket water system. NOTE:
When the temperature of the engine coolant ALCO engines generally use the jacket is below the set-point of the valve, coolant is water system to cool the intercooler water.
bypassed around the jacket water heat exchanger. When the coolant temperature 6.1.2.1 Expansion Tank - Many engine is above the set-point, the valve directs the use an expansion tank with a pressurized coolant through the heat exchanger where closure, or the expansion tank is mounted the excess heat is transferred to the raw or high enough to maintain the necessary head service water system. Service water flow is (Net Positive Suction Head NPSH) on the automatically initiated upon any type of system. That head pressure is specified by diesel engine start. the water pump manufacturer and is the minimum required to prevent cavitation.
From the outlet of the heat exchanger, or bypass line, the water returns to the jacket The expansion tank is usually located water pump and thereby to the engine. In slightly above the highest point in the jacket many systems, the lube oil system is cooled cooling water system and vent lines are by a heat exchanger in the jacket water used to continuously purge air from the system. On engines where it is desirable to system. Some expansion tanks may be keep the lube oil at a temperature lower than pressurized to maintain a higher cooling that in the jacket water system, the oil heat system pressure, which is helpful because it is transferred directly to the service/raw raises the boiling point of the cooling fluid.
water system through the lube oil system heat exchanger as shown in Chapter 5. 6.1.2.2 Standpipe - A standpipe is a vertical tank mounted at the same elevation As the coolant enters the cylinder block, it is as the engine. It stores engine coolant while directed by internal passages and/or piping providing an air space to compensate for to the lower end of the cylinder liners. The thermal expansion of coolant. Standpipes fluid flows around the cylinder liners moving are generally vented to the atmosphere upward and into the cylinder heads. The providing a non-pressurized cooling system.
coolant leaving the cylinder heads passes The level of water in the standpipe must be into an outlet header and to the thermostatic sufficient to provide the required NPSH, valve. otherwise the tank must be pressurized.
On some engines equipped with inter- 6.1.2.3 Jacket Water Pump - The engine-coolers or aftercoolers, a portion of the driven jacket water pump, shown in Figure jacket water passes through the intercoolers 6-2, is a single stage centrifugal pump absorbing the excess heat from the driven by the engines crankshaft through a incoming air charge. On many engines with series of gears.
intercoolers or aftercoolers, a separate heat exchanger passes this excess heat to the Water enters the inlet of suction of the pump service / raw water system. This is most as shown. The pump drive gear, being desirable in as much as it is best to cool the driven by the engine gear train, causes the Rev 3/16 6-3 of 11 USNRC HRTD
Emergency Diesel Generator Engine Cooling Systems pump shaft and impeller to rotate. Rotation 6.1.3 Jacket Water Keepwarm Systems of the impeller throws the coolant outward, increasing its velocity by centrifugal force. When an engine has been shut down for a As the coolant enters the pump casing, its period of time, the temperature of the engine velocity decreases with a corresponding internals drops substantially. Rapid starting increase in pressure. The coolant, now at and fast loading of a cold engine, typical of an increased pressure, discharges from the nuclear application EDGs under emergency pump casing into the jacket water header to conditions, causes very high stress and the lower end of the cylinder liners. increased wear until the engine reaches its normal operating temperature. This can be 6.1.2.4 Thermostatic Control Valve - The reduced with a keepwarm system. (Other thermostatic control valve shown in Figure measures to minimize engine wear will be 6-3 is typical of those used on large diesel addressed in subsequent chapters.)
engines in nuclear service. Engine coolant enters the valve at the bottom. When the The jacket water keepwarm system is coolant temperature is low, the sliding valve shown along with the normal jacket water poppet remains in the upward position, as cooling system on the same schematic in shown on the right part of the diagram, and Figure 6.1. This system functions to keep bypasses the coolant around the heat the overall temperature of the engine exchanger. coolant at or near its normal operating temperature. This is not to say that each As coolant temperature increases, pellets of component is at its normal temperature.
wax (mixed with various amounts of copper grindings, for different temperature settings) Since diesel engines rely on the heat of inside the thermostats control elements compression for ignition, keeping the engine expand. This pushes the element tube and warm substantially decreases the start time slides the valve poppet down. As this and reduces the chances of a failure to start happens, bypass flow is blocked or throttled, because of low intake air temperature.
as shown on the left side or the diagram, and coolant is directed to the heat exchanger. 6.1.3.1 Keepwarm Pump - The keepwarm pump is an electrically driven, single stage In operation, the valve modulates over a centrifugal pump similar to the engine-driven temperature of about 10 to 15oF to balance pump, which maintains the flow of heated flow between the heat exchanger and coolant through the engine while the engine bypass to maintain a fairly constant coolant is shut down.
temperature.
6.1.3.2 Keepwarm Heater - Jacket water 6.1.2.5 Jacket Water Heat Exchanger - keepwarm heaters, like those used in lube Jacket water heat exchangers are typically oil keepwarm systems, are the electric of the shell and tube type, similar to that immersion type. They are mounted in the shown in Chapter 5. Generally, engine standpipe or separate heating tank and coolant passes over the tubes in the shell, thermostatically controlled to maintain the and service water passes through the tubes. engine at the desired temperature.
Rev 3/16 6-4 of 11 USNRC HRTD
Emergency Diesel Generator Engine Cooling Systems 6.1.3.3 System Operation - When the especially in cold weather or when the engine is in the standby mode, the engine is at light load, to keep condensation keepwarm system is energized. Its pump of moisture in the combustion air to a draws a suction on the system and minimum. In a few systems, there is an discharges water into the jacket water inlet interconnection between the jacket water to the engine. There may be check valves system and the intercooler water system to installed to prevent reverse flow in the assist in heating the intercooler when keepwarm system when the engine is required.
operating. The heated coolant flows through the engine, warming the cylinders, Engine start time, light load performance, cylinder heads, and other water-cooled and cylinder liner lubrication may be engine components. degraded if the inlet combustion air is too cold. To minimize the effect, some 6.2 Intercooler Water System manufacturers thermostatically throttle cooling water to the intercooler and/or The intercooler water system supplies water provide heated jacket water to the cooler to the intercooler or aftercooler mounted in when required.
the engines combustion air inlet piping. It is a radiator like heat exchanger that cools the The purpose of the thermostatic valve in the combustion air following the turbocharger circuit shown in Figure 6-4 is to keep the compressor and before the engines air intercooler water (and thus the air into the manifold / plenum. Cooling increases the engine) from being too cold. This can cause density of the air, thereby providing more condensation in the engine. Also, intake air oxygen to burn more fuel, for higher power that is too cold can cause 'white' smoke in output. The combustion air also provides the exhaust.
cooling for the piston crowns.
6.3 Other Cooling Requirements Water for the intercooler generally needs to be very near atmospheric air temperature. The diesel generator unit is typically housed Therefore, it is usually desirable to use in a building that has few openings. There service water to do this cooling rather than are a number of sources of heat within the jacket water, which is at a much higher EDG room including the engine and temperature (160 to 180oF). generator. Some of the equipment in this room such as the switchgear, control A typical schematic for the intercooler/ panels, monitoring equipment, fuel day tank, aftercooler water system is shown in Figure air compressor(s), and air storage tank(s) 6.4. The components in this system are very must be kept cool to work properly. The similar to those used in the jacket water usual limit for the temperature within the system and will not be detailed further here. EDG room is 122oF (50oC). Therefore, it is necessary to bring enough cool air (ambient In some intercooler water systems, there air) into this space to remove the heat and may be a thermostatic control used to keep keep the room below the maximum the intercooler water from getting too cold, allowable temperature.
Rev 3/16 6-5 of 11 USNRC HRTD
Emergency Diesel Generator Engine Cooling Systems While the engine itself is not severely affected by the temperature within the room, the generator and other components can be impacted by excessively high EDG room temperatures. If the engine combustion air is taken from within the room, too high a temperature of inlet air to the engine can affect the engines ability to produce power.
The following are sources of heat within the EDG room (in order of usual magnitude).
- Radiation from the engine - This is approximately 2% of the value of the heat content of the fuel input to the engine.
- Radiation from the generator - This is approximately equal to the inefficiency of the generator, or 3 to 5% of the generator rated KVA (KW).
- Radiation from the excitation equipment
- This is approximately 0.5% of the generator rated KVA (KW).
- Radiation from engine exhaust piping.
- Radiation from switch gear, cabling, transformers, etc. in the electrical system.
EDG room coolers may be required, if ambient outside air cooling is not adequate.
Rev 3/16 6-6 of 11 USNRC HRTD
Emergency Diesel Generator Engine Cooling Systems Figure 6-1 Jacket Water Cooling System with Keepwarm Rev 3/16 6-7 of 11 USNRC HRTD
Emergency Diesel Generator Engine Cooling Systems Figure 6-2 Jacket Water Pump Rev 3/16 6-8 of 11 USNRC HRTD
Emergency Diesel Generator Engine Cooling Systems Figure 6-3 Thermostatic Control Valve Rev 3/16 6-9 of 11 USNRC HRTD
Emergency Diesel Generator Engine Cooling Systems Figure 6-4 Intercooler Water-Cooling System Rev 3/16 6-10 of 11 USNRC HRTD
Emergency Diesel Generator Engine Cooling Systems WALKAROUND SESSION 6
- The return path from the heated water header to a 3-way thermostatic valve 6.0 ENGINE COOLING SYSTEMS which directs the water through either the radiator / cooler or back to the inlet Purpose header if the water doesnt need cooling Keepwarm circulating components of the The purpose of this session is to system will be shown including their location complement classroom instruction of and power supply.
Chapter 6 The instructor will use the rotatable cutaway Learning Objectives 4-stroke cycle ALCO to cover differences in cooling water flow from that of the OP Upon completion of this lesson you will:
engine. It will include cooling water flow into and out of the cylinder heads.
- Become familiar with the appearance, location, function, and operation of the 6.2 Components engine cooling system.
The instructor will show cutaways and 6.1 Jacket Water Cooling Systems discuss the functioning of the following components:
The instructor will illustrate and explain the jacket water system including its flow paths
- Jacket water pump through the engine and around components to remove waste heat.
- Thermostatic valve
- Jacketed water cylinder liners and direct The instructor will use the rotatable cutaway contact cylinder liners 2-stroke cycle OP to illustrate and explain
- Pielstick cylinder head to show water the following jacket water flow path: passages from the block through the cylinder head, around the valves and fuel
- From the radiator / cooler to the jacket injector and adjacent to the firing face to water head tank and to the suction of the remove exhaust heat jacket water cooling pump
- Radiator / cooler
- From the pump to the engine cooling water header(s) which take water into
- Turbocharger intercooler the engine block for cooling the block and the individual cylinder liners
- From the header to the turbocharger(s) and
- Back into the cylinder block
- Around the exhaust belts
- Then heated water from the engine and its components flow into a common return header.
Rev 3/16 6-11 of 11 USNRC HRTD