Natural Gas Engines EPT 07-T-02 November 1992 Draft
Version 0
EPT 07-T-02
Natural Natural Gas Engine Eng iness
Nove No vemb mber er 1992 19 92 Draf Draftt
Table of Contents 1.
Scop Sc ope......................................................................................................................................... e......................................................................................................................................... ..6 .. 6
2.
Refer Ref erenc ences es ................................................................................................................................. 6
3.
4.
2.1.
MEPS–Mobil MEPS –Mobil Engineering Practices .............. ..................... .............. ........... ........... .............. .............. .............. ........... ............ ............ ....6 6
2.2. 2.2 .
Mobil Tutorials .................................................................................................................. 6
2.3. 2.3 .
AP I–American I–American Petroleum Institute ................................................................................. 6
2.4.
GPSA–Gas GPSA –Gas Processors Proces sors Suppliers Supplier s Association Associa tion ............ .................. ............ ............ ............ ............ ............. ............. ......... ...7 7
Engine Eng ine Select Sel ection ion and Horsep Hor sepowe owerr Rating Rat ings s ............ .................. ............ ............ ............ ............ ............ ............ ........... ........... ...........7 .....7 3.1.
...........................................................................................................................................7
3.2. 3.2 .
Project Proje ct Definition Defin ition and Economics Econo mics ................................................................................. 8
3.3. 3.3 .
Selecti Sele ction on of Operati Oper ating ng Speed......................................................................................1 Spee d......................................................................................1 0
3.4. 3.4 .
Load Determin Dete rminatio ation.......................................................................................................1 n.......................................................................................................1 2
3.5.
.........................................................................................................................................13
3.6. 3.6 .
Engine Ratings ...............................................................................................................1 4
3.7. 3.7 .
Engine Engi ne Selecti Sele ction............................................................................................................17 on............................................................................................................17
Tor T orsio siona nall Analys Ana lysis is.................................................................................................................. .................................................................................................................. 18 4.1.
.........................................................................................................................................18
4.2.
.........................................................................................................................................19
4.3.
.........................................................................................................................................19
4.4.
.........................................................................................................................................19
4.5.
.........................................................................................................................................20
4.6.
.........................................................................................................................................20
4.7.
.........................................................................................................................................20
© Mobil Oil,1998
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EPT 07-T-02
Natural Natural Gas Engine Eng iness
Nove No vemb mber er 1992 19 92 Draf Draftt
Table of Contents 1.
Scop Sc ope......................................................................................................................................... e......................................................................................................................................... ..6 .. 6
2.
Refer Ref erenc ences es ................................................................................................................................. 6
3.
4.
2.1.
MEPS–Mobil MEPS –Mobil Engineering Practices .............. ..................... .............. ........... ........... .............. .............. .............. ........... ............ ............ ....6 6
2.2. 2.2 .
Mobil Tutorials .................................................................................................................. 6
2.3. 2.3 .
AP I–American I–American Petroleum Institute ................................................................................. 6
2.4.
GPSA–Gas GPSA –Gas Processors Proces sors Suppliers Supplier s Association Associa tion ............ .................. ............ ............ ............ ............ ............. ............. ......... ...7 7
Engine Eng ine Select Sel ection ion and Horsep Hor sepowe owerr Rating Rat ings s ............ .................. ............ ............ ............ ............ ............ ............ ........... ........... ...........7 .....7 3.1.
...........................................................................................................................................7
3.2. 3.2 .
Project Proje ct Definition Defin ition and Economics Econo mics ................................................................................. 8
3.3. 3.3 .
Selecti Sele ction on of Operati Oper ating ng Speed......................................................................................1 Spee d......................................................................................1 0
3.4. 3.4 .
Load Determin Dete rminatio ation.......................................................................................................1 n.......................................................................................................1 2
3.5.
.........................................................................................................................................13
3.6. 3.6 .
Engine Ratings ...............................................................................................................1 4
3.7. 3.7 .
Engine Engi ne Selecti Sele ction............................................................................................................17 on............................................................................................................17
Tor T orsio siona nall Analys Ana lysis is.................................................................................................................. .................................................................................................................. 18 4.1.
.........................................................................................................................................18
4.2.
.........................................................................................................................................19
4.3.
.........................................................................................................................................19
4.4.
.........................................................................................................................................19
4.5.
.........................................................................................................................................20
4.6.
.........................................................................................................................................20
4.7.
.........................................................................................................................................20
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EPT 07-T-02
5.
Natural Natural Gas Engine Eng iness
Nove No vemb mber er 1992 19 92 Draf Draftt
4.8.
.........................................................................................................................................21
4.9.
.........................................................................................................................................21
Engin En gine e Syste Sy stems ms ......................................................................................................................2 1 5.1. 5.1 .
Air Intake......................................................................................................................... Intak e......................................................................................................................... 21
5.2. 5.2 .
Exhaust System .............................................................................................................2 2
5.3. 5.3 .
Starting Start ing Systems............................................................................................................2 Syste ms............................................................................................................2 2
5.4. 5.4 .
Cooling Water Systems ................................................................................................2 3
5.5.
Jacket Water Systems (Cooling of the Engine Proper) ............ .................. ............ ............ ........... .......... .........24 ....24
5.6. 5.6 .
Lubrication Lubrica tion Systems System s ......................................................................................................2 6
5.7. 5.7 .
Heat Recovery Systems................................................................................................2 Systems ................................................................................................2 6
5.8. 5.8 .
Ignition Systems .............................................................................................................2 7
5.9. 5.9 .
Fuel System.................................................................................................................... 28
5.10. 5.1 0. Speed Governo Gove rnorr ............................................................................................................3 0 5.11. 5.1 1. Instrumentation and Safety Shutdowns........................................................................3 Shutdowns ........................................................................3 1 5.12. 5.1 2. Miscellaneous Requirements Requirement s .......................................................................................3 2 Appendix Appen dix A –Nome –N omencl nclatu ature...... re............. .............. ............... ............ ........... .............. .............. .............. ........... ........... .............. .............. .............. ........... ........... ..........3 ...33 3 1.
Power Pow er (Horsep (Hor sepowe ower) r) ............ .................. ............ ............ ............ ............ ............ ........... ........... ............ ............ ............ ............ ............ ............ ............ ........... .........33 ....33
2.
BHP BH P ................................ ............................................................. ........................................................................................................ ............................................................................3 .33 3
3.
British Briti sh Thermal Unit (Bt (Btu) u) ........... ................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ .......... ......3 ..34 4
4.
Torq To rque ue (T) (T ) ................................ ............................................................ ................................................................................................. ..................................................................... 34
5.
Bore Bor e and an d Stro St roke ke ......................................................................................................................3 4
6.
Engi En gine ne Disp Di spla lace ceme ment.............................................................................................................3 nt.............................................................................................................3 4
7.
Compres Comp ressio sion n Ratio Rat io ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ..........35 ....35
8.
Octane Oct ane Number Num ber .......................................................................................................................3 6
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EPT 07-T-02
9.
Natural Gas Engines
November 1992 Draft
HHV and LLV ...........................................................................................................................3 6
10. Thermal Efficiency..................................................................................................................3 6 11. Piston Speed............................................................................................................................3 7 12. BMEP ............................................................................................................................................. 37 13. NA
.........................................................................................................................................38
14. Turbocharger (T).....................................................................................................................38 15. Turbocharged-Aftercooled (TA)..........................................................................................38
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EPT 07-T-02
Natural Gas Engines
November 1992 Draft
Table of Figures Figure 1: Typical Engine Duty Cycles .....................................................................................10 Figure 2: Section of a crankshaft with an exaggerated twist. This illustrates torsional vibration, which is a repeated twisting of a rotating shaft about its axis of rotation..........................................................................................................................19 Figure 3: Single-loop cooling water system. B. Two-loop cooling water system......25 Figure 4: Altronic III CPU System Overview ...........................................................................28 Figure 5: Engine Fuel System....................................................................................................30 Figure 6: Engine Cylinder Terminology ..................................................................................35
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EPT 07-T-02
1.
Natural Gas Engines
November 1992 Draft
Scope This tutorial is intended to review the basic design requirements and considerations associated with the selection of high speed (600 to 1800 rpm) spark ignited internal combustion engines in the 110 to 1860 kW (150 to 2500 hp) range. The discussion and considerations are limited to natural gas fueled four cycle naturally aspirated and turbocharged engines as manufactured by Caterpillar, Superior, or Waukesha. These manufacturers have been identified as providing a known and proven product. Consideration of other engine manufacturers shall be given only after consultation with MEPTEC's Field Processing/Feasibility Studies Department. Although this tutorial does make some recommendations as to engine options, it is essential that the Project Engineer consult with the end users before selecting a particular engine or available options. The Maintenance and Operations personnel can provide valuable input based on existing equipment, past experience, maintenance philosophy, parts and service availability, and operating preference for a particular area. These are all very important factors in selecting an engine.
2.
References The following Mobil guides and industry publications shall be considered a part of this EPT. Refer to the latest editions unless otherwise specified herein.
2.1.
MEPS–Mobil Engineering Practices
MP 15-P-18
High Speed Reciprocating Compressor & Packaging
MP 15-P-27
Natural Gas Engines
2.2.
Mobil Tutorials
EPT 01-T-03
2.3.
Air Emission Control
API–American Petroleum Institute
API SPEC 7B -11C
Specification for Internal-Combustion Reciprocating Engines for Oil-Field Service Ninth Edition
API RP 7C-11F
Recommended Practice for Installation, Maintenance, and Operation of Internal-Combustion Engines Fifth Edition
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EPT 07-T-02
API SPEC 11P
2.4. EDB-I
3.
Natural Gas Engines
November 1992 Draft
Specification for Packaged Reciprocating Compressors for Oil and Gas Production Services Second Edition
GPSA–Gas Processors Suppliers Association Engineering Data Book–Volume I, 1987
Engine Selection and Horsepower Ratings 3.1. This Section describes the recommended procedure for selecting a natural gas engine to drive a load such as a compressor, pump, or generator. The selection process includes the following steps: 1. Defining the requirements and the economics of the project. 2. Selecting the operating speed of the equipment. 3. Load determination. 4. Engine ratings per Mobil-ISO standard conditions. 5. Engine ratings at site conditions. 6. Engine selection.
3.1.1. The selection process is a relatively complex procedure whose importance shall not be underestimated. If too small an engine is selected, the engine will be overloaded and repeated mechanical failures will occur. These failures will cause high maintenance and repair costs in addition to the cost of lost production. If too large an engine is selected, the capital cost will be greater than necessary, the engine operation may be erratic because of insufficient load, and on some engines (such as turbocharged clean-burn type engines) the emissions may be excessive because of the light load conditions. As a general statement, engines operate best at or near their design rating.
3.1.2. For a high speed, spark ignited engine of this type, one of the most common applications is driving a horizontally opposed, reciprocating gas compressor. For example, a Waukesha engine may be used to drive a reciprocating © Mobil Oil,1998
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EPT 07-T-02
Natural Gas Engines
November 1992 Draft
compressor manufactured by Dresser-Rand. This type of unit is called a "separable" unit because the engine is separate from the compressor, as opposed to the "integral" type of unit with power cylinders and compressor cylinders connected to the same crankcase. Integral units are outside the scope of this tutorial.
3.2.
Project Definition and Economics 3.2.1. It is first necessary to define the process requirements for the driven equipment. The engine can operate under any of the following conditions. 1. Constant Speed An example of this type of load is a direct connect generator. Common synchronous speeds for 60 cycle generators are 1800, 1200, 900, and 720 rpm. The variable torque (generator load) for this application determines the engine horsepower. Speed control for this type of application is very critical. 2. Constant Torque An example of this type of load would be an oil field gas sales compressor with constant suction and discharge pressures. The speed of the engine driver determines the horsepower developed by the engine. Another application of this type is reciprocating or plunger-type pumps with constant suction and discharge conditions. 3. Variable Speed and Torque An example of this type of load would be a centrifugal pump operating with variable suction/discharge conditions and using speed control to maintain a constant flow condition. The horsepower for this application is a function of the pump and associated system requirements.
3.2.2. When selecting an engine for any of the above conditions, it is important to consider the required speed, range, and associated horsepower requirements.
3.2.3. The magnitude and duration of overload peak periods when peak production is required shall be determined. What are the consequences of not meeting these peak demands? Is there a production or contract penalty involved, or is the penalty only the loss of a small increment of production? To
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EPT 07-T-02
Natural Gas Engines
November 1992 Draft
accommodate a small peak in production, it may be necessary to select the next larger size engine, which may not be economically justified.
3.2.4. The duty ratings of engines can be further defined as follows. 1. Continuous Heavy Duty An example is a field gas lift compressor. This type of unit operates near full load conditions 24 hours a day. 2. Continuous Intermittent Heavy Duty An example would be an offshore generator system with intermittent "high" horsepower pumping loads. As a result of crude pumping conditions, this type of unit may operate on a high horsepower load for several hours and a relatively light load for a short period of time. 3. Variable Load Heavy Duty An example of this type of load would be a field booster gas compressor where the pipeline conditions vary throughout the day. 4. Variable Load Light Duty An example of this type of duty cycle would be an engine driven crude oil pump pumping against a widely varying pipeline pressure and then entering an idle mode upon crude tank pump-down.
3.2.5. For a graphical depiction of typical duty cycles as described above, refer to Figure 1. What are the life and economics of the project? Generally, heavy duty, slow speed equipment is very expensive in comparison to high speed engines, but will operate 30 or 40 years. However, the project under consideration may have marginal economics and a projected life of only 5 to 10 years. In this case, the high speed, less expensive equipment would be the appropriate choice.
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EPT 07-T-02
Natural Gas Engines
November 1992 Draft
Figure 1: Typical Engine Duty Cycles
3.2.6. The installation and operating costs of the different types of equipment shall be considered. The installation cost of high speed engines is considerably less than for heavy duty, low speed engines. However, the maintenance cost of slow speed engines is less. Some studies indicate that the maintenance cost of engines increases with the square of the operating speed. That is, if the operating speed is doubled, the maintenance costs quadruple. The life expectancy of high speed equipment is generally much shorter than the life expectancy of low speed equipment. Als o, consider the fuel efficiency and fuel cost for the different engines. The total cost for the life of the project shall be considered.
3.2.7.
Summary It is important for the project engineer to define all of the above factors carefully before proceeding with the engine selection process. This is especially true if the load factors fall at the break-point of selecting the next larger size engine, which may be considerably more expensive.
3.3.
Selection of Operating Speed 3.3.1. The operating speeds of both the engine and the driven equipment shall be considered. For some combinations, the engine speed will be limiting, and for others the compressor speed will be the limiting factor. For example, CooperSuperior engines generally have a rated speed of 900 rpm and can be used to drive a compressor by Dresser-Rand that has a rated speed of 1200 rpm. In this case, the unit would be limited to the lower speed of 900 rpm. However, the more common combination is for the engine to have a higher rated speed than the compressor, such as a 1200 rpm Waukesha driving a 1000 rpm © Mobil Oil,1998
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EPT 07-T-02
Natural Gas Engines
November 1992 Draft
Worthington CUB compressor. In this case, the operating speed shall be limited to 1000 rpm, which significantly reduces the power capability of the engine.
3.3.2. A combination that is becoming more popular are units with operating speeds of 1400 to 1800 rpm, such as a Caterpillar engine driving an Ariel compressor. These high speed units are attractive because the installed cost is generally considerably less. However, the maintenance costs can be higher and the life shorter on these high speed units.
3.3.3. Therefore, before actually selecting an engine size, it is necessary to determine the design speed for the compressor, pump or generator package. The operating speed has a direct effect on the power rating of the engine. Also, determine any speed "turndown" requirements. Note that the more modern, turbocharged engines generally have higher emissions if the speed is decreased below approximately 75 percent. See the tutorial EPT 01-T-03 on Air Emission Control.
3.3.4. Of course, it is possible to have a high speed engine driving a low speed pump or compressor if a V-belt drive or gear box are employed. However, it is recommended that V-belt drives for engines be limited to approximately 110 kW (150 bhp). For higher horsepower applications, gear units are also discouraged because of possible gear failures due to torsional vibrations, backlash, etc., caused by misfiring of the engine or rough combustion.
3.3.5. The project engineer shall consult with the operating and maintenance personnel who will be responsible for the engine. Ask for their opinions regarding the various types and brands of engines, the quality of parts and service support, etc. Where is the nearest service location, and do they stock a sufficient inventory of spare parts so that the field operations can operate with minimal inventory? Also determine if there are similar engines in the same operating area which could have an impact on the spare parts costs for the new engine.
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EPT 07-T-02
3.4.
Natural Gas Engines
November 1992 Draft
Load Determination 3.4.1. The total load to be carried by the engine shall be calculated. The total load is the sum of the following factors: Total Load = Driven Load x Application Factor + Mechanical Transmission Load + Auxiliary Loads (For an example of load determination, a gas compressor application will be used, but the general calculation procedure can also be used for generators and pumps.)
3.4.2.
Compressor Load The driven compressor load equals the sum of the theoretical gas load plus the mechanical losses in the compressor frame, generally considered to be 5 percent. In calculating the theoretical gas loading, be certain that pressure losses in the piping, bottles, and valves are included. The pressure losses are especially important for low suction pressure applications.
3.4.3.
Application Factor The calculated load shall be multiplied by an appropriate factor to compensate for possible variations and uncertainties in defining actual field loads. This factor varies because there is more uncertainty in some types of packages. The following application factors are recommended: 1. Generators: F = 1.00 2. Pumps: F = 1.05 3. Compressors: F = 1.15
3.4.4.
Mechanical Transmission Load Includes factors such as reduction gear unit losses, generally 2 percent for gear ratios less than 6:1, and 4 percent for ratios greater than 6:1.
3.4.5.
Auxiliary Loads Includes loads such as fin fan, hydraulic pumps, etc. For example, the load for a large fan on an aerial type gas and water cooler can be as high as 5 percent of the total load.
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EPT 07-T-02
Natural Gas Engines
3.4.6.
November 1992 Draft
Example Problem Metric Units 3
Compress 13,450 std m /hr Gas x 4 Ratios = 723 kW Mechanical Losses in Frame, 723 x 0.05 = 36 kW Total Calculated Compressor Load = 759 kW Application Factor X 1.15 Total Calculated Compressor Load = 873 kW Mechanical Transmission Load, None (Direct Drive) = 0 kW Auxiliary Load, Aerial Cooler Fan = 43 kW Total All Loads, 873 + 0 + 43 = 916 kW
3.4.7.
Example Problem Customary Units Compress 11.4 MMSCFD Gas x 4 Ratios = 970 bhp Mechanical Losses in Frame, 970 x 0.05 = 48 bhp Total Calculated Compressor Load = 1018 bhp Application Factor X 1.15 Total Calculated Compressor Load = 1171 bhp Mechanical Transmission Load, None (Direct Drive) = 0 bhp Auxiliary Load, Aerial Cooler Fan = 55 bhp Total All Loads, 1171 + 0 + 55 = 1226 bhp
3.4.8. With the above determined economic conditions, speed, and load, it shall be possible to tentatively select several different engines that may be suitable for the particular application.
3.5. Any discussion of high speed engines shall include turbochargers. Turbocharger and engine development has resulted in very reliable engines with more horsepower per cubic inch displacement at less cost per horsepower than naturally aspirated engines. Today's modern engines have been designed to withstand the higher peak pressures and increased
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EPT 07-T-02
Natural Gas Engines
November 1992 Draft
thermal loading associated with turbocharging the combustion air. As a result, the modern turbocharged engine is very reliable with maintenance and operating costs comparable to naturally aspirated engines of similar horsepower ratings. Some federal and state clean air regulations cannot be met without utilizing turbochargers.
3.6.
Engine Ratings 3.6.1. The subject of engine ratings is discussed in two sections. The first section defines the engine ratings per a uniform set of conditions so that all engine manufacturers are compared on an equal basis. The second section describes the method for rating the engines under actual site conditions.
3.6.2. Some readers may fail to see the necessity for the first of the above two steps, since the engine does not operate under standard conditions and will only operate at site conditions. The two step approach is recommended because the problem of rating engines is a difficult and complicated matter in which some vendors may fail to include all the factors. The two step method allows a more reliable comparison of the engine alternatives.
3.6.3.
Engine Standard Ratings 1. Engine manufacturers rate their engines with a variety of rating systems such as the following: a) DEMA-1972 Diesel Engine Manufacturers Association (USA) b) BS-649 British Engine Standard c) DIN-6270-71 German Engine Standard d) ISO-3046/1 International Standard Association 2. This variation in engine rating systems makes it difficult to compare engines. Therefore, engine manufacturers shall be requested to specify the "continuous rating" of the tentatively selected engines in accordance with the following Mobil-ISO rating system, which is based on
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EPT 07-T-02
Natural Gas Engines
November 1992 Draft
International Standards Organization Procedure No. ISO-3046/1, International Combustion Engine Performance. 3. Continuous Rating is the power that an engine can deliver at a specified speed for continuous duty (24 hours per day, 7 days per week). This includes an overload capability of 10 percent of the continuous rating for a period of up to 2 hours per 24 hour period, except for shutdowns to perform scheduled maintenance.
3.6.4.
Mobil-ISO Operating Conditions 1. Ambient Temperature: 25°C (77°F) Barometric Pressure: 100 kPa (29.5 in Hg) Relative Humidity: 30 percent Aftercooler (if used) Water Temp: Ambient + 17°C (30°F) Fuel Gas: Pipeline quality natural gas with LHV = 33.5 MJ/std m 3 to 33.7 3 MJ/std m (900 to 905 Btu/SCF) and Octane Rating of 115. 2. While driving lubricating oil and cooling water pumps, with inlet and exhaust pressures as specified by manufacturer. 3. Once the engine manufacturers have specified the Continuous Ratings in accordance with the above Mobil-ISO definition for the different engines under consideration, it shall be possible to compare the engines on an equivalent basis. However, if it is not possible to obtain from the manufacturer the continuous rating according to the Mobil-ISO system, the following adjustment factors may be used. a) Waukesha Engines No adjustment required as the Waukesha rating system is very similar to the Mobil-ISO system. b) Cooper-Superior Engines Increase the published Cooper-Superior ratings by approximately 2 percent because the Cooper-Superior rates at 32°C (90°F) and 96 kPa (28.25 in mercury). The 2 percent increase equates this rating condition to the Mobil-ISO conditions at 25°C (77°F) and 100 kPa (29.5 in mercury). c) Caterpillar Inc. Decrease the ratings by 5 percent to allow for the fact that Caterpillar does not include the 10 percent overload for 2 hours per 24 hour period.
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EPT 07-T-02
Natural Gas Engines
3.6.5.
November 1992 Draft
Engine Ratings at Site Conditions 1. It is then necessary to adjust the Mobil-ISO rating to the specific conditions at the installation site. Request that the engine manufacturer specify the continuous rating per the site conditions, the site fuel, and with the recommended accessories and control systems. Corrections shall be allowed for the following: a) Maximum Ambient Temperature If maximum power is required during maximum ambient temperature, approximately 1 percent deration for each 5.5°C (10°F) above standard conditions. If a turbocharger is used the maximum aftercooler water temperature is 54°C (130°F). b) Altitude Correction Approximately 2 percent deration for each 305 m (1000 ft) above 915 m (3000 ft) elevation. c) Fuel Quality Give the engine manufacturer a complete fuel gas composition analysis including inerts and H2S. The fuel gas shall have no liquid hydrocarbons or liquid water. If these are present, it shall be necessary to install scrubbers to remove the liquids. The H2S content shall be generally less than 0.1 mol percent. Small quantities of the heavier hydrocarbon components can cause violent detonation in engines. Generally, the total of C 4 and heavier in the fuel gas shall be less than 0. 30 mol percent for modern high speed rated engines. d) Fuel/Air Ratio Controls Modern engines shall be equipped with the highest quality ignition systems and shall have control systems to adjust the fuel/air ratio and to adjust the ignition timing. The ignition timing system shall be equipped with a detonation sensor and circuitry to retard the ignition slightly to bring the engine out of detonation before serious damage results. If the engine is not equipped with a detonation sensing system, and if the fuel quality is variable, an additional deration factor of 2 percent shall be applied. e) Maintenance Deration Factor The ratings specified above by the manufacturer assume that the engine will receive excellent maintenance attention (such as in a large power plant) with mechanics available 24 hours per day, good spare parts and an onsite machine shop.
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November 1992 Draft
For a normal oilfield application with no assigned mechanics, and/or remote locations, an additional 5 percent deration factor shall be applied. 2. Example: Site Deration Factors Altitude (1525 m - 915 m = 610 m x 2 percent/305 m ) or
=
4
percent
Altitude (5000 ft - 3000 ft = 2000 ft x 2 percent/1000 ft)
=
4
percent
Temperature (36 °C - 25 °C = 11° C x 1 percent/5 .5° C ) or
=
2
percent
Temperature (97 °F - 77 °F = 20 °F x 1 percent/10 °F)
=
2
percent
Fuel Deration per Manufacturer
=
3
percent
Detonation Controls , Installed
=
0
percent
Maintenance Factor , Unattended Operation
=
5
percent
Total Deration
=
14
percent
3.7.
Engine Selection 3.7.1. The next step is to make a tentative selection of several engines that have power ratings greater than the calculated load. In making this selection, take into consideration the recent performance of each type and brand of engine, the amount and quality of parts and service support, etc. Also consider the history of the particular engine model being contemplated. How long has this model been on the market and how many have been manufactured in the past two years? If the engine is a relatively new model, request a list of engines in similar service and the names of individuals who can be contacted as reference. For new models the factory test shall be witnessed, extensive testing shall be required, and special parts, service, and warranty coverage be negotiated.
3.7.2. Request that the engine manufacturers rate the tentatively selected engines to the Mobil-ISO standard conditions and the site conditions. Select an engine with an at-site rating equal to or greater than the load calculated by the "Load Determination" as defined above.
For the Compressor Example Problem Load per example , 3.4 .6 and 3 .4.7
= 916 kW (1226 bhp ) at 950 RPM
Tentative Engine - Waukesha Model Selection
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7042GL
9390GL
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November 1992 Draft
Catalog Rating at 950 RPM
1224 bhp
1633 bhp
Mobil-ISO Rating at 950 RPM
1224 bhp
1633 bhp
Site Deration Factor (14 percent )
x0 .86
Site Continuous Rating at 950 RPM
785 kW (1052 bhp )
x 0.86 1047 kW (1404 bhp )
3.7.3. Therefore, the Model 9390GL is the correct choice for this example.
4.
Torsional Analysis 4.1. All equipment with rotating components has inherent torsional vibrations (refer to Figure 2) that occur at various speeds. Manufacturers design their equipment so these inherent vibrations are below set limits and/or well outside the equipment's operating speed range. However, the engine/load combination will have its own torsional characteristics where the torsional vibrations may exceed the limits in the equipment's operating range. This is why it is important to perform a torsional analysis on every new combination of engine and load. The manufacturers have copies of torsional analyses that have been performed on popular combinations, such as a Waukesha driving a four-throw Worthington compressor.
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EPT 07-T-02
Natural Gas Engines
November 1992 Draft
Figure 2: Section of a crankshaft with an exaggerated twist. This illustrates torsional vibration, which is a repeated twisting of a rotating shaft about its axis of rotation.
4.2.
This tutorial briefly describes what is entailed in performing a torsional analysis, torsional vibration limits, and possible problems resulting from operating above these limits.
4.3. A torsional analysis is a mathematical study of a unit's mass elastic system (moving components). This is not an actual test but an analytical analysis using a model of the unit's individual components. This analysis is performed to determine if the inherent torsional vibrations of the unit result in vibrations that exceed designated limits.
4.4. This is an analysis of the inherent vibrations only and assumes there are no vibrations caused by external factors (i.e., misalignment, electrical imbalance, shock loads, etc.). An
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November 1992 Draft
instrumented torsional vibration check is also available as an option from most engine manufacturers and packagers.
4.5. A torsional analysis performed using a mathematical model versus an instrumented test has a distinct advantage. The mathematical analysis is performed after the components have been engineered but before they are purchased and assembled. Thus, if the torsional vibrations are determined to exceed the calculated limits, components such as couplings can be changed before being purchased. Changing components results in new torsional characteristics for the combined equipment, and components can be modified until the torsional vibrations are below acceptable levels. Each unit's vibration will be affected differently by changing its individual components. Thus, to improve the unit's torsional vibration, it may be necessary to change only a minor part such as a coupling, or as extensive a change as changing the driven unit (i.e., generator, pump, etc.) may be necessary.
4.6. The items required to perform a torsional analysis are as follows: 1. Engine Model Number of cylinders, inline or vee cylinder configurations broken down to the following major moving component assemblies affecting torsional vibration: piston, connecting rod, flywheel, pulley(s), crankshaft, and vibration damper. 2. Driven Equipment Same type of information as required for the engine; e.g., for a generator, single or two bearing, induction or synchronous, mass of the rotating components, etc. 3. Coupling Air flex, steel flex, or flex disc plates. The coupling required is determined mostly by the type of driven equipment. 4. Job Specifics, such as speed, kW or hp rating.
4.7. Torsional vibration stress limits have been set by various manufacturers of driver and driven equipment along with classification societies and inspection agencies.
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4.8. Operating a unit above the manufacturer's recommended limits may cause severe damage such as fracturing shafts and couplings, rapid wearing of gears, etc. Visual observation of an operating unit is not an accepted method of determining if a unit is torsionally safe. A unit may appear to be operating very smoothly with little visible sign of torsional vibration and still have shaft stresses that exceed the limits. The Torsional Analysis is a very important part of assuring the proper design and packaging of any engine driven equipment.
4.9. It is the packager's responsibility to ensure the assembled components are torsionally compatible and that the unit will operate within the specified torsional limits.
5.
Engine Systems 5.1.
Air Intake Although MP 15-P-27, Natural Gas Engines, specifies a dry-type air filter, the type and size shall be specified and supplied by the engine manufacturer. Dry filters have replaceable filter elements, made of special fire resistant water repellant pleated paper. They have an air cleaning efficiency in excess of 99.75 percent down to 15 µm (microns) particle size. Table 1 shows the cleaning effectiveness of commonly used filters. The initial cost of the dry type is much lower than other types, they are much easier to service, they work equally well offshore, and they operate virtually frost-free in cold northern climates. Filters usually come equipped with a differential pressure indicator which serves as a monitor and indicator for servicing. If the engine location is subject to excessive dust, fog, drizzle, and rain, a two stage air cleaner is recommended. This type forces the air and dirt through an inertial separation by imparting a centrifugal motion to the air. It effectively filters out 70 to 90 percent of the large dirt particles, thereby reducing the dust load passed on to the dry element or second stage of the filter. Air ducting pipes shall run directly from the engine air intake to a location away from dirt, soot, warm air or exhaust gasses. The air inlet pipe shall be at least one pipe size larger than the air inlet connection on the engine. All pipe bends shall be long-radius elbows. The number of bends shall be kept to a minimum. The maximum pressure drop shall not exceed the engine manufacturer's recommendation. A flexible joint or connection shall be provided to eliminate stress on the turbocharger inlet. The filter shall be mounted high enough to avoid blowing surface dirt, while remaining easily accessible for servicing and maintenance. Backfire relief valves on the air inlet system of four cycle engines are ineffective and unnecessary, and are not an option offered by the engine manufacturers.
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Table 1 Filter Type
Contaminants Dust
Soot
Fog, Drizzle ,
Ice, Snow
Lint, Chaff
Rain Oil Bath Dry Type Two Stage
Effectiveness Rating
= 1 Most Effective =2 = Least Effective
5.2.
Exhaust System The exhaust system shall be designed to achieve the required degree of silencing dictated by local regulations and OSHA requirements, while not exceeding the system back pressure specified by the engine manufacturers. Increased sound attenuation generally results in a corresponding increase in engine back pressure. Limitations on back pressure will determine the actual exhaust pipe sizes and configuration and influence the silencer selection. To avoid imposing any strain on the engine exhaust manifolds, it is important to provide independent support for the exhaust piping. This is especially important on turbocharged units, to avoid distorting the turbocharger housing and leading to early failure. A flexible stainless metal bellows type connector with internal sleeve shall be installed between the engine manifold and the exhaust system to absorb vibration shock and expansion forces. The system shall be supported so that thermal growth is away from the engine. This is especially critical for more remotely mounted silencers as tremendous deflection due to thermal expansion of piping can occur in improperly designed systems. The outlet end of the exhaust shall be designed to keep out rain and snow. Exhaust piping shall be insulated where necessary to protect for flammable material and to provide personal protection.
5.3.
Starting Systems Air or gas expansion starters are required on all engines. Preference shall be given to the turbine-type pneumatic starter over the traditional vane -type expansion models. These turbine-type starters are designed for low pressure starting utilizing either compressed air or sour/sweet natural gas. No lubrication in the drive air/gas supply is required, thereby eliminating failure due to loss of lubrication. Oily film residue at the exhaust outlet is also eliminated. Since the turbine motor does not have any rubbing parts, it is much more tolerant of dirty gas or air supply and is especially effective in low ambient temperature
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installations, because there are no rubbing internal parts coated with oil to freeze up. The rate of air or gas consumption by turbine starters is only one half to two thirds of that of vane-type starters. The starter shall be supplied with the necessary block valve, pilot operated valve, and exhaust pipe to carry the air/gas to a safe atmosphere.
5.4.
Cooling Water Systems 5.4.1. Cooling water systems maintain the engine at an operating temperature below the maximum specified by the engine manufacturer. Cooling is accomplished by removing heat from the cylinders, cylinder heads, the lubricating oil and the intake air (if required for a turbocharged engine). Engine cooling systems are normally called "jacket water systems"; whereas separate lube oil or turbocharger aftercoolers are referred to as "auxiliary water systems."
5.4.2. The coolant shall flow through the engine at all times, and the coolant flow shall never be throttled to raise the outlet temperature. Some factors that shall be considered when designing a cooling system and selecting its equipment are as follows: 1. Water Supply a) Quality of available water. b) Supply ample or limited. c) Type of supply water for shell and tube cooler systems. 2. Atmospheric Conditions for fin-fan or radiator type coolers. a) Maximum and minimum wet and dry bulb temperatures. b) Average wind velocities and directions. c) Locality specifics (dust storms, sea salt, etc.). 3. Space Available a) Indoors or outdoors installation. b) Available space for cooling equipment. 4. Heat Recovery a) Desirability to recover heat from the jacket water or engine exhaust system.
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5.4.3. The engineer shall always obtain the amount of heat to be removed from the engine jackets, lubricating oil, and turbocharger aftercooler from the manufacturer. The limiting water temperatures (minimum/maximum) for the particular engine shall also be obtained. It is the packager's responsibility to supply adequate heat exchange equipment to dissipate the specified amount of heat for actual service conditions during the life of the equipment.
5.4.4. Soft water or water treated with additives is used only to circulate through the engine. The coolant characteristics shall be such that it does not leave any deposits, is free of corrosive properties, and has a pH value between 8.25 and 9.75 in the cooling cycle.
5.5.
Jacket Water Systems (Cooling of the Engine Proper) 5.5.1. Only closed systems with treated water are suitable for engine cooling. There are two basic jacket water systems; single -loop systems and two-loop systems. (Refer to Figure 3.) The single -loop system is normally used on naturally aspirated engines, and the two-loop system is used on turbocharged engines. The advantage of the two-loop system for turbocharged engines is that the auxiliary water system can be operated at a lower temperature, which will yield a lower temperature for the combustion air supply to the cylinders. The jacket water normally operates at a higher temperature.
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Figure 3: Single-loop cooling water system. B. Two-loop cooling water system.
5.5.2. All water systems shall be supplied with a stand pipe or elevated expansion tank. These provide adequate suction head for the pump, and allow any air or gas in the water to escape.
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5.6.
Natural Gas Engines
November 1992 Draft
Lubrication Systems 5.6.1. The primary functions of the lubricating oil are to prevent contact between moving engine parts and remove heat . The lubricating oil is drawn from a sump by a pump which forces the oil through a cooler-filter system and to the engine system at a controlled pressure. The lube oil is sent through drilled passages or tubing into the crankshaft in order to lubricate the main and connecting rod bearings. On some large units the connecting rods contain an axial passage which conducts oil to the piston pin and the underside of the piston crown to remove combustion heat of the piston. Lubrication of cylinder liners and piston rings is normally accomplished by splash lubrication. Auxiliary tubing is used to distribute lube oil from the main inlet header to the camshaft bearings, cams, tappets, rocker arms, gears, and other accessory drives.
5.6.2. The oil returns to the engine sump/tank by gravity flow. Lube oil pumps may be engine driven or electric motor driven. Where required by design or specification, a pre/post lube oil pump is utilized. The pre/post lube pump is normally driven by an independent power source; either air/gas motor or electric motor.
5.6.3. Lubricating oil filters shall be full flow and may be simplex or duplex types. If lube oil sump/tank electric heaters are used, the use of the pre/post pump to circulate oil when the heater is energized is recomme nded to prevent oil coking and oil deterioration.
5.7.
Heat Recovery Systems 5.7.1. Heat may be removed from the cooling water for use in space heating or for other purposes. The outlet coolant from the engine is passed through radiators or other heat exchanging devices before being cooled further for return to the engine.
5.7.2. Where fuel gas costs are high, the exhaust heat recovery system becomes the most attractive means of increasing the overall system efficiency. Such
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systems that utilize the engine jacket water and exhaust systems are called Total Energy Systems, known to achieve overall thermal efficiencies of 67 percent or higher.
5.8.
Ignition Systems 5.8.1. The recommended choice for Caterpillar, Superior, and Waukesha engines is the Altronic III - CPU ignition system.
5.8.2. The Altronic III CPU is a microcircuit based, self power, capacitor discharge ignition system for medium to high speed engines. The system features crankshaft triggered timing accuracy and the capability to vary timing by several means as outlined below. 1. Total electronic control is implemented by an external 4 to 20 mA control signal. The control signal is usually supplied by an efficiency control computer which processes inputs such as engine rpm, fuel manifold pressure, air manifold temperature, and detonation sensors, etc. 2. A dual timing setting actuated by a set of external switch contacts. This is a user selected timing step-change which can be used to adjust timing for temperature or fuel variations. 3. A conventional manual setting which can be used to operate the engine in the event of a CPU system component failure.
5.8.3. The system consists of the Altronic III unit with electronic timing option, a CPU control unit, two magnet pickups, wiring harness, and an ignition coil for each spark plug. The two pickups input a count from the engine ring gear and a reset pulse once per engine revolution. These inputs taken from the engine crankshaft provide for the basic accuracy of ignition timing, since the normal magneto drive train mechanical variations are eliminated. A schematic of the Altronic III system is presented by Figure 4.
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Figure 4: Altronic III CPU System Overview
5.8.4. Shielded high temperature cables shall be used for primary and secondary leads, where required by code. High tension coils are mounted close to each spark plug to allow for shorter secondary leads, or integral coils which mount directly to a shielded spark plug are available. The shielded Altronic system is CSA certified and Factory Mutua l system approved for Class 1, Group D, Division 2. Parts and service can be provided through either the engine vendor or an Altronic distributor.
5.9.
Fuel System 5.9.1. The fuel gas shall meet composition criteria set by the engine manufacturers. The gas cannot contain any hydrocarbon condensate, solids, or excessive hydrogen sulfide (H2S). If the (H2S) content exceeds engine manufacturers' limits, (usually less than 0.15 mole percent) sulphur compounds will dissolve in the lube oil, causing the oil to break down. The result will be excessive wear and corrosion of internal parts, especially copper and copper bearing alloys. Heavier components in the fuel gas (C 4+) contribute to violent detonation, resulting in high peak firing pressures, loss of power and damage to engine parts. It is important to provide the engine vendor with an accurate fuel analysis so that he can determine if additional filtering, separation, or sweetening is required in order to meet the engine fuel specifications. The
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vendor may rerate the continuous horsepower rating to accommodate the available fuel.
5.9.2. The fuel system shall consist of the necessary pressure regulator and a three way, pneumatically actuated block and vent valve to facilitate quick engine shutdowns and to vent surplus gas. A proven quality two stage fuel filter/separator shall be used on all fuels except commercial quality natural gas. Manufacturers of such devices include Peco, Pall, Peerless, and King Tool. A typical schematic of an engine fuel system is presented in Figure 5.
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Figure 5: Engine Fuel System
5.10. Speed Governor 5.10.1. Governors are available in three categories: mechanical, mechanical hydraulic, and electronic. The mechanical-hydraulic governor is the most commonly used for compressor or pump driver service. The governor supplied by the engine vendor shall be a Woodward UG-8 as a minimum, which has a manual speed adjusting knob. If automatic or manual speed setpoint control is desired, a Woodward PG-PL can be us ed with a 20 to 100 kPa (3 to 15 psi) pneumatic signal. This governor can also be controlled manually. For frequency control and load sharing in generator applications, the Woodward 2301 Electronic Governor is required.
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5.10.2. If the engine application requires computer interface for remote or totally automated installations, the CSA approved Woodward model 700 accepts 4 to 20 mA control signal. The model 700 can be tied directly into a PLC or a SCADA system to operate and monitor the engine control function and provide precision speed control.
5.11. Instrumentation and Safety Shutdowns Engine instrumentation and safety shutdowns shall include the following as a minimum.
5.11.1. Safety Shutdowns 1. High Jacket water temperature 2. Low Lube oil pressure 3. High Lube oil temperature 4. Low Engine oil level 5. Low Jacket water level 6. Engine Overspeed 7. High Vibration
5.11.2.
Instrumentation 1. Digital tachometer (range 0 to 10 percent above trip speed) 2. Exhaust thermocouples for each cylinder and pre and post turbocharger, wired to common readout. 3. Engine hour meter 4. Panel mounted gauges a) Coolant outlet temperature b) Lube oil pressure c) Fuel pressure, before and after throttle. d) Intake manifold pressure/vacuum 5. Additional gauges a) Engine jacket water temperature (in/out) b) Engine oil temperature (in/out)
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c) Oil filter differential pressure d) Air filter differential indicator e) Oil cooler temperature (in/out)
5.12. Miscellaneous Requirements 5.12.1.
Manuals It is essential that the vendor provide Maintenance/Operating and Parts manuals for the engine and associated auxiliary equipment, to arrive on site with the engine. This allows the Maintenance and Operating personnel the opportunity to familiarize themselves with the new equipment and have a stock of consumable and critical spare parts on hand prior to start up.
5.12.2. Special Tools Special tools may be required in order to perform complete overhaul or routine maintenance on some engines. These tools, available through the manufacturer, may be very costly. Based on the location and availability of qualified service personnel with access to these tools, decision can be made whether to purchase or rent the tools as required.
5.12.3. Barring Device Barring over large engines, as required during maintenance inspections or overhauls, can be very difficult. A power operated engine device shall be installed on engines over 750 kW (1000 bhp). A manual, ratchet-type barring device shall be provide below 750 kW (1000 bhp).
5.12.4. Crankcase Relief Valves All engines require crankcase explosion relief valves to protect personnel and the engine from crankcase explosions. Crankcase explosions can be caused by overheated bearings, damaged pistons or other sources, igniting the oil mist present in the crankcase. The relief valves usually mounted in the crankcase 2 doors shall be sized on a ratio of 34,200 mm of relief area per cubic meter 2 (1.5 in of relief area per cubic ft) of crankcase volume. These valves incorporate an internal flame trap which keeps flames inside the crankcase, and they limit internal pressures. The Bicera rapid pressure relief valve has been used successfully for many years and is Factory Mutual approved and meets API specifications.
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Appendix A–Nomenclature
1.
Power (Horsepower) Power is the work done in a given time or the rate of doing work. In the English, or customary system of measurement it is expressed in Horsepower (hp), and in the metric system it is expressed in Watts (W) or kilowatts (kW).
1 hp =
550 ft - lb sec
33,000 ft - lb
=
min
= 2545
Btu hr
and 1 hp = 746 W = 0.746 kW
2.
BHP BHP is the abbreviation for Brake Horsepower. It is the useful power in kW or hp delivered by the engine at the crankshaft coupling. The published engine rating by the manufacturers are bhp ratings. Most published engine ratings exclude the cooler fan drive power and are based on one of the recognized engine test standards that outline the specific test parameters and conditions. BHP can be calculated by the following formulas:
etric : BHP (tk W ) =
T ( N - m ) × RPM 9545
Customary : BHP (hp ) =
Rev 3/30/98
T ( ft - lb ) × RPM 5252
EPT 07-T-02
3.
Natural Gas Engines
November 1992 Draft
British Thermal Unit (Btu) The British thermal unit is defined as the amount of energy required to increase the temperature of one pound of water by 1°F at a barometric pressure of 14.6 psi.
4.
Torque (T) Torque is the turning effort due to a force applied at a distance from a center point. The standard unit of measurement for torque utilized in engine calculations is the "ft-lb."
5.
Bore and Stroke "Bore" is the diameter of the engine cylinder expressed in centimeters or inches. "Stroke" is the distance the engine piston travels from bottom dead center (BDC) to top dead center (TDC) expressed in centimeters or inches.
6.
Engine Displacement Engine displacement is the volume expressed in cubic centimeters or cubic inches displaced by all the pistons during one upward stroke of each piston.
Displaceme nt =
( Bore )2 ×π 4
× Stroke × Number of Cylinders
Displacement is a measure of the "size" of an engine. it refers to the physical dimensions which are not subject to the many varied horsepower interpretations and speed considerations. For a graphical representation of Displacement, refer to Figure 6.
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Figure 6: Engine Cylinder Terminology
7.
Compression Ratio Compression Ratio (R c) is the ratio of the piston displacement plus clearance volume divided by clearance volume.
Rc
=
Total Volume Clearance Volume
=
Displaceme nt + V c V c
The actual compression ratio is considerably less because of late intake valve or port closing. For the engines under consideration there are two compression ratios available; a low compression ratio (on the order of 8 to 1) and a high compression ratio (on the order of 10 to 1). The low compression ratio is generally used with fuel gas with heavy hydrocarbon components and turbocharged engines while the high compression ratio is used for "pipeline quality" gas. The latter fuel is primarily methane (CH 4) which has a lower tendency to detonate (knock).
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November 1992 Draft
Octane Number Octane Number refers to ability of a fuel to resist detonation (knocking). A high octane number indicates a fuel with a high resistance to knock so that a higher compression ratio (more efficient) engine can be utilized.
9.
HHV and LLV HHV is the abbreviation for the Higher Heating Value of a fuel. For methane the HHV is 37.7 3 MJ/std m (1012 Btu/SCF). LHV is the abbreviation for the Lower Heating Value of a fuel. For 3 3, methane the LHV is 33.9 MJ/std m (911 Btu/SCF). The difference (3.8 MJ/std m , or 101 Btu/SCF) between the two heating values is the energy that can be obtained by condensing the water vapor (steam) in the exhaust gas. LHV is normally used for engine calculations because engines do not condense the water in the exhaust gas. BSFC is the abbreviation for Brake Specific Fuel Consumption, which is expressed in Btu/hp-hr. BSFC is a measure of the amount of fuel required to carry a 1.0 bhp load for 1.0 hour. For example, for the engines under consideration the BSFC is approximately of 7500 Btu/bhp-hr.
10. Thermal Efficiency Recognizing that 1 hp = 2545 Btu/hr the brake thermal efficiency of the engine is calculated as follows:
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N B
=
BHP × 2545 SCF LHV × hr
Work Output = 1 HP = 2545 Btu / hr Energy Input for 1 HP
= 7500 Btu / HP hr × 1 HP = 2545 Btu / hr N B
=
2545 7500
= 33.9
For the engines under consideration, the brake thermal efficiency is on the order of 34 percent. Heat recovery systems can be designed to recover heat from the engine exhaust and the jacket water system, which can increase the overall thermal efficiency to approximately 67 percent.
11. Piston Speed Piston speed is expressed in fpm (ft per minute) and is calculated as follows:
Piston Speed =
Stroke(in ) × RPM 6
Piston speed is sometimes useful in comparing the relative wearing vibration tendencies of unlike engines. As an example, an engine with a long stroke and operating at 900 rpm has a higher piston speed than an engine with a short stroke operating at 1200 rpm and presumably might experience higher piston and cylinder liner wear. An accepted range of piston speeds for modern engines is approximately 1200 to 1800 ft per minute.
12. BMEP Brake Mean Effective Pressure is defined as that constant pressure, which if acted on the engine piston for one stroke, would do the same as is done by the varying pressure in the cylinder for one cycle. The units for BMEP are given in psig. The BMEP is a useful quantity for comparing the performance of two engines, because it is proportional to the work done per cycle per unit of cylinder
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size. For the engines considered in this tutorial, the BMEP ranges from approximately 110 psig for naturally aspirated engines to approximately 190 psig for turbocharged engines. In short, BMEP is the mean average cylinder pressure to give a measured, resultant torque at the fly wheel, and as such, is a purely artificial value. It has meaning only when comparing similar engines, and then shall be tempered with engine design and other parameters. BMEP for any four cycle engine can be calculated by:
[
BHP = [ BMEP ( psig )][Stroke( ft )] Bore( ft )
BMEP =
2
] RPM ( No. of Cyl.) 2
792,000 × BHP RPM × Displacement (in 3 )
13. NA Naturally Aspirated four cycle engines are those that receive their combustion air directly as a result of atmospheric pressure.
14. Turbocharger (T) Turbochargers are exhaust driven compressors used to increase the combustion air charge for the engine. As a result the turbocharged engine(s) develop more horsepower per unit volume of displacement.
15. Turbocharged-Aftercooled (TA) The abbreviation TA refers to a turbocharged engine with an aftercooler. The aftercooler is used to lower the discharge temperature of the compressed air which allows the engine to burn more fuel and carry more load from the turbocharger. This action results in a higher air density and subsequently a higher fuel rate for the engine combustion process. For the engines under consideration in this tutorial, two types of TA engines are offered: 1. Aftercoolers using a low cooling water temperature (approximately 27°C, or 80°F) such as water from wells, lakes, or streams.
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