1、SAE AIR*qL52 94 7943725 0520236 O92 I . I. - AEROSPACE INFORMATION The Engineering Society Advancing Mobility -Land Sea Air and Spacecc 1 N TE RNLT-1- 0-N A L -. 400 Commonwealth Drive Warrendale PA 15096-0001 RE PORT Siihmit!eo for recoanition as ali American National Standard E1I - AIR4152 Issued
2、1994-02 RECIPROCATING ENGINE PNEUMATIC STARTERS 1. SCOPE: The purpose of this SAE Aerospace Information Report (AIR) is to present a brief discussion of pneumatic starters for reciprocating engines. This AIR also provides a general analysis guide for preliminary sizing of pneumatic starter systems f
3、or reciprocating engines. 2. REFERENCES: 2.1 SAE Publications: Available from SAE, 400 Commonweal th Drive, Warrendale, PA 15096-0001. SAE J476a Dryseal Pipe Threads SAE 5516 JUN91 Hydraulic Hose Fittings SAE 5542 JUN91 Starting Motor Mountings SAE 3543 JUN88 Starting Motor Pinions and Ring Gears 2.
4、2 Definitions: STARTING TORQUE: Torque required to initiate engine flywheel rotation. CRANKING TORQUE: reaches self-sustaining rotation. Torque required to crank the engine until the engine 3. PNEUMATIC STARTER: Pneumatic starters are a category of starters which are driven by a pressurized gas sour
5、ce. The pressurized gas energy is converted to mechanical shaft power for engine starting by the pneumatic starter. For the wide range of reciprocating engine starting requirements, pneumatic starters typically operate on gas pressures of 15 to 200 psig at output speeds up to 5000 rpm, and provide o
6、utput power up to 100 HP. SAE Technical Standards Board Rules provide that: This report is published by CAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability tor any particular use. including any patent inf
7、ringement arising therefrom, is the sole responsibility of the user.“ SA reviews each technical report at least every five yeais at which time it may be reaffirmed. revised, or cancelled. SAE invites your written comments and suggestions. Copyright 1994 Society of Automotive Engineers Inc All rights
8、 reserved. Printed n I! SA SAE AIR14152 94 7943725 0520237 T29 9 SAE AIR4152 3. (Continued): Generally, pneumatic starters provide higher cranking speeds than electric, hydraulic, or mechanical systems, and the pressurized gas source loses less energy at low temperatures. Current pneumatic starters
9、convert the stored energy into mechanical energy by one of three methods. 3.1 Vane Type: In this type, pressurized gas is expanded between vanes that slide within rotor body slots forming seals between an elliptically offset rotor body and a cylindrical casing. The resulting force on the vanes conve
10、rts rotation of the rotor to the engine flywheel. 3.2 Gear Type: This type usually incorporates two spur, he1 ical, or lobed gears closely meshing inside a housing. the housing. engine flywheel. Pressurized gas is swept from inlet to outlet of The resulting forces on the gears convert rotation to th
11、e 3.3 Turbine Type: This type converts the stored energy of a pressurized gas into mechanical energy by the expansion of the compressed gas. velocity is directed through a rotor. rotor is translated into rotation to the engine flywheel. The expanded gas at high The change of gas velocity through the
12、 4. PNEUMATIC STARTER/RECIPROCATING ENGINE SYSTEMS: Figure 1 shows the basic elements found in a typical pneumatic starter system. Pneumatic starter mounting is defined for reciprocating engines per SA 5542. All starters are required to provide sufficient torque to initiate the starting sequence and
13、 to crank the engine until engine firing speed is reached. When the engine fires consistently, its rotation is self-sustaining and the starter torque is no longer needed. starter is then provided. A means of disengaging the -2- SAE AIR*4L52 94 7943725 O520238 965 SAE AIR4152 Starter gas control valv
14、e Pressure regulator (if required) I I Pressurized gas supply Engbe Flywheel FIGURE 1 - Basic Components of Pneumatic Starter System 5. PNEUMATIC STARTER INTERFACING: The mechanical energy of the pneumatic starter is transmitted to the engine flywheel through a driving pinion in mesh with a ring gea
15、r on the engine flywheel. The cranking ratio is defined as the number of teeth on the ring gear divided by the number of teeth in the starter pinion (see Equation i). The driving pinion and ring gear should conform to SAE 3543. number of ring gear teeth number of starter pinion teeth Cranking Ratio
16、= The starter pinion must engage and mesh with the engine flywheel to initiate a start. each engine start to prevent damage to the starter and ring gear. Currently, two methods are uti1 ized to provide pinion engagement and disengagement. The driving pinion must also disengage from the ring gear at
17、or after 5.1 Inertial Method: The starter pinion is mounted on a helical support shaft. the starter inertially thrusts the pinion mass outward for meshing. a minimum acceleration of 600 rad/s per second is required. occurs when the pinion is accelerated by the ring gear (starting engine) combined wi
18、th the deceleration of the starter. out of mesh. Inertially operated starters generally wi 11 incorporate an energy absorption device (such as a friction clutch) to diminish the shock loading on starter components after pinion/ring gear engagement. Acceleration of Disengagement Usually The pinion is
19、 inertially spun -3- SAE AIR*4152 94 m 7943725 0520239 BTL m SAE AIR4152 5.2 Preengage Method: In this method, the pinion is thrust forward into mesh before energizing the starter. actuator, usually a piston. Once full meshing is completed, compressed gas is released to the starter. Disengagement is
20、 initiated by de-pressurization of the actuator and spring return of the pinion. sometimes also triggers deenergization of the starter. Preengage starters generally will incorporate an energy absorption device, such as a friction clutch or rubber bumper to diminish the shock loading. Preengage start
21、ers should have provision for overrunning in the event of no disengagement. This engagement is accomplished through pressurization of an lhe return action of pinion 6. DETERMINING STARTER REQUIREMENTS: In many cases it will be necessary to determine the starter size and compressed gas pressure and f
22、low requirements. An initial size may be selected using engine data. These parameters may be determined from engine manufacturers data or may be estimated. lhe engine manufacturer may provide engine data sufficient to properly size pneumatic starters for their engines. curve (see Figure 2) or tabula
23、ted data (see Table 1). These data can take the format of a Engine Cranking Speed, RPM FIGURE 2 - Typical Engine Cranking Torque Versus Speed SAE AIRJ4152 94 - 7943725 0520240 513 - SAE AIR4152 TABLE 1 - Engine Starting Data Par ame t er Value Engine number of strokes/cycl es Engine compressi on rat
24、io Lowest ambient starting temperature “F Engine minimum firing speed rpm Starting torque at flywheel Cranking torque at flywheel 1 b-f t 1 b-f t Diametral pitch of ring gear Number teeth in ring gear NOTES: Number of teeth in rin ear * pitch = pitch Diameter of ring qea;: inches 2. Starting Torque
25、at flywheel is the torque to initiate f 1 ywheel rotat ion. Cranking Torque at flywheel is the torque at which flywheel rotation is self-sustaining. 3. 6. (Continued): The engine torque and speed characteristics are usually specified at the engine flywheel. follows in Equation 2: The starter horsepo
26、wer required is then determined as (Eq.2) Cranking Torque (lb-f t) x Cranking rpm Starter Power (HP) = 5252 Once the starter power is determined, the required gas pressure and starter size can be determined from the starter manufacturers specification data, which is usually provided in the format sh
27、own in Figure 3. a 4 o L- e- I io 8 3 I o I 0 a c x c .- L a tz o a3 a .- c ti 5 Statter Output Speed, RPM FIGURE 3 - Typical Starter Performance Curves -5- SAE AIRx4352 94 W 7943725 0520243 45T SAE AIR4152 6. (Continued): Performance values for pneumatic starters typically show horsepower and torqu
28、e at different operating pressures through the rated pressure ranges of the starter. conditions . The performance curves are generally for 68 OF gas temperature The speed and torque curves represent performance values at the starter pinion. following equations are used: To determine the torque devel
29、oped at the engine flywheel, the Engine Torque = Star ter Torque x Cranking Ra tio (Eq.3) Starter Speed Cranking Ra tio Engine Speed = By matching torque requirements, the size of the starter and required operating pressure can be determined. If the manufacturers data are not available, the guidelin
30、es in Table 2 may be used to estimate starter size and gas pressure requirements. TABLE 2 - Starter Power Requirements Natural Gas or Carbureted Engine Di ese1 Engine 1 HP for each 200 CID (3.27 L) 1 HP for each 100 CID (1.63 L) CID = cubic inch displacement CID = 0.785 x (bore in inches) x (stroke
31、in inches) x (number of cylinders) The cranking ratio may be estimated if the diametral pitch of the ring gear and outside diameter is known (see Equation 5). (OD of ring gear x pitch) - 2 Cranking Ratio = Number of teeth in starter pinion The starter manufacturers performance values can then be use
32、d, as descri bed, for starter sizing and compressed gas pressure requirements. The final determination of starter requirements will also be dependent upon expected ambient operating temperature, type of application, accessory load on the engine, and types of driven equipment. In most cases, the reco
33、mmendations of the starter manufacturer should be followed. Gas consumption of the starter may be determined from consumption specification curves provided by the starter manufacturer. consumption curves are shown in Figure 4. Typical -6- SAE AIR*4152 94 7943725 0520242 396 3 e a 1 SAE AIR4152 FIGUR
34、E 4 - Typical Starter Flow Curves 6. (Continued): The consumption curves units are generally free air at 14.7 psia and 68 OF. Consumption at a given power level and pressure may be used to estimate the required starter reservoir size, and piping size. 7. STARTER EFFICIENCY: The efficiency of a pneum
35、atic starter is defined as the actual power delivered at a given operating pressure divided by the ideal power available at that pressure (see Equation 6). Actual power Ideal power Starter Efficiency = The power actually delivered at a given pressure is available from the performance specification o
36、f the starter. power is also available from the gas consumption specifications. power at the given operating pressure may be determined from Equation 7. The gas consumption to produce that The ideal Power (HP) = 1.4145 Cp Ti 1- - ( (2 -7- SAE AIR4152 7. (Continued) : where: Cp = Specific heat,a BTU/
37、lb-OF (for air Cp = 0.24) Ti = Inlet Temperature, OR Pi = Inlet pressure, psia n = Cp/Cv (for air n = 1.40) Po = Outlet pressure, psia M = Starter gas flow, lb/s Using SCFM, Equation 8 takes the form: Power (HP) = 0.0945 (y - TI -( 1- (%)+)M where: R = Gas constant, ft-lbf/(lbm-R) (for air R = 53.35
38、) M = Starter gas flow, SCFM, standard cubic feet per minute 8. GAS RESERVOIR SIZING: Reservoir size is a function of the air consumption of the start r, pressure of reservoir tank during cranking, and cranking time. Starter air consumption is usually taken as an average consumption for the change i
39、n pressure during cranking. Equation 9 may be used to initially size a reservoir. where: V = Reservoir size (ft3) F = Starter gas consumption (std ft3/s) P = Ratio of atmosphere pressure to change in tank pressure: T = Cranking time (seconds) 14.7 psia Max -Min tank pressuze The amount of tank capac
40、ity required for adequate starting is not constant. Cranking time per start depends on the engine model, engine conditions, ambient temperature, oil viscosity, fuel type, and design cranking speed. Normally, the total cranking time is about 6 to 8 s (about 3 starts). Depending on the application, lo
41、cal codes and regulations should be followed. For example, in diesel driven fire pump systems, the National Fire Protection Agency requires six 15-s start attempts (NFPA-20 regulation). SAE AIR*4152 74 7743725 0520244 Lb9 SAE AIR4152 8. (Continued): For 6 s of cranking on engines with a displacement
42、 of less than 1200 CID (20 L), a tank of 82 to 90 gal (310 to 340 1) is adequate, and above 1200 CID (20 L) a tank size of 120 to 130 gal (450 to 500 L) is adequate. The air reservoir size determined by Equation 9 should be increased by a safety factor to account for all engine variables, pipe losse
43、s, and adiabatic discharge of the tank. Gas storage tanks should be ASME pressure vessel certified and should be equipped with a relief valve and drain provisions. 9. PIPING SIZE: Piping and connections for pneumatic starters should be SAE JIC 37O hose fittings per SAE J516 or NPT tapered pipe with
44、dry seal threads per SAE 5476. As a guideline to minimize pipe or hose losses, Table 3 should be followed for hose or pipe sizes. TABLE 3 - Minimum Pneumatic Starter Line Size 10. 11. Pipe Size Pipe Size Starter Consumption Starter Consumption Hose Size Std ft3/s LIS SAE 100R5 ID (in) ID im) 4 113 -
45、12 0.75 19 5 142 -16 1.00 25 8 226 -20 1.25 31 12 340 -24 1.50 38 LUBRICATION CONSIDERATIONS: Vane and gear pneumatic starters may require lubrication to increase motor flexibility and extend motor life. available. starter and inject a metered amount of oil or diesel fuel into the starter. Light mot
46、or oil SAE 10 or 1OW is recommended with a metered flow of 1 to 3 drops/s during starter operati on. When 1 ubri cators are used, care should be taken to exhaust oil or diesel mist in exhaust gas away from possible hot areas. Various lubrication devices are Most operate with the compressed gas norma
47、lly piped to the ENVIRONMENTAL CONSIDERATIONS: The noise from an unmuffled pneumatic starter may be objectionable in some appl ications. Silencers are, therefore, recommended. Local noise codes should prevail, but noise levels over 90 dbA, at 10 ft (3 M) should be muff 1 ed . -9- SAE AIR*4L52 74 M 7
48、743725 0520245 OT5 M SAE AIR4152 12. SAFETY CONSIDERATIONS: With increasing use of reciprocating engines in hazardous atmospheres, the use of pneumatic starters has grown because of their safe operation in unusual or hazardous environments. Starters that use a flammable gas (such as natural gas) for
49、 the compressed power source should be leak tested before being placed into service. These starters should be statically bubble tight at 10 psig back pressure. If leakage is present, provisions for venting must be provided. Allowable gas leakage concentration should not exceed 10% of the lower flammability limit of the gas used or be in compliance with local codes. Construction of pneumatic starters should follow material requirements of the National Association of Corrosion Engineers, NACE, Standard MR-01-75 (1980 Revision) for Sulfide Stress cracking considerations with sweet and
