ASHRAE HVAC APPLICATIONS IP CH 17-2015 ENGINE TEST FACILITIES.pdf

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1、17.1CHAPTER 17ENGINE TEST FACILITIESEngine Heat Release 17.1Engine Exhaust 17.1Internal Combustion Engine Test Cells . 17.2Test Cell Supply 17.3Gas-Turbine Test Cells. 17.3Chassis Dynamometer Rooms 17.3Ventilation 17.4Combustion Air Supply. 17.4Cooling Water Systems. 17.4Noise. 17.4NDUSTRIAL testing

2、 of turbine and internal combustion enginesI is performed in enclosed test spaces to control noise and isolatethe test for safety or security. These spaces are ventilated or condi-tioned to control the facility environment and fumes. Isolated enginesare tested in test cells; engines inside automobil

3、es are tested on chas-sis dynamometers. The ventilation and safety principles for test cellsalso apply when large open areas in the plant are used for productiontesting and emissions measurements.Enclosed test cells are normally found in research or emissionstest facilities. Test cells may require i

4、nstruments to measure coolingsystem water flow and temperature; exhaust gas flow, temperature,and emission concentrations; fuel flow; power output; and combus-tion air volume and temperature. Changes in the temperature andhumidity of the test cell affect these measurements. Accurate controlof the te

5、sting environment is becoming more critical. For example,the U.S. Environmental Protection Agency requires tests to demon-strate control of automobile contaminants in both hot and cold envi-ronments.Air conditioning and ventilation of test cells must (1) supply andexhaust proper quantities of air to

6、 remove heat and control temper-ature; (2) exhaust sufficient air at proper locations to prevent buildupof combustible vapors; (3) supply and modulate large quantities ofair to meet changing conditions; (4) remove exhaust fumes; (5) sup-ply combustion air; (6) prevent noise transmission through the

7、sys-tem; (7) provide for human comfort and safety during setup, testing,and tear-down; and (8) treat the exhaust effluent. Supply and exhaustsystems for test cells may be unitary, central, or a combination of thetwo. Mechanical exhaust is necessary in all cases.Special Warning: Certain industrial sp

8、aces may contain flam-mable, combustible, and/or toxic concentrations of vapors or dustsunder either normal or abnormal conditions. In spaces such as these,there are life-safety issues that this chapter may not completelyaddress. Special precautions must be taken in accordance withrequirements of re

9、cognized authorities such as the National Fire Pro-tection Association (NFPA), the Occupational Safety and HealthAdministration (OSHA), and the American National StandardsInstitute (ANSI). In all situations, engineers, designers, and install-ers who encounter conflicting codes and standards must def

10、er to thecode or standard that best addresses and safeguards life safety.1. ENGINE HEAT RELEASEThe special air-conditioning requirements of an engine test facil-ity stem from burning the fuel used to run the engine. For internalcombustion engines at full load, 10% of the total heat content of thefue

11、l is radiated and convected into the room or test cell atmosphere,and 90% is fairly evenly divided between the shaft output (work),exhaust gas heating, and heating of the jacket cooling water.Air-cooled engines create a forced convection load on the testspace equal to the jacket water heat that it r

12、eplaces. For turbineengines, the exhaust gas carries double the heat of the internal com-bustion engine exhaust and there is no jacket water to heat. Theengine manufacturer can provide a more precise analysis of heatrelease characteristics at various speeds and power outputs.Test facilities use dyna

13、mometers to determine the power suppliedby the engine shaft. The dynamometer converts shaft work into heatthat must be accounted for by a cooling system or as heat load into thespace. Often, shaft work is converted into electricity through a gen-erator and the electric power is dissipated by a resis

14、tance load bank orsold to the local utility. Inefficiencies of the various pieces of equip-ment add to the load of the space in which they are located.Heat released into the jacket water must also be removed. If aclosely connected radiator is used, the heat load is added to the roomload. Many test f

15、acilities include a heat exchanger and a secondarycooling circuit transfers the heat to a cooling tower. Some enginesrequire an oil cooler separate from the jacket water. Whichever systemis used, the cooling water flow, temperature, and pressure are usuallymonitored as part of the test operation and

16、 heat from these sourcesneeds to be accommodated by the facilitys air conditioning.Exhaust systems present several challenges to engine test celldesign. Exhaust gases can exit the engine at 1500F or higher. Com-monly, the exhaust gas is augmented by inserting the exhaust pipeinto a larger-bore exhau

17、st system (laboratory fixed system), whichdraws room air into the exhaust to both cool the gas and ventilate thetest cell. Both the exhausted room air and combustion air must besupplied to the room from the HVAC or from the outdoor.Radiation and convection from exhaust pipes, catalytic converter,muf

18、fler, etc., also add to the load. In most cases, the test cells HVACsystem should account for an engine that can fully load the dyna-mometer, and have capacity control for operation at partial and noload.Large gas turbine engines have unique noise and airflow require-ments; therefore, they usually a

19、re provided with dedicated test cells.Small gas turbines can often be tested in a regular engine test cellwith minor modifications.2. ENGINE EXHAUSTEngine exhaust systems remove combustible products, unburnedfuel vapors, and water vapor. Flow loads and operating pressure needto be established for de

20、sign of the supporting HVAC.Flow loads are calculated based on the number of engines, theengine sizes and loads, and use factors or diversity.Operating pressure is the engine discharge pressure at the con-nection to the exhaust. Systems may operate at positive pressureusing available engine tail-pip

21、e pressure to force the flow of gas, orat negative pressure with mechanically induced flow.The simplest way to induce engine exhaust from a test cell is tosize the exhaust pipe to minimize variations in pressure on the en-gine and to connect it directly to the outdoor (Figure 1A). Exhaustsdirectly c

22、onnected to the outdoor are subject to wind currents and airpressure, however, and can be hazardous because of positive pres-sure in the system.The preparation of this chapter is assigned to TC 9.2, Industrial Air Condi-tioning.17.2 2015 ASHRAE HandbookHVAC ApplicationsMechanical engine exhausts are

23、 either unitary or central. A uni-tary exhaust (Figure 1B) serves only one test cell, and can be closelyregulated to match the engines operation. A central exhaust (Figure1D) serves multiple test cells with one or more exhaust fans and aduct system with branch connections to the individual test cell

24、s. Re-lief of a possible explosion in the ductwork should be considered.Engine exhaust pressures fluctuate with changes in engine loadand speed. Central exhausts should be designed to minimize effectsof load variations in individual test cells on the system. Enginecharacteristics and diversity of op

25、eration determine the maximumairflow to be handled. Dampers and pressure regulators may berequired to keep pressures within test tolerances.An indirect connection between the engine exhaust pipe andmechanical exhaust gas removal (Figure 1C) eliminates variation inback pressure and augments exhaust g

26、as flow by inducing room airinto the exhaust stream. In this system the engine exhaust pipe ter-minates by being centered and inserted about 3 in. into the augmen-tation pipe, which is at least 1 in. larger in diameter. The inducedroom air is mixed with the exhaust gases, yielding a much coolerexhau

27、st flow. However, the potential for increased corrosion in acooler exhaust must be considered when selecting constructionmaterials. The engine muffler should be located upstream of theaugmentation connection to control noise. The indirect connectionshould be considered a potential point of ignition

28、if the exhaust isfuel rich and the tail pipe reaches temperatures above 700F.Exhaust pipes and mufflers run very hot. A ventilated heat shieldor a water-jacketed pipe reduces cell heat load, and some exhaustsare equipped with direct water injection. Thermal expansion, stress,and pressure fluctuation

29、s must also be considered in the design ofthe exhaust fan and ducting. The equipment must be adequately sup-ported and anchored to relieve the thermal expansion.Exhaust systems for chassis dynamometer installations mustcapture high-velocity exhaust from the tail pipe to prevent fumebuildup in the ro

30、om. An exhaust flow rate of 700 cfm has been usedeffectively for automobiles at a simulated speed of 65 mph.Engine exhaust should discharge through a stack extendingabove the roof to an elevation sufficient to allow the fumes to clearthe building. Chapter 45 has further details about exhaust stacks.

31、Codes or air emission standards may require that exhaust gases becleaned before being discharged to atmosphere.3. INTERNAL COMBUSTION ENGINE TEST CELLSTest Cell ExhaustVentilation for test cells is based on exhaust requirements for(1) removal of heat generated by the engine, (2) emergency purg-ing (

32、removal of fumes after a fuel spill), and (3) continuous cellscavenging during nonoperating periods. Heat is transferred tothe test cell by convection and radiation from all of the heated sur-faces, such as the engine and exhaust system. At a standard airdensity of = lb/ft3and specific heat cp= 0.24

33、 Btu/lbF,Q = whereQ =airflow, cfmq = engine heat release, Btu/hte= temperature of exhaust air, Fts= temperature of supply air, FThe constant (1.08) should be corrected for other temperatures andpressures.Heat radiated from the engine, dynamometer, and exhaust pip-ing warms surrounding surfaces, whic

34、h release heat to the air byconvection. The value for (te ts) in the equation cannot be arbi-trarily set when a portion of q is radiated heat. The section onEngine Heat Release discusses other factors required to determinethe overall q.Vapor Removal. The exhaust should remove vapors as quicklyas pos

35、sible. Emergency purging, often 10 cfm per square foot offloor area, should be controlled by a manual overriding switch foreach test cell. In case of fire, provisions need to be made to shutdown all equipment, close fire dampers at all openings, and shut offthe fuel-flow solenoid valves.Cell Scaveng

36、ing. Exhaust air is the minimum amount of airrequired to keep combustible vapors from fuel leaks from accumu-lating. In general, the NFPA Standard 30 requirement of 1 cfm persquare foot of floor area is sufficient. Because gasoline vapors areheavier than air, exhaust grilles should be low even when

37、an over-head duct is used. Exhausting close to the engine minimizes theconvective heat that escapes into the cell.In some installations, all air is exhausted through a floor gratingsurrounding the engine bed plate and into a cubicle or duct below. Inthis arrangement, slots in the ceiling over the en

38、gine supply a curtainof air to remove the heat. This scheme is particularly suitable for acentral exhaust (Figure 2). Water sprays in the underfloor exhaustlessen the danger of fire or explosion in case of fuel spills.Trenches and pits should be avoided in test cells. If they exist, asin most chassi

39、s dynamometer rooms, they should be mechanicallyexhausted at all times. Long trenches may require multiple exhausttakeoffs. The exhaust should sweep the entire area, leaving no deadFig. 1 Engine Exhaust SystemsFig. 2 Engine Test Cell Showing Direct Engine Exhaust: Unitary Ventilation Systemq60cptets

40、-q1.08 tets-=Engine Test Facilities 17.3air spaces. Because of fuel spills and vapor accumulation, suspend-ed ceilings or basements should not be located directly below theengine test cell. If such spaces exist, they should be ventilated con-tinuously and have no fuel lines running through them.Tabl

41、e 1 lists exhaust quantities used in current practice; the ex-haust should be calculated for each test cell on the basis of heat to beremoved, evaporation of possible fuel spills, and the minimum ven-tilation needed during downtime.4. TEST CELL SUPPLYThe air supply to a test cell should be balanced

42、to yield a slightlynegative pressure This is accomplished by having either an exhaustairflow 10% greater than the supply air or a differential pressure ofthe test cell at least 0.05 in. of water less than the surrounding space.Test cell air should not be recirculated. Air taken from nontest areascan

43、 be used if good ventilation practices are followed, such as usingair that is free of unacceptable contaminants, is sufficient for tem-perature control, and can maintain the proper test cell pressure.Ventilation air should keep heat released from the engine awayfrom cell occupants. Slot outlets with

44、 automatic dampers to main-tain a constant discharge velocity have been used with variable-volume systems.A variation of systems C and D in Figure 3 includes a separateair supply sized for the minimum (downtime) ventilation rate andfor a cooling coil with room thermostat to regulate the coil to con-

45、trol the temperature in the cell. This system is useful in installa-tions where much time is devoted to the setup and preparation oftests, or where constant temperature is required for complicated orsensitive instrumentation. Except for production and endurancetesting, the actual engine operating ti

46、me in test cells may be sur-prisingly low. The average test cell is used approximately 15 to20% of the time.Air should be filtered to remove particulates and insects. Thedegree of filtration is determined by the type of tests. Facilities inrelatively unpolluted areas sometimes use unfiltered outdoor

47、 air.Heating coils are needed to temper supply air if there is danger offreezing equipment or if low temperatures adversely affect tests. Forlow-temperature applications, a desiccant wheel with pre- and post-cooling may be needed with appropriate environmentally friendlyrefrigerants.5. GAS-TURBINE T

48、EST CELLSLarge gas-turbine test cells must handle large quantities of airrequired by the turbine, attenuate the noise generated, and operatesafely with a large flow of fuel. These cells are unitary and use theturbine to draw in untreated air and exhaust it through noise atten-uators.Small gas turbin

49、e engines can generally be tested in a conven-tional test cell with relatively minor modifications. The test-cell ven-tilation air supply and exhausts are sized for turbine-generated heat asfor a conventional engine. The combustion air supply for the turbineis considerable; it may be drawn from the cell, from outdoors, orthrough separate conditioning units that handle only combustion air.Exhaust quantities are higher than from internal combustion en-gines and are usually ducted directly to the outdoors thr