c~~ififf$\? --A- CANC&LLtk, -j&$&+u 7&Czte-/ - &St , Au / 7 B ‘@. El4 3 5 is RE’SEARCH MEMORANDUM
STUDY OF COMPRESSOR SYSTEMS FOR A GAS-GENERATOR ENGINE c .-? By Bernard I. Sather and Max J. Tauschek I I Lewis Flight Propulsion Laboratory i I’; Cleveland, Ohio
Th~5oxulxa- -Lb-I EiE?ia p$g$p~gyg”~ym”& n&dmccdaat*Lnuj-mr. mM.a~-y yn 1L ,rO.Lblt.d m Irr. -wb!me sty I p.r.*ll. In th mm&y md mnl mwrvb.althabEd~.~ Ct*Ur omM~~~mycmarra~~ . SC- M*. aml Lil --.2iHmMMkDZD= L?hudd!szatl:r*d-munba NATIONAL ADVISORY COM M FOR AERONAUTICS WASHINGTON April 13, 1949 viJ!=s-! $ AC .c 3mkuy - --m!sv Awcf+AlrlliAL -km --L \ WV F-a-3 VI - ---
--S~~l~~~~~~~lll~ NACA RM No. RCA28 ._..-___- -- .-.--- NATIONAL ADvIsaaY colNEEE Fak AERo~mIcs
ByBernardI.SatheramdMaxJ.T'auschek
Various methods of providing omessor-capacity and pressure- ratio control in the gas-generatm type of compound engine over a range of altitudes frcm sea level to 50,000 feet ax8 presented. The analythal results indicated that the best method of con- trol is that in which the first stage cf compression is carried out in a variable-speed supercharger driven by a hydmulio slip coupling. The second stage of oc~apression oould be either a rotazy constant-pressure-ratio-type cmpressor or a piston-type ccaspressor, both driven at oonstant speed. The a.n3lysis also iradioatedthat the variation Crp the value of the load coefficient for the first and second stages cd? the rotary constant-pressure-tgpe cqessor combination was within reasonable limits and that the valve timing . of the piston-type ccunpressor Gould be kept oonstarxt for the mnge of altitudes covered. With respect to engine performance, other control schemes 8180 appeared feasible. A variable-area turbine . nozzle was shown to be unnecessary for cruiehg operation of the =a-. I
An analysis of anaircmft-propulsion system known as a piston- type gas-generator engine is presented in referenoe 1. En this power plant a two-stroke-cycle, omrpression-ignition engine drives a compressor, which in turn supplies air to the engine. No other shaft work is abstracted from th? engFne. The gases from the gen- erator comprising the ccmpessor-engine cmbination are then uti- Lazed in a turbine, which prcduces the net useful work of the cycle. A diagramatio sketch of this power plant is shown in figure 1. The analysis of reference 1 indicates that such an erg&e may have low specific weight cabined with low fuel consumption 09 the order CCF 0.32 pound per brake horsepow=-hour, whioh has been con- firmed, to a certain etient, by the experimental results reported 2 NACA RM No. E9A28
Inreference 2. The reference analysis is idealized, however, In that the problem of engine oontrol was not oonsidwed. In order for the performanoe cf an actual engine to approach that of the ideal ourves, at least three steps must be accomplished: (1) A ocmpres- sor that is capable cf operating over a range of air flows and pressure ratios must be obtained; (2) similarly, a turbine that will operate over the range cxf air flows and ~essure ratios must be obtained; and (3) satisfactory means of maintaining proper engine limits (peak cylinder lzessure and turbine-inlet temperature) must be evolved. The first c& the preceding steps, which pertains to the control of canpressor capacity and compression ratio, is treated herein. The speolfio objective of this investigation, which was conducted 8t the NACALewis laboratory, is to evaluate various comibinations cf corn- lessors and driving mechanisms with respect to engine performance as a function of altitude. Because It is currently impossible to make a oomplete evaluation with due oonsideratlon for such items as oanpressor weight, development problems, and control stability, the present analysis Is based on the degeneration cf the power output and the fuel eoonomy of the gas-generator ee In question when oe with the ideal engine. Some qualitative disoussion aP com- . pTessorweight,however, is included. . METHOD OF ANALYSIS
The various compressor-control systems that were investigated 0 inoluded the followlng ocunbWtions of eleanen-bs: (1 Constant-pressure-ratio ccmDt?essor with throttled inlet (2 i Multistage constant-pressure-ratio ocsapressor with first stage (supercharging stage) driven by three-speed gear (3) Multistage constant-pressure-ratio compressor with first stage (supercharging stage) driven by hydraulic slip ooupling 4) Constant-volume single-stage ocun~ssor I 5)Constant-volume c~essorwiththrottled inlet (6) Constant-volume ccmprressor tith means of varying volumetric capacity (7) Supercharged constant-volume cwessor cc%tprisFng constant- pressure-ratio first stage (supercharging stage) driven by hydraulic slip couplm followed by final stage aP compres- sion in constant-volume compressor In the preceding lfst, the terms %x&ant volume" and "constant pressure" refer to compressors exhibiting these oharacteristios at NACARMNo. E9A28 3
const8nt speed or effective speed. Thus the oentrifug8l0npl~ssor Y . or the mixed-flow cunpressor (reference 3) would most nearly rep- resent the constant-presslule-ratio group. Theconstant-volme class would lnolude any.of the positive-displacement c~essors, such 8~ the piston-type campressor or Roots blower. The d&l-flow ccm- pressor would 8180 fit into this olass ff suitable means were avail- 2 8ble for broadening its operating range so as to maint8fnhIgh eSfi- 4 cienoy over 8 tide range of pressure ratios and air flows. Schfrmatic diagrams cfthe various systerma are showninfigure 2. These possible oaubinations were Berived by setting up the ideal requiraments for the ccmpressor for the gas-generator engine 8nd then selecting the owessor systsPns most likely to fulfill these demands. The ideal requfrennents for the ccm@ressor (fig. 3) were computed frcuz reference 1. Engine speed was not included 8s a control means because aP the necessfty for keeping the scavenge ratio within reasonable limits (reference 1). Thus, (8) If means . were provided for keep- the soavenge lgtio constant, such as a variable-area turbine nozzle, the reduction in engine speed neces- saryto decrease the ocmpressor-pressure ratio to the required
c value as altitude is deoreased (fig. 3) would result in greatly reducedairwefghtfUw8ndhence reduced 8ngZne power output; and (b) If no means are wovided for controlling eoavenge ratio at . will., as tithe c8se at' the fixed-area turbine nozzle, reduction in engine speed would result in inoreasIng the scavenge ratio and hencebm mixture r8tio beyond the usable range. All the ccpnbin8tions were investigated with the an8lysis of reference 1 used as a basis. The changeerequiredintheanalysis 8s 8 r8SUlt of the use of8 8pedfl.O canpr8ssor are given in the &pPand-88. All the combilrrtions were analyzed with a feed-area turbine nozzle and, In addition, eystams 2 to 6 were also treated with a variable-are8 nozzle. In analyzing the various ocmbinations, the design cotitions of the compessors were set to provide,sufficient camcity and pressure ratio for engine operatfon 8t 8n altitude of 20,000 feet. At this altitude, the engine w8s 888lrmed to operate with design operating limits of peak cylinder pressure of 1600 pounde per square inoh, turbine-inlet temperature of 16KI°F,8ndsc8venge ratio of 1.0. For caloulationa of operation at higher altitudes, the turbine-inlet temperature and the oqesaor speed were held constant and the peak cylinder pressure w8s allowed to decrsase. At lower altitudes, the generator-inlet pressure was so varfed 8s to maintain both engine limits, unless the characteristics of the c~essor system precluded this possibility, in which case the 4 NACA RI4 Ho. E9A29
oykbd8r pressure was 8llCWed to vary. when turbine-nozzle area was fixed, it was impossible to hold the soavenge ratio to 8 con- stant value of 1;O at altitudes other than the design altitude because under choked oonditions the area of the turbine nozzle determines the gas flow through the engine; however, the value of soavenge ratio did not vary mtly from 1.0 over the range of alti- tudes consiijered. When the ar8a of the turbine nozzle wa6 made va;riabl8, the saavenge ratio was kept son&ant at a value af 1.0. The scavenge ratio of the Ideal gas-generator engine was 1.0 for 811 8ltitud88. Systsans 2, 3, and 7, which utilize a rotary sup8roharging compr8ssor, were so arranged that the supercharger operated at rated Speed at an altitude of 20,000 fe8t and idled 8t Sea 18V81. In th8 eystam Irrvolvlng the three-speed gear wbination, the eup8rCharger Was aSSum8d to idle 8t et p3XSSUr8 ratio of l&t alti- tudes below 10,000 feet a& to operate in the low-speed gear ratio at altitudes b8tw88n 10,000 and 20,000 feet. Above 20,000 feet, the supercharggr op8X'ated in high Speed. . The over-811 efficiency c& a.ny ocmbination of campressorswas made equal to 0.85 at an altitude of 20,000 feet. Although thie prsotioe resulted in rather high stage efficiencies, it was neoes- earJithatth8 dat&ag?.%ewith that cxfr8f81~1~elat thiSbaSiC oonditfon. Th8 lack cxf 8CCurate data on the affiCien0188 of ConSt~t-VO;lum8 O~SSOZ?S, as, for erample, that of the axial- flow o~essor at off-design WtiitioXIS or th8 piStoPtype cam- pressor at high piston speeds, pwluded oomDe,rison of the oone~-pressureandoonetant-volzmw compr888ors onan efficiency b8sis. Th8 most reliable hAgA data on 8ffiCienCy of piston-type ccm~8ssor8, however, indloate values in the ra,nge from 0.85 to 0.95, whioh is entirely oompatibl8 with the general assumption. No chang88 In sffioienoy with ohanges in the specific f&w for the constant-pressure compr8ssoTs were considered; Instead, the pres- . sure r&i08 & th8Se compressors were limited t0 VdUeS that would p8rmit a moderate operating r&1388. This limitation vas necessary in order to &Void consfderations of ccmpressor design, which are beyond the scope of this report.
RESULTS AND DBCUESIOA BeOaU88 of the inherent differenCe8 in Compressor character- istics, the results 09 the analyses of constant-pressure-ratio caqeessors and oonstant-volume compressors are disaussed separately. The effects of fixing the turbine-nozzle area and of designing for high altitudes are also oonsidered. NACA RM No. E9A28 5
Constant-Presieure-Ratio Com~ssor Effeotofthrottling. -The 8ffectof'throttlingthe compr8seOr inlet as a control means is shown in figure 4, which shows that throttling provides 8 means of IMiPt&w the eI3giIB limit8 (peak burner pressure and turbine-inlet t8mp8rature) In the altitude range up to 20,000 feet, but that the engine is penalized by large . rgductions in brake output. 'Phi8 p8IBlty iS 8 rl&Ural r8SI.Ilt of the high aompr8ssor power load in the gas-generator typ8 ti engine. COnsequent4, although throttling is OOnSid8red to b8 8ppliCabl8 t0 the gas-geIUU??&tOr 811gi.133 with th8 oOILStaI&-~SSllre-ratio coap- pzessor, it iS undesirable from 8 S&aIIdpoiI& Of lOW-8ltitude pOWIF output. ZXfectofthree-8p88dsup8rcharging -COmpreseor drive. - An iZlS~tiOIldfigur8 5 iZIdkat8Sthatth8 PerfOZXlanC 8 d 8&M- generator engine with 8 three-speed supercharging compr88sor is subject to large power losses at altitude6 just below those at which thegearohang88 take pkLUe. This fsct, coupled with the difpiculty . of providing 8 Chsnge'gear and 8 olutch capable of handling the required pow8rs, indicates that this systam is undesirable for @.a- generator applioation. . Xff8ot of hydraulic-slip-couplinp; Superdhargi~-o~88Or drive. -The p&OnaanOS ofthe~S-g~&t~8I@llewh8n~uipp8d with 8 multistage oonstant-pr8esur8-ratio capr8ssor ocenprising 8 supercharging ccmpr8ssor driven by 8 hydcaulio slip ooupl3ng and followedby oonstant-sp88dfinal oanpr8ssion stage is meanted infigure 6. Itti~benot8dth&only& small lOa8 inpoWar b8tWe8n 888 level 8nd 20,000 feet occurs when the ~upling is used. The 8ffioiency of th8 coupling is 8 linear function Crp the slip; it iS equal t0 Z-0 8t lCC-perOent Slip and 8pproaOh88 1C.C p83338nt 88 the Slip 8ppZWCheS ZBY'O. Because th8 oompressor'torque varies with the square of the spe8d, it canbe shown that the oo@Ung power loss is 8 max&mm~ 8t %-perCent Slip, and iS 8qUal t0 One- ' fourth of the full-load ccmpr8ssor power if the air flow remafns oonstsnt. FurtheTmoTe, the oompressor driven by the ooupling Oomprises 8 fraction of the total compressor lathe gaS-g8zWatOl? engine. !The small coupling-power loss relative to the tot81 cc+ pressor load indicates a logical reason for the amall influence of the coupling on the over-all perforrs?UN 8 af the gas-g8nerator engine. 6 NACA RM No. E9A28
Constant-Volume Compressor . In the case of the constant-volume compressor, the piston-type mnpressor, in particular, has numerous inherent unique advantages for gas-generator-engine applications, some of which may be listed 88 fOlkWS: (a) Provides 8 CcSQaCt, light machine for operation at the low air flows and high pressure ratios required by the gas-generator 843ti. (b) Possessee 8 broader operating range (high efficiency over Wide range af pressure Z&i08 and air fkM8) than eqtiVE&lent rotary- cmpr8ssor types. (c) Permits a higher campressor efficiency to be obtained at high pressure ratios. (d) DeliVeX? 8 pO8itiVe Supply of air under all OpWating con- ditions, Wluding startisg and IdUng. . Advantage (8) d888rves some elaboration. The same piston-type compressor is capable of operating over an extremely wide mmge af pressure ratios, for example, from 2 up to values of’ 20 or 25. At the same time, the weight is fixed by structural stiffness require-' . merits, so that little if any ohange in weight accompaniee 8 change in pressure ratio. In the equivalent constant-pressure-ratio cm- pressor, an inm8ase in pressure ratio cau be obtaIned only by staging with a oonsequent Increase in we-t. Thus, 8s the required pressure ratio is increased, the piston-type ocmpreseor becomes lighter r8htiVe to the constant-pressu$e compressor. Also, because of the staging required to obtain high pressure ratios, the efficiency of each stage of the constant-pressure corn- pressor must be extremely high in order that the over-811 efficiency of the comstazit-pressure-compressor ocmbination may approaoh the txffioiency easily attainable with the constant-volume piston-type ompressor (on the order of 0.85). The fact that such efficienoiee may not be obtainable tith the constant-pressure ccmpressor increases the desirability of using the piston-type compressor. 728 prime advantage of the CO3.ISt8lrt-~eSSUT8 O~eSSOr is, of course, its extremely high volume-flow capacity, lea- to 8 low specific weight. At low volumetrio flow rates, however, this advan- tage disapp8ars to 8 oertain extent because cxf the difficulty of designing these oppressors tith small flow passages and clearames and with high rotational speeds. NACA RM No. E9A28
Consequently, the ideal circumstances for the use of the piston-type ccqressor are low volume-flow rates a& high pressure ratios. These circumst~es are present in the gas-generator engine, particularly L.n the final stages of owession. The size of the piston-type cwessor need not be excessive. The ratio of ccm-pessor volume to burner volume is 10.35 for the case of the gas-generator engine with the unsupercharged piston- tgpe ccmpressor and the fixed-area turbine nozzle at 20,000 feet. If the compressor is superuharged for all altitudes other than sea level, this ratio becomes 6.01. If supercharging is used also for sea-level operation, however, the commasor-volume - burner-volume ratio may be made to approach unity. Inlet ram due to flight speed further reduces the required volume ratio, Furtherwu. 8, fittUg the required compressor volume into the gas-generator engine and furnishing the neoessary reciprocating motion is not a great design problem. Ih certain engine collf~tions, such as the axial engine, the reciprocal&q motion is readily available and a compact, small- frontal-erea engine may be easily attained. Further deorease in size of the piston-type ooqcessor may be obtained by making the ocunpressor double-act-. One disadvantage may be ascribed to the piston-type c-es- sor In that considerable work will be required. to develop it into a praoticalhigh-speedmaohtie; however, this same disadvantage applies to rotary cvssors required to operate at very high pressure ratios and efficiencies. Bkwm these praotical considerations, the piston-type ocqres- sor seemed an attractive ohoiae for a constant-volume-type com- pressor for use tith the piston-tgpe gas-generator engine, although the results would be applicable to other forms of oonstant-volume compressors. Par these reasons, the piston-tgpe ccm~essor was included In the analysis. Effect of fixed-displacement oonstant-volume ccmpressor. - Figure 7 shows the perfcrmanceof agas generatorusingaftied- displacement piston-type ccqressor (that is, one equipped with automatic compressor valves), as compared with the performanoe of the ideal gas-generator engine. With this type of compressor, rate of air flow through the engine is substantially dependent upon only compressor speed. Consequently, with a fixed restriotion in the turbine, turbine-inlet pressure must inorease until the flow through the turbine matches that through the oaanpssor. The resultant high manifold pressures and compressor loads cause the
. 8 NACA FM No. E9A28 . burner pressure to increase above the limit- value at altitudes below the 20,000-foot orltical altitude; therefore, the system is not usable. Xfeot of throttled fIxed-displacement constant-volume com- pressor. - Throttling the exhaust from the fixed-displacament piston-type ocqressor will only make the situation regarding burner pressure worse inasmuch as such a change will increase the ccmpressor load tithout appreciably affecting the manifold pres- sure. !Ihrottling the inlet to this ucxnpressc~, however, permits the air flow and consequently the manffold pressure to be reduced to a point atwhioh limiting values of burner pressure are attained at altitudes below the critioal altitude. Actually, the oompressor load is higher than that of the ideal engine, so the manifold -es- suremustbelowerthanthatoftheldealengine, oausinga reduc- tion In performance. Figure8showstheperformance of such a throttled engine. The large loss In brake output and the increase in fuel consumption between 20,000 feet and sea level makes this system unattractive for gas-generator use. Effect of variable-displacement oonstant-volume compressor. - The performanc e d a gas-generatorenglne equippedwith avariable- displacmnt cca~essor, that is, a piston-type ccqressor equipped with mechanIcally actuated valves that permit variable ttilng with this device, is illustrated in figure 9. On the basis of engine performance, this system is quite satisfaotory. !the piston ocan- pressor, however, must handle air at ambient atmospheric conditions. UMer this circumstanoe of high volumetrio air flow, the piston oompressor may beczome relatively heavy as oompared with equivalent rotary types. This fact, in addition to the valve compliuation, makes this scheme undesimble for gas-generator use. Effect al? supercharged fixed-displacement constant-volume ccgnpressor. - The use aP a variable-speed supercharger driven by a hydraulic slip ooupling with a fixed-displacement piston-type oompressoraffords ameans of adjustingairflowthroughthe engine and utilizing all the piston-type-compressor displaoament at all altitudes. The performanc e of such a oombination is presented in fQure 10. The ourves of this figure indicate that this scheme is the most promising of those inoorporating a piston-type compressor. It is interest* to note that, when a superch8rging oompressor is used, the time at which the reciprocating-compressor valves open and close is substantially oonstant with changes in altitude (fig. II), 80 that meohanioal valves ~5th fixed timing oan be sub- stituted for the automatic valves without Incurring a penalty In engins performance. . C~son of R&ton-Type and Rotary Ccqressors The two most successful m&ho&~ of satisfying the compressor recpiraments in the gas-generator engine appear to be the use of a variable-speed superoharging compressor followed by either a constant-volume piston-type or a constant-pressure stage for com- $ression of the air to burner-inlet pressure. Unfortunately, the laok of data conoernLng the piston-tyRe=capressor weights and effioiencies precludes a definite evaluation of the two compessor tgpes. Figure 12 shows the performance cf the two gas-generator engines as calculated by the methods of this report. Below the critical altitude, the performance of the combinstian with the piston-type constant-volume aompressor is slightly superior to that obtained with the constant-pressure combination. The slight difference in performance between the two systems is causedby the fact that the peesure ratio across the constant-pressure oom- pressors iu a function of the inlet tsmpe3Mxare, whereas that for the reciprooating oom~ssor is consta,nt. The varia%ions Crp values of load coefficient Q/n for the first stage (supercharger) and second stage a8 a function of alti- tude for the multistage rotary constant-*ssure ccmpressor with first stage driven by a hydraulfc slip coupling is shown in fig- ure l-3. Although the values aC Q/n vary widely for the super- oharger below an altitude of 10,000 feet, the tip speed of this compressor is quite low, whioh may keep it out of a surging con- dition. The variation of Q/n for the second stage Cs tithin present'aooeptable limits. The perf ormsnce cxP the supercharger when used with the piston-type compressor fs substantially the same as that shountifigure 13.
Ef'feot 09 Variable-Area Turbine Nozzle Examination of the data ocuopsring the fized-area nozzle with the variable-area nozzle (figs. 14 to l9) Irdicates.that only a slight reduction fp performebnoe is incurred through the use of the fixed-area nozzle. Grjnerally, a small drop in power occurs at altitudes below the 20,000-foot critical alt9tude, which is caused byachange inscavenge ratio inourredthrough lackofadequate air-flow control, In general, the Rower loss is small Fn com- parison with the problms Incurred in the sucoessEM. developent cf such a devioe; therefore, the variable-area turbine nozzle will not be further aonsidered in this report. 10 . NACA REI No. E9A28
gPfect of Designing for High Altitudes The performance curve fck the gas-generator engine equipped with a variable-speed supercharger driven by a hydraulio coupling c (fig. 6) indicates that some losses are incurred in going from sea level to the design altitude. Because these losses increase in magnitude as the design altitude is raised, it is af interest to examine the case in which the engine is designed for a very high altitude. In figure 19, the performance Ccc the gas generator with the variable-speed superchargfng ccmpressor is shown when the optimum altitude is 40,000 feet. It is noted that in this case, the loss in brake output at moderate altitudes (0 to 20,000 ft) is more serious than for the case of the engine designed for 20,000-foot optimum altitude. More brake output, however, is available for climbing to an altitude of 40,000 feet and above, and this engine should therefore be more satisfaotory in applica- tions where a high-altitude engine is warranted.
The results of the analysis mesented herein for various methods of providing compressor-capacity and pressure-ratio control for the gas-generator engine operating over a range of altitudes with oonstant peak cylinder pressure and constant turbine-inlet . temperature may be summarized as follows: 1. The best method of compressor control appeared to be that in which the rlrst stage of compression consisted of a varfable- speed supercharger that was driven by a hydraulic slip coupling. The second stage of compression could be either a rotary constant- peesure-ratio-type compressor or a piston-type comIreesor, both driven at constant speed. The variation of load coefficient Q/n for the first and second stages af compression when a oonstant- ~essure-ratio final-compression stage was used remained within reasonable limits over the altitude range considered. With a oonstant-volume comlxressor for final oompresslon, the valve timing of the piston-type compressor could be held constant over the alti- tude range oonfddered. 2. Other control methods, which appeared feasible with regard to en&ne perfwnoe, are the use of a constant-volume, piston- type ccnnpressor with variable valve timing or a constant-pressure compressor, the first stage c&' whioh is driven by a three-speed g-. NACA RMtio. ES&Z8 11
3. Throttling generally produued large power losses at other than the design altitude In the gas-generator engine. 4. For oruisIng operation & the engine, the complication of a vazia.ble-areaturblnenozzlewas notwamanted.
LewisFlight PropulsionLaboratory, National Advisory Committee'for Aeronautfos, Cleveland, Ohio.
8
. 12 NACA RM No. E9A.28
. me follmdng Eqpibols are used in this report: C percentage clearance W piatcm-type cogqres~or 1 %a specific heat at ccmstant pressure of compreaaor air, 0.243 Btu/(lb)(~) specific heat at cmtsknt pressure of turbine gases, cPA3 0.270 Btu/(lb)~(oR)
g accelera-tim due to savity, 32.2 ft/sec2
bc lower heat of codbusticm of fuel, 18,500 Btu/lb fuel 3 mechanical equivalent of heat, ft-lb/l3bu N agine speed, cycles/set P total pressure, lb/sq 9.1. absolute
pe burner exhaust pressure, lb/aq in. absolute pIn burner-inlet mmifold pressure, lb/sq in. absolute P 8tatic pressure, lb/sq In. absolute
pa mibien-t air pressure, lb/sq An. PC burner ccqresaicm pressure, lb/aq in. absolute Q/n load coefficient, cu ft/revolutim
%a pre8m.n-e coefficimt of corupressm
R* expansfcm ratio of fluid in burner %l aver-all mixture mtio, lb fQel/lb air mixture ratio in burner, lb fuel/lb air _ %b pressure ratio in piston-type cmpressor Rp t MACARMNo.ESA28 I.3
pressure ratio in first stage of compressicm, rotary 5211 ccmrpressor
pressure ra.tio'ti second. stage of ccxqressicn, %J rotary compressor %,O over-all pressure ratio across compressors SCaVenge ratio (ratio of volume of air flow5ng i2?rou& RS burner per cycle ~sured at burner-inlet cmditicms tovolume of burner) T temperature, OR
Ta ambient air teqerature, oR
Tc burner c~essfcmtengmrature,"R T meanturbine-inlettengmxt~e, %f
< burner-inlet temperature, oR
Ts te7ipratme inburneratmd of sca.vangIng, OR v volume, cu ft vb total volume of bumer above ports, cu ft Vc total volume of reciprocatiag campressart ciz ft wc work of compressort Btu/lb air wt work of turbtie, Btu/lb aLr Y ratto of specifio heats of turbine gases
'lad adiawtic over-all effYciancy ofrotsryc~ssor qb burnerInake thermal efficiency(actual) %s adiabatio efficiency of piston-type cmessor
%,l adiabatic efficiency Ocp rotary ccrmpressor, first etwe $2 adiabatic efficiency ti rotary ocanpressor, second stage oompessor k,O over-all adiabatic. efficiency of unit 14 NACA RM No. E9A28 .
reduotion-gear efficiency, 0.95 'r scavenging efficitmcy (rakio of volume of a3r remaining %l in burner at end of scav~ process, neasured at inlet conditians, to volume of burner)
effioiancy of q SZ slip coupling l-h adiabatic turbine effioimcy, total to stfatic, 0.85 P density, lb/cu ft NACARMNo.ESAZ8 I.5
s ANALYSSS OF cycm
In gmeral,the analysis of the cycle is s~lsrtothatof reference 1. A ccmdensation of that snalysis is given hme for convenience. Because reference 11s en idealized snalysis, certain variationsm.wtbemadewhenc~siderIngthe gas-gmemtor at@ne with regezd to cmtrol. These specific detxL2.s till be presented in the succeeding amixes. The follow3ngmethod of8nalyai8wasuf3edto estimate the idealized performnce of the gas-generatar engine. Compressor calculations. - The over-all perforrcan ce of the caurgressmunit Oglthebasis of workdmeperpomd ofafrhsndled IS
G = 4 ~,oo-283 + Ta %,o ma Scaveaqjeefficiencyand scavengeratio, -The scavengeratio of the pisto+typeburneris givenbytbe equaticm Rs =I 0.0910 ,/(l-P$p,) Tm
and the scavenge efficiencybyt&e equatim -R, . ?S =1-e
The -taqperature of the gases In the cylinder at the end of the scavenge process is
St is assumed that the inlet and exhaust ma&folds are suf- ficientlylsxge so tha.ttotsl and static pressuressxe ap~oz&3&el.y equal. 16 NACA RM No. E9A28
Burner efficiency. - The brake themnal efficimcy of the pistcQ-type Imt-ner 18 n 'lb = 0.925 - 1 0Re where
p = 0.3667 - 6.5 - O.043 (W R,
Therelrttionbetweentheworkoftie coqressorandthebumer output is glen by the equation
WC = %.9&c (37) Because no siqple relation between qb and R, exists, a trial-and-error method of solutim is necessmy~ The bumer efficiency was first approximated by the equatim 0.32 qb' = 0.925 - ml
(The me of the prime on the symbols indicates an approxbnaticm.) With this value, the over-aJl flzel-akr ratio was estlmted by
This value of over-all mirturf3 ratio was modified to re-pesmt appr~telythemltiure ratio etistiqinthe cyllnderbyuse of the equation
. with this vd.ue of G,b', the burner-efpiciency caloulations w-me repeatedandthe cmrectedmixtureratioswere foundfromequa- tions (B7) and (mo). NACA RM No. E9AZ8 17
Mkximmubumer~essure, - Curves of the ratio of ideal peak burner pressure to cnmpressicn pressure as a funqtim of mixture rat+0 andwlth ccmpressicmtenperature as apsrsmeterwerepre- pared by use of the fuel-air cycles and metlmas of reference 4 for the rich zzixtures end by use of air cycles for very lean mixhres. These pressure ratios were modified by the factar F= - 3.75 s,b + 1.0 - to bring the ideal ratios into accmdance with [email protected] data. Compression pressure and temperature were ccmguted from the equations 1.35 PC zpe R, m2)
c.35 Tc =T, Re Turbine-inlettemperature.- Aheatbslance a=liedto the @a-genera&or t5ngine showed tit, tiththeassunptkz~ofaheat loss equivalent to 18 percmt of the fuel-heat tiput, the turbine- inlet temperature N&B given bythe equatim
(l-0.18) h& + Cp,$a (1+&J Tg = m41 Cp,g (l+%J
Turbine power. -The ouiqutof t;he turbtie ingtUperp6md of ati is
wt = rlt %tg Tg (l+Q) (=I
where
Y = 1.34.
= 0.27 cP,E3
IBitperformsn ce calculations. -The outputofthe gas- generator engine cm the baais of Btu per cycle per cubic i&h of burner volume is I.6 NACA RM No. Egti8
Brake output = 71rwtRs1728 144 pm 53.s and the brake specific fuel can~tion is 2545 s bsfc =- (=7) Gwt
.
. l!UCA RM No. E9A28 19
The pressure ratio amoas the piston-type ovssor uniquely determines the scaven@;e mxtio of the piston-type burner, as may be shown by the following ocmpressor-cycle analyeis, which uses as a basis th? idealized preesure-vdtume indiOa%r diagmm of 8 piston-type ccmpressor: I
L Volume Inasmuchasthetenperature rise across the ocm~ssoris based on the adiabatic efficiency, for the ratio of specific heats of 1.395
Ts,l+~'lo q-283 - 1) (Cl) T2 (
If the permntage of olearame C ia defined as
v4 C= v2 - v4 where v2 - v4 is the compressor displacement, then
The weight ofairdeliveredbythe oompressmperoy~leis
(v3 - v4) 03 and the sca.venge ratio Rs ie
. NACA RM No. E9A28
v3 - V4 v3 - V4 vb p3 %= vb when ft is assumed that both the burner and compressor operate at the same nunber of cyoles per unft Mm. Beoause
-=-p4v4 PIVl T4 Tl
p3v3 pzv2 Tg=-q- then
1 T3 V3 -44-2 (-I---Rp 2 A> so that
vg 1 Rs = vb up 1 + & m3 Cr . The value of C in this analgels is 0.03. The volm ratio v&b is detemnined --the limftiw acmdItlons Of engim oper- &ion at an altitude of 20,COC feet and a scavenge ratio of 1.0. For an unmperoharged oompressor, the value of this rettio 18 10.35. EIACA RM No. E9A28 21
Vaziable-diaplacement ocanpressor. - The displaoenentofthe piston-type compreeecr my be effectively varied by corrt;rolling the valv9timlngbymeans ofecme~chanicalammgem?nt. It is possible to decrease the dieplacemznt by: (1) closing the inlet valve early, (2) closing the inlet velve late, or (3) closing the exhaust valve late. Method (3) is the cme ccmidered in this analyeis,andif X i~3the pementage ofthe pietonstrokethat the piston has returned when the exhaust valve ie closed late, the scavenge ratio will then be
0.283 -- (C3) 22 NACA FM No, E9A28
The hydmulio slip coupling is perhaps the simplest and most ~otioal means of obtaining ohemges in the speed of the first- &age canlpessor. In addition, the hydra11110 coupling provides ~109~3 shook and vibration isolation. Reference 4 lists scme of the design features of current slip oouplings. The size of the ooupling needed to transmit the power to the first-stage ocmpressor need not be excessive because the torque and the horsepower of the fluid ooupling varies as the fifth power of the diamsterand only a relatively small change indiemter will be neoessazy to oover a large range intrammitted parer. Cument fluid oouplIngs oan therefore be used in the gae-generator engine with only a mall variation in the size of the coupling unit. The type ofhydraulic oouflingoonsidered inthisanelysis is the sooop-oontrol hydraulic ooupling. Variations in speed of the seoondary me nade possible by means of an adjustable-sooop tube, extending franthe impeller seotiontoa rotatingreservoir. Oil passes fkonthe worki= cimuit through the nozzles provided intheinner oasingand collectsinthe rotating reservoirfYom which it is returned to the ooupling cirmit. The sooop tube Is mounted off oenter, so that in its fully extended position it handles all the oilinthe rot&tingreservoir,butwhenbraught to a fully retracted posftion, all the oil drains into the ~MWJVO~~ asd the 0a~pling i8 fhny ai8c~oted. varying the scoop position frm a fully erterded to a fully retracted position variee the rspeed of the seoondary unft ti maximum to zero vslues. In the tspe 0f fluid 0arpling canemma, in whioh there is notorque-reactionlaeniber,thetorque inputeqWf3thetorque output, and the effioienoy is equal. to the ratio of seoondary to primary speed, so that
NP pri=.mpeed, rps =El 6emndm-y epsea, rpe HACA RM No. E9A28 23
. RcmRY CCMPHESSOR The rotarytmqres~~inthieEbnalyaisis oonaideredtobe either a centrifugal or a ~&&L-flow ocsnpressor. sts perfonnanoe chamcteristios are aesumed to follow the B lawa aa those underwhioha centrifugal cornpressoropera.tes. The temperature rime aurom each stage is therefore
where u ieths stage efficiency& P&l isthe pressure ratio across the stage. TheworkzquiredinBtuperpazndof air is
WC - cp,a AT Whenspeedchanges andtheireffecte onthe performas~e of the oompressm are oormidered, it is oomenient to use the forme involving the pres8ure ooefficdellt
@3) where VT is the tip speed in feet' per second. BoaUSe
then
=-e%d vT2 WC @5) %d g 24 NACA RM No. E9A28 and .
? = k + ~~~~~~~~~~~ ' 036)
Rotary compmseor with slip ooupl.inR - If t&e value K repsente the epeed ratio of the slip o&iLing
=I3 K,--= 037) #P St then the work put into the pimesy side of the slip oouplfng is
w, = -qad -vT2 1- 'lad g K 033) and if
where D lstb diameteroftha oau~asor . Q& Ns2S NJ W,=-- %a g Ns
80 that WC = -QN1P2g %3d@I B
For8 ~venoomprese~ ITp and D arecormtants~&re seleoted after detiermiration of the operating range 3=quirea. NACARM No. E9A28 25
The pressure ratio is given by the equaticm
*2 8 3s35 p2 l+qaa q- Jg cp,a Tl ( * > When @this amlyeis a two-stage omupreesor is used with the first stage driven at a variable speed, the value of K2 necessary to obtain a desired over-al3 pressure ratio across the ompreesore maybe fcundbythe followIngprocedure: %,1 = (l + 8 $=5 where the oonatant A takes intoaccount the diameter of the first-stage compressor, the speed of the primary DW&S? of the ooupling, the pressure coefficient, a& Jgop. Then,
Tl 0.283 -l+rlol T2 = 'lo,l tRP,l I > where T2 is the temperature of the air leaving the first stage,
Rp,2 = l+ +30535 ( > where B is a oclnertant that takes into amount the dieter of the eeoond-stage ~mpresam, its epeed, the pressure coeffioient, and Jgop. Now 3 Tl 0.283 -1 -x- (%,l > .
26 NACA RM No. E9A28 so that
This equatlm may be transposed into a quadratio equation in K? fkom whioh I6 nay easily be found. l Cc8npreesors in series. - When two ooanpressors are oormected. in series, the over-all efficiency is different from the stage effi- oiermies. Became oorqarieon of the performaneinthieEuldyBis is to be made tith that of reference 1, it is necessary to know the relation between stage aad over-all efficiency in order that the 0ver-d.l compressor efficiency in this analysis at an altitude of 20,000 feet may equal the ocmpmssor efficiency at 20,000 feet ,@v*n in referem 1.
The overall adiabatio effioiemy is given by the equation
T)a,o= 1 - Rp,$L263-1 + (S,20.283,1) j'lo,l (EJ-2)
(E13) ' RP,l ?I?,2 - %,o c HACA RM No. IEM28 27
APPEnDIxB
The mass flow through EL ccmergent nozzle tith cri&xCL flaw is
where W weight flow, lb/set A area, sq f% B gas constant, ft-lb/,(=) (%I if y = 1.34
R = 53.35
W = 75.35 A pe- ma F8 Thismsssflarmust;beequaltothieeuraoftheairflowthrough theburnerandthefuelflow. Thus
pm =?I 75.35 Ape 144 Rs Tm %- = l+%l y Jg so that
+7-;k7g ; $*l+qJ ( where e+ 28 NACA RM No. E9A28 but
2 =I Ii - (&) (O.ZlO)
80 t2tEat if Ts = 2260' R em (I+ qJ 0.5862 -Tm - 120.8 Rs R, >
A990 (1 + qJ2 + 82 0.7065 (1 + G) l&2-- l 100 e2 8 Tm' 8 1 0-w For fixed turbAne-nozzle-area operation, the value of turbine- nozzle area is fixed at that required for operation at an altitude of 20,000 feet at a eoavenge ratio of 1.0, a peak burner preeEnzre of 1600 pound6 per square inohabeolute, andaturbine-lnletpareesure of 2260° R. Thfs value of turb%zxe-nozzle area 8 was 0.001686 squazz foot per cmbio foot of burner volume per ogle per secmd. When a fixed-turbine-nozzle area is used in conjunction tith the reciprooating oompressor, it is necleasary that the operating oonditiona, for whioh the scavenge ratio determined by the reoip- roosting oompxssor equala the scavenge ratio determined by the turbine nozzle, be obtained by nmns of a gral;hical solution. Other graphic& solutimsare, of course, neceseary even if the turbine-nozzle acre& is nut fixed as there is no convenient expression re~ting~r-inletpaLessure,~r-e~ionratio,ehnd~~~ ratiotothelimiting oonditions of peakburner pressure andturbWe- lzitettempemture.
1. Tauechek, Max J., and Biermenn, Arnold E.: An myeie of a Piatc&Xype Gse-Generator Engine. WA M Ho. E7U0, 1948. 2. Foster, Hamgton H., SchFicht, F. Ralph, and Tauschek, Mar J.: Experiment&L Study of Loop-Scavenged Cacipression-Ignition Cylinder for Gas-Generator Use. NACA IM No. E8L30, 1949. NACA RM No. E9A28 29
3. Ginsburg, Ambrose, Creagh, John W. R., and Ritter, William IL: Performame Investigation of 8 Iarge Centrifugal Ccmpreseor fromanExperimntal Turbojet Engine, IVACAMBo.Ea, 1948. 4. Hersey, R. L., Eberhardt, J. E., ad. Hottel, H. C.: Thermo- dynamic Properbies oftheWorking FluidinInternal-C~stion Engines. SAE Jour. (Tram), vol. 39, no. 4, Cct. 1936, pp. 409-424. . 5. Alieon, N. If.: Fluid Tranemissiun of Power. SAE Jaw. (Tmns.), vol. 48, no. 1, Jan. 1941, pp. l-8.
.
. Two-stroke-cycle compression-ipnltlon engine Reduction Compressor, gear 7
.I
Flgum 1. -Dfagranmatic sketch of gas-generator engine used In analysis (reference 1).
, 8LO-t NACA RM No. E9A28
constant- Two-stroke-cycle pressure-ratio
(a) Constant-pressure-rrla comprsssor sith thlvttlad inlet.
Sscond- First- stags stage I constant- CoastslIt- Two-stroke-cycle
(b) Yultlsta&e mmtant-prsaaure-ratlo oonprsaaor with first stage driven by three-speed gsrr.
Second- Flrst- stags stage oonst.ant- aonatant- prssrura- prssaure- !l'wo-stmks-cycle ratio rrtkl oomprsss lon- canprasaor coxpmssor
(c) Multistage constant-pmsaura-ratlo comprassor with first stage driven by hydraulio slip coupling. Plgurs 2. Schematic diqgram of systems usad in analrsls.
. .
32 NACA RM No. E9A28
Two-stroke-cycle Turb lne aompresalon-
(d) Constant-volme single-stage dompreasor OF ounatant-volume conp~esaor with means of varying the volumetrlo capaoity.
Two-stroke-oyol Turbine oompreasion-
(e) Constant-volume ompreasor with throttled inlet.
First- stage Second-stage wnstant- constant- Two-stroke-oyole VOlUCN3 EL:~""- Turbine wmpreaaion- aomprsssor WDlpZW88OF
- (f) Multistage oompreaaor comprising oonstant-pressure-ratio first-stage compressor driven by hydraulic slip coupling Pollored by final-stage constant-voltme oompreaaor. Y Figure 2. - Conoluded. Sohematlo dlagfams of 8ystm8 used In malysls. . NACA Rh4 No. E9A28 33
60 I I Hi ,o / +I 60 . L / I I I / Et 5 I t t 5 . 2 40 $4 s :: Lo B
. a3 Jo 40 so 6oflo3 Altitude, ft Figure 3. - Compressor mqulrslasnta or ideal gps-gensratcr en&m. scmwlge ratlo. 1.0. 34 NACA RM No. E9A28
.08
$2 .06 -IS-22 .04 S-“1 sit .03 82 *93 i% .02 .Ol
D -.2m - - K - 4 ii: 0 82 p. 0
; 180 b-l g 2 160
a' 140 $ \ f: 120
Fj 100 . a B 80 :: ?tj *O
= 40
.40 I - Ideal gas-generator engfns - - Gap-gensrstpr engine r!th throttled r&irj compreseor driven et .96
2 k .32 si \ 5 . i! z .28 - 1 -IeI .24 0 10 20 30 40 -X2103 Altitude, ft Figure 4.- Comparison of perrormance of ideal gae-generator engine with that of gas-generator engine lncorporatlng throttled rotary coaprseeor driven at fixed gear retlo ard turbine having fixed-area nozzle. NACA RM No. E9A28 35 .
F .OS ak- 22c7 .04 S- 09 a';l .os 3% "3 .02 4.2 ul
2om
j Cl,,
o" . a -- Oas-generator engine rim rctary cmprssaor having rariablo-epsed gear drive .M and turbins having fixed- area nozele + $ .32 w :: s .m 20 30 40 5oiLos Altitude. it Fl@xre 6.- Comuarlson of psrPormance of ideal gas-generator engine 81th that ot gas-generator engine incorporating two-stage rotary compreaeor with first stege driven by three-apeed gear and turbine having fixed-area nozzle. 36 NACA RM No. E9A28 . - .-_. .06 . .OS .04 .03 .oe -01 P 2 -- _.-W IL& 2000 N- A- bp$ $d 0 0 B I I t I I t I ‘jc s a’ :: >c-l f \ 80 Fi \ ZI 60 ci \ 3 40 .32 .28 .I -+EJ7 I I .24 0 10 20 30 40 SO Altitude, ft Figure B.- Comparison of performance of ldsal gas-generator engine with that of gas-generator snglne lncorporatlng two-stage rotary compressor with ilrat stage driven by allp coupling and turblns having fixed-area nozzle. NACA RM No. E9A28 37 . . .06 4000 ifk! a00 co ~tL+a3 l-l0” 0 0 2 % 9 2 z ‘n-4;; 160 . [ za 80 2 9 * . 0 ‘,- - - --. l = 8, 2 .34 \ k \5 f: _-.-- m ---7-xI I\ : .30 x \ I I I I I- _---26 -- 0 10 20 30 40 AltUxde, tt Figure 7.- Comparison of performance or ideal gas-generator engine rith that of s-generator engine incarporating rixed-displacamnt pPston-type 4ompr4ssor and turbine f hod-are8 mszla. 38 NACA RM No. E9A28 .06 . .a’ .05 85 .04 *;a 04 et .03 fS . .02 “2 .Ol k 2ooo I pi - E N - p::: Z pi2 0 180 100 . . 140 E i,% 120 &L: 100 24 3s 80 9% .42 - Ideal gas-gsnemtar engIn t , - - Char-ume+at~-w &airia with ---throttled ~ ------fkxed-displace- _____ ---- \\ ment piston-type com- .38 pr44wr and turbine having fixed-area notzlo 0 t-+-H'. 5 rl .34 . :: p” .30 . .26 0 .lO 20 90 40 50 Altitude. It sigure 8.- Comparison of porformanoe of ideal mr-nmerator &glne with that ot gaa~gsnerator engine InoGrpoGating throttled fixed-dlmlaoement Dinton-tmm oommoasor and turbine having fixek-araa no&e. -- - NACA RM No. E9A28 l 39 .06 l .05 ;i 22 CI- .04 S- 00 l-4 .03 ;$ 27 .02 e m .Ol 2000 c ii . . .- s:, . . xx - pz 0 160 160 ;:: 22 . ;5$ a: , \I z:a loo I ! ! ! ik s> =I+ .36 B .34 k g \ 2 . :: .30 z -2s 0 20 30 40 Altitude, ft Figure S.- Comparison of perfomance of ideal gas-generator 0ngLne with that of gas-generator engine inaorporating vsrlable-displacement piston-type oompreasor and turbine having fixed-area nozzle. . 40 NACA RM No. E9A28 .06 .a’ .OS Fis*- .04 S- 00l-4 9% .03 qj .02 .01 moo ii a. I .- \, BE -- $5 -.-- 0 as-l aI 0 . - Ideal gas-generator - - Caa . 0 10 20 30 40 50X103 Altitude, i't . Figure lO.- Comparison of performance oi ideal gas-generator engine with that or gas-generator engine inoorporathg fixed-dlaplaaement compressor, a eupercharger driven by slip 0ouplLKlg, and turbine having fixed-area nozzle. NACA RM No. E9A28 41 Altitude ___ )I c t-l-l-i ---- ,,,oci(ft) 160 80 I I ml I 0 40 80 120 160 200 Crankshaft degrees, simple harmonic motion Figure ll.- Effect of altitude on indicator diagram of super- charged fixed-displacement piston-type compressor and turbine having fixed-area nozzle. 42 NACA RM No. E9A28 .06 PZ,c ii 2ooo xx2 ti4$1 PI 0 0 180 '; p”';I 160 cd a’ 140 $ 120 2 f loo :: 80 -- -_ a 2 60 2 =I3 5 * .38 -- + or and fixed-area f tor engine al .34 d compressor . t 2 .30 0 10 20 30 40 5OXlO’ Altitude, ft Figure 12.- Comparison of Derformanae of gas-generator englnn incorporating fixed-displacement piston-type compressor, superchar er driven by slip coupling , and fixed-area turbine nozzle wi &h performance of gae-generator engine having two- etage rotary compressor with first stage driven by slip coupling and turbine having fixed-area nozzle. 1 . 1070 .8 I I I - First stage -- Second stage IV 0 10 20 30 40 50 60f103 Altitude, ft Flgum 13.- Load coefficient Q/n at various altitudes relative to load coefficient Q/n at 20,000 feet for multIstage rotary compreteaor with first stage driven by hydraulic alip coupling and turbine having fixed-area nozzle. t NACA RM No. E9A28 .OB .05 .04 .03 .02 .Ol 2000 &1- rZ ; 120 2 j 160 d i 140 $ > 120 t-l e i =O" 80 .40 d . x:: .32 .28 0 10 20 30 40 5or10= Altitude. ft. Figure 14.- EPPsat oP Pixed- anti variable-area turbine noxrles on performmae 0P gas-generator engines incorporating tro- stage rotary aompresaor with Pirat stage driven by a thrse- speed 6SW. 45 NACA RM No. E9A28 .06 .05 i 62CL- .04 2; Olj $5 .03 $13 iz .02 .Ol k “+i 2000 $2 PZ$ rm> $L 0 Q) 180 % rl $ 160 2 . : k 80 I- Gas-generator engine with I - variable-ares turbine a nozzle; constant g 60 eoavenge ratio, 1.0 I -- Gas-Renerator ennine with 9 fixed-&ea tur6lne nozzle( I I I P 40 I .36 .32 .28 Altitude, it . Figure 15.- Effect of fixed- and variable-area turbine nozzles on performance of gas-generator engInea incorporating two- stage rotary aumpressor with first stage driven by slip uoupling. NACA RM No. E9A28 .lO m %g .06 $X 24 OK .04 tl2 22 .o!a 0 a6000 . 0 nozzle; constant scavengs ratio, 1.0 -- Qas-generator engine with fixed-area turbine nozzle \P 2 . 180 g z a 00 z 2 B r 0 .34 r,2 cp" ;$ .30 0 10 20 30 40 5oxlo3 Altitude. ft Figure 16.- Effect of fixed- and variable-area turbine nozzles on perfonmnce of gas-generator engines incorporating fixed- displaoement platoon-type compreasora. NACA RM No. E9A28 .06 .06 -4d 43 FL& CI- .04 a 0”0 s’;: .03 22 .02 B ELI -01 !zz ,O”y r:< t kft h 0 50 160 j 140 a i 120 x > 100 s-f . 1 8o il =O ; 40 2 3 20 .42 - Gas-generator engine with variable-area turbine nozzle; constant aoavenge ratio, 1.0 ? -- Gas- 2 .38 e f: - I I I :: -34 I I I I 2 1 I t I I I ‘==--t------ 0 10 20 30 40 5oxlo3 Al tituae , rt Figure 17. - Effect of fixad- and variable-area turbine ~1~188 on performance of gas-generator engines in- corporating throttled flxed-diaplacemant piaton-type oompressors. 48 NACA RM No. E9A28 a ‘;z a- *- 22 0 3% B5 & k 2 o’d 20”, rgs &0 a.+ 0 2 % 160 c e . 140 a x 120 \ fl . 100 4 80 : n 2 60 2 9 40 5i 20 Altltuds, Pt Figure 18. - Effsot of flxed- and variable-area turbine nozzles on performance of gas-gsnerator engines lnpor- porating variabls-displacement piston-type compressora. NACA !?h4 No. E9A28 49 .06 -i- .05 . sa 32 .04 a-00 25r( .03 "2 .oa .Ol 0 180 *; $ 160 l #j 140 P 2 120 l-8 i 100 \ \ \ \ \ El 80 . * \* \\ 2 60 \. zj 40 I t .40 eal gas-generator engine -- aas-generator engine with design altituda oi 40,000 rest .36 ---Gas-genaratoor engine with daalgn altitude or 20,000 feet .32 . .24 0 10 20 30 4.0 5oxLo3 Altitude, it Figure lQ.- Effect of design altitude on performance of gas- generator engines incorporating two-stage compressor with first stage driven by slip coupling and tcrblne having fixed-area nozzle. .