IMMUNE l E I E | ‘IHIHNHIE MW I — — WE «NM 1133‘ E. 26".: GP” o3v.3"‘1 oi}! ¢é&§:\ ‘fJEEAQCQCE {Us GE‘K SL333" “magma 3 K’aifiiag ”'43?“ la"!!! £235 Tim-sis far The [Manse (35 $3. 5. ffiSCii‘iEGIi" “in! '1: {:24 Lila-5E - w: . :9 l‘ at: ‘1' ’ ""'. 4‘? :93“ . .12 3531313523.? 33 A; shaft ._ 5'51'25'53 I THESIS -—MH_—._—.~_...__—._i, A. A, This is to certify that the thesis entitled THE EFFECT OF INTAKE AIR TEMPERATURES 0N SUPERCHARGE METHOD FUEL RATINGS presented by BERNARD ARTHUR JOHNSON has been accepted towards fulfillment of the requirements for MASTER or SCIENCE degree in MECHANICAL ENGINEERING flit—{4,141 OZ E. 6? _ LA 1/"1-9" Lg. M 7%Zg‘sz1'1 7 Major professor DateW 3!; lfi't. a“ 0-169 't qt. «NEH IL‘V‘ ' .7 l v 1 V'Y vfr ‘ V I 4 E“ \l—V—f‘a in“: 16 “If?"fn" E ' k F S 1“], {161; I‘ll” (' E. XE [T J W " mdl‘ f“? 'E‘f’ " " gr. 7" I'A-v' V! ‘5 3 l,t\ ‘ ‘. j '7', .‘ .=_,. E - , 5 E K 'I-' .4 1 1 4’ ." l E) Hr (. “w 1"l ~ - "A. E ' E I“ E' ‘ . , ‘9 l I ( f ' ‘ w ‘ 5‘!“ 1 \.—,"~ .\ »‘ xi" . V ‘ 1+ '~ " ' ‘ l - ‘ e an . *3 H A»: 1-3 ‘ '. * é a a ’ , ' a. t, 1.,4 ‘ ,_ A?“ 'r ' . V; ‘ rf if“ x th 7. 1 l‘ \ E ' r I.- ‘ ‘ ‘1 - \ "LEE \ , 1 2"", THE EFFECT OF INTEKE AIR TEMPERflTURES ON SUPERCHARGE METHOD FUEL RRIINGS By BERNARD ARTHUR JOHNSON A THESIS Submitted to the School of Graduate Studies of Kichigcn State College of Agriculture and Agplied Science in partial fulfillment of the requirements for the degree of “ASTER OF SCIENCE Department of Mechanical Engineering THESIS €ffi/KJ“$. ACKNOWLEDGMENT — The author wishes to take this opportunity to eXpress his sincere thanks to Dr. L. L. Otto, under whose kind guin- ance and unfailing interest this investigation was undertaken. The author also wishes to thank Mr. R. V. Kerley of Ethyl Corporation, Mr. Mr. R. M. Gooding of the Bureau of Mines, and Mr. J. M. Snell of Standard Oil Company for furnishing valuable information in connection with this investigation. 3751,5337 If“ B I: E IRIRUUUCIIUN APPARATUS PROCEDURE . DISCUSSION . SUMUIRI . . CRIRHS . L . APPENDIX Procedure for Running Knock Limited Mean Effective Pressure OF CONTENTS Versus Fuel—Air Curves . TABLES . . . LISI OF REFERENCES . . .g. 0 O N) CD N) (O (‘37 O3 INTRODUCTION An inportant requisite of an aircraft engine operating at high altitudes is that it use a minimum amount of air for each unit of energy it produces. This is necessary since the density of air decreases as the altitude increases, and the difference between the available air and the necessary air at that altitude must he made Up by the supercharger. Con- sequently, a greater amount of engine output must be diverted to the supercharger for operation at higher altitudes. The shaller the engine's ajpetite for air for a given output, the less energy will be lost to the SUpercharger. Some of the fsctors which hrve an influence on the energy- air relationship of an engine are engine Speed, manifold ores— sure, g'ade of fuel, intake air tenperature, snark advance, cylinder compression ratio and cylinder terperature. Nearly all of these are inter-relatei. It is the purpose of this paper to investigate the effect of intake air temperatures on the fuel properties rfich influ- ence the energy—air characteristics of the engine. The fuel progerties that will be consirered are octzne ratio? and sen— m sitivity. .ensitivity indicates the tendency of a fuel to lose octane nunher as the engine conuitions get nore severe. A considerable amount of work is now being carried on by the American Society of Testing Materials and the National Advisory Committee on Aeronautics on the "effect of intake air temperatures on the octane rating of aviation fuels," which is a closely related subject, but very little of this information has been published. It was the intention of the investigation described in this thesis to assist the efforts of these agencies by determining the effects of intake air temperature variations Upon the knock rating produced by a SUpercharge fuel testing engine. . APPRRATUS All tests were conducted with the aid of a modified F~4 CFR "Supercharge Method" testing unit. This unit consists of 'a standard CFR engine with an air induction system which per- mits Operation over a wide range of inlet pressures. The engine is Operated at a constant compression ratio of seven to one, and at a constant Speed of 1800 RPM. Spark ad- vance is set at 45 degrees before tOp dead center. an evaporative cooling system closely controls engine jacket temperature. The boiling point of the coolant, a mix- ture of ethylene glycol and water, is fixed by varying the con- centration of the solution. The coolant is maintained at the boiling temperature. The vapors given off are passed into a water~cooled reflux.condenser, and, having been condensed, drop back into the system. The induction system consists of-a series of surge tanks and pressure regulators. air, under pressure, enters the in- duction system through a filter which eliminates entrained solids, and then passes through an automatic pressure~regulating valve before entering the air flowmeter. The flowmeter con- sists of a sharp-edged orifice in a flange mounting between two surge tanks with a water manometer indicating the pres- sure differential. The manometer is calibrated in minutes per 1/4 pound of air, which makes the calculation of fuel- air ratio a very simple matter. Air leaving the flowmeter passes through another pressure-regulating valve before it enters the engine. The two surge tanks, one on each side of the flowmeter, are used to reduce pulsations to a minimum. A third surge tank is used between the air inlet to the engine and the pressure-regulating valve which controls the manifold pressures under which the engine operates. To this surge tank is connected a lOO~inch mercury manometer which measures the manifold or boost pressure. Two thermostatically controlled heaters preheat the air to the correct temperature before it enters the engine. The power absorption system used with this engine has been changed from that used by the regulation F-4 testing unit. The regulation F-4 CFR testing unit employs a twenty-five horse- power alternating current synchronous induction generator for motoring and loading. In place of this, a fifteen horsepower direct current dynamometer (Fig. 1) was employed. A slide wire rheostat, mounted on the control panel (Fig. 5), was connected in series with the field circuit so that the load could be varied smoothly as the fuel and the manifold pressure were varied. The exhaust system employed by the regulation F-4 CFR testing unit consists of a flexible water-cooled hose leading v\\ \\ ».\\\\‘\\ ‘\_\\\\‘\ Figure l F-4 unit showing D. C. Dynamometer - "\_-\\: '- ‘.,\.‘¥"\—\ \,'\ “\x“\-\_\o\‘\\.\,\\x\ ‘\\ \\’—\'~ Figure 2 F-4 unit showing the exhaust surge tank ' \ I ‘HHH \ h |U“\“ ‘Y ‘-\-‘\“r-\"~\"‘\‘¥x\\v “'\‘—\.\\“\\ ‘\_,\\\\ “ *\\7\\\_s. Figure 8 Control panel and fuel weighing apparatus from the engine exhaust ports to a double-wall surge tank. Water jets are placed in the entrance to the surge tank and water is removed from the bottom of the tank. In this ex- periment, a single-wall surge tank (Fig. 2) meeting the dimensional requirements of the regulation tank were employed and no water injection was used. Exhaust back pressure was held to one-half inch of mercury. The fuel weighing apparatus consisted of a balance and weights, a fuel container and stOp watch. No allowance was made for the bouyancy of the inlet and outlet tubes in the fuel container. Complete details as to the description, Operation and maintenance of'a regulation F~4 CFR testing unit are given in the “ASTM Manual of Engine Test Methods for Rating Fuels", 1948. PROCEDURE The F-4 "Supercharge Method" testing unit was designed primarily to simulate engine conditions at take off or at other situations requiring rich fuelaair ratios. Since the energyaair relationship is not very important at these con- ditions, the F-4 unit is not the ideal apparatus for these tests. The American Society for Testing Materials employs a F-5 unit for lean fuel-air ratio tests. However, the lean end of the fueloair ratio range of the F-4 should at least show the trend of the energy-air relationship with changing intake air temperatures. T The following four objectives were sought in this ex— periment: first, to determine the percent of energy loss due to increasing air temperatures; second, to determine the rela- tionship between intake temperature and fuel sensitivity; third, to investigate the effect of intake air temperatures and fuel sensitivity on the energy-air relationship of the engine in reSpect to fuel it consumes; and, fourth, to investigate the accuracy of the test by determining the relationship between the recorded intake temperatures and the actual intake tempera- tures. 10 The first three objectives were investigated 6Xp6r1~ mentally by running five knock-limited mean effective pres— sure versus fueleair ratio curves over a temperature range extending from 150 degrees to 500 degrees Fahrenheit. In- dicated mean effective pressure, weight of fuel and air con- sumed, and fuel-air ratio were recorded. The exact procedure used to run these curves is given in the Appendix. To determine the effect of fuel sensitivity, the pre- ceding curves were run fon.both, an insensitive fuel and a sensitive fuel. A reference fuel made up of 95 percent iso- octane-and 5 percent normal-heptane was used for the insen- sitive fuel and a commercial aviation gas with-a 91/96 octane rating was used as the sensitive fuel. The fact that the latter fuel is sensitive is indicated by its double rating. 91 indicates its lean mixture rating as made by the F-8, while 96 indicates its rich mixture rating as made by the F—4 used in this eXperiment. The reference fuel actually has a 95/95 rating. To determine the drop in temperature in the inlet pass- age between the surge tank and the engine, two thermocouples were placed in the inlet elbow as shown in Figure 4. The temperatures at these points were determined for two reasons: first, to see how the temperature drOp varied with air flow rate, and, second, to determine the effect, if-any,which ll Inlet elbow showing positions of thermocouples Figure 4 l2 vaporization of the fuel has on cooling the charge. The tem- peratures were recorded, both, with the engine running, and with the engine being motored. 13 DISCUSSION One of the early obstacles in fuel testing was the in- consistency of ratings made by different testing machines. To correct this situation, testing units like the F-4 were develOped and standardized so that different Operators in different parts of the country could all give the same rating for the same fuel. Along with the standardization of testing equipment, certain fuels possessing desirable characteristics were also standardized and called reference fuels. For the F-4 testing unit, a series of reference curves of knock limited indicated mean effective pressure versus fuel-air ratio were run using these reference fuels and standardized into a reference chart. Thus, by running a certain reference fuel in the testing unit and comparing the resultant curve with those in the reference chart, it can be seen whether that particular testing unit is rating fuels prOperly. If not, the unit must be checked and the difficulty remedied. It was never possible to duplicate these reference fuel curves with the F-4 unit used in this investigation. A consider- able amount of time was Spent investigating the possible rea- sons for this discrepancy. PeOple with a great deal of ex— perience in this field were contacted and their suggestions 14 followed, but an answer to the difficulty was not found. However, it appeared that the results were always in error in the same direction and, therefore, this should not limit the ability of the engine to make comparison of different fuels with sufficient accuracy for this investigation. The series of curves in Figures 5, 6, and 7 illustrate how the engine knock-limited power drOps off as the inlet gtemperatures are increased._ The knock-limited power at the rich end of the mixture range drOps off nearly inversely to the absolute temperature rise,while on the lean end the power drops off almost inversely to the square of the temperature rise.. Another important characteristic of these series is that the maximum points all shift toward the right or toward richer fuel—air ratios as the intake temperature is increased. Figures 5 and 7 show a comparison between sensitive and insensitive fuel characteristics. The lepes of the mean effective pressure curves for the sensitive fuel become steeper at higher inlet temperatures, while the lepes for the insen- sitive fuel remain relatively constant. Thus, the sensitive fuel has lost a much more power on the lean side than has the insensitive or reference fuel. 0n the other hand, close scrutiny of the curves shows that the sensitive fuel has not lost as much of its power on the rich side of the mixture range. Two conclusions can be drawn from these curves. First, 15 intake temperature has a profound effect on fuel sensitivity, and, second, fuel sensitivity is only a factor at lean fuel- air ratios. Figures 10 and ll show the effect of intake tenperatures on the energy-air characteristics of the engine when Operating with the two different fuels. In Figure 10 the energy per weight of air decreases as the inlet temperatures increase, and at rich fuel-air ratios the energy per unit weight of air increases as the intake temperatures increase. For the 91/96 octane sensitive fuel in Figure ll, the Opposite is true. Here the energy per weight of air increases at lean fuel-air ratios and decreases at rich fuel-air ratios as the intake temperature is increased. For both fuels at the fuel-air ratio of .100, the amount of energy per weight of air remains nearly constant. Obviously, from the preceding curves, the energy-air characteristics are very dependent on the sensitivity of the fuel in a severe engine or an engine that heats excessively during Operation. The tendency of the sensitive fuel to make better use of its air at rich fuel-air ratios is probably due to the fact that the sensitive fuel actually loses less power at rich mixtures than at lean mixtures. In connection with fuel sensitivity, it might be pre- sumed by some peOple that since there is not much difference 16 between the octane ratings at rich and lean mixtures (vi and 96; this fuel is not very sensitive. This is not true, however, as the octane rating is not an indication of knock-limited power. If it is desired to compare the ratings from a stand- point of power, which is the only logical way to do it, the performance number must be used. The actual performance num- bers of this fuel would be 75/90. Table VI indicates the amount of temperature drop in the passage between the surge tank and the engine at different air flow rates. At 800 degrees there is a sizeable drOp of 20 degrees. However, on an absolute temperature basis, this drop only amounts to two percent. At 180 degrees, the temperature drOp is negligible. Figure 12 shows the amount of temperature drop, when the engine is running, for five temperature ranges from 180 degrees to 300 degrees. Once again the drops only amounts to a few degrees. Figure 12 does show, however, that the heat of the engine eliminates any cooling effects that weflipresent when the engine was being motored. From these curves it is logical to assume that the temperatures recorded at the final surge tanks are sufficiently accurate for the temperatures up to 300 degrees Fahrenheit. 17 SUMMARY The following conclusions were obtained from this investigation: 1. Knock limited power varies nearly inversely to the absolute temperature rise at rich fuel-air ratios, and inversely to the square of the temperature rise at lean fuel-air ratios. 2. The maximum peaks of the indicated mean effective pressure curves move toward richer fuel-air ratios at higher intake air temperatures. 3. Fuel sensitivity is only a serious factor at lean fuel-air ratios. 4. The energyeair relationship of an engine is greatly effected by the sensitivity of the fuel. 5. The recorded intake air temperatures for the F-4 unit are accurate to within two percent for intake tempera— tures up to 500 degrees Fahrenheit. FUEL-AIR 4.0 ml. 3.0 ml. 2.0 ml. 1.25 ml. 0.5 ml. 100 RATIO 0.13 IMEP. 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TI II > > y w h p w . 0 8 2 300 {a .n «Emdofiim :5 mos. 22 3552: 02:3» :8 >588 525.: 0 0 2 .Z .233: ”25:: 2:: 9.222 8 0.08 0.09 0.10 0.11 0.12 0.13 FUEL - AIR RATIO 0.07 0.06 ‘iDD____-_ Figure 7 09mm _ __ J01 FRAMEWORK N0.-_______._____ OATE___.._______._ 4') C;______.____ DATA SHEET N0.-. Pounds of air per minute 21 Figure 8 WEIGHT OF LIB VERSUS F'EL~AIR RATIO Engine running with 91 octofie Commercial Fuel 1.40 4_flf_.,_oA__ W / / 220 F / . O / 1.00///// // 2§9/F//// /// / 3000? /7* .60 .20 .085 .095 .105 .115 Fuel~a1r ratio 22 Figure 9 WEIGHT OF AIR VERSUS FUEL AIR RATIO Engine Junning with 95 Octane reference fuel 1.40 / / / IZOOF / / %/ , 00 s: ...—q a p (D Q. h // ‘H r w (H // o ’//’// a; ..Q +4 .60 .20 .085 .095 .105 Fueldair ratio 5 Ft. “'2 CU Figure 10 WORK PER WEIGHP OF AIR VERSUS IEMPERIURE 91 octan e commerci al aviation fuel lbs. work per lb. air x10 4.0 .090 \ \085 F/A .100 \b\ M x j o lob/— .110// z .o 2.0 100 200 300 Inlet temperature . of air x105 .L lbs. work per lb Ft. WORK PER WEIGHT OF AIR VERSUS 24 Figure 11 TEMPERATURE 95 octa be referen ce fuel 4.0 .085 F/A ..————" A007 , 3.0 NTIIQ\\ 2.0 100 200 300 Inlet temperature Inlet temperature 25 Figure 12 Lbs. of air per min. TEMPERATURE DROP IN INLET PISSAG -— Position 1 Position 2 300 ‘1"==::; ______ 4__4ju—— 200 __, 4.5;sr l4_.:ib”' 100 .6 .8 1.0 1.2 1.4 JXPPENDIX PROCEDURE FOR RUNNING KNOCK LIMITED MERN EFFECTIVE PRESSURE VERSUS FUEL-AIR RATIO CURVES . After the engine has been started-and allowed to warm up sufficiently, the following testing conditions must be adhered to: Oil temperature Oil pressure Orifice air pressure Orifice air temperature Surge tank air temperature Coolant temperature Spark advance Valve clearance Exhaust cooling temperature 165° i 5° F 60-3 5 psi gage 54.4 1' 0.5 psi absolu 9 125° 1 5 F 225° 1' 5° F 575° r 50 F 45 t 1 deg btdc 0.008 intake, 0.010 exhaust 200° F The following procedure, recommended by the American Society for Testing Materials is used in rating fuel samples: 1. does not produce knocking so that the previous fuel lines. 2. effective pressure on the The fuel control dynamometer scale. The engine is Operated at a manifold pressure which for a period of about 10 minutes »can be purged from the pumps and is adjusted for maximum brake mean If knock is present, the manifold pressure is reduced until the knock disappears, and then the fuel control is readjusted again for maximum brake mean effective pressure. E. Manifold pressure is gradually increased until standard knock intensity is obtained. Standard knock intensity is the least knock that the Operator can definite- ly and repeatedly recognize by ear. The engine is then allow— ed to reach equilibrium. Minor adjustments are made at this time to insure that the engine is running under the testing Specifications listed previously. After this period, if the knock intensity has changed, the manifold pressure is adjusted until standard knock intensity is regained. 4. The following readings are then recorded: brake mean effective pressure, manifold pressure, oil pressure, air flow, and the temperatures of the inlet air, orifice air, water and oil. 5. Fuel consumption is then measured by recording the time for 1/4 pound of fuel. Since the air flow is calibrated in minutes per 1/4 pound, the fuel-air ratio can be found by merely dividing the recorded value for air flow by the recorded value for fuel consumption. 6. The fuel is then shut off and the engine is motored by the dynamometer at 1800 RPE. The friction mean effective pressure is then recorded from the dynamometer scale. This reading must be taken withina period of 10 seconds after the fuel has been shut off. The fuel and dynamometer controls are then changed back to their previous positions. 7. The indicated mean effective pressure, which is the sum of the brake and friction mean effective pressures, is then plotted on the reference fuel chart at the corres- ponding fuel-air ratio. This is the first point for the knock limited power curve and should be on the lean side of the fuel-air ratio range. 8. The fuel control is adjusted for more fuel and the manifold pressure is increased until the engine begins to knock. The manifold pressure is then decreased slowly until the knock disappears. The fuel control is then ad- justed for maximum brake mean effective pressure on the dynamometer scale. The remaining steps in the procedure are identical with those mentioned above. The value for the indicated mean effective pressure is then plotted on the reference chart for this second fuel-air ratio. At least five points over the fuel—air ratio range ex- tending from .080 to .120 are obtained and a smooth curve is drawn through these points. 29 era med OQHH. mba mm emH HmH. meH. b.mm «ea mvH owoa. mwa w HMH mbH. ewfl. e.mw mba ova wwoa. me em QWH mmH. mma. 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Had an mea ma.a mea. 0.0a mm wHH umofi. , mvH mm mwa mm.H mvH. @.mw NWH vHH mama. wvH vm mMH mm.H Hma. o.vw wma vHH wmwo. ova vm Hma vm.m omH. v.mm ma vHH Ummo. wmfi vw mmfi O¢.w mmfi. m.mm m oowH mnoumhmoawe uchH m .momt H .mom Hoom pfifi .mm .:H Bopam uchH oflpwm mmSH mmzm mmam .QH mm.o whomwmnm pwmwsogmthSme Afiqnaoom you mmpocfis naomaam: mmma “H nonmS "mama Hash monogamom semanom .m “Houmnomo mcmpoo mm “Hash mommmg mommmommmsm Semq mom Hmmmm mafia >H mqmda 33 lit :1: ovHH. mwfi vw moa mw.H omH. ¢.®m it: :1: OMOH. me vw HOH oo.w wow. m.mw at: 1:: ommo. mma mm mm mm.w mam. w.ww 1:: run oomo. HOH ow Hm em.m mow. ©.©w m ooow whopmnmmama poHcH m.mom ya .moa Hess ham .mm .eH sopam uchH ofipmm QHSH mmam mmmm .QH mm.o whommoam um.mosopmpmoSoa nHmIHmom pom mmuqus oaomemfi bl ‘ll ‘ 11'. mama .H seems “memo GOmQSOH .m uHOQmpomo Hmom oodmmmmmm mcmuoo mm oomemfl mommmommmam fiamfi mom ammmm flmga > mamas “Hmsm Unit being motored by dynamometer 54 TABLE VI TEMPERATURE DROP IN INLET PASSAGE Operator: Johnson. Manifold pressure Airflow Temperature drOp F0 In. Hg. Min. per g lb. Pos. 1 Pos. 2 Inlet temperature 1800F 27.2 .252 216 214 54.5 .192 218 214 57.9 .172 218 215 40.9 .156 22 215 45.6 .146 219 215 47.4 .155 22 216 50.5 .127 224 219 54.9 .116 22 220 55.6 .108 224 225 Inlet temperature 5000F 27.5 .275 290 279 55.8 .220 295 281 58.0 .192 294 285 42.5 .175 295 286 46.0 .157 296 286 50.0 .148 500 291 TABLE VII EFFECT OF INLET TEMPERATURE ON IMEP A Temperature 150 180 220 260 500 Fuel-air ratio Using 96 Octane Commerical fuel .085 156 125 108 112 80 .090 164 156 125 116 95 .095 169 147 156 127 105 .100 175 157 147 155 115 .105 175 165. 157 142 125 .110 176 170 164 148 151 .115 175 172 166 155 158 Using Iso-octane, heptane .085 - 160 ' 126 110 .090 168 128 119 .095 175 138 127 .100 178 147 155 .105 180 155 158 .110 181 160 142 M 01 LIST OF REFERENCES Dubois and Cronstedt. High Output in Aircraft Engines. SAE Journal. June, 1957. Ethyl Corporation. Aviation Fuels And Their Effect on Engine Performance. 1951 Heron, S. D. Fuel Sensivity and Engine Severity in Aircraft Engines. SAE Journal. September, 1946. Wheeler and Lovell. Fuels and Engines. STE Journal. August, 1947. .ROOM. USE ONLY .6!“ MICHIGAN STATE UNIV RSITY L BRARIES II I" lie I“ ||1| i II? II 0 3047 0508 3 1293