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TRANSCRIPT
P.M No. E8B06
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NACAI
RESEARCH MEMORANDUM
CORRELATION OF CYLINDER-HEAD TEMPERATURES OF A
MULTICYLINDER, LIQUID-COOLED ENGINE
OF 1710-CUBIC-INCH DISPLACEMENT
By Bruce T. Lundin, John H. Povolny, and Louis J. Chelko
Flight Propulsion Research Laboratory Cleveland, Ohio
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
WASHINGTON August 31, 1948
NPICA RM No. E8B06
NATIONAL ADVISORY COMMiTTEE FOR AERONAUTICS
REARCH, M4ORAJM
CORRELATION OF CYLINDER-HEAD TEERATUR QF A
MULTICUINDER, LIQUID-COOLED ENGINE
OF 1710-CUBIC -INCH DIS24ENT
By Bruce T. Lundln, John H. Povolny, and Louis J. Chelko
Data obtained from an extensive investigation of the cooling characteristics of four muitloylinder, liquid-cooled engines have been analyzed and a correlation obtained between the cylinder-head temperatures and the primary engine and coolant variables. The method of correlation was previously developed by the NACA from an analysis of the cooling processes involved in a liquid-cooled-engine cylinder and is based on the theory of nonboiling, forced-convection heat transfer. The present correlation, which covers engine power outputs up to 1860 brake horsepower, coolant flow rates from 50 to 320 gallons per minute, and coolants composed of ethylene glycol - water mixtures varying in composition from 100-percent water to 97-percent ethylene glycol and 3-percent water, included ranges of engine speed, manifold pressure, carburetor-air temperature, fuel-air ratio, exhaust-gas pressure, ignition timing, and various coolant temperatures. The effect on engine 'cooling of scale formation on the coolant passages of the engine and of boiling of the coolant under various operating con-ditions is also discussed.
The results of this analysis indicated thatthe correlation method is applicable to inulticylinder, liquid-cooled engines of the type investigated and permits the prediction of the cylinder-head temperature between the exhaust valves within approximately ±120 F for any operating condition within the range of the 'investigation.
INTRODUCTION
An investigation of the cooling characteristics of recipro-cating aircraft engines is of importance in order to insure sat-isfactory engine 'Performance at extreme conditions of operation.
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NACA EM No. E8B06
A considerable amount of data on the cooling characteristics of various air-cooled engines have been published by various inves-tigators but little data have been published on the cooling char-acteristics of liquid-cooled, engines.
An extensive research program to determine the cooling char-acteristics of liquid-cooled engines was therefore instituted at the N&CA•Cleveland laboratory in 1943. The initial phase of this program consisted of an investigation conducted on a single-cylinder engine to provide data for a fundamental study of the heat-transfer processes involved. The final results of this investigation are reported in reference 1 in which an analysis, based on the theory of nonboiling forced-convection heat transfer, was made of the cooling processes in a liquid-cooled engine. This analysià resulted in a semiempirical method, similar to that pre-sented in reference 2 for air-cooled engines, of correlating the cylinder-head, temperatures with the primary engine and coolant variables and this method was successfully applied to the data.
Following the investigation on the single-cylinder engine (reference 1), a comprehensive Investigation of the cooling char-acteristiçs of a multicylinder engine of 1710-cubic-inch displace-ment was conducted. The primary data obtained in this Investiga-tion are presented in reference 3, which presents plots of the cylinder temperatures and the coolant heat rejection against the basic engine and the coolant variables. In order to determine the applicability of the correlation method of reference 1 to a multi-cylinder engine, this method was employed in slightly modified form to correlate the cylinder-head temperature data of reference 3, and the results are presented herein. In reference 4, a variation of this correlation method is used to. correlate the coolant heat rejection data of reference 3 with the basic engine and coolant parameters.
The data used in the correlation presented in this report cover wide ranges of engine and coolant conditions including engine power outputs up to 1860 brake horsdpower, coolant flows from 50 to 320 gallons per minute, and coolants composed of ethylene glycol - water mixtures ranging in composition from 100-percent-water to 97-percent ethylene glycol and 3-percent water.
APPARATUS AND PROCEIXJRE
The investigation of reference 3, which provided the data for this analysis, was conducted on a dynamometer stand. The data used In the analysis were obtained from four V-1710 engines
NACA EM No. E8B06
which are desiiated engines A, B, C, and D in reference 3 and herein. All these engines are standard production models; engine B was equipped with an aftercooler for part of the investigation. These engine models are 12-cylinder ,, liquid-cooled, V-type engines with a displacement of 1710 cubic inches, a 5.5-inch bore, and a 6.0-inch stroke. The compression ratio is 6.65 and the engines are fitted with single-stage gear-driven superchargers having a gear ratio of 9.6:1 and an impeller diameter of 9.5 inches. 'The stand-ard 1iition system is timed to fire the intake spark plugs 28° B.T.C. and the exhaust spark plugs 340 B.T.C. The valve over-lap extends over a period of time equivalent to 74 0 rotation of the crankshaft.
The cylinder-heed temperatures were measured by iron-conatantan thermocouples Installed in each cylinder between the exhaust valves, between the intake valves, and in the exhaust spark-plug boss at the locations shown in figure 1. A schematic diagram of the coolant system is shown In figure 2; further details of the Instrumentation and a description of the general setup and auxiliary equipment are given In reference 3.
A summary of the engine and coolant conditions covered by the Investigation is presented In table I. The tests on engine A covered typical engine operating conditions varying from cruise to take-off power and included data for several coolant flows and temperatures and a range of engine coolant-outlet pressures from 10 to 30 pounds per square Inch gage. The effects of coolant tem-perature and engine power on the cylinder temperatures and coolant heat rejection were further determined In the part of the investiga-tion conducted on engine B. Tests in which an aftercooler..•vaa mounted on this engine were also made to determine the effects of varying the charge flow, the manifold temperature, the fuel-air ratio, and the àftercoollng conditions on engine cooling. The part of the investigation on engines C and D was conducted to extend the range of this correlation and to provide data essential to the correlation that were not obtained on the other two engines.
C0RR1ATION MODS
Symbols
The following symbols are used in the correlation:
B1 . . . B5 constants
0 specific heat of coolant, (Btu)/(lb)(°F)
4 N&CA RM No. EBB06
specific heat ' air at constant pressure, (Btu) /(1b) (°r)
• acceleration due to gravity, 32.2 (ft)I(aec2)
J mechanical equivalent of heat, 778 (ft-lb)/(Btu)
k thermal conductivity of coolant, (Btu)/(eec) (sq ft) (OF/ft)
M. n, a exponents
N engine speed, (rim)
Pr Prandtl number of coolant,
T0 carburetor inlet-air temperature, (°P)
T effective cylinder-gas temperature, (SF)
Th average cylinder-head temperature, (°F)
T 2 average coolant temperature, (°i)
Tm dry inlet-manifold temperature, (°F)
U supercharger impeller tip speed, (ft)/(sec)
WC engine charge flow (air plus fuel), (lb)/(sec)
coolant flow, (lb)/(sec)
Z factor that accounts for temperature drop through cylinder head
absolute viscosity of coolant, (lb)/(ft)(sec)
Correlation Equation
One form of the equation developed in reference 1 for cor-relating the cylinder temperature with the primary engine and coolant conditions is
NACA RM No. EBB06 5
(Th T Z 1)m (1)
where T Is a function of fuel-air ratio, Inlet-mrmifold tempera-
ture, ignition timing, and exhaust pressure, k, , and Pr are functions of the coolant composition and temperature, and Z is a factor that accounts for the temperature drop through the cylin-der head.
In equation (1), the coolant-flow factor Is the sepa-
rated variable, the effect of charge flow being Incorporated with the temperature parameter. It may be desirable in many cases, however, to separate out the effect of charge flow. By rearrange-ment of equation (1), the following alternative form is obtained In which the charge flow is the separated variable:
fTg - Th\ [(B1\ $.Lin + z] = W,
-n' (2) h T) [ ( )
The constant B1, the factor Z, and the exponents in, n, and 5 are determined from the test results and the details of their evaluation are given later in this report. The siiificance of other factors appearing in the correlation equation or used in the analysis Is discussed in the following section. When these factors are evaluated, the relations among Th and the various operating conditions will be completely defined by equation (1) or (2), and these equations will then serve to correlate and per-mit the prediction of the cylinder-head temperature for any engine and coolant operating conditions.
If modes of heat transfer other than normal forced convection are predominant, or if variables other than those contained in the correlation equation have an effect on the cylinder temperatures, the data may be expected to depart from a satisfactory correlation. Two such factors that may be encountered In engine operation are boiling of the coolant and scale build-up on the coolant passages. The effects of these two factors are illustrated in figures to be presented subsequently.
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NACA RM No.. E8B06
Significance of Factors
Cylinder temperature Th. - The average of the temperatures
measured between the exhaust valves for the 12 cylinders is used for the cylinder temperature Th In this analysis. This tempera-ture location was chosen because it Is the most widely used tern- - perature for this engine and, being in the hottest region of the cylinder head, may be considered. Indicative of critical cooling conditions. Although an average cylinder-head, temperature Is Indicated In the derivation of the equation and is used In the correlation presented in reference 1 a satisfactory correlation would be expected for any single temperature location. This. possibility of satisfactorily correlating the temperature of any Iodation Is a result of the linear relation (reference 3) that exists between temperatures at various locations In the cylinder head.
In order to permit an evaluation of the maximum cylinder-head temperature obtained for any operating condition, the relation between the average temperature for the 12 cylinders and the tern-, perature of the hottest cylinder Is presented.
Effective cylinder-gas temperature Tg• - The effective
cylinder-gas temperature T Is the gas temperature effective In transferring heat fran the cylinder gases to the cylinders, and, as previously Indicated., Is considered a function of the fuel-air ratio, inlet-manifold temperature, ignition timing, and exhaust pressure. The value Of T for the various engine conditions is determined fran tests described and illustrated subsequently.
Dry Inlet-manifold temperature TM. - The true Inlet-manifold temperature in a conventional multicylind.er engine is difficult to measure because of the presence Of unevaporated fuel in the charge mixture. For cooling correlations, the expedient Of using a cal-culated dry inlet-manifold temperature Instead of the measured manifold temperature is adopted. This dry Inlet-manifold, tempera-ture Is defined as the sum of the air temperature at the carburetor inlet and the calculated temperature rise Of the air incurred in passing through the supercharger. This temperature rise was cal-cülated on the assumption that there was no fuel vaporization. By assuming a value of 0.96 for the ,slip factor, which is the ratio of the pressure coefficient to the adiabatic efflcienoyof the super-charger, the dry inlet-manifold temperature Tm may be written as
NI41A RM No. E8B06 7
0.96 U2 Tm=Tc+ Jgc (3)
For the single-stage engines used., this relation reduces to
f
çTm = Pc + 25.28 N i000) (4)
For the tests of the engine fitted with the aftercooler, the temperature drop of the charge mixture incurred in passing through the aftercooler was calculated from the heat rejected to the after-cooler coolant and subtracted from the manifold temperature deter-mined fran equation (4).
Charge flow W. and fuel-air ratio. - The value of charge
flow We was taken as the total charge flow (air plus fuel) to the engine, although similar correlations may also be made on the basis of the air flow alone. The fuel-air ratio used was the mean fuel-air ratio to all cylinders as obtained from the total air and fuel flows.
Coolant flow W1 and coolant temperature P2 . - The coolant flow W2 was, for simplicity, taken as the total coolant flow to
both cylinder banks. Although the construction of the coolant passages in the engine is such that the flow varies considerably from cylinder to cylinder, it is shown In reference 3 that changes in the total flow effect proportional, changes in the flow over any one cylinder. The coolant temperature T 1 was taken as the average of the inlet and outlet temperatures of both cylinder banks.
Physical properties of coolants. - The physical properties of the coolants (specific heat c, absolute viscosity Li thermal conductivity Ic, and therefore the Prandtl number Pr were evaluated at the average coolant temperature P 2 . The values used are presented in convenient curve form In reference 1.
EVALUATION OF FACTORS
Erfective Cylinder-Gas Temperature Pg
The method used to evaluate Tg, which has been successfully applied to the correlation of cooling data obtained for a large
8 NACA RM No. E8B06
number of air-cooled engines and the liquid-cooled engine or refer-ence 1, constitutes first the establishment of a reference value of Tg for a given set of operating conditions and then the deter-
mination of the variation of T with each of the pertinent engine
conditions. On the basis of previous correlation work, a reference value or 11500 F for T8 was chosen for a fuel-air ratio of 0.080,
an inlet-manifold temperature of 800 F, standard ignition timing (approximately maximum power setting), and an exhaust pressure of 30 inches of mercury absolute. Investigation has shown that the correlation Is insensitive to changes in the magnitude of this reference value of Tg; it is important, however, that its varia-
tion with engine conditions be accurately determined..
The variation of T with fuel-air ratio, manifold tempera-
ture, ignition timing, and exhaust pressure was determined from the tests in which these factors were independently varied while hold-ing all other engine and coolant conditions constant. For such conditions, correlation equation (1) reduces to
T-T1=
T8 Thconstant (5)
-
This constant is evaluated from the cylinder-head and coolant-temperature data at the reference operating conditions for which the value of T6 has already been established. The value of. T
for other than the reference value of the aforementioned variables is then calculated from the value of the constant and the coolant and cylinder-head temperatures obtained at the operating conditions in question. The engine and coolant conditions for which each of these tests was conducted are listed under each pertinent variable in table I.
Variation of Tg with fuel-air ratio. - The variation of Tg
with fuel-air ratio is shown in figure 3. The values of T pre-sented have been corrected to a dry inlet-manifold. temperature of 800 F in accordance with a relation between the manifold tempera-ture and T that will be subsequently discussed. A maximum
value 'of T is reached at a fuel-air ratio of about 0.067, which is approximately equal to the fuel-air ratio for the stoichiometric mixture. Data obtained from three different engines, one of which was fitted with an aftercooler, are included in figure 3 and close agreement among the three is noted. The variations obtained for both the single-cylinder engine of reference 1 and the air-cooled
NACA RM No. EBB06 9
engine of reference 5 are also shown in this figure. The values of T8 for the single-cylinder engine are seen to be somewhat
lower than those for the multicylind.er engines of the present investigation, particularly in. the rich region, but close agreement between the multicylinder liquid-cooled and. air-cooled engines is evident.
Variation of T8 with dry inlet-manifold temperature TM. - The variation of T with the calculated dry Inlet-manifold tem-
perature, T, Is shown In figure 4. The data, which are presented
for three engines and various engine operating conditions, have been adjusted to a fuel-air ratio of 0.080 in accordance with the• relation between T and the fuel-air ratio that is presented In
figure 3. As indicated in equation (4), the inlet-manifold tempera-ture may be varied by changing either the carburetor inlet-air tem-perature or the engine speed.. Data obtained from tests wherein each of these quantities was independently varied are presented (fig. 4) and both sets of data fall on a common curve.
An average change In T of about 0.25 0 F per degree Fahrenheit change in Tm is indicated and correction of T8 to
other than 800 F manifold temperature is therefore made In accord-ance with the relation
AT = 0.25 (Tm - 80)
(6)
Variation of T with exhaust pressure. - The effect of
exhaust pressure on T for three values of fuel-air ratio and
various engine conditions is presented in figure 5. These values of T . been corrected to an inlet-manifold temperature of 800 F by means of equation (6). An Increase in exhaust pressure results In an increase In Tg, and., for the range of fuel-air ratios covered, the increase is somewhat greater at the lean than at the rich mixtures. A similar effect of exhaust pressure on Tg was obtained In the tests of an air-cooled engine which are reported In reference 6 and also in unpublished tests of another liquid-cooled engine conducted at this laboratory. -
For convenience, a cross plot of these curves Is shown in figure 6 in which T is plotted as a function of fuel-air ratio
for exhaust pressures of 10, 20, 30, 40, and 50 inches of mercury
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NACA.RM No. E8B06
absolute. The curve for an exhaust pressure of 30 Inches of mer-cury was obtained from figu.re 3 and. the shape ' this curve was used. as a guide in drawing those for the other exhaust pressures.
Variation of T with Ignition timing. - The variation of T
with ignition timing for engine speeds of 2600 and 3000 rim is. pre-sented in figure 7 as a plot of AT, against spark advance. This
variable ATg represents the change in effective cylinder-gas
temperature from the value at the standard ignition timing (exhaust spark plugs) of 34 0 B.T.C. The magnitude of the correction to T for other than standard ignition timing increases positively as the spark setting is increased or decreased frQn the normal position. The data separate somewhat with engine speed for spark advances less than the normal setting but, for simplicity, a single curve has been drawn through all the data.
Exponent n on Charge Flow
The value of the exponent n on charge flow W 0 was obtained
from tests at constant coolant conditions In which the charge flow was varied by changing the engine speed, manifold pressure, or exhaust pressure. For such conditions,equation (1) reduces to
Th - T1
Tg - Th = B2WQ (7)
T - T A logarithmic plot of
Tg Thagainst W is shown in
- figure 8 and the slope of the line through the data, which is equal to the value of the exponent n, is 0.60. Although the absolute
Th - T1 value of' the factor
would be different for different TgTh
coolant conditions, the slopes of the resulting lines would be the same. The data for the runs with a coolant flow of 300 gallons per minute were adjusted to a flow of 250 gallons per minute to be con-
Th - T s istent with the rest of the data by changing the factor
TgTh In accordance with the effect of coolant flow on the cylinder-head temperature presented in reference 3. Data covering a wide range of engine speed, manifold pressure, and exhaust pressure are pre-sented for each of two engines and close agreement is noted.
N.ACARMNo. EBB06 11
The Factor Z
The factor Z was determined from tests in which the coolant temperature and composition were-held constant while the coolant flow W, was varied. For these conditions, equation (1) may be written
(Th_-_T1 ( - Z = B
(Dl(8)
\Tg Th) Q)
A plot of (' = ) (_
against 11W1, using the
previously determined values od T and the exponent n, is ahown in figure 9 for five different coolant compositions. Extrapolation of these data to 11w 1 = 0 (at which point the value of /T -T\ h 1) (
C 0 is equal to the Z factor) results in a \Tg_ThJ\O.G)
value of 0.13 for Z. Inasmuch as the extrapolation was necessarily made over a fairly wide range of flow rates, it may be considered somewhat arbitrary. The value of 0.13 was chosen by drawing curves
- Thaving the same general shape as those - presented f or a-similar-plot-in reference 1 and then plotting a final correlation using three different values of Z; the value that gave the most satisfactory correlation (0.13) was finally chosen.
In the Investigation of reference 3, it was found that the cylinder-head temperature, particularly in the exhaust or hot side of the head, increased with engine running time during the initial operation of the engine. This increase In temperature is illus-trated in figure 10 and it is noted that the temperature between the exhaust valves increased about 25° F during approximately the initial 100 hours of engine running time and remained substantially constant as the operating time was further increased. Unlike the variation exhibited by this temperature location, the temperature at the exhaust spark-plug boss increased only slightly and the tem-perature between the intake valves remained constant over the entire period of the investigation. As discussed in reference 3, an inspection of the coolant passages of a scrapped cylinder head revealed scale deposits. on the exhaust side of the cylinder head but none on the intake side. This increase in temperature was therefore attributed to the scale deposits on the coolant passages. Because the Z factor accounts for the temperature drop through the cylinder head, this Increase in cylinder-head temperature with engine running time will be reflected as a similar variation in
12 NAQA RM No. E8B06
the Z factor. The determination of the Z factor (0.13), which was made after about 100 hours accumulated engine running tine, 18 therefore applicable only for this or greater engine running times. Although the final correlation Is insensitive to the magnitude of this basic value of Z, it Is necessary that the variation of which occurs during the initial engine running time, be accurately determined and included In the final correlation.
The variation of Z during the initial engine running time was determined from cylinder-head-temperature data obtained at a reference, operating condition. For this reference condition, the coolant and engine conditions were constant; accordingly, equa-tion (8) may be written
/Th -T1\(W601 - Th)
) - Z = constant (9)
The value of the constant is determined from the substitution into the equation of the previously determined value of Z and the pertinent engine and coolant data obtained at 100 hours engine running tine. The value of Z at other engine running times is then determined from the value of the constant and the cylinder-head temperatures obtained at the running time under consideration.
A plot showing the variation of the Z factor for engine D with engine running time is presented in figure 11. Some of the data were obtained at the reference operating condition; other data, included in order to establish more completely the variation of Z with tine, were obtained at engine conditions other than the refer-ence condition and adjusted in accordance with the variation in and the effect of W previously presented. It can be seen that
the Z factor increases during the initial engine operating time in a manner similar to that for the cylinder-head temperature (fig. 10) and that there Is no significant change In the value of Z after about 100 hours running tine. It is expected that this phenomenon will vary from engine to engine depending upon the history of operation. The range of conditions and engine running time over which this variation was established is indicated by the schedule of engine operating time in table I.
For engine D, the value of Z used in the subsequent correla-tion plots was determined from the curve of figure 11. For engines A, B. and C. the data were Insufficient to provide separate evaluation of Z, but most of the correlation data provided by these engines were obtained after the engines had been run for a
NACA RM No. E8B06 13
considerable length of time so a value of 0.13 was used. Because this value resulted in satisfactory correlation of the data from engines A. B, and C with those of engine D, it may be assumed that the coolant passages of these engines were in about the same con-dition as those of engine D after about 100 hours engine running time.
Exponent m on Coolant-Flow Parameter
The value of the exponent m on the coolant-flow param-eter was determined from tests in which the coolant tem-perature and composition were held constant while the coolant flow W, was varied (similar to data for determination of Z factor). For these conditions, equation (1) may be written
[^
h - T1\k = B4
(10) - Th) w') ]
- - (^ 6=01
60)_ k
against W,/p. is shown in figure 12 for five different coolant compositions. The slope of the straight lines through these data is equal to the exponent on w1/. Lines having the same slope are drawn through the data for each coolant and the value of the exponent m is accordingly established as 0.48. This value for the exponent m, which Is established from these selected data, will, of course, be verified by the slope of the line through all the data on the final correlation plot based on equation (1).
Exponent s on Prandtl Number Pr
The value of the exponent s on the Prandtl number Pr was determined from data for a constant value of and for constant engine conditions. For these conditions, equation (1) may be reduced to
(Th -
^Tg: z] k = B5Pr (11)
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NACA RM No. E8B06
The slope of the line determined, by a logarithmic plot of
IN - ) - z] k against Pr (or 2) would, then Th
establish the value of the exponent a. A wide range of Prandtl number for this plot may be obtained if data for several different coolants are used. In order to construct this plot, It Is conven-
r -\/ \ 1 lent to obtain values of the factor h
T 1 1- zi k g - ThJ \W 0.60/
from figure 12 for a constant value of W 1/1,t and then to cross-
plot the values of this factor against the Prandtl number Pr of the different coolants. Data obtained from a cross plot of figure 12 at a constant value of W j /1.i equal to 55,000 Is shown
In figure 13 and the slope of this line thus establishes the value of the exponent s on the Prandtl number Pr as 0.33.
FINAL CORRELATION
Final Correlation with Coolant-Flow Factor w 1 /1.1 as
Independent Variable
The final correlation based on equation (1), which Is obtained by plotting the factor
1 [Tg - T
h) (WCO.65) - Z] k Pr°33
against j/I.i for all test data on logarithmic coordinates, Is
presented, in figure 14(a). Although the data points scatter con-siderably, the maximum variation in' Th resulting from this scatter Is not large. A variation In Th of R20 F for typical engine conditions at normal rated power is represented by the dashed lines In the figure, and It is seen that almost all the data for the four engines lie within this band.
The value of the exponent m, which Is obtained from the slope of the line through the data, Is, as previously determined, equal to 0.48 and the value of the constant B1, found by sub-stitution of the values of the coordinate of any point on the line Into the correlation equation, Is equal to 0.00163. The final equation Is accordingly written
NACA RM No. E8B06 15
[(Th - T\ 1 [Tg Th) (Wo.6o) - z] k O33 = 0.00163 (W__o.4S
(12)
and will apply over a considerable range of engine operating con-d.itions, coolant temperatures, coolant flows, and coolant compositions.
In order to illustrate the variation in the correlation obtained among the four engines, the correlation of figure 14(a) is replotted in figure 14(b) using a different symbol for each engine. The separation of the data between engines is slight and the scatter for one engine is almost as great as the total scatter for all engines.
Final Correlation with Charge Flow W as
Independent Variable
Correlation of the test data based on equation (2), wherein the factor
(Tg - Th\r000l63 /p0.48 \ + - T 1)[( W10.48)k 0.33)
is evaluated by using the previously determined values of in, BY
Z, and B 1 and plotted against the charge flow Wc, is shown
in figure 15. A straight line with a slope of -0.60, which is equal in absolute value to the value of the exponent n on We, previously determined, is drawn through the data. As a result of the different arrangement of the terms in this equation, the apparent scatter of the data is considerably less in figure 15 than in figure 14; the over-all accuracy of the correlation Is, of
course, the seine. -
When equation (12) is rearranged In accordance with this plot, the following form is obtained
(Tg - Th\[o 00163 0.48
Th - T1) L(w 0.48)(k 0.33) + Z]= W 060 (13)
As previously mentioned, the values of the factor Z for engine D used. in plotting the final correlation of figures 14 and 15 were obtained from figure 11. If a constant average value were
16
NACA RM No. E8B06
used for Z. the scatter of the data would be increased from approximately ±12 to about *220 F, depending upon the engine running time.
In order to facilitate the computation of head temperatures by means of equation (13), values of the coolant-property
/ 0.48\ parameter ( 33) are presented in figure 16 for various
\k pr I coolant mixtures of ethylene glycol and water over a range of coolant temperatures.
Effect of Boiling of Coolant on Correlation
It was found In the investigations of reference 3 that under some conditions of operation a reduction In coolant flow Increased the amount of boiling of the coolant and reduced the normal tend-ency of the cylinder-head temperature to increase with reduced coolant flow. In order to determine the effect of this boiling of the coolant In the correlation, the relations given by equation (13) were considered. The left-hand side of this equation should nor-mally be a function of only charge flow and, if boiling of the coolant were negligible, would be Independent of the coolant flow. If, however, boiling occurs to an appreciable extent, the value of the left-hand side of this equation would be expected to vary with the coolant flow. A plot of this parameter against coolant flow is shown in figure 17 for two different engine operating conditions and several coolant compositions. For coolant flows greater than about 100 gallons per minute, the value of the plotted parameter Is Independent of the coolant flow, which indicates that boiling of the coolant did not occur to a noticeable degree in this range. For coolant flows less than about 100 gallons per minute, however, the value of the parameter increases with reduced coolant flow (depending on the engine power and coolant), which Illustrates the tendency of boiling of the coolant In this range of flow rates to reduce the cylinder-head temperature.
The maximum variation of the parameter plotted in figure 17 Is equivalent, to a decrease in head temperature of less than 100 F. Because this variation is within the normal scatter of the data, the correlation is not seriously, affected by boiling for the ranges of variables covered. Extrapolation of this correlation to com-binations of higher engine power, lower coolant flows, or lower coolant pressures than those covered by this Investigation would, however, be subject to uncertainties and reduced accuracy of pre-diction of cylinder temperatures.
NACA RM No. E8B06 17
Relation between Average and Maximum Cylinder-Head Temperatures
In figure 18 the average temperature of the 12 cylinders is plotted against the temperature of the hottest cylinder for the location in the cylinder head between exhaust valves. Good cor-relation of these data is obtained for all conditions and for all engines with the maximum cylinder-head temperature ranging from 100 to 200 F higher than the average temperature. From the cor-relation of the average cylinder-head temperature with the primary engine variables and coolant variables given In figure 14 or 15 and from the relation between the maximum and average head tempera-tures shown In figure 18, an estimation of the maximum cylinder-head temperature between exhaust valves Is possible for a large range of engine and coolant conditions.
USE OF CORRELATION EQJPTI0N
The use of the correlation equation in determining cylinder-head temperatures is illustrated by the following example:
The maximum cylinder-head temperature between the exhaust valves is to be determined for the following engine and coolant conditions:
Engine charge flow (air plus fuel), lb/sec . . . . . . . . . . 3.0 Engine speed, rpm ............ . . . . . . ... . . 3000 Fuel-air ratio .........................0.095 Carburetor-inlet air temperature, OF . . .......... 60 Exhaust pressure, in. Hg absolute . . . . . . . . . . 40.0 Ignition timing (exhaust spark plugs)., deg B.T.0 . . . . . 40 Accumulated engine running time, hr . . . . . . . Over 100 Coolant flow, lb/sec . . . . . . . . . . . . . . . . 30.0 Average coolant temperature, . . . . . . . 0. . . . . 250 Coolant composition, ethylene glycol - water
(percent by volume) . . . . . . . . . . . . .0 30-70
The value of the average cylinder-head temperature is first evaluated from equation (13) and the maximum cylinder-head tempera-ture then determined from figure 18. Although either oquation (12) r (13) may be used to evaluate the average cylinder-head tempera-ture, the grouping of the coolant-property terms of equation (13) results in greater convenience of application.
The dry inlet-manifold temperature Is computed from the, carburetor-air temperature and the engine speed by means of equation (4) as follows:
18 NPCA PM No • E8B06
Tm = Tc + 25.28 ( N 2
(000'\2 = 60 + 25.28 i000)
= 288° F
In order to determine the effective cylinder-gas tempera-ture Tg, a value of T for a fuel-air ratio of 0.095, 811
exhaust pressure of 40 inches of mercury absolute, standard igni-tion timing, and a dry inlet-manifold temperature of 800 F is first determined from figure 6 as 1069 0 F. The correction for an Igni-tion timing of 400 B.T.C. is obtained for figure 7 as 240 F. For a dry inlet-manifold temperature of 288 0 F, the correction to T
is determined from equation (6)
AT = 0.25 (Tm - 80)
= 0.25 (288 - 80)
= 52° F
The value of T6 Is then determined by adding algebraically
the corrections for ignition timing and manifold temperature to the value obtained from figure 6.
T = 1069 + 24 + 52 = 1145° F
Because the variation of Z with engine running time was shown to be constant at a value of 0.13 (fig. ii) for any engine running time over 100 hours, this constant value Is used. The
/ k 0.48\ coolant-property parameter 0 33) is determined from fig-
\Pr / ure 16 for the specified coolant and coolant temperature as equal to 164.
Substitution of the values of the various parameters into equation (13)
(T - Th\o.00163'\( 0.48 \\ 1 -0.60 Th - T2J w 0.48Ak 0.33) + Zj = Wc
NACA PM No. E2B06
ii:]
gives the following
(1145-T
2.00163 [( 300.48)0.00163
\Th-250 I (i) + 0.13] = 3.00s60
f1145-Th\ Th-25O )(0.0522 + 0.13)
Therefore
(1145-Th\ \Th-25O )= 2.839
Solving for the value of Th.,
= 0.5173
2.839 Th + Th = 1145 + 2.839 x 250
3.839 Th = 1855
Th = 4830 F
For this value of the average cylinder-head temperature, the maxi-mum cylinder-head temperature between the exhaust valves is found to be 4990 F (fig. 18).
SUMMARY OF RESULTS
An analysis of the data obtained from four multicylind.er, liquid-cooled engines of 1710-cubic-inch displacement, which included power outputs up to 1860 brake horsepower, coolant flows from 50 to 320 gallons per minute, and coolants composed of ethylene glycol - water mixtures varying in composition from 100-percent water to 97-percent ethylene glycol and 3-percent water gave the following results:
1. The NACA correlation method, which is based on the theory of heat transfer by normal forced convection, provided satisfactory correlation of the cylinder-head temperature between the exhaust valves with the primary engine and coolant variables for a wide range of engine and coolant conditions.
2. The correlation method as applied herein permitted the prediction of the cylinder-head temperature between the exhaust valves within approximately ±12 0 F.
20
NACA PM No. EBB06
3. The increase in the cylinder-head temperatures, which occurred during about the first 100 hours of engine operating time for constant operating conditions, (attributed to scale build-up in the coolant passages) was incorporated, in the correlation.
4. Boiling of the coolant, which was encountered at several engine powers under certain conditions of coolant flow, coolant temperature, and coolant composition ., did not seriously affect the correlation for the ranges of variables covered in this investigation.
Flight Propulsion Research Laboratory, National Advisory Canmittèe for Aeronautics,
Cleveland, Ohio.
NACA PM No. E8B06 21
RECS
1. Pinkel, Benjamin, Wnganie].1o, Eugene J., and Bernardo, Everett: Cylinder Temperature Correlation of a Single-Cylinder Liquid-Cooled Engine. NACA Rep. No. 853, 1946.
2. Pinkel, Benjamin: Heat-Transfer Processes in Mr-Cooled Engine Cylinders, NPCA Rep. No. 612, 1938.
3. Povolny, John H., and Chelko, Louis 3.: Cylinder-Bead. Tempera-tures and Coolant Heat Rejections of a M.ilticylinder, Liquid-
Cooled Engine of 1710-Cubic-7.tc1i Displacement. NACA TN No. 1606, 1948.
4. Povolny, John H., and Lundin, Bruce T.: Correlation of Coolant Heat Rejections of a Milticylind.er, Liquid-Cooled Engine of 1710-Cubic-Inch Displacement. NACA PM No. E8B06a, 1948.
5. Manganiello, Eugene 3., Valerino, Michael F., and Bell, E. Barton: High-Altitude Flight Cooling Investigation of a Radial Air-Cooled Engine. NACA TN No. 1089, 1946.
6.Valerino, Michael F., Kaufman, Samuel 3., and Hughes, Richard F.: Effect of Exhaust Pressure on the Cooling Characteristics of an Air-Cooled Engine. NACA TN No. 1221, 1947.
22
NACA RM No. E8806
TABLE I - SUMMARY OF ENOIN
Variable or Engine Engine Manifold Charge Fuel-air arburetor-type of test power speed pressure flow ratio air temper-
(bhp) (rpm) (in. Hg (lb/sec) ature absolute) (°F)
Charge flow 400-1180 2600 24-48 1.03-2.47 0.080 60 275-1260 2600 21-54 .84-2.76 .095 85 925,-1860 3200 41-73 2.35-4.40 .005 -5 860-940 2300-3200 40 1.70-2.18 .060 60 750-873 1800-3200 40 1.54-2.14 .095 86 430-630 1400-3200 30 .88-1.60 .095 86 370-640 1200-3200 30 .73-1.57 .080 60
Lnnifold 786-794 2600 34-36 1.33 0.095 80-184 temperature 555-590 2600 27-30 1.39 .090 -20-170
659-675 2600 30-34 1.58 .005 -27-144 798-846 3000 36-40 2.04 .095 -43-146 662-825 2300-3200 32-36 1.72 .080 17 647-812 2300-3200 34-40 1.72 .080 140 662-868 2000-3200 33-40 1.76 .095 17 546-742 2000-3200 31-40 1.58 .095 143
Fuel-air ratio 740-790 2600 35 1.75 .064-0.11 66 731-837 2600 34-36 1.84 .062- .10 120 760-960 3000 39-41 2.20 .064- .11E 25
Ignition 577-656 2600 30 1.53 0.005 40 timing 780-922 3000 40 2.19 .095 19
Exhaust 540-612 2600 28-35 1.43 0.063 24 pressure 506-703 2600 30-40 1.60 .100 4
620-726 2600 30-42 1.50 .085 39 944-904 3000 40-47 2.20 .085 -2 592-682 3000 30-41 1.66 .085 19 427-882 2600 35 1.36-1.02 .085 32
Coolant flow 1000 2600 44 2.21 0.092 75
1000 2600 44 2.21 .003 80 780, 1160 2600, 3000 36, 50 1.78, 2.71 .095 83 780, 1160 2600, 3000 36, 50 1.78, 2.71 .095 83 780, 1160 2000, 3000 36, 5 1.72, 2.71 .095 63 780, 1160 2600, 3000 36, 50 1.76, 2.71 .095 03 780, 1160 2600, 3000 36, 50 1.78, 2.71 .005 83
Engine 1000,1250,1450 3000 42, 51, 60 2.39, 2.94 0.095 50 calibration 3.40
310-1200 2000-3000 24-53 .73-2.60 .064-.096 75
aEngine equipped with aftercooler. bAN_E_2 ethylene glycol.
NACA RM NO. E8B06
23
bJJfl ('OflI.AWP CONDITIONS
Exhaust Dry-inlet Coolant, Coolant Average Engine Engine Engine
Ignition pressure manifold ethylene flow coolant coolant- running
timing (In. Hg temper- glyool-water (gal/mm) temper- outlet time (hr)
(deg B.T.C.) .bsolute) ature (percent ature pressure (°F) by volume) (°F) (lb/sq in.
gage) Exhaust Intake Glycol Water
34 20 230 30 30
70 70
255 250
245 245
33 35
C D 38.9- 45.8
34 34
28 28
256 254 30 70 300 245 35 D 153.6-156.5
34 28 29-30 104-319 30 70 255 250
245 245
33 35
C D 47.2- 51.2
34 34
28 28
168-345 135-345
30 30
70 70 250 245 35 D 45.8- 47.2
34 28 96-319 30 70 255 245 30 C
34 28 223-275 30 70 230 245 25 Be C
34 28 150-340 30 70 70
270 300
245 245
30, 35 D 15.2- 19.7
34 34
28 28 . 29-30
143-314 1-85-374
30 30 70 300 245 35 D 19.7- 24.5
34 28 152-277 30 70 300 245 35 D 24.5- 28.3
34 28 274-396 30 70 300 245 35 8 28.3- 31.2
34 28 118-277 30 70 300 245 35 8 31.2- 33.7
34 28 244-403 30 70 300 245 35 B 33.7- 35.8
34 28 236 30 70 270 245 35 C
34 28 - } 29 30 229-250 30 70 220 245 27 Be
34 28 _252 .30 70 250 245 35 D 37.5- 38.9
14-54 8-48}29_3o
210 30 70 300 245 245
35 35
8 D
112.2-116.1 116.1-119.3
13-52 10-46 246 30 70 300
34 28 645 194 30 70 250 245 35 8 148.5-151.4
34 28 10-60 174 30 70 250 245 35 8 142.2-145.6
34 28 10-61 209 30 70 250 245 35 8 136.5-188.5
34 20 12-52 226 30 70 250 245 35 D 140.6-142.2
34 28 12-59 246 30 70 250 245 35 1) 138.5-140.6
34 28 10-61 202 30 70 250 245 35 1) 145.8-140.5
34 28 245 97b 3 200-300 215, 245, 10 A 270
34 28 250 30 70 100-200 215, 245 10-30 A 34 28 29-30 253, 310 0 100 50-300 245 35 D 05.6- 90.7 34 28 253, 310 30 70' 50-300 245 35 8 90.7- 95.3 34 28 253, 310 50 50 50-300 245 35 D 95.3- 99.1 34 28 253, 310 70 30 50-300 245 35 D 99.1-103,1 34 28 253, 310 97b 3 50-320 245 35 D 103.8-110.2
34 20 278 30 70 220 245, 270 0,25,35,38 B
-3034 28 176-303 97b 3 144-255 245 10-30 A.
24
- N-ACA RM No. E8806
In Cylinder head between intake Face of valves exhaust
Cylinder head between exhaust valves -p
Tace of intake port It'
V
P
—Exhaust spark-plug boss
Section A-A
Figure I. - Installation of cylinder-head thermocouples.
NACA RM No. E8806
25
Compressed
- Bleed line
Vapor_ separator vent line
- - - - -- -
—En€ine -outletventlthe
IVapor separator
Lht bank
Expansion tank
Engine pump Venturi Left bank
valve separator
Bypass 1 valve
ary pump
I- Three-way mixing valve
Cooling water Pressure tap
0 Signt glass
0 Thermocouple
c1 Valve Main line Bypass line
-- Vent line
Figure 2. - Schematic diagram of engine coolant system.
76
NACA RM No. E8B06
907 •08 009 010 .11 .12 Fuel-air ratio
Figure 3. - Variation of effective cylinder-gas temperature with fuel-air ratio. Data corrected to dry inlet-manifold temperature of 80° F. Exhaust pressure, 29-30 inches mercury absolute;standard ignition timing.
1300
0
1200
4.3
1100
4.)
0
I80O
Engine Engine Manifold Charge Carburetor-air speed pressure flow temperature (rpm) (in. Hg (lb/sec) (°F)
absolute)
r+ C 2600 35 1.75 66 •1 0Ba 2600 34-36 1.84 120 L X D 3000 39-41 2.20 25
Single-cylinder, liquid-cooled engine (reference 1)
- - - Air-cooled engine (reference 5)
aEngine equipped with aftercooler
—7 (NCX
-------\
NACA RM No. E8806
27
o 1240
Jo
1220
1200
0
to1180
H
1160 0
4.) C) 0
1140
1120 120 160 200 240 280 320 360 400 Dry inlet-manifold temperature, Tm' OF
Figure 4. - Variation of effective cylinder-gas temperature with manifold temperature. Data corrected to fuel-air ratio of 0.080. Exhaust pres- sure, 29-30 inches mercury absolute; standard ignition timing.
.LLL.I. .U.J.J 1...L.LL .I_LAJ.
p... •.,. rr r y .... Tr m, ... .... .... ....
Engine Engine Manifold Charge Carburetor- Fuel- speed pressure flow air tempera- air (rpm) (in. Hg (lb/ ture ratio
absolute) sec) (°F)
. B 2600 34-36 1.83 80-184 0.095 v C 2600 27-30 1.39 -20-170 .090 o D 2600 30-34 1.58 -27-144 .095 + D 3000 36-40 2.04 -43-146 .995 G D 2300-3200 32-36 1.72 17 .080
D 2300-3200 34-40 1.72 140 .080 X D 2000-3200 33-40 1.76 17 .095 o D 2000-3200 31-40 1.58 143 .095
aEngine equipped with aftercooler
-
-
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28
NACA RM No. E8806
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43 C)
900
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MEN R! •I.
IMMEMEMEMMEME EMEMMEMMEMEMEMER REMEEMEMMEME REMEEMMEMEMEEPE" REEMEMMEMERASNEER REEMENEEMMEMEEM REEMEEMSEMOMP"091WE MMEEMIAPMM PRIMMEME MINI-PIEWME -mdNR•Ui
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Exhaust pressure, in. Hg absolute
Figure 5. - Variation of effective cylinder-gas temperature with exhaust pressure at several fuel-air ratios. Data corrected to dry inlet-mani-fold temperature of 800 F; standard ignition timing; engine D.
0
to
Cd 42
0
0 4,
0
H
U
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1200
1100
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900
NACA RM No. •E8B06
29
1400
Exhaust pressure (in. Hg absolute
50
800 1 I I I I I
.06 .07 .08 .09 .10 .11 Fuel-air ratio
Figure 6. - Variation of effective cylinder-gas temperature with fuel-air ratio at various exhaust pressures obtained from cross plot of figure 5. Data corrected to dry inlet-manifold temperature of 80° F; standard Ignition timing; engine D.
Engine Manifold Charge Carburetor-air Fuel-speed pressure flow temperature air (rpm) (in. Hg (lb/see) (°F) ratio
absolute)
o 2600 30 1.53 40 0.095 + 3000 40 2.19 19 .095
----0
0
16 24 32 40 48 56
120
80
4C bo
Li
30
NACA- RM No. E8806
Spark advance, deg B. T. Co (Intake timing 6 0 later than exhaust)
Figure 7. - Variation of change in effective cylinde±'-gas tempera-
ture with ignition timing. Engine D.
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NACA RM No. E8806
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39
r 'd_/O''/j_— Iz +r-° L \o I oo-2j I — il
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Coolant composition, ethylene glycol-water (percent by volume)
420
380
CD n 340 . Y.
00
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260
.4.) CD
04 0
220
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70-30
50-50
180
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100200 220 240 260 280 300
Coolant temperature, °F(
Figure 16. - Variation of coolant-property parameter 0.48
(\ k fro.33
with coolant temperature.
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