An investigation of the effect of various factors including fuel quality on the performance characteristics of a high speed diesel engine

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An investigation of the effect of various factors including fuel quality on the performance characteristics of a high speed diesel engine

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AN INVESTIGATION OP THE EFFECT OF VARIOUS FACTORS INCLUDING FUEL QUALITY ON THE PERFORMANCE CHARACTERISTICS OF A HIGH SPEED DIESEL ENGINE

A Thesis Presented to The School of Engineering The University of Southern California

In Partial Fulfillment of the Requirements for the Degree Master of Science in Mechanical Engineering

by Albert Nathaniel Baxter and Elmer King Frey August 1950

UMI Number: EP60502

All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion.

Dissertation Publishing

UMI EP60502 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code

uest ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48 10 6 - 1346

/ This thesis, w ritten by

ALBERT NATHAN IgL BAXTER

AND

under the guidance ofih.f*%?. Faculty Committee, and approved by a ll its members, has been presented to and accepted by the Council on Graduate Study and Research in p a rtia l f u lfill­ ment of the requirements fo r the degree of

MASTER OP SCIENCE

IN

MECHANICAL EN&I3MRIN&

D ate _

Faculty Committee

Chairman

lii TABLE OF CONTENTS CHAPTER I.

PAGE THE PROBLEM...................................... Definitions of terms used.

II.

1

...............

3

Organization of balanee of thesis............

7

HISTORY OF PREVIOUS RESEARCH.................. Fuel heating..................................

8 8

Cooling water temperature variation.......... 10

III.

Effect of engine speed.......................

11

Effect of cetane number......................

12

Theory........................................

14

Nozzle selection..............................

19

Other variables..............................

20

TEST PROCEDURE..................................

21

Equipment.....................................

21

Procedure..........................

21

Instrumentation and measurements............. 24 IV.

ANALYSIS OF RESULTS AND DISCUSSION.............

34

Fuel heating..................................

34

Effect of jacket water temperature........... 40 Engine speed versus fuel properties.......... 47 Nozzles........... . V.

CONCLUSIONS AND RECOMMENDATIONS.

61 .............

68

Fuel requirements............................. 68 Fuel heating....................

68

lv CHAPTER

PAGE Coolant temperature..........

69

Nozzle selection...............................

70

BIBLIOGRAPHY.

...... *.................................

71

APPENDIX A Engine experimental data......................

74

Diesel fuel specifications,...................

85

APPENDIX B

APPENDIX C List of equipment used........................

88

APPENDIX D Engine drawings................................

92

Generator tests..........

95

APPENDIX E

V

LIST OF FIGURES FIGURE

PAGE

X.

View of the Engine..,..............................

22

2.

Diesel Engine and Auxiliary Equipment Connections..

25

3*

Engine Test Panel

............................

26

4.

Generator Output Electrical Connections...........

2?

5.

Fuel Metering Electrical Connections..............

28

6.

Fuel Heater and Electrical Connections............

31

7.

Nozzle Spray Patterns..............................

33

8.

Effect of Measured Fuel Temperature on Fuel Con­ sumption at Low Speeds and Loads........

9.

Effect of Measured Fuel Temperature on Fuel Con­ sumption at Various Loads........................

10.

.......

50

Effect of Engine Speed on Fuel Consumption Twenty Cetane.........

15.

49

Effect of Engine Speed on Fuel Consumption Thirty Cetane.....................................

14.

45

Effect of Engine Speed on Fuel Consumption Forty Cetane

13.

44

Jacket Water Temperature Effect on Fuel Consump­ tion at High Speeds.......................... ..

12.

38

Jacket Water Temperature Effect on Fuel Consump­ tion at Low Speeds................................

11.

35

51

Comparison of Fuel Consumption for High and Low Grade Fuels at Low Speeds.........

54

Vi FIGURE 16.

PAGE

Comparison of Fuel Consumption for High and Low Grade Fuels at High Speeds....... ........ .......

17.

The Effect of Speed on Cetane Number Requirements for Constant Fuel Consumption....................

18.

57

Fuel Characteristics and Consumption as a Function of Cetane Number........

19.

55

60

Effect of Injection Pressure on Mean Drop Size as Determined by a Number of Different Investiga­ 62

tors.................. 20.

The Variation of Fuel Consumption as a Result of Nozzle Changes: Low Speed..

...................

65

2 1 . The Variation of Fuel Consumption as a Result of Nozzle Changes: High Speed.......

66

CHAPTER I THE PROBLEM The performance and operational characteristics of any engine are a function of its design and the fuel con­ sumed.

The properties of the fuel are affected by both the

raw material from whence it is derived and the refining methods used in Its manufacture. Prom 1941 to date, competition for the petroleum distillates boiling in the range of 350-750°F has been heavy. Since the advent of compounded diesel engine lubricating oil (1930's), the high speed engine has become increasingly popular.

The demand for fuel for industrial and domestic

heating facilities, combined with that made by engine manu­ facturers on petroleum refiners has caused much catalytically and thermally cracked stock to find its way into gas-oil sales and large quantities of this material are being burned in diesel engines. Statement of the problem.

The ignition quality of a

cracked gas-oil is not as high as the corresponding straightrun gas-oil from the same crude; therefore, extensive refining must be employed when cracked gas-oils are used, if the diesel fuel quality is to be maintained.

Although refining processes

for these stocks are known, some difficulties may be encountered in their commercial application.

In some areas the price of

2 high-quality diesel fuel is approaching that of gasoline, and as more refining of diesel fuels becomes necessary, the price differential may be further reduced.

Since one of the most

desirable characteristics of the diesel engine is that of low cost fuel, it becomes evident that manufacturers will eventu­ ally be forced to develop engines which can make economical use of low cost, low grade fuels. A search of the literature revealed that little infor­ mation exist8 regarding the effect of certain factors on the operation and performance characteristics of the high speed, low power, precombustion type engine.

Therefore, the objects

of this investigation were as follows: 1.

To determine the effect of fuel heating on

combustion characteristics and efficiency. 2.

To determine the effect of Jacket water tempera­

ture on engine performance. 3.

To determine the effect of engine speed on fuel

consumption while using each of several different fuels. 4.

To compare the operation and performance charac­

teristics of various fuels. 5.

To study the effect of nozzle design on engine

performance. 6.

To demonstrate that cetane number is not neces­

sarily a major consideration in fuel comparison.

Importance of the Investigation.

Many authorities

in both the refining and engine manufacturing industries are agreed that little, if any, Justification exists for the continued demand for fuels having improvements in such pro­ perties as diesel index, cetane rating, ignition quality, decreased mid-boiling temperature, et cetera.

Engine manu­

facturers still retain, in many instances, excessively high fuel ratings for their engines; therefore, if diesel engine technology is to progress, the problem of designing engines which can profitably employ lower grade fuels will be of prime importance. The large increase in the number of high speed diesels during World War II, together with the fact that many of them had to be operated in cold climates and at high altitudes far from the sources of the superior paraffin-base gas-oils, has brought the whole problem of fuels for high speed diesel engines prominently to the front.

With these problems facing

the manufacturers of diesel engines, it is imperative that much research be done in order that the high speed diesel engine not face future extinction. J.

DEFINITIONS OF TERMS USED

Aldehydes, alcohols, and keytones.

During the combus­

tion process, intermediate oxides are sometimes formed and because of their relatively high stability, they persist and

4 are expelled with the other gases.

Probably the most impor­

tant of these compounds are aldehydes, alcohols, and keytones. Aniline point.

The aniline point is determined by

heating a mixture which contains equal volumes of aniline and the fuel sample in an insulated test tube until a clear solution is formed.

The solution is then cooled until tur­

bidity occurs; the temperature at this condition is called the "aniline point". The relationship between cetane number and aniline point is given by the following: Cetane number « Aromatics.

1.95

Q

- 31.5

The term "Aromatics" applies to the low

boiling point hydrocarbons such as benzene, toluene, and methyInaphthalene• Asphaltenes.

Asphaltenes are a class of compounds

that occur in the higher boiling fractions of crude oil. Brake specific fuel consumption.

Brake specific fuel

consumption (abbreviated B.S.P.C.) is defined as the quantity of fuel required by an engine in pounds per hour to produce one horsepower. Another specific consumption (b.s.f.c.) has been de-

# Superscripts refer to bibliography

5 fined as the number of cubic inches of material (at atmos­ pheric pressure and sixty degrees Fahrenheit) consumed per horsepower-hour. Both of the above definitions have been used in this report. Cetane number1 . The A. S.T.M. cetane number of a diesel fuel is defined by, and is numerically equal to, the percent­ age by volume of cetane in a mixture of cetane and alphamethylnaphthalene ( C ^ H 1 0 ) which the fuel matches in ignition quality.

By definition, alphamethylnaphthalene has a cetane

number of zero, and cetane of one hundred. Cetane

H3 4 ) is a straight-chain hydrocarbon of

the paraffin series.

The ignition quality of this material

may be readily duplicated in a manufactured fuel. methylnaphthalene is a coal tar product.

Alpha­

Properties of these

two primary reference fuels are given below. Cetane Specific gravity,

60/60°F 0.775

Alphamethylnaphthalene 1.025

Boiling Range

°F 544.1«553

469.6

Freezing Point

°F 81.5

-7.6

Iodine Number Density. in degrees A.P.I.

Nil

-

The density of fuels is generally designated The relationship between degrees A.P.I.

6 and specific gravity Is defined as follows: Specific Gravity at 60/60°P........ . 141.5— — y 131.5 4- degrees API at 60°F Fuel boiling point.

In accordance with A.S.T.M.

specifications, one hundred cubic centimeters of a fuel sample are heated and the vapors yielded are condensed at the rate of ten cubic centimeters every one and one half to two minutes In a brass tube surrounded by cracked Ice.

The

Initial boiling point Is the vapor temperature read In the flask at the Instant the first drop of condensate falls Into the graduated cylinder the condenser.

Mid-boiling point is

the vapor temperature when one half the material is distilled and the end point Is the highest temperature indicated during the test. Gas-olls.

Oils with boiling points and viscosities

in the Intermediate range between kerosene and lubricating oil are given the Indefinite term **gas-oilsM .

They are often

a combination of a straight-run and cracked products and are used for the manufacture of certain types of high speed diesel fuels. Ignition lag.

The time interval between the beginning

of Injection and the start of combustion is defined ignition lag or Ignition delay.

7 Performance and operation.

Engine performance is

generally considered to be the ability on the part of the engine to utilize the energy placed at its disposal in the most profitable manner.

Thus, specific fuel consumption is

an appropriate unit by which performance can be rated. Such factors as engine roughness, smoke formation, exhaust odors, and starting difficulty could be classified under the caption of operation. II.

ORGANIZATION OP BALANCE OF THESIS

To thoroughly understand the material used to explain the phenomena observed during the test, a survey of the related work which has been done in the diesel engineering field is first presented.

The procedure followed In operat­

ing the engine is then outlined.

Results obtained are

analyzed with the benefit of both previous research and theory.

A final chapter of conclusions and recommendations

is then presented. All references which yielded useful information are listed in the Bibliography. Five appendixes that contain information not necessar­ ily pertinent to the discussion, conclude the report.

CHAPTER II HISTORY OF PREVIOUS RESEARCH A search of the literature revealed that It Is Im­ possible to parallel this study to those performed by others, not because the types of tests were entirely different, but because the fuels used and the engine can hardly be com­ pared with those previously utilized. It should be noted that in most other tests the engines involved were of much lower compression ratio, slower speed, and of different chamber design.

There is little

published data pertaining to tests made wherein fuels of thirty cetane or less were conclusively studied. I.

FUEL HEATING

Several attempts have been made by various researchers to determine the effect of fuel heating immediately prior to its being injected into the combustion region.

Each of these

tests has been made with reasonably high quality fuel and low compression ratio, low speed engines* An experimental investigation was performed by p Gerrlsh and Ayre , wherein the fuel temperature was varied from 124°F to 750°F in an electric heater.

Only very slight

Improvement was detected in such things as specific fuel consumption or power output.

Because oil at an elevated

temperature is naturally more compressible, an advance in cam position with respect to that of the piston had to be made* Hawkes3 reported a decrease in engine performance with an increase in fuel temperature up to 400°F.

This was

due to the fact that during these tests no compensation was made for the above mentioned change in fuel compressibility with temperature. Nozzle spray pattern was beneficially affected by Increased fuel temperature.^

At higher temperatures, the

cone angle was approximately tripled as compared to that pro** duced at the lower temperatures, while the central core was essentially eliminated.

At the higher temperature, all fuel

dribbling was eliminated; the start and stop of injection being well defined.

At the highest temperature, with the

fuel being injected into the atmosphere, the start of injec­ tion was characterized by a loud crack and the fuel expanded from the orifice diameter to one fourth inch immediately at the face of the orifice. Ignition lag.

Increasing the temperature to 500°F

had an adverse effect on the Ignition lag.^

This was probably

because of the increase in volatility of the fuel as it was ejected from the nozzle, resulting in a sudden decrease in envelope temperature.

As the bulk temperature of the fuel

increased, this localized cooling was more than compensated

10 for and a decreased ignition lag occurred Performance and operation.

Heating the fuel apparent­

ly had a beneficial effect on engine operation.

Combustion

knock' was perceptibly decreased and exhaust regions were fre­ quented to a lesser degree by flames.

Smoke formation was

noticeably less for high fuel temperatures.^ Nature of combustion.

As previously mentioned, fuel

heating above 500°F reduced ignition lag; therefore, fuel was injected into the combustion area during fuel ignition. Pressure rise per degree of crank angle was decreased as a result of combustion taking place at a more reasonable rate. Examination of the combustion region of the test engine re­ vealed practically no carbon formation when elevated fuel temperatures were used.

A previously polished piston showed

such slight carbon deposition as to be negligible.

With low

fuel temperatures employed, carbon deposit was very pronounced even after a much shorter period of o p e r a t i o n . ^ II.

COOLING WATER TEMPERATURE VARIATION

Other investigators have shown that the temperature within the combustion chamber has a rather severe effect on

A

combustion.’

Of the several factors which affect the

chamber temperature, cooling water is probably the greatest. Ignition lag.

The ignition lag of some fuels may be

11 decreased considerably by raising the jacket water tempera­ ture, providing other factors such as engine speed and fuel injection advance angle are not changed.4 Maximum to normal pressure ratio.

It has been shown

by Rothrock4 that the ratio of maximum to the normal com­ pression pressure remains practically constant for a very wide range of injection advance angle, provided the jacket o coolant temperature is maintained at from 200°F to 300 F. "In each case where detonation occurred, it came at the first maximum value of the ratio.

With the highest jacket

temperature, the engine did not detonate regardless of the injection advance angle".4 Combustion efficiency.

Another effect of jacket

temperature increase was the slightly decreased air tempera­ ture and decreased air density.

This effect is reinforced

by the fact that the area on a pressure-time diagram was measurably reduced.4 III. Combustion.

EFFECT OF ENGINE SPEED It is an established fact that the rate

of combustion in a diesel engine is so greatly dependent on turbulence that the time required for combustion is roughly inversely proportional to engine speed.

That is, the number

of degrees of crank rotation required for combustion is

12 practically independent of speed.

Thus, for a constant in­

jection advance, R.P.M. has practically no effect on the length of time expired between actual fuel ignition and maximum cylinder pressure* On the contrary,

some researchers have reported that

for a constant quantity of fuel Injected, the ignition lag in crank degrees decreased with an increase in engine speed.0 Friction horsepower and wear*

It is common knowledge

that curves can be plotted with R.P.M. and friction horsepower as coordinates which result in straight lines when plotted on log-log paper.

From the curves the relationship between

R.P.M. and friction horsepower can be related by the follow­ ing equation: FHP = K (RPM) n where the value of n usually approximates 1.60 and K is a function of engine construction. IV.

EFFECT OF CETANE NUMBER

Much emphasis has been placed by most writers on fuel cetane number in an apparent endeavor to make it a criterion upon which to base the predicted performance of any engine. In some instances, it would seem as If this were reasonable and, as yet, there is no conclusive evidence available to the contrary.

However, other available test data indicate a

13 trend in another direction. Much of the literature search revealed a close correlation between cetane number and engine performance traits, but it should be stated that in the majority of tests, the engines used were of much different construction and speed than the one from which data were taken for this report. Relative engine performance.

A plot of such opera­

tion and performance characteristics as starting, exhaust odor, engine deposits and smoke formation reveals that im­ provement results in each with an increase in cetane number.® Exhaust characteristics.

Because of the increased

demand for economical diesel engines in transportation, it is desirable that engines be able to consume the lower grade, less expensive fuels.

However, experience has shown that

products of partial combustion are a result when engines use low cetane fuels.

Aldehydes in the exhaust are inversely 7 proportional to cetane number. Ignition character1sties. of ignition lag. engine speed.

Cetane number is a measure

However, ignition delay is affected by

It has been shown^ that the cetane number

requirement for a constant ignition delay time decreases with an increase in engine R.P.M.

The ignition delay in

milliseconds decreases with an Increase in engine speed for

14 any particular fuel. V.

THEORY

Since the problem did not Include measuring ignition delay, injection timing, intensity of fuel knock, et cetera, it is necessary to consider certain phenomena from a theoretical standpoint. Mechanical mixing.

When fuel is injected into the

combustion region it is rapidly disbursed and mixes with the air.

As this occurs, vaporization takes place and the

gasified fuel begins to mix with appropriate quantities of air.

Up to this point, the fuel has not been in an inflam­

mable condition and the lag between the time of injection and the time of some local stoichiometric mixing is frequently called the physical delay. Stoichiometry.

From the perfect gas law and chemical

equations it can be shown that there is nearly a straight line relationship between the quantity of air required for complete burning in volumes, and the number of carbon atoms in a hydrocarbon molecule.

Thus, for the ordinary diesel

fuel it can be estimated that at the end of compression, an individual droplet of fuel will require from five hundred to one thousand times its own volume of air for proper oxida­ tion, depending on the fuel constituents.

Fuels with a

15 smaller number of carbon atoms per molecule have lower boil­ ing points and consequently present less mixing difficulty.

8

Droplet vaporization.

As the individual droplet

travels, fuel is liberated from its surface and a vapor trail is left behind.

If the path is a straight line, a

cone of properly mixed air and fuel will be generated whose length can be computed from the above mentioned chemical relations.

Thus, the length of the cone will be:

L * Kxd0 Where:

(1)

is a constant dependent upon the fuel and dQ is

the original droplet diameter. If the fuel drop size and the relative velocity between the droplet and the air is known, it can be strated that the time required for vaporization

is:

t = Kg-^a Where:

demon­

(2)

= a constant dependent upon the fuel type. dQ = the original droplet diameter. V

= the relative velocity between droplet and air. It has previously been shown that heating the fuel

has a beneficial effect on spray dispersion.

Consequently,

from the above equation it can be assumed that the physical delay period could be measurably reduced by fuel heating since drop size diameters are reduced.

16 Chemical delay.

“The period of chemical delay in

the diesel engine is measured by the time that elapses between the beginning of chemical reaction and the beginning of inflammation or ignition. In 1889 Arrhenius discovered that a general relation between reaction rate and temperature can be expressed by the following equation:^ d(lnk) » E dt RT2

(3 )

Where: k - reaction velocity T s absolute temperature R » molecular gas constant. E

z

constant characteristic of the reaction.

When Integrated, this yields

K - --- 1---

(4)

+ C) If E and R are known to be constant, an increase in T may produce a very large increase in K, the reaction rate. Chain reaction.

If a statistical analysis of com­

bustion is made on the basis of the kinetic gas theory, it can be demonstrated that the probability of a molecule of fuel finding the correct number of molecules of oxygen with which it must simultaneously unite for complete combustion is so slight, that in the case of the very long chain

17 hydrocarbons, it would take millions of years for the mole­ cules of one gram of diesel fuel to burn.

It is evident

from both experience and the above mentioned analysis that the oxidation of hydrocarbons must take place by stages and cannot occur in one step as indicated by the ordinary chemical equations.

Consequently,

the original hydrocarbon

must be partially oxidized in a collision of the hydrocarbon with an oxidizing agent.

During the chemical delay, direct

oxidation reactions occur slowly at first and subsequently with increasing rapidity until ignition begins. If a study were made here of the intermediate stages of oxidation, it could be shown that the aldehydes previously mentioned are products of partial combustion and that should the chain reaction be stopped, these aldehydes and other partial products would subsequently appear as undesirable exhaust products or deposits on engine surfaces.

(A dis­

cussion of chain reaction is not presented here since one can be found in any good text on combustion.) It is noteworthy that combustion in the diesel engine often takes place in three stages.

First, primary oxidation

occurs with a consequent liberation of heat and increase in temperature.

This heat flows to the uncracked and unvaporized

fuel, causing a rapid temperature decrease but prepares more fuel for further oxidation.

Secondary oxidation then occurs

with a result similar to that of the primary oxidation.

18 Tertiary oxidation follows which generally completes the combustion process*

This final process may result in fuel

knock if the oxidation occurs at a very rapid rate. Ignition delay at low and high temperature.

It has

been stated in this report that the ignition delay is comprised of two periods: delay.

(a) Physical delay and (b) Chemical

A plot of actual ignition delay^0 '3^* versus the

reciprocal of the absolute fuel temperature^ reveals that at lower temperatures a change of temperature, delta T, results in a very large decrease of ignition lag and that at higher temperatures for the same delta T, only a slight change in ignition l&g occurs.

It might be reasoned from

this that at lower temperatures, because of the fact that the chemical reaction delay is taking place at a relatively slow rate, most of the ignition lag consists of chemical delay.

However, at higher temperatures the chemical delay

is tremendously reduced and the ignition lag consists mainly of physical delay.

Thus, for a diesel fuel, an equation

expressing the ignition lag time might be written as follows b T time 3 t 3 tp ■ftg — a(e)

d T — c(e)

(5)

Where: tp - physical lag. t0 = chemical lag. e

a 2.718

a,b,c,d » constants depending on the fuel composition.

19 Since physical delay is the rate determining factor at an elevated temperature, the temperature at which physical delay becomes the controlling factor increases as the chemical reactivity of the fuel diminishes. Effect of pressure.

Investigators13 have found

that ignition delay is decreased by an Increase in pressure. However, the effect is much greater at lower pressures.

An

expression relating the chemical delay, t, to absolute tem­ perature and pressure may be written as follows:

t = J(-w-) (®)

§

p

^

Where: T - absolute fuel temperature, p - absolute fuel pressure j,m,n « constants depending on the fuel, e = 2.718 Equation 6 shows that Increases in either/or both pressure and temperature have a beneficial effect on the chemical delay period. VI.

NOZZLE SELECTION

Injection nozzles for the precombustion type engine are usually of the pintle type.

Although the pintle nozzle

is available with spray cones having angles as large as sixty degrees, it is evident from the general shape of most

20 precombustion chambers that they could not accommodate sprays having this shape.

Consequently, pintles have been developed

which have cone angles as small as two degrees. A nozzle is selected whose spray envelope will supposedly fill the chamber cavity without depositing an excess of raw fuel on the chamber walls.

After this pre­

liminary selection is made, nozzles with larger and smaller cone angles are tried until optimum operation and performance are attained. VII.

OTHER VARIABLES

Although the Ignition quality of fuels has an effect on operation and performance which cannot be disregarded, other characteristics such as heating value must be considered. It is a well known fact that various fuels can have the same cetane number and yet have different distillation lineament or A.P.I. gravity numbers.

It is fairly well established

that specific fuel consumption increases with a decrease in mid-boiling point for fuels of the same cetane rating or A.P.I. gravity.

CHAPTER III TEST PROCEDURE I.

EQUIPMENT

The diesel engine used in this investigation was a Hallett, eight horsepower, Appendix C).

single cylinder model,

(See

The engine was loaded with a direct current

generator coupled with four Vee-belts.

Both the engine and

the generator were bolted to a steel frame which in turn, was bolted to the concrete floor. II.

(Figure 1 ).

PROCEDURE

Before the testing started, the engine was run more than thirty hours as a break-in period, during which time the load and speed were varied. In accordance with the A.S.M.E. Test Code, the engine was run for at least one hour prior to a test run, in order that equilibrium be reached.

During this warm up period the

speed and load to be used in the following run were set. After a change of variables between runs, the engine was allowed to operate at least fifteen minutes before the next run was started. Fuel temperature.

After the Installation of the fuel

heating apparatus a series of runs was made during which time

22

VIEW OF THE ENGINE Figure 1

23 various settings of speed and load were used*

The fuel tem­

perature was increased at appropriate intervals while all other variables were held constant.

Fuel temperatures

ranging from 100°F to 300°F were employed.

When artificial

heating was discontinued the fuel temperature remained appro­ ximately constant and fuel temperature data was no longer recorded* Cooling water temperature.

In the

the cooling water temperatures were varied

next group of runs from 140°F to 212°F,

during which time the load and speed were changed as before. After a sufficient number of runs had been made to determine the effect of Jacket water temperature on engine performance, fuel A was drained from the system and fuel B introduced. Cetane number variation.

A series of runs was made

using fuels B, BC and C in which the speed and load were varied to determine specific fuel consumption.

The fuel and

Jacket water temperatures were held nearly constant. Engine speed.

In runs using fuel A, the speed was

held constant at approximately 1000, 1300, R.P.M.

1600 and 2000

When using fuels B, BC and C, an engine

speed of 1000

R.P.M. became impractical. Loading.

The even ampere loads of 10, 20, 30, 40 and

50 amperes were used to facilitate the computation of generator

24 efficiencies.

For fuels B, BC and C, the 10 ampere runs

were discontinued since they produced such light engine loads. In order to compute the engine output it was necessary to determine the generator efficiency for every run.

The pro­

cedure and results of this determination are shown in Appendix E. Loading the generator was accomplished with a resis­ tance bank.

The output voltage was regulated by adjusting

the generator shunt field resistance. III.

INSTRUMENTATION AND MEASUREMENTS

A block diagram of the connections between auxiliary equipment and the engine is shown in Figure 2.

The test

panel layout is shown in Figure 3 and the panel equipment and generator connections are shown in Figure 4.

The test

panels the weighing scale and the clock were shock mounted. Fuel measurement.

The duration of some of the test

runs was as short as fifteen minutes; therefore, an accurate semi-automatic fuel metering system was a necessity.

A

system of relays, a clock, a scale balance and switches were connected as shown in Figure 5.

By following the diagram it

can be seen that as fuel was consumed, the balance arm would descend until contact was made with the clock starting circuit. Any time after the clock was started, the "Clock Hold Switch”

** Atmosphere

Silencer Thermometer

Fuel Radiator

Supply

Overflow Exhaust

Injector Thermometer

Fuel

Metering

FIGURE

Heater — ►To Electrical Power

Compression Release Gauge

Fuel_Pump

ri

Fuel Filter Filter Lubricating Oil

Powe

>-To Generator Starter Switch

DIESEL ENGINE AND AUXILIARY EQUIPMENT CONNECTIONS

1 Storage Battery

26

ENGINE TEST PANEL Figure 3

Load Current Ammeter

Generated Voltage Voltmeter Variable Resistance Load

— t 50 Millivolt Shunt

LoJ

Terminal Board Shunt Generator From Engine

ower (r)Socket8 T o r Adding (©Resistance

RPM Field Rheosta Field Current Ammeter GENERATOR OUTPUT ELECTRICAL CONNECTIONS

Clock Operating Relay Clock J3L

m

-J Balance Arm Holding Magnet o = >

Balance Contact

Start Run, End Run Switch

i Fuel i Tank Clock Scale

Hold Switch

12 Volt Storage Battery

FUEL METERING ELECTRICAL CONNECTIONS

110 Volte A.C.

29 was used to allow the clock to continue operating, while the other switch was used to reverse the relay operation when a certain increment of weight was set on the balance arm.

As

this Increment of fuel was consumed, the balance arm again descended, automatically stopping the clock at the same point of balance at which it started.

The connecting line between

the fuel tank and the fuel filter was flexible, causing a constant tare in the gross weight. The accuracy of the scale was checked with standard weights before testing began. sent.

Ho measureable error was pre­

The estimated timing error using this system was less

than one second. Speed measurement.

The R.P.M. of the engine and

generator were measured by means of a hand tachometer.

Read­

ings were taken immediately before, during and after each run.

For each of these readings of either engine or generator

R.P.M., an average of at least two consecutive readings was taken and recorded. Compression ratio.

The compression ratio was computed

by filling the combustion cavity with a measured amount of oil while the piston was at top dead center.

Knowing the

engine bore and stroke, the compression ratio was computed. Fuel designation.

For the purpose of easy reference

30 the four fuels used were given the following letter and approximate number designations:

Fuel A, 50 cetane, Fuel B,

40 cetane, Fuel BC, 30 cetane which is a physical blend of fuels B and C, and Fuel C, 20 cetane*

A rather complete

analysis of these fuels is given in Appendix B, When it became necessary to change the type of fuel used, the system was thoroughly drained and the engine operated long enough on the new type fuel to completely purge the system before a new test run was started.

No difficulty

was encountered in starting the engine while fuels A, B and BC were used.

Starting the engine with fuel C required the

use of hot water in the cooling Jacket, and a starting wick. Fuel heating was accomplished by placing an electric heater between the fuel pump and the injector.

The heater

shown in Figure 6 consisted of a nichrome element electrically insulated from the fuel line and thermally insulated from the atmosphere.

The heater received power through a variac,

which made temperature control possible.

An insulated copper

tube thermometer well was soldered to the fuel line between the heater and the injector. Coolant temperature regulation.

The jacket water

temperature was measured with a mercury thermometer at the top of the radiator.

The Jacket water temperature was raised

by restricting the air passage through the radiator and lowered

Measured Fuel Temperature Thermometer

Fuel to Injector

Electrical Insulation

Magnesia

FIGURE

V

Fuel From Pump

/

Tape

/ Nichrome Element

Insulation

Variac

FUEL HEATER AND ELECTRICAL CONNECTIONS

110 volte

32 by applying forcing cold

cold water to the outside of the radiator and/or tap water in at the bottom of the radiator.

Nozzles.

In order to determine the effect of injec­

tor design, three American Bosch injector nozzles were em­ ployed: I.

ADN-4SI, pintle type, recommended for and

supplied with the engine.

Used with fuels A, B, BC and C.

II.

ADN-4S24, throttling type, used

with fuel C.

III.

ADN-21NE, throttling type, used

with fuel C.

In order to obtain more accurate knowledge of the spray characteristics for the nozzles, each was mounted in a hydraulic Jack which recorded the opening pressure.

The spray pattern

was allowed to strike glass plates covered with lamp black. Before the oil could run, photographs were quickly taken of the back lighted plates.

(Figure 7).

From the photographs

it can be seen that the lighter portions of the plate are the areas where the lamp black was dispersed by the larger amounts of oil.

33

Nozzle II

\Nozzle

III

NOZZLE SPRAY PATTERNS Figure 7

CHAPTER IV ANALYSIS OP RESULTS AND DISCUSSION I. Plotted Data.

FUEL HEATING

The beneficial effect of Increasing

the fuel temperature during this particular test can be seen in Figure 8.

At the lower fuel temperature the specific

fuel consumption was well above 1 lb./HP.-HR.

(A temperature

of 110°F or lower represents the approximate temperature of the fuel inlet line at this particular load and speed without the heater).

During the progress of the fuel heating, the

B.S.F.C. decreased approximately fifteen percent.

After

200°F the slope decreased and became nearly horizontal at the elevated temperature. Between the fuel and the engine block (a region which will have a lower or higher temperature than any of the measured fuel temperatures) there are essentially six im­ pedances to heat flow:

First; the holder or nozzle body,

depending upon the relative location of the fuel; second, a metal to metal contact consisting of either screw threads or a press fit; third, the cap nut; fourth, an air gap be­ tween the injector thimble and cap nut; fifth, the injector thimble; sixth, an air gap between the injector thimble and engine block.

35

!

i

•!

EFFECt OP XFskSVk%D FTKL T^TPiaRATIIRE!ON FDEL CONSUMPTION;AT LOW SPEEDS AND LEKX S

86 TABLE B1 FUEL SPECIFICATIONS Shell Oil Company Identification No.: W-5412 Fuel: A Tank Noe: 15 UO-IO Date____________________ ____________ 7-1-49 Gravity, °API Color, ASTM Flash Point, PM, cc., °F W & S, % vol. Sulphur, % wt. Calorific value, BTU/lb. Carbon ree., Con., % wt. Ash, % wt. Pour test, °F Carbon res., % wt. last 10^ botts.(Hams.) Alkali or mineral acid Corrosion, Cu strip at 212©F Cetane No., F-5 Water by dist., % vol. Asphaltenes (Holde), % wt. Cloud point, °F Aromatics, % vol. (uncorrected) Aniline point, °F Cu corrosivity, ppm Vise., Univ. at 100OF, sec. Vise., Kin. at 100°F, ctks.

W-5414 B 19 UO-9 6-29-49

38.4 1 164 Trace 0.42 19,730 0.01 0.01 -5

33.3 4 1/2 170 Trace 0.87 19,450

0.02 None Pass 51.5 Nil -2 5-10 159 35 -

0.24 None Neg. 42.9 Nil 0.07 +10 20-30 32 36 3.6

340 654 434 508 586 98.0

370 688 442 500 614 98.0

W—5413 C UO-10 Ext. 6-30-49 21.7

6 164 mm

1.8S 18,930

0.20 0.01 -10 0.40

22.1

72.3 35

ASTM Distillation. °F Initial boiling point Final boiling point X0% rec. 50% rec. 90% rec. % recovered

348

688 424 492 585 98.0

87 TABLE B2 COMPUTED FUEL SPECIFICATIONS*

___________Fuel___________ A B BS