EFF ECT OF WATER INJECTION ON
COMBUSTION CHARACTEMSTICS
OF A SPARKJGNYHON
ENTERNALCOMBUSTION ENGINE

 

THESIS FOR THE DEGREE 0F M. S
MECHEGAN STATE COLLEGE

EDWARD E. TOWE
3955

THES‘S

6.1

This is to certify that the

thesis entitled

Effect of Water Injection on Combustion maractOriatica
of a Spark-Ignition Internal-Combustion Engine

presented by

Edward E. Tove

has been accepted towards fulfillment
of the requirements for

M, 3. degree in M..—

r? ' *2 2“”

Major professor

 

Date '1qu 29: 1955

O~169

EFFECT OF WATER INJECTION
ON
COMBUSTION CHARACTERISTICS
OF A

SPARK—IGNITION INTERNAL-COMBUSTION ENGINE

By

Edward E. Towe

A THESIS

Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Mechanical Engineering

1955

THEE

Q".

THEES

 

 

 

ACKNOWLEDGEMENTS

The author wishes to express his sincere appre-
ciation to Dr. Louis L. Otto under whose supervision
and guidance this investigation was made.

The author also wishes to thank Mr. Richard
Jenkins for his aid.in setting up the test equipment.
He would like to thank his wife, Deonne, for her help

in typing the manuscript.

359308

VITA

The author was born April 2, 1951 at Battle Creek,
Michigan. Elementary and college preparatory education
was taken at the Maurer and Charlotte High School re-
spectively. Graduating from high school in June, 1949
he entered Michigan State College in September of the
same year. In March, 1954 the author received a Bachelor
of Science degree in Mechanical Engineering. He was
married in Febuary, 1954.

From March 1953 to April 1954, the author was em-
ployed by Atlas Drop Forge working summer and part time
during the school year in the cost estimating department.
While working toward a Master of Science degree, the
author has held a graduate assistantship. His duties
consisted of teaching in the thermodynamic and welding
laboratories.

The author is a member of Delta Chi, a national

social fraternity.

Edward E. Towe

ABSTRACT

This investigation was carried out to determine
the effect of water injection on the combustion char-
acteristics of a spark-ignition engine. Among the
items investigated was the effect of water upon power
output, relative peak pressure, knock-severity, timing
of initial pressure rise, delay of peak pressure and
the slope of the initial pressure rise.

In an ordinary nonknocking combustion process the
progress of the flame front is more or less orderly
across the combustion chamber. The knocking process
has the same flame progress for part of the flame
travel, but terminates with the extremely rapid in-
flammation of the balance of the unburned fraction.

A comparatively high local pressure occurs as the
result of the almost instantaneous combustion of the
lastSfraction of the charge to burn when knocking occurs.
This inequality of pressure in the combustion chamber
is of very brief duration, for the last fraction of the
charge almost immediately expands to equalize the pres-
sure. This creates a pressure-wave disturbance that
increases the heat transfer and results in loss of
power in the case of severe knocking. Also, this pres-
sure wave travels with the speed of sound, back and forth
through the gases in the combustion chamber, until dis-

sipated by friction effects. The frequency is dependent

THE

 

Edward E. Towe

on the velocity of the waves and the space in which they
are confined, and the knocking sound, or ping, is deter-
mined either by the_frequency of the pressure waves, or
by natural frequency of the vibrating member.

As an aid to pictorial representation of combustion
characteristics, a pressure pickup and flywheel-gradua-
tion magnetic pickup were used and the corresponding
signals fed into a dual-beam osilloscope. A normal
nonknocking pressure curve will be smooth in the rise
and fall of pressure. In a knocking process the pres-
sure curve will rise smoothly, but when falling off the
pressure curve has a superimposed pressure wave which
indicates knock.

Among the factors which influence the knock process
are fuel characteristics, mixture conditions, compression
ratio, ignition timing and combustion chamber design.
One method to eliminate combustion knock is the cool-
ing of mixture before induction into the engine. The
most simple method of cooling the intake charge is to
inject a volatile fluid with high latent heat into the
charge. In this investigation the volatile fluid used
was water.

This investigation indicates that the addition of
water to the intake charge has some effect upon all the

items investigated. A standard knock pattern was obtained

Edward E. Towe

by using a 87.5% octane fuel at a 7 to 1 compression
ratio, and 30 inches of Hg. absolute manifold pressure.
The injection of a 32% water-to-fuel ratio, resulted in
a complete elimination of knock. The power output
measured in indicated mean effective pressure decreased
as the percentage of water increased. The relative
peak pressure was decreased by over one-half with the
addition of 79% water. The timing of the initial pres-
sure rise and the delay of peak pressure point were
both delayed the same amounts with an increase in water
injected. In other words the pressure curve was shift-
ed to the right with the rise of pressure occuring on
the left side. The slope of the initial pressure rise
decreased as the addition of water increased. The
maximum amount of water injected was 79%. As the water
increased toward this amount the output became unsteady,
indicating a tendency to completely drown out the com-
bustion. If the water was injected in amounts over 80%,
a complete loss of power would occur.

This investigation produced satisfactory conclusions
to most of the questions indicated above. However, more
work should be done to eXplain the wide variance in the
peak pressure which occured even during normal combustion.
This was a serious handicap for the author in obtaining
desirable results and photographs of the effect of water

injection.

II
III

IV

VI
VII

VIII

TABLE OF CONTENTS

Introduction . . . . .
Discussion of the Problem .

Data . . . . . . . .

A. Preliminary Investigation
B. Water Injection Investigation

C. Presentation of Combustion

Photographs . .
Calculated and Plotted Results
Discussion of Results .
Conclusion

Appendices . . . . . .

A. Description of Equipment

B. Description of Test Equipment

Assembly . . .

C. Calibration of Measuring

Equipment . . .

D. Calculations Leading to
Published Results

Bibliography 0 e o e e

10
10
11

1‘2
18
22
2:5
25
25

27

28

29
32

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.

Run
Run
Run
Run
Run
Run
Run
Run
Run
Run
Run

Run

NHHmQWHUOwib'

t" .

FIGURES

100% Octane - No Water . .

90% Octane - No Water . .

87.5% Octane - No Watero -

80% Octane -
87.5% Octane
87.5% Octane
87. 5% Octane
87.5% Octane
87.5% Octane
87.5% Octane
87.5% Octane

87.5% Octane

Supercharged Engine

Camera, Pressure Monitor and Oscilloscope

Water Injection Tank .

No Water . .

12.2%‘Water
19.8%'Water
32% Water .
54.6% Water
39% Water .
62% 'Water .

75% Water .
79% Water .

Assembly . .

O

GRAPHS

Water (%) vs Imep and Relative Pressure . . 19

Water (%) vs Initial Pressure Rise and

Delay of Peak Pressure . . . . . . . . 20

Water (%) vs Slope of Initial Pressure
Rise . . . . . . . . . . . . . 21

.y'"~.'lm'. . -

um ”

6

INTRODUCTION

Knocking has imposed a serious limitation upon
the maximum power obtainable from an internal-com-
bustion engine. Increasing compression ratio or
manifold pressure or both will increase power output,
but both also increase the tendency to knock. Re-
duction in knock can result in increased power. One
method of decreasing knock is the addition of water
to the intake charge.

The addition of water also has an effect upon
other characteristics connected with combustion. If
the related effects are not too adverse, the addition
of water could be an important factor in the ability
to incrase power output and efficiency of an internal-

combustion engine.

DISCUSSION OF THE PROBLEM

Much work has been done with water injection, with
the primary interest in the gain in the resulting power
output without knock. It is accepted that water acting
as an internal coolant will suppress knock by lowering
the intake-charge temperature. Little is known about the
effect of water on the actual combustion process. With
that in mind this investigation was instigated to obtain
some results that pictorially represent the effect of
water injection on combustion characteristics.

In the selection of variables the compression ratio,
manifold pressure, air temperature, and engine tempera-
ture were either considered constant or held constant.
The air temperature'during the runs varied from 113
degrees F. to 115 degrees F. Both the oil and and air tem-
perature were considered as being constant. The compres-
sion ratio was 7 to l and the manifold pressure was held
at 50 inches of Hg. absolute.

A single-cylinder, variable-compression, CFR knock-
testing engine was used. A pressure pickup was inserted
into the cylinder head, and its signal fed through a
monitor into a dual-beam oscilloscope. A magnetic pick-
up was used to pick up the flywheel graduations, which

were also fed into the scope. A Palaroid-Land camera

was used to record the signals. This camera was select-
ed because of the ability to observe the photograph
when the test run is being made. The water injection
equipment consisted of a small cylindrical tank, which
was filled with water. Regulated compressed air acting
upon the tOp of the water forced water out the bottom
line to a nozzle into the intake manifold. By varying
the air pressure the amount of water injected could be
changed.

The testing procedure was divided into two sections.
In the first section the octane number was lowered in
order to obtain a standard knock pattern. Runs were
made at 100%, 90%, 87.5% and 85% octane and photographs
were made of each run. The power output was found
by using the brake force in pounds, subtracting the
friction force in pounds and multiplying by 4.23, which
gives the units in pounds per square inch (Imep). The
brake force is the scale reading when engine is run-
ning and the friction force is the scale reading when
the engine is being motored. A octane number of 87.5%
was selected as the one with a standard knock pattern,
which could be held on the scope satisfactorly. If the
knocking was too intense the pressure signal would jump
off the range of the oscilloscOpe and be very difficult

to photograph.

Using a 87.5% octane gasoline, water was injected
in various amounts measured in percent of fuel used.
During all the runs the air and fuel flow were measured
and the fuel-air ratio calculated. Photographs were
taken of each run.

Due to the wide variance of pressure in the engine
all of the photographs have to be interpreted in re-
spect to an average pressure curve. The timing signal
appears on the sc0pe as a series of pips, which are
five degrees apart measured on the flywheel. Top dead
center is one of the pips which is a little bit higher
than the rest. In all the photographs this top dead

center point is indicated by an arrow.

TABLE I

PRELIMINARY INVESTIGATION

The Determination of Octane
Number for Desired Knock Pattern

Conditions of Operations:

10

7:1 Compression Ratio
Constant Manifold Pressure

(30 in. Hg. abs.)

Constant Air Temperature
Constant Engine Temperature

Vary Octane Number

 

 

 

 

 

 

 

 

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a.
A 100 .215 2.8a .075 23.2 8.4 62.6 no knock
B 90 .214 2.54i.oe4l 23.0 8.5 61.5 no knock
C 87.5 .224i2.64l.085 23.0 8.5 61.5 some knock
D 85 .224 2.66 .08 23.0 8.4 61.9 more knock
i very unstable

 

 

 

 

 

 

 

 

 

TABLE II

11

Water Injection Investigation

The Determination of the Effect

Conditions of Operations:

of Water Injection on Combustion Characteristics

7:1 Compression Ratio
Constant Manifold Pressure
(50 in. Hg. abs.)
Constant Air Temperature
Constant Engine Temperature
Constant Octane Number (87.5)

Vary Water to Fuel Ratio

 

 

 

 

 

 

 

 

 

 

 

 

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a.
E 12.2 .250 2.78 .090 22.6 8.6 59.2 light knock
F 19.8 .240 2.62 .091 22.5 8.5 59.2 very light
knock
G 52 .217 2.08 .104 21.5 9.2 52.0 no knock
output steady
H 54.6 .240 2.64 .091 21.4 8.9 54.0 no knock
output steady
I 59 .225 2.52 .097 21.2 9.0 51.6 no knock
output steady
J 62 .258 2.48 .096 20.2 9.6 44.9 no knock
output steady
K 75 .258 2.54 .102 19.6 9.0 44.8 no knock
output unsteady
L 79 .227 2.50 .091 20.0 9.0 46.5 no knock

 

 

 

 

 

 

 

 

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Fig. 1 100% Octane
No Water-Run A

 

Fig. 2 90% Octane
No We ter—Run B

_ 12

 

Fig. 3 87.5% Octane
No Water-Run C

 

Fifi. 4 80% Octane
o Water-Run D

 

Fig. 5 87.5% Octane
12.2% Water-Run E

 

Fi . 87.5 Octane
lg.8§‘Water?Fun F

15

   

 

Fig. 7 87.5% Octane
652%'Water-Run G

 

F1 . 8 87.5% Octane
5%.6% Water—Run H

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Fig. 9 87.5% Octane
59% Water—Run I

 

%. 87.570 00133116
62% Water-Run J

_

 

§ .

Fig. 11 87.5% Octane
75% Water-Run K

 

’ ' x

 

‘4‘ ‘ I

Fig. 12 87.5% Octane
9% Water-Run L

CALCULATED RESULTS

Water (% of fuel)

V8.

Power Output (Imep)
Peak Pressure (Relative)
Timing of Initial Pressure
Rise (deg. before TDC)

Delay of Peak Pressure

18

(deg. after TDC)
SIOpe of Initial Pressure
Rise (deg.)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Water (56) o 12.2 19.8 :52 54.6 :59 62 '73 '79
Power Output
61.5 59.2 59.2 52.0 54.0 51.6 44.9 44.8 46.5
(Imep)
Peak Pressure
8.7 8.0 7.0 7.0 6.0 6.0 6.0 5.0 4.0
(Relative)
Timing of ITxitia1
Pressure Rise 12 10 10 6 5 5 5 5 2
( deg. before TDC)
ODelay of Peak
Pressure 18 20 20 22 22 22 22 25 28
(deg. after TDC)
sIope 01' Initial
Pressure Rise 40 59 58 57 55 55 54 55.% 52
(deg.)
La.

 

19

CURVES

AAN C n;

I
1

PERFUR

Water(%) vs Imep and

Relative Pressure

mpHCD

.HQMW
smehqw

 

Water % of Fuel

2O

PERFORMANCE CURV 3

Rise and Delay of
Peak Pressure

Nater(%) vs Initial Pressure

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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22
DISCUSSION OF RESULTS CBTAINhD

As expected the addition of water was very success-
ful in completely eliminating knock. When the percent-
age of water had reached 32% all traces of knock had
been removed from the pressure wave. With the addition
of a maximum of 79% water the Imep. was reduced by about
25% in roughly a straight line relationship. The same
addition reduced the relative peak pressure by over
50%. This might indicate a means of having the same
power output without a high peak pressure. The tim-
ing of initial pressure rise as measured in degrees
before TDC decreases as the water injected increases.
The delay of peak pressure as measured in degrees after
TDC increases. When these two items were plotted on
the same graph it can be seen that the two slapes are
nearly equal. This fact when applied to the pressure
diagrams means that the curves are displaced down on
the combustion cycle. The slope of the initial pres-
sure rise decreases as the amount of injected water

increases.

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23

CONCLUSION

The effect of water injection on the combustion

characteristics of an internal-combustion engine is
something that can not be readily found by just the
measurement of shaft output. Observation of the
pressure wave and timing signal pattern and their
relationship to one another provides an excellent
means of finding the actual effect of water on the
combustion process. The items that were investigated
include the relative peak pressure, knock-severity,
timing of initial-pressure rise, delay of peak pres-
sure and the slope of the early-combustion line.
All of these factors can be found by inspection of
the photographs taken during each run. The indica-
ted mean effective pressure is calculated from the
scale reading.

As the amount of water injeCted into the manifold
increased the indicated mean effective pressure de-
creased in straight line relationship with a 25% drop
occuring with a 79% water injection. This drOp in
power could be explained as a result of one or two
factors. If part or 311 of the water vaporizes dur-
ing the intake stroke this would decrease the amount
of air available for combustion and thus lower the

Imep. The water will probably be heated into the

24

superheated steam region, which will require energy.
Some of this energy will be returned to the cycle

on the power stroke, but a good percentage would be
exhausted into the atmosphere as in any Rankine steam
cycle. This would also result in a overall power
decrease.

The latent heat of the water injected will de-
crease the temperature of the intake charge, which
will lessen the severity of knock. This was veri-
fied by the author as the severity of knock deereas-
ed with water addition. The complete elimination of
knock under test conditions was accomplished with 32%
water injection.

The relative peak pressure was decreased by over
one-half with the addition of 79% water.

The timing of the initial-pressure rise and of
the peak pressure point were both delayed the same
amounts with an increase in water injected. In other
words the combustion pressure curve was shifted to the
right (rise of pressure occuring on the left side).

As the addition of water increased, the lepe of early-
combustion line decreased. ,When the amount of water
reached 73% the output became unsteady, and in amounts
over 80% there was a tendency to completely drown out
the combustion, which might result in a complete loss

of power.

25

APPENDIX
A. Description of Equipment

The engine used in this investigation was a ASTM-CFR
knock-testing engine made by the Waukesh Motor Co. This
engine is a single-cylinder four-stroke valve-in-head
engine with a,3 1/4 - in. bore and a 4 1/2 - in. stroke.
It is of the variable-compression type having a compression
ratio from 4:1 to 10:1. The test compression ratio was
7:1. The same engine may be run in five ASTM methods;
motor, research, aviation, supercharge and cetane. The
supercharge method was used in this investigation.

The engine is connected to a synchronous induction
motor, which maintains a constant engine speed. The motor
is used for starting purposes and then floats on the line.
Fig. 13 is a photograph of the supercharge unit. 7

Water for injection purposes was obtained by com-
pressed air acting upon a small cylindrical tank forcing
water through a nozzle into the intake manifold. Water
flow was varied by changing tank pressure by means of a
pressure regulator. Fig. 15 is a photograph of the water

injection tank.

26

A. cent.

The timing signal was obtained by a magnetic pick-
up mounted to record the flywheel graduations.

For pressure measurement a EP-2000 model pressure
pickup made by Control Engineering Corportion was used.
This pickup has a range of ~15 to 2000 psi for dynamic
pressures up to 20,000 cycles per second.

A DuMont twin-beam cathode-ray oscillosc0pe Model
332—A was used to observe the pressure-wave and timing
graduations. A Polaroid-Land camera recorded the cor-
responding patterns on film. Fig. 14 is a photograph

of the camera, pressure monitor and oscillOSCOpe.

27

B. Description of Test Equipment Assembly

The supercharge induction system consists of a com-
pressed air line with a control valve which is connected
to an air tank. Between this air tank and a second tank
is a calibrated orifice with a water monometer attached.
From the second tank the air goes through an adjusting
valve to a surge tank mounted over and connected to the
intake man ifold .

The fuel system uses an injector pump connected to
a corresponding injector nozzle.

The scale connected to the dynamoneter is calibrated
in pounds of friction force and brake force which read

to the left and right of zero respectively.

28

C. Calibration of Measuring Equipment

The air flow manometer is calibrated in minutes to
consume 1/4 lb. of air. The fuel calibration was in
minutes to consume 1/4 lb. of fuel. By dividing the
first by the second the F/A ratio can be found directly.
The water injected was calibrated the same as the fuel
so the percentage could be found by dividing the two.

The manifold pressure reads in inches of mercury
absolute.

The timing signal observed on the oscillosc0pe
photographs show relatively high pips. These pips are

5 degrees apart.

D. Calculations Leading to Published Results

The results were obtained by in large from the
inspection and measurment of the combustion process
photographs. The mean effective pressure was found
by multiplying the indicated load by 4.23. The indi-
cated load is the difference between brake load and

friction load.

30

any ..
,T. Li...

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.Il

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l.”

 

 

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Fig. 13 Supercharged
Engine Assembly

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Camera, Pressure

Monitor and Oscillosc0pe

Fig. 14

 

 

 

 

 

Fig. 15 Water
Injection Tank

31

 

BIBLIOGRAPHY

Lichty, Lester C., Internal Combustion Engines,
Sixth Edition, McGraw-Hill, New York, 1951.

 

Rowe, M.R. and Ladd, G.P., Water Injection for
Aircraft Engines; SAE Journal, Fan. 1945, pp-

 

 

26-37

Cattaneo, A. C., Bollo, F. G. and Stanly, A. L.,
A FetrOLeum Engineer Looks at Aircraft Fuels,
SAE Journal, Feb. 1946, pp- 55-33.

 

 

 

Eaton, D.C., Cruising Economy b Use of Water

 

injection, SAE Journal, ‘Feb. 1 6, pp-81-87.

 

Thompson Products, Inc., Thompson Vitameter
Brochugg, 1951.

 

 

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090 16 '57

 

 

 

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