a study of cooling system of a spark ignition engine to improve thermal efficiency
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7/30/2019 A Study of Cooling System of a Spark Ignition Engine to Improve Thermal Efficiency
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A Study of Cooling System of a Spark Ignition Engine to Improve Thermal Efficiency
Tatsuya Kuboyama1, Yasuo Moriyoshi
1, Mitsuru Iwasaki
2and Junichiro Hara
2
1Department of Artificial Systems Science, Chiba University, Chiba, Japan
(Tel : +81-43-290-3916; E-mail: tkuboyam@faculty.chiba-u.jp)2Calsonic Kansei
Abstract: To improve thermal efficiency of gasoline engines, the effect of coolant system on fuel consumption rate is
studied in this report. The authors tried to control the flow of cooling water to find an optimized flow system to improve
thermal efficiency, especially for the cold start condition. Experiments were carried out using a four-cylinder SI engine.
Three test conditions of i) normal cold start, ii) cold start without operating the water pump and iii) cold start but with
heated engine oil were measured. Temperatures of cooling water at some positions were measured during the
warming-up time. Secondly, the effect of cooling water temperature on thermal efficiency at a steady state condition wasexamined. As a result, a higher temperature causes an improvement of thermal efficiency due to a reduction i n
mechanical friction.
Keywords: Gasoline engine, Thermal efficiency, Cooling system, Cooling water temperature
1. INTRODUCTION
Improvement of thermal efficiency has been strongly
demanded for internal combustion engines. One of themethods to increase theoretical thermal efficiency is an
increase in compression ratio. However, the increase
in compression ratio is limited by knocking. A
reduction in energy loss including cooling loss and
mechanical friction also improves brake thermal
efficiency. It is well known that cooling watertemperature and combustion chamber wall temperature
largely affect cooling loss and knocking. Temperatureof lubricant oil affects mechanical friction. High oil
temperature reduces oil viscosity leading to decreasing
friction loss. In summary, thermal management has
been more important for combustion engines forimproving thermal efficiency. In recent days,
electrically controlled water pump and electric thermo-
stat have been utilized to optimize cooling water
temperature according to operating conditions[1], [2].
It is considered that the development of these
electrically controllable devices allows more precise
thermal management for improvement in performance
of gasoline engines.
In the present study, as a first step to develop asophisticated controlling method for a cooling system of
a gasoline engine, thermal efficiency during cold
start operation and steady state operation were
experimentally investigated using a
commercially available four-cylinder gasoline
engine.
2. TEST ENGINE AND CONDITIONS
Table 1 shows the specifications of the test engine. Acommercially available four-cylinder gasoline engine
was used. The engine has a displacement volume of
1240 cm3, and a compression ratio of 9.8. The ECU
(Electronic control unit) which is normally applied to
production engine was used for controlling of engine
operating parameters, such as an ignition timing and a
fuel injection timing. Figure 1(a) shows cooling water
path and measurement locations of cooling watertemperature for cold start testing. During the warm up
period, thermo-stat closes, and cooling water circulates
through the bypass. After a cooling water temperature
increases, thermo-stat opens, and cooling water
circulates through the radiator which is soaked in the
water tank. Figure 1(b) shows a cooling water pathand measurement locations of wall temperature for
steady state testing. In the steady state testing, thecoolant water path for the cylinder block and that for the
cylinder head are separated. This allows independent
control of temperature and flow rate of cooling water
for the cylinder head and the cylinder block of the testengine.
In this system, temperature in the water tank is
controlled. A cooling water temperature is not directly
controlled but determined by the water tank temperature
and operating conditions. Cooling water temperature
was measured at ten locations shown in figure 1 (Ch 1
Ch 10) during cold start experiment. Additionally,
intake and exhaust gas temperature, cylinder head wall
temperature at the spark plug location was measured.In-cylinder pressure of #3 cylinder was measured by a
piezo-electric pressure transducer (Kister 6117B).
Concentrations of exhaust emissions including CO, O2,
NO, HC, CO2 and mass ratio of air to fuel (A/F) were
measured by an exhaust gas analyzer (HORIBA,
MEXA-584L).
Experiments were carried out during cold start
condition and steady state conditions. During the cold
star testing, the engine operation was started with a
cooling water temperature of 25oC, and the cooling
water temperature and exhaust emissions were
measured for 15 minutes with a sampling rate of 1 Hz.
In-cylinder pressure of #3 cylinder was measured at twotimes, at 4 minutes and 13 minutes after start of engine
SICE Annual Conference 2011September 13-18, 2011, Waseda University, Tokyo, Japan
PR0001/11/0000-0467 400 2011 SICE- 467 -
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operation.
The cold start testing was conducted with threedifferent conditions.
a) Normal cold start operationb) Cold start operation without operating a water
pump. In this case, cooling water did not circulate
during warm up duration.c) Initial temperature of lubricant oil increases up to
100oC.
Table1 Engine specifications
Engine TypeIn-line
4-cylinder
Compression ratio 9.8
Displacement [cc] 310.0
Bore x Stroke [mm] 71.0 x 78.3
Connecting rod length [mm] 120.75
Idle speed [r/min] 700
Thermostat open temperature [oC] 821.5
Thermostat close temperature [oC] 77
In the steady state testing, to investigate the effect of
cooling water temperature on thermal efficiency,
cooling water temperature for the cylinder block and
that for the cylinder head were varied as shown in Table
2. Mass averaged cooling water temperature was fixed
among the three cases. A higher cooling water
temperature for cylinder head would have effect on
indicated thermal efficiency because the cylinder head
wall temperature affects combustion characteristics and
knocking limit. Also, a higher cooling water
temperature for the cylinder block is expected toimprove a brake thermal efficiency by reducing
mechanical friction due to an increase in lubricant oil
temperature. In this experiment, the engine was
running at 2000 rpm. Spark timing was set at the
minimum advance for best torque (MBT). The engine
load was varied from IMEP of 300 kPa to 900 kPa.
Table 2. Experimental conditions
Cylinder block
coolant water
temp. C
Cylinder head
coolant water
temp. C
Case 1 80 C 80 C
Case 2 60 C 100 C
Case 3 100 C 60 C
3. RESULTS AND DISCUSSION
3.1 Effect of cooling system on engine performance
during cold start condition
Figure 2 shows temporal variation in cooling water
temperature during cold start testing.With a normal cold start operation (a), cooling water
temperature increases during warming up operation
(until 590 sec after start of engine operation). This isbecause the thermo-stat does not work during warming
Fig.1(a) Cooling water path and cooling watertemperature measurement locations for cold start
experiment
Figure 1 (b) Cooling water path and wall
temperature measurement locations for steady stateexperiment
up operation. It is found that difference in measured
temperature at location Ch 2 and Ch 8 is 20oC. This
indicates that there is temperature difference between
the cylinders. Cylinder wall temperature distribution
should be reduced to improve total performance of agasoline engine, because engine operating parameters,
such as ignition timing, are determined and restricted by
the worst cylinder. Once a cooling water temperature
increases (after 590 sec. from start of engine operation),temperature of cooling water suddenly decreases. This
is because the thermo-stat begins to work, and relatively
low temperature cooling water is introduced into the
engine cooling path from the radiator. Shortly after the
decrease in cooling water temperature, the thermo-stat
closes again, and cooling water temperature increases.After warming up operation, cooling water temperature
is kept constant.
In case that the water pump is stopped during warmup operation (b), cooling water temperature increases
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even though thermo-stat opens because low temperature
water is not introduced.In case that the initial lubricant oil temperature
increases up to 100oC, temporal variation in cooling
water temperature is similar to the normal cold start
conditions. However, warm up duration decreases by
approximately 95 seconds. High temperature oilwould warm up engine components. This would reducewarm up duration. The similar variation in cooling
water temperature between different measurement
locations to the normal cold start operation is observed
in the case (b) and (c). It could be concluded that the
cooling water temperature distribution during cold start
operation would not be affected by cooling watercirculation and lubricant oil temperature. To realize
uniform water temperature distribution and uniform
cylinder wall temperature distribution, a basic design of
the cooling water path must be optimized.
0
20
40
60
80
100
120
140
0 300 600 900
Time[sec]
Temperature[]
CH1
CH2
CH7
CH8
(a) normal cold start condition
0
20
40
60
80
100
120
140
0 300 600 900
Time[sec]
Temperature[
]
CH1
CH2
CH7
CH8
(b) cold start w/o water pump condition
0
20
40
60
80
100
120
140
0 300 600 900
Time[sec]
Temperature[]
CH1
CH2
CH7CH8
(c) cold start with initially warmed oil
condition
Fig.2 Temporal variations of coolant temp.
Figure 3 shows engine speed, exhaust gas
temperature, lubricant oil temperature during cold start
operation. It can be seen that the difference in the
experimental conditions does not affects engine speed
and exhaust gas temperature. Figure 4 shows fuelconsumption rate and cumulative fuel consumption. The
engine operation started 2 seconds after start of data
acquisition. From these figures, it can be seen that a
large amount of fuel is consumed during first 5 seconds
after start of engine operation. It is also found that the
amount of fuel consumed during cold start with normal
operation (a) is largest among the three cases. Fuel
consumption with high initial oil temperature is lowest.
Fuel consumption during cold start operation could beimproved by 2.6 % with stopping cooling water
circulation, and by 3.5 % with an initial high
temperature lubricant oil.
(a) Engine speed
(b) Exhaust gas temperature
(c) Lubricant oil temperatureFig.3 Temporal variation engine speed, exhaust
gas temperature and lubricant oil temperature
for different cold start conditions
3.2 Effect of cooling system on engine performance
during steady state operation
Figure 5 shows effect of cooling water temperature
on cylinder head wall temperature. It is found that
cylinder head temperature increases with increasingcoolant water temperature on cylinder head. Also, it
0
200
400
600
800
1000
1200
1400
1600
1800
0 300 600 900
Time[sec]
Enginespeed[r/min]
Normal
Without belt
Hot oil start
0
50
100
150
200
250
300
350
400
0 300 600 900
Time[sec]
Temperature[]
Normal
Without belt
Hot oil start
0
10
20
30
40
50
60
70
0 300 600 900
Time[sec]
Temperature[]
Normal
Without belt
Hot oil start
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can be seen that the exhaust side wall temperature is
more sensitive to the cooling water temperature.Figure 6 shows effect of cooling water temperature on
thermal efficiency. Indicated thermal efficiency was
not affected by the cooling water temperature.
However, brake thermal efficiency could be improved
by increasing the cooling water temperature for thecylinder block. Brake thermal efficiency with Case 3(Block 100
oC) was improved by 3 to 5%, compared to
Case 1(Block 80oC). This is probably because of a
reduction in mechanical friction due to an increase in
lubricant oil temperature with the increase in a cooling
water temperature for the cylinder block. From the
results obtained in this study suggest that thermalefficiency could be improved by appropriate controlling
of cooling water temperature depending on the
operational conditions. As a next step, the authors will
try to develop a controlling strategy of cooling water
temperature for improving a thermal efficiency.
(a) Fuel mass flow rate
(b) Fuel mass flow rate (expanded)
(c) Cumulative fuel consumption during coldstart oeration
Fig.4 Effect of cold start conditions on fuelconsumption
Fig. 5 The effect of coolant water temperature oncylinder head wall temperature
(upper: intake side, lower: exhaust side)
Fig.6. The effect of coolant water temperature on
thermal efficiency and mechanical loss
0
0.5
1
1.5
2
2.5
0 300 600 900
Time[sec]
Gasolinemassflow
rate[g/s]
Normal
Without belt
Hot oil start
0
0.5
1
1.5
2
2.5
0 5 10 15 20
Time[sec]
Gasolinemassflow
rate[g/s]
Normal
Without belt
Hot oil start
0
2
4
6
8
10
12
0 5 10 15 20
Time[sec]
Gasolinemassflow
rate[g]
Normal
Without belt
Hot oil start
80
90
100
110
120
130
140
150
160
#1 #2 #3 #4
Walltemp.
(Intakeside)oC
Cylinder number
Head 80/Block 80
Head 100/Block 60
Head 60/Block 100
80
90
100
110
120
130
140
150
160
#1 #2 #3 #4
Walltempe.(Exh.side)oC
Cylinder number
Head 80/Block 80Head 100/Block 60
Head 60/Block 100
15
20
25
30
35
40
0 200 400 600 800 1000Brakethermalefficiency%
IMEP kPa
Head 60/Block 100
Head 80/Block 80
Head 100/Block 60
15
20
25
30
35
40
0 200 400 600 800 1000
Brakethermalefficiency%
IMEP kPa
Head 60/Block 100
Head 80/Block 80
Head 100/Block 60
10
15
20
25
30
35
40
0 200 400 600 800 1000
Mechanicalloss%
IMEP kPa
Head 60/Block 100
Head 80/Block 80
Head 100/Block 60
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4. SUMMARY
As a first step of developing a control strategy of
cooling system of gasoline engines for improvement in
thermal efficiency, thermal efficiency during cold start
operation and steady state operation were
experimentally investigated using a commerciallyavailable four-cylinder gasoline engine. Experimental
results can be summarized as follows;
(1) Fuel consumption during cold start operation couldbe improved by 2.6 % with stopping cooling water
circulation, and by 3.5 % with an initial high
temperature lubricant oil.
(2) During cold start operation, a spatial distribution ofcooling water temperature which would result in
wall temperature variation between the cylinder
was not affected by oil temperature and cooling
water circulation. This indicates that a basicdesign of the cooling water path is dominant factor
for the spatial distribution of a cooling water
temperature.
(3) A higher cooling water temperature for the cylinderblock could improve brake thermal efficiencyduring steady state operation because of a reduction
in mechanical friction. With the increase in
cooling water temperature for the cylinder block
from 60oC to 100
oC, break thermal efficiency was
improved by 3 to 5%.
ACKNOWLEDGEMENT
The authors would like to thankKistler Japan, Co.
ltd., for their support in the pressure
measurements. Mr. S, Notoya and K. Toida of
Chiba University are also acknowledged for theirsupport in the experimental works.
REFERENCES
[1] E.Sonntag et al., The New Family of Small 4
-Cylinder Engines, JSAE paper No.20075365, 2007.[2] A. Eiser et al., The new 1.8L TFSI engine from
Audi, Part 1 Base engine and Thermo-management,
MTZ vol. 72, pp. 23- 39, 2011.
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