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78: 10–2 (2016) 47–53| www.jurnalteknologi.utm.my | eISSN 2180–3722 |
Jurnal
Teknologi
Full Paper
PERFORMANCE OF A WATER PUMP IN AN
AUTOMOTIVE ENGINE COOLING SYSTEM
Mohamad Lazim Mohamed Tasuni, Zulkarnain Abdul Latiff*, Henry
Nasution, Mohd Rozi Mohd Perang, Hishammudin Mohd Jamil,
Mohd Nazri Misseri
Automotive Development Centre (ADC), Faculty of Mechanical
Engineering, Institute for Vehicle Systems and Engineering (IVeSE)
Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor,
Malaysia
Article history
Received
5 May 2016
Received in revised form
17 May 2016
Accepted
25 May 2016
*Corresponding author
zkarnain@fkm.utm.my
Graphical abstract
Abstract
A cooling system employed in an automobile is to maintain the desired coolant
temperature thus ensuring for optimum engine operation. Forced convection obtained by
means of a water pump will enhance the cooling effect. Thus it is necessary to understand
the system’s pump operation and be able to provide for the ultimate cooling of the
engine. The objective of this laboratory investigation is to study the water pump
characteristics of an engine cooling system. The crucial water pump parameters are the
head, power, and its efficiency. In order to investigate the water pump characteristic a
dedicated automotive cooling simulator test rig was designed and developed. All of the
data obtained are important towards designing for a more efficient water pump such as
electric pump that is independent of the power from the engine. In addition to this fact,
the simulator test rig can also be used to investigate for any other parameters and
products such as radiator performance and electric pump before installation in the actual
engine cooling system. From the experiment conducted to simulate for the performance
of a cooling system of a Proton Wira (4G15), the maximum power equals to 37 W which
indicates the efficiency of the pump is relatively too low as compared to the typical power
consume by the pump from the engine which are about 1 to 2 kW. Whereas the maximum
power and efficiency obtained from the simulator test rig simulator is equals to 42 W and
15% respectively.
Keywords: Water pump characteristic, cooling system, Proton Wira (4G15), simulator
© 2016 Penerbit UTM Press. All rights reserved
1.0 INTRODUCTION
The burning of fuel in the internal combustion engine
of a vehicle will produce enormous heat. During the
burning of air-fuel mixture in the engine cylinders, the
burning gas temperature can achieve to 2200OC or
higher [1, 2 & 3]. The heat produced is transformed into
kinetic energy by the pistons, connecting rod and
other mechanical components in the engine to
operate. However, not all the heat can be transferred
into useful mechanical power [4, 5]. There are about
one third of the energy produced by combustion is
converted to the mechanical power. Meanwhile,
another one third is dissipated as heat through the
exhaust and the rest of the energy are transferred by
the cooling system [6, 7].
To remove excess heat that produce by the engine,
it is necessary to have cooling system. If the high
temperature that produce by the burning air-fuel
mixture are not controlled, it will cause the breakdown
of the lubricating oil and lose its lubricating properties
[8]. However, removing too much heat through the
cylinder walls and head can lower engine thermal
efficiency .The main purpose of the cooling system are
48 Zulkarnain Abdul Latiff et al. / Jurnal Teknologi (Sciences & Engineering) 78: 10–2 (2016) 47–53
to keep the engine its most efficient operating
temperature at all engine speeds and all driving
conditions [9]. When the engine is in cool condition,
the cooling system will not normally operate to make
the engine reach operating temperature quickly. The
cooling system will only remove the excess heat when
the engine reaches normal operating temperature.
Water pump is one of the important components of
the engine’s cooling system. The pump is a centrifugal
type in a tight metal casing. The main purpose of the
pump is to maintain the circulation of the coolant
through the system. Coolant will enters pump through
the suction side and is forced to rotate by its impeller.
Then, the impeller that rotates will pull the coolant at
the outlet of the radiator and transmit to the water
jacket. The water pump is driven by the crank of the
engine through a belt. In designing the engine cooling
system, the pump performance is important which is
takes about 4.5% to 5% of the mechanical power from
the engine [3].
In the engine cooling system (Figure 1), the
circulation starts from the water pump. The role of the
pump is to circulate the coolant throughout the
system. Firstly, it will transmit the coolant to the water
jacket. Subsequently, the coolant is transferred to the
thermostat. The purpose of the thermostat is to
regulate water circulating in the system. When the
system is under the warm-up condition, the coolant
will not flow to the radiator but will be reroute via
bypass pipe. Whenever the coolant temperature
achieve the thermostat setting temperature, the flow
will be diverted to the radiator and it will cool the
coolant due to air being induced by the cooling fan.
Figure 1 Circulation of coolant [10]
The function of a water pump is to maintain the
circulation of the water through the system. Usually
water pumps are impeller-type centrifugal pumps and
are fitted at the front end of the cylinder block. The
components in the water pump are housing, with inlet
and outlet, and an impeller. The pump inlet is
connected to the lower tank of the radiator by a hose.
It is driven by the crank through a belt [4]. When the
impeller rotates, the water between the blades is
thrown out by centrifugal force and is forced to the
pump outlet into the water jacket of the cylinder
block. The water from radiator is drawn by the impeller
into the pump to replace the coolant forced out
through the outlet to water jacket.
Overall pump efficiency (Eq. 1) can be defined as
the ratio of liquid power produced by the pump to the
power transferred by the shaft [5].
(1)
The head of the pump can be determined by the
experimental arrangement as in the Figure 2 by using
the energy equation as Eq. 2:
(2)
Typically the differences in elevations and
velocities are small so Eq. 2 is then finalized as Eq.3.
(3)
Figure 2 Typical experimental arrangement for determining
the head rise gained by a fluid flowing through a pump [5]
The affinity law is the rules of the performance of a
centrifugal pump when the speed or impeller
diameter is changed. There are two sets of affinity laws
which are the impeller diameter (D) is constant and
the speed (N) is constant [6].
a) Impeller diameter is constant, D
(4)
(5)
(6)
49 Zulkarnain Abdul Latiff et al. / Jurnal Teknologi (Sciences & Engineering) 78: 10–2 (2016) 47–53
b) Speed is constant, N
(7)
(8)
(9)
2.0 METHODOLOGY
The experiment is conduct for both using real engine
cooling system and simulator test rig that has been
developed.
Figure 3 shows the schematic diagram of the real
engine cooling system with its instrumentation that has
already installed. Figure 4 shows the schematic
diagram of the simulator test rig engine cooling system
with its instrumentation installed. Figure 5 on the other
hand shows the completed simulator test rig.
Figure 3 Schematic diagram of the real engine cooling
system
Figure 4 Schematic diagram of the simulator test rig
Figure 5 Simulator test rig
The different between the real engine and
simulator is that the water jacket in the former is
substituted with the thermal storage and its
mechanical pump is substitute with the electric motor
pump.
3.0 RESULTS AND DISCUSSIONS
3.1 Real Engine
Figure 6 to 10 show the temperature profiles for
different locations using thermocouple probes placed
in the engine cooling system, at engine speed ranging
from 1000 rpm to 3000 rpm. This results are obtained
when the car in the static condition.
The cyclic shape in Figure 6, 7 and 8 means that the
electric fan at the radiator is switch off and on
automatically for a certain period of time. Moreover,
the controller will automatically switch off and on the
thermostat attached near to the outlet of the radiator.
Whenever the temperature of water at the thermostat
switch reaches at certain temperature, the thermostat
switch will switch on to allowed the fan to rotate and
pull air from in front of the radiator and vice versa
when the temperature is decrease.
There are different period of time for each cycle at
different engine speed. The higher the engine speed,
the longer the time taken to complete the cycle. This
indicates that the cooling system need more time to
gain heat generated from the combustion chamber
before cool it down because of the combustion inside
the combustion chamber continuously burn rapidly
and the temperature inside the combustion chamber
is increase as the engine speed increase [13].
50 Zulkarnain Abdul Latiff et al. / Jurnal Teknologi (Sciences & Engineering) 78: 10–2 (2016) 47–53
Figure 6 Graph of temperature against time at 1000 rpm of
engine speed
However, the temperature profiles for the 2500 rpm
and 3000 rpm as shown in the Figure 9 and 10, do not
indicate the cyclic pattern. The temperature keeps
increasing for the whole period of time as shown in the
graph. This indicates that the fan will keep on rotating
because there is a lot of heat produce in the
combustion process inside the combustion chamber.
In addition to that, the cooling system also cannot
lower down the temperature and maintain it as the
heat produce is too large. This graph may be vary if
the experiment is done while the car move at the
highest speed as there will be lot of air come from the
in front of the radiator.
Figure 7 Graph of temperature against time at 1500 rpm of
engine speed
Figure 8 Graph of temperature against time at 2000 rpm of
engine speed
Figure 9 Graph of temperature against time at 2500 rpm of
engine speed
Figure 10 Graph of temperature against time at 3000 rpm of
engine speed
In Figure 11, the flow rate of the cooling water
increase linearly to the engine speed. In addition to
that, the highest flow rate is equal to 0.00038 m3/s at
3000 rpm of the engine speed. Furthermore, the
equation obtained from the graph is Q = 1E-07N. The
linear relationship shows that the relationship between
the engine speeds and the flow rate is obeying the
affinity law. Affinity law states that the flow rate is
proportional to the shaft speed of the pump [12]. It is
also note that the engine speed is not equal to the
shaft speed of the pump. The ratio of the engine
speed to the pump shaft speed is 1.1 [14].
51 Zulkarnain Abdul Latiff et al. / Jurnal Teknologi (Sciences & Engineering) 78: 10–2 (2016) 47–53
Figure 11 Graph of coolant flow rate against engine speed
From Figure 12, the power of the water pump is
increased as the flow rate of the cooling system
increase. The maximum power is recorded as 37 W at
0.00037 m3/s of the flow rate, which is at 3000 rpm of
the engine speed. In addition to that, the power here
means that the output power gained by the water
from the engine crankshaft rotation.
Figure 12 Graph of power of water pump against flow rate
of water with different engine speed
It is observed that not all of the power from the
crankshaft is being transferred to the fluid. Basically,
there are three losses in the pump i.e. i) hydraulic
losses, ii) mechanical losses and iii) volumetric losses.
Hydraulic losses are the internal losses in the impeller
and volute or diffuser due to friction in the walls of the
liquid passageways and the continual change of
direction of the liquid as it moves through the pump.
Besides, the mechanical losses is the frictional losses
that occurs in the moving parts of the pump which are
in contact especially bearings or seal. Lastly, the
volumetric loss is due to leakage of a usually small
amount of liquid from the discharge side of the
centrifugal pump to the suction side.
The water pump is predicted to consume
approximately 1 to 2 kW of power supplied via the
engine crankshaft [15]. Based on the maximum power
shown in Figure 12, the efficiency of the water pump is
too low. By replacing the engine driven water pump
with a small electric water pump of 30 to 60 W rating,
the fuel consumption can be reduced further thus
increase the performance of the engine especially for
traction.
3.2 Actual Engine
In Figure 13, the power, head, and efficiency of the
pump against flow rate is plotted in the same graph to
get more clearly view of the pump characteristic with
the constant motor speed of 2000 rpm. Based on the
graph, the maximum head or shut-off head is equals
to 30.50 m and the maximum flow rate is equals to
0.00053 m3/s.
The efficiency reaches a maximum value at the
certain value of the flow rate. This point referred as the
normal or design flow rate or capacity for the pump.
Moreover, the points of power and head curve that
correspond to the maximum efficiency are denoted
as the best efficiency point as shown in the graph.
Based on the graph, the value for the best efficiency
point for the power is equals to 42 W, head equals to
17 m and efficiency equals to 15%. In addition to that,
the normal or design flow rate is equals to 0.00025
m3/s.
In addition, the graph in the Figure 13 is almost the
same with the typical performance characteristic of
centrifugal pump [11] and the experiment result from
the previous study [9].
Figure 13 Graph of power, efficiency, and head of the pump
against flow rate at the speed of motor 2000 rpm
Figure 14 is the graph showing the power
requirement of the tested water pump for both real
engine and simulator cooling system. The data for the
simulator is taken at 80OC to create similar operating
condition in the real engine.
52 Zulkarnain Abdul Latiff et al. / Jurnal Teknologi (Sciences & Engineering) 78: 10–2 (2016) 47–53
Figure 14 Graph of power of water pump against flow rate
for the real engine and simulator cooling system
The real engine water pump power is increasing as
the engine speed is increased but not for the
simulator. For the simulator cooling system the water
pump power is increase and reaches peak at 0.00026
m3/s and then decrease slightly. The differences
behavior of the water pump power between the real
engine and simulator are obvious. This is due to
different of the power input for the both condition. For
the simulator, the input power is almost same
throughout the experiment which is from the same
electrical source with the constant speed (2000 rpm)
of the motor. The different values of water pump
power is only due to the variation of valve opening.
Otherwise, the water pump power input in the real
engine system will depends on the engine speed
variation (1000 to 3000 rpm). The pump receives
power transfer from the engine crankshaft pulley to
the pulley that connected to the pump shaft through
the belt.
Figure 15 shows the effect of temperature on the
power of pump. The behavior of the power is not
constant for different temperature. This is due to
decreasing of water density when the temperature is
rise. When the water is heating, the volume will
increase. The pressure also will be not the same for the
different temperature.
Figure 16 shows the maximum power produced at
the each temperature based from the data in Figure
15. This graph indicates that the power will be
increased when the temperature is increased. The
increasing of power consumption is also due to the
increasing of the pressure when the temperature is
rise. In addition to this, the increasing of temperature
will cause the molecule of the water move rapidly thus
raising the temperature.
Figure 15 Graph of power against flow rate for different
temperature
Figure 16 Maximum power against Temperature
4.0 CONCLUSION
The outcome of this investigation can be divided into
two parts focussing on i) experiment work on a real
engine cooling system and ii) experiment work using a
simulator test rig that has been fabricated for the
purpose of this evaluation.
4.1 Real Engine Cooling System Experiment
i) The temperature profile, flow rate and pressure
inside the system can be determined by installing
the thermocouple, flow meter and pressure gauge
in the real engine cooling system.
ii) The linear relationship between flow rate and
engine speed is obtained. The equation is Q = 1E-
07N where Q equals to volume flow rate in m3/s
and N equals to engine speed. In addition to that,
the relationship is obeying the affinity law.
iii) From the value of the pressure and flow rate, the
power of the pump can be worked out. The
53 Zulkarnain Abdul Latiff et al. / Jurnal Teknologi (Sciences & Engineering) 78: 10–2 (2016) 47–53
maximum power obtain from the plotted graph is
equals to 37 W. Moreover, the efficiency of the
pump can be said relatively too low when
comparing the value of the highest power with the
power consume by the pump as stated in the
discussion. The engine driven pump can be
replaced by the small electric water pump that
can give the same flow requirement to the engine
which can increase the performance of the
engine.
4.2 Simulator Test Rig Experiment
A water pump characteristic can be determined from
a series of experiment using a simulator test rig. The
pump characteristics will include power, head, and
efficiency of the pump. The maximum efficiency of
the pump is 15%, maximum power of the pump is
equals to 42 W and the head at this point is equals to
17 m. The point is refers to design flow rate of 0.00025
m3/s. In addition to that, the shut-off head where there
is no flow for this pump is 30.5 m.
Acknowledgement
The authors would like to acknowledge with thanks
the research funding (Cost Centre:
A.J090803.5551.07133), provided by Automotive
Development Centre, Universiti Teknologi Malaysia,
that has made this investigation possible.
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