A Thermoelectric Generator Replacing Radiator for Internal Combustion Engine Vehicles

Abstract

Abstrak Pada makalah ini diusulkan dan dikembangkan sebuah generator termoelektrik (TEG) temperatur rendah menggunakan pendingin air mesin untuk kendaraan ringan. Hasil eksperimen dari kendaraan uji, yang mana ukuran mesin adalah sekitar 2,0 liter, menunjukkan bahwa purwarupa generator termoelektrik yang dibuat dapat membangkitkan lebih dari 75W untuk kondisi pengemudian 80 km/jam, dan daya output adalah sekitar 28W selama kondisi diam. Hasil penelitian menunjukkan bahwa TEG yang diusulkan dapat menggantikan radiator konvensional tanpa penambahan pompa air atau peranti mekanis, kecuali untuk komponen dasar sistem pendingin air radiator. Kata kunci: generator termoelektrik, kendaraan ringan, pendingin air mesin, pipa panas Abstract We have proposed and developed a low temperature thermoelectric generator (TEG) using engine water coolant of light-duty vehicles. Experimental results from test vehicle, of which engine size is about 2.0 liters, show that fabricated prototype Thermoelectric Generator generates more than 75W for driving condition of 80 km/hour, and output power is about 28W during idle condition. The proposed TEG can replace conventional radiator without additional water pumps or mechanical devices except for basic components of legacy water cooling system of radiator.

Full text

TELKOMNIKA, Vol.9, No.3, December 2011, pp. 523~530
ISSN: 1693-6930
accredited by DGHE (DIKTI), Decree No: 51/Dikti/Kep/2010  523
Received July 7
th
, 2011; Revised July 25
th
, 2011; Accepted August 6
th
, 2011
A Thermoelectric Generator Replacing Radiator for
Internal Combustion Engine Vehicles
Nyambayar Baatar
1
, Shiho Kim
2
1
Department of Electrical Engineering, Chungbuk National University
2
School of Integrated Technology and Yonsei Institute of Convergence Technology
Yonsei UniversitySongdo, Incheon 406-840, Korea Ph./Fax: +82-327495836
e-mail: nyambayar@chungbuk.ac.kr
1
, shiho@yonsei.ac.kr
2
Abstrak
Pada makalah ini diusulkan dan dikembangkan sebuah generator termoelektrik (TEG) temperatur
rendah menggunakan pendingin air mesin untuk kendaraan ringan. Hasil eksperimen dari kendaraan uji,
yang mana ukuran mesin adalah sekitar 2,0 liter, menunjukkan bahwa purwarupa generator termoelektrik
yang dibuat dapat membangkitkan lebih dari 75W untuk kondisi pengemudian 80 km/jam, dan daya output
adalah sekitar 28W selama kondisi diam. Hasil penelitian menunjukkan bahwa TEG yang diusulkan dapat
menggantikan radiator konvensional tanpa penambahan pompa air atau peranti mekanis, kecuali untuk
komponen dasar sistem pendingin air radiator.
Kata kunci: generator termoelektrik, kendaraan ringan, pendingin air mesin, pipa panas
Abstract
We have proposed and developed a low temperature thermoelectric generator (TEG) using
engine water coolant of light-duty vehicles. Experimental results from test vehicle, of which engine size is
about 2.0 liters, show that fabricated prototype Thermoelectric Generator generates more than 75W for
driving condition of 80 km/hour, and output power is about 28W during idle condition. The proposed TEG
can replace conventional radiator without additional water pumps or mechanical devices except for basic
components of legacy water cooling system of radiator.
Keywords: engine water coolant, heat pipe, light-duty vehicles, thermoelectric generator
1. Introduction
Conversion of waste heat to electricity using thermoelectric generators(TEG) in internal
combustion engine (ICE) powered vehicles has been focused as a green energy technology to
improve fuel economy and consequently to reduce emission of the green house gas of CO
2
[1-
4].
Figure 1. Typical energy split in internal combustion engines

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Only 30% of the fuel combustion energy is converted to mechanical energy, while about
40% is wasted through exhaust gas, and waste heat of engine coolant constitutes up to 30% of
the fuel consumption energy [1-2]. Only about 25% of the fuel consumption energy is used for
vehicle operations due to frictional losses. A recent study revealed that the fuel economy of ICE
vehicles can be increased by up t0 20 percent simply by capturing the waste heat of gas and
conveting about 10% of it to electricity[1-2]. Every major automobile manufacturer is working
with waste heat recovery system for improving the fuel economy of ICEV, and some of them are
trying to develop Thermoelectric Hybrid Electric vehicles [1-3]. A hybrid vehicle using Rankine
cycle co-generation system has been developed, increasing overall engine efficiency by 3.8% in
100km/h constant driving mode [3]. In order to utilize advantages and benefits of an high
temperature of exhaust gas which is more than 500˚C near the engine manifold, most of
automotive manufacturing companies are working for developing thermoelectric generator
systems using only exhaust gas [1-3]. Since the engine coolant is an important source of waste
energy, we need to develop thermoelectric generators using engine coolant as well as exhaust
gas to improve the overall fuel economy. Figure 2 shows a configuration of dual generation
waste heat recovery system for passenger vehicles [5-6].
Figure 2. Dual thermoelectric generation waste heat recovery system [5-6]
We have proposed and developed a low temperature thermoelectric generator using
engine water coolant of passenger vehicles, of which engine size is about 2.0 liters. We tried to
substitute conventional radiator for proposed TEG without additional water pumps or
mechanical devices except for basic components of legacy water cooling system based on
radiator. We also proposed a SPICE equivalent electrical model of the engine coolant
thermoelectric generator.
2. Proposed Engine Coolant Termoelectric Generator
We have aimed to substitute conventional radiator for proposed TEG without additional
water pumps or mechanical devices except for basic components of legacy water cooling
system of radiator. Since the proposed thermoelectric system generates electricity from waste
heat of coolant, it takes a heat out of the engine coolant.
The proposed engine coolant thermoelectric generator has air-cooling structure
composed of heat pipes and heat sink. The cooling performance of proposed TEG compared
with the radiator can be considerable, due to the air-cooling structure and additional cooling
effects by heat conversion to electricity. The framework of proposed TEG is composed of hot
side block and cold side block consisting of heat pipes and heat sinks as shown in Figure 3.

TELKOMNIKA
A Thermoelectric Generator Replacing Radiator for Internal
(a)
Figure 3.
Prespective illustration with detailed
thermoelectric generator. (c) The inner structure of hot side block. The arrows indicate
direction of coolant flowing Dimension is in mm scale.
The hot side block of TEG has inlet and outlet ports of engine coolant to link water cooling
system of a vehicle. Cooling plates and hot sid
Thermoelectric modules can be attached on both side of the hot side block. There are a number
of partitions to increase effective surface area of the hot side block as illustrated in
Interior structu
re of the hot side block with partition
heat to the hot side of thermoelectric modules and uniform distribution of the hot side
temperature of the thermoelectric generator. The Cold side of proposed TEG has an a
system combined with heat pipes and a heat spreader. The dimension of fabricated TEG is
about 80mm(W) ×
250mm(H)
original radiator of the vehicle. 72 thermoelectric modules and 128 h
prototype of the proposed thermoelectric generator. We can replace the conventional radiator
by proposed thermoelectric generator without additional devices or redesign of engine water
cooling system.
The cold side the TEG has an efficient heat spreading structure consisting of heat pipes
and heat sinks. A heat pipe is a heat transfer device that combines the principles of both
thermal conductivity and phase transition to efficiently manage the transfer
solid interfaces [7].
ISSN: 1693-6930
A Thermoelectric Generator Replacing Radiator for Internal
…. (
Nyambayar
(c)
Prespective illustration with detailed
parts
(a) and side view (b) of the proposed
thermoelectric generator. (c) The inner structure of hot side block. The arrows indicate
direction of coolant flowing Dimension is in mm scale.
The hot side block of TEG has inlet and outlet ports of engine coolant to link water cooling
system of a vehicle. Cooling plates and hot sid
e block are placed like a sandwich structure.
Thermoelectric modules can be attached on both side of the hot side block. There are a number
of partitions to increase effective surface area of the hot side block as illustrated in
re of the hot side block with partition
-
walls enables proper transferring of coolant
heat to the hot side of thermoelectric modules and uniform distribution of the hot side
temperature of the thermoelectric generator. The Cold side of proposed TEG has an a
system combined with heat pipes and a heat spreader. The dimension of fabricated TEG is
250mm(H)
×
740mm(L), which is same length and almost half height of the
original radiator of the vehicle. 72 thermoelectric modules and 128 h
eat pipes are used in the
prototype of the proposed thermoelectric generator. We can replace the conventional radiator
by proposed thermoelectric generator without additional devices or redesign of engine water
The cold side the TEG has an efficient heat spreading structure consisting of heat pipes
and heat sinks. A heat pipe is a heat transfer device that combines the principles of both
thermal conductivity and phase transition to efficiently manage the transfer
of heat between two

Nyambayar
Baatar)
525
(b)
(a) and side view (b) of the proposed
thermoelectric generator. (c) The inner structure of hot side block. The arrows indicate
direction of coolant flowing Dimension is in mm scale.
The hot side block of TEG has inlet and outlet ports of engine coolant to link water cooling
e block are placed like a sandwich structure.
Thermoelectric modules can be attached on both side of the hot side block. There are a number
of partitions to increase effective surface area of the hot side block as illustrated in
Figure 3(c).
walls enables proper transferring of coolant
heat to the hot side of thermoelectric modules and uniform distribution of the hot side
temperature of the thermoelectric generator. The Cold side of proposed TEG has an a
ir-cooling
system combined with heat pipes and a heat spreader. The dimension of fabricated TEG is
740mm(L), which is same length and almost half height of the
eat pipes are used in the
prototype of the proposed thermoelectric generator. We can replace the conventional radiator
by proposed thermoelectric generator without additional devices or redesign of engine water
The cold side the TEG has an efficient heat spreading structure consisting of heat pipes
and heat sinks. A heat pipe is a heat transfer device that combines the principles of both
of heat between two

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526
The heat energy is transferred from cold side block to heat sink by the internal
processes of heat pipe. At the hot interface within a heat pipe, pressurized fluid in contact with a
thermally conductive solid surface turns into a vapor by absorbing the latent heat of that surface.
The vapor naturally flows through the system at atomic speeds, because of the low pressure,
and condenses back into a liquid at the cold interface, releasing this latent heat. The liquid then
returns to the hot interface through either capillary action or gravity action where it evaporates
once more and repeats the cycle.
3. Expermental Results
The proposed TEG system was fabricated and mounted on a test vehicle with engine
size of about 2.0 liters after radiator was eliminated as shown in Figure 4. The test vehicle is a
remodeled ICE vehicle simulator having engine, front wheel drive-train and electric powder
break system. We can simulate actual driving condition on the road using the test vehicle in an
indoor experimental laboratory. During experiment, we placed 72 Bismuth telluride(Bi
2
Te
3
)
thermoelectric(TE) modules with area of 4.0mm × 4.0mm to the TEG. The experiment was
performed under both idle and driving condition of vehicle.
Figure 4. Fabricated prototype TEG mounted on the ICE vehicle with engine size of
about 2 liters. Fabricated prototype TEG replaces radiator as a cooling device.
Figure 5 shows a structure and thermal imager for measuring temperature profile of
TEG during operation. Infra red images were taken from the bottom part of the TEG. Figure 6 is
a temperature profile across the Hot side block and Cold side block along with the strait line
marked in Figure 5(b) The temperature profile was measured after the test vehicle was in
steady state.In idle condition the temperature profile result of hot side block was ranged from
90˚C to 95˚C, and cold side temperature profile was about 70˚C. In this condition the
temperature difference between hot side and cold side of the thermoelectric modules is about
25˚C.
In driving condition of 80km/hour, the temperature distribution of hot side block was
from 95˚C to 100˚C , and cold side temperature profile was about 45˚C. In this condition the
temperature difference between hot side and cold side of the thermoelectric modules is about
55˚C. The cold side temperature in driving condition of 80km/hour is lower than that of idle
condition, thanks to an assistance of incoming cooling air flow since the vehicle is running. The
radiator air-cooling fan of the test vehicle was off during experiment in the driving mode to make
an equivalent condition.
Experiment results in the idle condition, the measured open-circuit voltage (OCV), short
circuit voltage (ISC) and power at the maximum point were 30V, 3.8A, and 28.5 Watts,
Coolant
in
Coolant
out

TELKOMNIKA ISSN: 1693-6930 
A Thermoelectric Generator Replacing Radiator for Internal …. (Nyambayar Baatar)
527
respectively. We used 72 thermoelectric modules (TEM) during experiments, so the maximum
output power is about 0.4 W per module at the idle condition.
(a)
(b)
Figure 5. (a) Bottom side view of the proposed TEG. (b) Infra-red image when the vehicle of
was operating in driving condition of 80 km/hour.
Figure 6 Temperature profile across the Hot side block and Cold side block along with
strait line marked in Figure 5.(b)
Hot side block
Coolant in
Heat pipe
Cold side block
TEM
Coolant out

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Figure 7. Simulation and experimental result of Voltage versus current characteristics of
proposed TEG, when the vehicle was in idle and driving conditions.
In driving mode, the increment of hot side temperature is about 5˚C, on the other hand,
reduction of cold side temperature due to incoming air-cooling is about 25˚C. The measured
OCV, ISC and maximum power point were 50V, 6A, and 75Watt, respectively. The maximum
output power is about 1.04W per module at the driving condition.The electro-thermal behavior of
a thermoelectric module has modeled as an equivalent electric circuit with model parameters of
thermal resistance(Θ
m
),Seebackcoefficient(α
m
),electric resistance(R
m
), thermal capacitance and
thermal resistance of heat spreader(R
air
)[8]. Figure 8 shows a proposed electro-thermal
equivalent electric model of an engine coolant thermoelectric generator. V
CLNT
is a heat supplied
by engine coolant; anda
f
I
f
is an incoming cooling air flow when a vehicle is running. During idle
mode incoming air flow is zero and V
CLNT
is 368V, which is representation of absolute
temperature of 95˚C. Measured R
m
is about 8.0 Ω, andα
m
is 1.36V/˚C at idle condition and
0.95V/˚C at the driving condition.
Figure 8. SPICE equivalent electrical model of the engine coolant thermoelectric generator.
WhereV
α
is α(T
h
-T
C
).
Maximum Power point tracking scheme and Lead-acid battery charging system for
conventional ICE vehicle was reported [9]. The SPICE equivalent electrical model of the engine
a
f
I
f
R
LOAD
V
CLNT
I
OUT

TELKOMNIKA ISSN: 1693-6930 
A Thermoelectric Generator Replacing Radiator for Internal …. (Nyambayar Baatar)
529
coolant thermoelectric generator will be helpful to develop a battery charge system of both
internal combustion engine vehicles and Hybrid Electric vehicles.
4. Discussions
The efficiency of the TEG in automotive applications can be estimated by [1, 4],
ε =

ౄ

ి

ౄ
√

√

౐
ి
౐
ౄ
(1)
where ZT is a figure of merit, and T
H
and T
C
are the hot-side and cold-side temperatures of the
thermoelectric materials, respectively. We used Bi
2
Te
3
TE modules with ZT ≈ 0.7. Calculated
efficiency of the TEG is 3.2% and 10.0%, in the experimental condition of idle and driving mode,
respectively.
Coolant flow speed for typical ICE vehicle is need to mechanically driven water pump
vary between from 1.0 to 1.7 L/min/KW [10]. The maximum power of test vehicle is about
100kW. The flow rate of engine coolant is about from 100 to 170 L/min. Since about 30 percent
of combustion energy is waste through engine coolant, the maximum waste power is about
30KW, which is huge amount of energy loss.
The output power of the fabricated TEG was only 75W at driving condition of 80Km/hour,
the overall efficiency of electric power generation from waste heat of engine coolant is only
about 0.4%, we estimate that the waste heat through engine coolant is about 18kW during the
driving condition with 100 KW engine.
The overall efficiency is only 0.4%, it means that we still have a lot of room to
regenerate electric energy from the waste heat of engine coolant. If we increase the number of
thermoelectric module attached on the TEG, the output power can be increased significantly.
Improvement of figure of merit of thermoelectric device is highly required for the automotive
applications.
5. Conclusion
We have proposed and developed a low temperature thermoelectric generator using
engine water coolant of passenger vehicles, of which engine size is about 2.0 liters. We also
carried out the experimental and computational modeling works to demonstrate the
performance of the proposed TEG. In the experimental results, maximum estimated output
power from proposed TEG is about 75W and calculated efficiency of the TEG is about 10.0%,
overall efficiency of electric power generation from waste heat of engine coolant is about 0.4%
in the driving mode of 80km/h. The proposed TEG can replace conventional radiator without
additional water pumps or mechanical devices except for basic components of legacy water
cooling system of radiator.
Acknowledgment
This research was supported in part by the MKE, Korea, under the “IT Consilience Creative
Program” support program supervised by the NIPA (NIPA-2010-C1515-1001-0001)
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