1. Acknowledgment
F. Tavano 1, D. Ben Ayoun 2, D. Granit 2, E. Taragan 2,3, Y. Sadia 2, Y. Gelbstein 2
Thermoelectric generator modeling for a Caterpillar C7 Engine
Introduction
Caterpillar C7 engine system serves multiple kinds of armored military vehicles all over the world and the waste heat emitted can provide energy for a wide variety of
support systems. Due to the latest efficiency enhancement of thermoelectric materials, there is a dramatic increase in applicative researches about Thermoeletric Generators
(TEG). In order to outline the feasibility of using a TE device on a real engine, a simulation has been carried out by using Caterpillar C7 engine distinctive parameters for
the determination of the maximal power that could be drawn from the device itself. More specifically, the exhaust gas of the engine has been able to reach up to 580°C,
while, on average, as much as 30% of the engine maximum power (200 [kW]) is dissipated by the exhaust pipe as waste heat. Thanks to the TE generator, which has been
able to achieve up to 14% efficiency by means of state of the art materials, the hybrid system would be able to harvest about 8 [kW] of extra electricity out of 60 [kW] of
otherwise wasted thermal energy.
Based on simulations and measurements, the expected results are promising both in economic terms, reducing fuel related costs, and improved troops safety, decreasing the
exposure time of military personnel on the battlefield while waiting for refueling.
Fig. 1. Upper (a) and lower (b)
thermocouple locations along
the exhaust pipe
References
Poster No. 173
We would like to thank I.T.E (Caterpillar, Israel) and RDT (Fluke, Israel) for assisting and
providing us the generator and thermal camera, respectively.
[1] E. Hazan, O. Ben-Yehuda, N. Madar, Y. Gelbstein, Journal of Advanced Energy Materials, 11
(2015) pp. 1-8
In order to analyze the temperature regime of the exhaust pipe
along the vertical axis, two K thermocouples (TC) have been
placed on the upper (Fig 1.a), and lower (Fig 1.b) locations, where
the TEG array will be mounted in future to come.
The temperature regime was measured under different power
loads: from lack of load up to 250[kW].
Figure 2 presents the steady state maximum temperature measured
along the exhaust pipe for each load.
It is clearly seen that there is a temperature gradient along the
pipe. Moreover, there is a direct correlation between the load and
the temperature, achieving higher potential for higher loads.
Preliminary experiments and conceptual design
Objectives
1. Verification of thermal feasibility for thermoelectric generator (TEG) array by engine’s exhaust pipe temperatures modeling.
2. Mechanical assembly design and materials optimization for TEG array, under nominal operation conditions.
3. Integration of state-of-the-art TEG [1] and further optimization of the energy consumption for armored military vehicles.
1. Energy Engineering, Polytechnic University of Turin, Italy
2. Energy Engineering Unit, Ben Gurion University of the Negev, Beer Sheva, Israel
3. NRCN, Israel
(a)
(b)
Thermal camera AnalysisTemperature Regime
Fluke thermal camera Ti300 has been used in
mapping the temperature distribution on the
surface of the exhaust pipe. Emissivity
calibration has been obtained by comparing the
thermal camera and the thermocouple
measurement.
Fig. 3. Temperature mapping for a load of 250[kW]
Fig. 2. Load dependence of the temperature
Gripper Design & Thermal characterization
Fig. 4. Temperature drop trend along the designated area
A mechanical gripper has been designed as an
interface between the exhaust pipe to the TEG
array. Also, in order to achieve reasonably high
efficiency, it is a crucial to generate an
appropriate temperature gradient across the
TEG.
Design considerations:
- Minimizing parasitic thermal losses.
- Decreasing the thermal contact resistance
between the components.
- Increasing the temperature drop within the
TEG by forced convection on the cold side.
- Service temperature, thermal conductivity,
thermal expansion coefficient etc. should be
all taken into account simultaneously.
Thermoelectric generator implementation
So far, in order to verify the feasibility of the whole study, a commercial TEG based on
bismuth telluride (5-7% efficiency) has been mounted on a Caterpillar C7 engine’s exhaust
pipe, although the main driver of this research is to integrate a higher performance TEG.
A recent study [1] displayed a remarkable efficiency of up to 14%, showing the highest
efficiency ever reported before (Fig. 7). It is well known that high thermoelectric conversion
efficiencies can be achieved by using materials with, as high as possible, figure of merit 𝑍𝑇. A
significant improvement of 𝑍𝑇 upon appropriate geometrical optimization will be applied in
the next stage of the research, together with n-type PbSn0.05Te 0.92 PbS 0.08 Functionally
Graded Materials (FGM) coupled with a phase separated p-type Ge0.87Pb0.13Te compound.
The aforementioned approach will guarantee impressive thermoelectric efficiency while
operating within cold and hot junctions temperatures of 50°C and 500°C, respectively.
Fig. 5. Gripper design and cooling ribs assembly
Fig. 7. Previous study results [1] Fig. 6. System cross section FEM analysis
Finally, Finite Elements Method (FEM) analysis
has been implemented in order to deeply
investigate the system behavior under various
loads and outdoor atmospheric conditions.