An exhaust heat recovery system turns waste heat energy in exhaust gases into electric energy for batteries or mechanical energy put on the crankshaft. The technology is of increasing interest as car and heavy-duty vehicle manufacturers continue to increase efficiency, saving fuel and reducing emissions. While technological improvements have greatly reduced the fuel consumption of internal combustion engines, the peak thermal efficiency of a 4-stroke Otto cycle engine is around 35%, which means that 65% of the energy released from the fuel is lost as heat.

1. Presentation on an exhaust heat
recovery system utilizing
thermoelectric
generators and heat pipes in car
Presented By
Rajbala Purnima Priya

2. Contents
Introduction
Why an exhaust heat recovery system in car
System design and components required
Experimental set up
Experimental testing
Conclusion

3. INTRODUCTION
An exhaust heat recovery system turns waste heat energy in exhaust
gases into electric energy for batteries or mechanical energy put on
the crankshaft.
The technology is of increasing interest as car and heavy-duty vehicle
manufacturers continue to increase efficiency, saving fuel and reducing
emissions.
While technological improvements have greatly reduced the fuel
consumption of internal combustion engines, the peak thermal
efficiency of a 4-stroke Otto cycle engine is around 35%, which means
that 65% of the energy released from the fuel is lost as heat.

4. Why an exhaust heat recovery system in car
Exhaust heat recovery systems are used to make use of wasted heat
from a car engine.
The purpose of exhaust heat recovery systems is to potentially reduce
the fuel consumption of the car and consequently reduce CO2 emissions
and running costs.
The reciprocating internal combustion engine, used in a majority of
automobiles, does not convert all of the energy in the fuel into mechanical
work.
.

5. Over a standard driving cycle approximately 40% of the energy used
is transferred as heat to the exhaust gases were expelled to the
atmosphere.
 An exhaust heat recovery system can extract some of this heat and
convert it into electricity.
This electricity will be used to charge a car battery therefore reducing
the load on the car alternator and potentially saving fuel.
 CO2 emissions are directly proportional to hydrocarbon fuel
consumption therefore CO2 emissions could potentially be reduced

6. System design and components required
The system consists of 8 TEG modules of 62 mm X 62 mm in size and heat
pipe modules in series
 A fan is used to simulate air flow from a car moving at speed.
A test car with exhaust system.
Fig. Cylindrical
copper/water heat pipe
Fig. A Thermoelectric
generator (TEG)

7. Fig. Schematic of the proposed car exhaust heat recovery
system

8. Experimental set up
The test car is used as the supply of the
exhaust gases.
 A flexible metal pipe is connected from
the car exhaust pipe outlet to the inlet of
the exhaust duct on the system.
 An extractor is attached to the outlet of
the exhaust duct to expel the exhaust gases
outside.
 A large cooling fan was placed at the
front of the car to prevent it from
overheating
Fig: The lab set up with the exhaust heat
recovery system attached to the exhaust pipe
of the car

9. Experimental testing
The system was tested to find its maximum power output in different orientation.
For the first test, the engine was run at 2500 RPM under no load. In this case, the
exhaust duct temperature was 218 °C and the mass flow rate was 0.0157 kg/s.
The cool air duct temperature was 31 °C and mass flow rate was 0.02 kg/s.
This test was conducted in a horizontal orientation.
When tested under above conditions, the system produced 15.17 W.
To improve the performance of the heat pipes, it was decided to test the system
upright so the heat pipes were in bottom heat mode rather than horizontal heat
mode.
After the above changes, the maximum power output of 37.85 W was recorded.
A heat pipe will perform best in bottom heat mode and perform worst in top heat
mode. Changing the orientation would therefore change the rate of heat transfer
and consequently change the power output.

10. Fig.1 Top heat mode orientation Fig. 2. Horizontal heat mode
orientation
Fig. 3.Bottom heat mode
orientation

11. Fig. Electrical power generated in 3 different orientations

12. Conclusion
An exhaust heat recovery system has been proposed with the
potential of reducing the fuel consumption, CO2 emissions and
running costs of a car.
This particular design proposed is completely solid state and
passive.
The system was tested in different orientations and the bottom
heat mode was found to be the best orientation.
The maximum power generated during testing was 38 W . This
results in a maximum TEG thermal efficiency of 2.46%.

13. All the references, contents, results are taken
in this presentation from the paper whose link
is given below.
B. Orr, A. Akbarzadeh, P. Lappas, “An exhaust
heat recovery system utilising
thermoelectric
generators and heat pipes”, Applied Thermal
Engineering (2016), doi:
http://dx.doi.org/10.1016/j.applthermaleng.
2016.11.019
REFERENCE