Power production from a car exhaust heat recovery system utilising thermoelectric generators and heat pipes

Orr, B 2016, Power production from a car exhaust heat recovery system utilising thermoelectric generators and heat pipes, Doctor of Philosophy (PhD), Engineering, RMIT University.

Document type: Thesis
Collection: Theses

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Title Power production from a car exhaust heat recovery system utilising thermoelectric generators and heat pipes
Author(s) Orr, B
Year 2016
Abstract The use of fossil fuels in a car internal combustion engine results in the release of CO2 gasses to the atmosphere. These CO2 gasses are one of the main causes of global warming. Efforts are being made to improve the efficiency of the internal combustion engine but as it is a relatively mature technology, improvements will start to plateau. Alternative methods to improve the overall efficiency of a car must be investigated. One possible area of investigation is the use of an exhaust heat recovery system. These systems have yet to be implemented in a mass produced car but they have the potential to reduce the fuel consumption of a car. A majority of the energy in the fuel used for a car is converted into heat. A large proportion of this heat is present in the exhaust gases. An exhaust heat recovery system would recover some of this heat and convert it into electricity to charge the car battery. This system could potentially reduce the load on a car alternator or completely replace it. The alternator draws power from the engine so reducing the load on the engine will result in a reduction in fuel consumption. CO2 emissions are directly proportional to fuel consumption.
Two potential technologies identified for use in an exhaust heat recovery system were thermoelectric generators (TEGs) and heat pipes. TEGs are small tile shaped devices that create electricity when there is a temperature difference over the top and bottom surfaces. Heat pipes are small cylindrical shaped devices which are used to transfer heat relatively long distances with minimal thermal resistance. A design has been proposed which uses the heat pipes to transfer heat from the exhaust gases to the TEGs and the TEGs convert some of this heat into electricity. The novelty of this design is that the system is completely passive and solid state.
Throughout the candidature, testing has been undertaken on TEGs, naphthalene heat pipes and prototype exhaust heat recovery systems. The naphthalene heat pipes were shown to have potential for high temperature heat transfer applications. An equation derived to predict TEG power output as a function of temperature difference has been validated by testing the TEGs and this equation was used for modelling of the second prototype exhaust heat recovery system. This second prototype exhaust heat recovery system produced a maximum of 38W of electricity at a thermal efficiency of 2.48%. The system consisted of eight 62mm by 62mm TEGs. If a full size exhaust heat recovery system with the same TEG thermal efficiency and heat exchanger effectiveness was fitted to a car, the predicted reduction in fuel consumption and CO2 emissions would be 1.57%.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Engineering
Subjects Automotive Engineering not elsewhere classified
Energy Generation, Conversion and Storage Engineering
Keyword(s) Automotive
Heat pipe
Thermoelectric generator
Exhaust gas
Power generation
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Created: Wed, 09 Nov 2016, 10:59:06 EST by Keely Chapman
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