13-08-2014, 12:40 PM
PROJECT REPORT ON THERMOELECTRIC GENERATOR IN RECOVERING WASTE HEAT OF ENGINE EXHAUS
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ABSTRACT
The main objective of this paper is to recover the waste heat from the automotive engine exhaust into useful electrical energy by using “thermoelectric power generator” .Automotive engines reject a considerable amount of energy to the ambience through the exhaust gas. Significant reduction of engine fuel consumption could be attained by recovering of exhaust heat by using thermoelectric generators. Changing the heat energy of the exhaust gases into electric power would bring measurable advantages. Modern cars equipped with combustion engines tend to have large numbers of electronically controlled components. Contemporary car engines exchange apto 30-40% of heat generated in the process of fuel combustion into useful mechanical work and losing roughly 15 terawatts of power in the form of heat to the environment. Thermoelectric devices could convert some of this waste heat into useful electricity. Therefore, even partial use of the wasted heat would allow a significant increase of the overall combustion engine performance. The observed tendency is to replace mechanical components with the electronic ones. This increases the demand for electric power received through the power supply systems of the vehicle. This tendency will undoubtedly remain at least due to the legal regulations connected with the on-board diagnostic systems, which force a more comprehensive control of operation of the vehicle components in the respect of safety improvement and emission control.
INTRODUCTION
Automotive Thermoelectric Generators (ATEG) recovers heat that escapes from a vehicle powered by an internal combustion engine, and generate electricity with the heat. This leads to the significant increase of demand for electric power in the vehicle which has to be generated by the alternator. It is predicted that if only 6% of the heat contained in the exhaust gases was changed into electric power, it would allow to lower fuel consumption by 10% due to the decreased waste resulting from the resistance of the alternator drive. Power generation system using the thermoelectric generator should generally consist of the following components: heat exchanger, thermoelectric module, cooling system and DC/DC voltage converter
PRINCIPLE OF TEG
When heat is applied to one of the two conductors or semiconductors, heated electrons flow toward the cooler one. If the pair is connected through an electrical circuit, direct current (DC) flows through that circuit. This effect is called as seebeck effect. The Seebeck effect is a phenomenon in which a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances
THERMOELECTRIC EFFECT
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice-versa. The thermoelectric effect refers to phenomena in which a temperature difference creates an electric potential or electric potential creates a temperature difference
WORKING OF TEG
When two different conductors are placed in contact, electrons flow from one to the other if the energy levels of the electrons are different in the two materials. The higher energy electrons cross the junction until the energy levels are the same on both sides. The thermoelectric module is made from two conductors whose energy levels change at different rates when the temperature changes. If the junctions are not at the same temperature, there are unequal differences in energy levels across the junctions. Thus, unequal numbers of electrons have to cross the junctions and unequal voltages are established. Since there is a net voltage around the loop, a current will
IMPARTANCE
Through the application of thermoelectric generators (TEG), in the future a proportion of the energy carried by the exhaust gases that would previously have been lost will be recovered as electrical energy. The German Aerospace Center (DLR) has developed TEG for use in vehicles for doing this, and, resulting from collaboration with the BMW Group, 200 W of electrical power in a test vehicle was achieved in a demonstration. Given the use of future materials, performances of up to 600 W can be expected, yielding a usage potential of 5 %. The current research focus is aimed at improving the manufacturing technique with a view to future standard production applications
LOCATION OF TEG IN AUTOMOTIVE ENGINES
The location of the thermoelectric generator is an important factor, decisive of its operability. The TEG generator can be installed on the exhaust pipe immediately between the collector and the catalytic converter or behind the catalytic converter. The heat is absorbed from the exhaust pipe and later converted into electricity by using TEG generator
The testing of the temperature distribution was performed at different engine speeds: 2300 and 3300 rpm. The temperatures received at lower engine speed are higher, even though the difference of temperature of the exhaust gases measured for the both engine speeds in front of and behind the heat exchanger is at every engine load point higher for the 3300 rpm by 50°C on average. However, in the first case the coolant flow of 21 l/h was used. At 3300 rpm the flow was 10 times higher, which lead to smaller differences in coolant temperature in front of and behind the coolers, and at the same time to the greater efficiency of heat absorption from exhaust gases. This situation is illustrated by Fig., which shows that the most efficient operation of the system was at 3300 rpm.
CONCLUSION
The performance of the heat exchanger system forms the basis for continuing the process of design optimization. The designed model of heat exchanger allowed for the utilization of 0.6 to 5.0 kW of exhaust gas energy depending on the operating parameters of the engine. However, the analysis of temperature distribution points out that, upon introduction of specific changes into the design, it is possible to recover even 25 kW of heat energy. Assuming the 5% efficiency of the thermoelectric modules it could allow to obtain the maximum electric power of app. 750 W. This power is comparable to the power of typical alternators used in cars with 1.3 dm3 engine capacity. It should be expected that much greater generator performance can be obtained by building it in the exhaust system of spark-ignition engine types, due to the higher temperatures of exhaust gases.