20-07-2012, 12:16 PM
thermoelectric waste heat energy recovery system
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ABSTRACT
This paper proposes and implements a thermoelectric waste heat energy recovery system for internal combustion engine automobiles, including gasoline vehicles and hybrid electric vehicles. The key is to directly convert the heat energy from automotive waste heat to electrical energy using a thermoelectric generator, which is then regulated by a DC–DC Ćuk converter to charge a battery using maximum power point tracking. Hence, the electrical power stored in the battery can be maximized. This is a two way power storing system. Energy form TEG and electrical generator cum motor can be stored in the battery. Both analysis and experimental results demonstrate that the proposed system can work well under different working conditions, and is promising for automotive industry.
INTRODUCTION
Even a highly efficient combustion engine converts only about one-third of the energy in the fuel into mechanical power serving to actually drive the car. The rest is lost through heat discharged into the surroundings or, quite simply, leaves the vehicle as “waste heat”.
Until just a few years ago, however, such thermoelectric generators (TEGs) were unsuitable for use in the automobile due to their low level of efficiency. But since significant progress has been made in materials research in recent times, the performance and output of such modules has increased significantly. To generate electric power in the vehicle a thermoelectric generator is integrated in the exhaust gas manifold.
While the electric power such a system is able to generate is still relatively small at a maximum of 200 W, rapid progress in materials research already makes the ambitious objective of generating up to 1,000 W a realistic and by all means feasible proposition. This energy regeneration system also offers additional effects, such as providing the engine or the heating system with extra heat when starting the engine cold. In future thermoelectric generators will be able to reduce fuel consumption under realistic, customer-oriented driving conditions by up to 5 per cent.
REVIEW OF LITERATURE
AUTOMOBILE APPLICATIONS
The utilization of waste heat energy from exhaust gas gases in reciprocating internal combustion engines (e.g. automobiles) is another novel application of electricity generation using thermoelectric power generators. Although reciprocating piston engine converts the chemical energy available in fossil fuels efficiently into mechanical work substantial amount of thermal energy is dissipated to the environment through exhaust gas, radiation, cooling water and lubricating oils. For example, in a gasoline powered engine, approximately 30% of the primary gasoline fuel energy is dissipated as waste heat energy in the exhaust gases; waste heat energy discharged in the exhaust gas gases from a typical passenger car travelling at a regular speed is 20-30 Kw. A comprehensive theoretical study concluded that a thermoelectric generator powered by exhaust gas heat could meet the electrical requirements of a medium sized automobile.
Wide scale applications of thermoelectric in the automobile industry would lead to some reductions in fuel consumption, and thus environmental global warming, but this technology is not yet proven. Since 1914, the possibility of using thermoelectric power generation to recover some of waste heat energy from reciprocating engines has been explored and patented. A schematic diagram showing this patent of converting waste heat into electrical power applied to an internal combustion engine using a thermoelectric power generator is shown in figure.
INDUSTRIAL WASTE HEAT APPLICATIONS:
Most of the recent research activities on applications of thermoelectric power generation have been directed towardsutilisation of industrial waste heat. Vast amounts of heat are rejected from industry, manufacturing plants and power utilities as gases or liquids at temperature which are too low to be used in conventional generating units (<450 K).
In this large-scale application, thermoelectric power generators offer a potential alternative of electricity generation powered by waste heat energy that would contribute to solving the worldwide energy crisis, and the same time help reduce environmental global warming. In particular, the replacement of by-heat boiler and gas turbine by thermoelectric power generators makes it capable of largely reducing capital cost, increasing stability, saving energy source, and protecting environment.