A study on the energy recovery system from waste heat of engine using a thermoelectric generator

Abstract

It is well known that the heat efficiency of internal combustion engines currently being used in the automobiles cannot exceed a maximum 35%. The reason is that only around one third of fuel is converted into a power energy and the rest of it is disposed as a cooling loss by the cooling water and the exhaust gas loss. It is possible to improve efficiency of engines for the automobiles if the cooling loss and the exhaust gas loss are minimized. The technology which uses waste heat from exhaust gas from automobiles draws attention as a solution. The objective of this study is to establish the basic technology of waste energy recovery system which obtains regenerated energy with thermoelectric elements using waste energy from the engines. In this study it was aimed to provide a basic information that is required for optimization of waste energy recovery system such as difference between the high temperature heat source and the low temperature heat source and shape of the heat sink to maximize the efficiency of waste energy recovery system. Also, it was intended to secure the basic technology necessary for developing an optimum waste energy recovery system according to operation condition of internal combustion engines. The heat efficiency of internal combustion engines used in the automobiles cannot exceed a maximum 35%. The reason is that only around one third of fuel is converted into a power energy and the rest of it is disposed as a cooling loss by the cooling water and exhaust gas. Therefore, the objective of this study is to secure a base technology for system development which recovers energy which otherwise disposed by using a thermoelectric element. The study comprises of forecasting the temperature distribution in the waste energy recovery system using a simulation model and then the theoretical power generation performance of the thermoelectric element was understood. After that an optimum thermoelectric module was selected and the thermoelectric generator was fabricated using the selected module. The power generation performance of the thermoelectric generator was measured and analyzed according to its attaching methods and the operation conditions. Meanwhile, the power generation performance of the thermoelectric element using the cooling water was analyzed in order to maximize the efficiency of waste energy recovery system with the low temperature heat source. The power generation performance was analyzed under different driving condition and then improvement direction was found. Finally the power generation performance of the thermoelectric generator according to the system operating condition was analyzed by attaching the thermoelectric generator on the real engine system. The fuel efficiency and CO2 reduction can be expected by applying technology which regenerates the waste heat energy which otherwise is disposed as an exhaust gas and a cooling water into a power energy. If this technology is developed and applied, it is possible to expand it towards the various fields not only in the current gasoline engines and diesel engines but also in the hybrid cars and engines for the industrial and power generation purposes. We also can expect a technologically superior position in the competitiveness in the overseas markets by developing a key technology of fuel efficiency and CO2 reduction. Therefore, the objective of this study is to provide a basis technology for developing the system which recovers waste exhaust gas energy by using a thermoelectric element.