Abstract
In an automotive engine, around 40% of the heat produced by fuel combustion is wasted through exhaust gas. Conversion of part of this heat into electricity by a thermoelectric generator has the potential to improve the vehicle fuel efficiency. Developing an automotive exhaust thermoelectric generator (AETEG) for such conversion involves many challenges. The performance evaluation of the generator at the system level is one among them. The present work describes the design and development of a test rig for the evaluation of various characteristics of an AETEG. The test rig simulates the typical thermo-physical conditions of the engine of a light-duty vehicle using hot air. The temperature and the mass flow rate of the hot air entering the AETEG can be varied independently. The instruments provided in the system can measure the pressure drop, voltage-current and power-current characteristics of the AETEG under various inlet hot air conditions. An AETEG designed and assembled containing 40 modules each of 5 W capacity is tested for its performance in this test rig. Under the highest inlet temperature of 385°C and mass flow rate of 255 kg/h tested, the AETEG showed less than 1 kPa pressure drop with maximum open circuit voltage of 157 V and power of 27 W. The test rig could successfully map the temperature non-uniformity in the hot side heat exchanger and its effect on power output from each module. The overall efficiency of AETEG is only 0.4% mainly due to poor efficiency of the hot side heat exchanger.
Highlights
The conversion of energy by any process usually results in a certain amount of its wastage
Pressure and temperature measurement In automotive exhaust thermoelectric generator (AETEG), the conversion efficiency and the pressure drop across the heat exchanger are some of the critical factors that needs to be evaluated
Based on the calculation using the above equations it was found that the ∆P due to the pin fin arrays was about 0.1 kPa at TiH of 385○C, corresponding to a hot air flow rate of 255 kg/h. Such a low value indicates that the pressure drop across the heat exchanger is predominantly due to the expansion and contraction losses at the truncated rectangular pyramidal structures
Summary
The conversion of energy by any process usually results in a certain amount of its wastage. In the case of chemical to mechanical energy conversion that occurs in an internal combustion engine (ICE), the wastage is very significant. In a typical ICE, only 30% of the thermal energy generated by the fuel combustion is converted into mechanical work, and the remaining 70% is wasted. The recovery of a part of this thermal energy, mainly lost through exhaust gas (nearly 40%) and its conversion into useful energy can improve the overall engine efficiency. Significant efforts have been made, especially in the past two decades, to utilize the exhaust gas heat by using various recovery methods.. Thermoelectric (TE) technology has gained prominence due to its distinctive advantage of direct conversion of thermal to electrical energy which can be stored and used Significant efforts have been made, especially in the past two decades, to utilize the exhaust gas heat by using various recovery methods. Among them, thermoelectric (TE) technology has gained prominence due to its distinctive advantage of direct conversion of thermal to electrical energy which can be stored and used
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