Development of an integrated waste heat recovery system consisting of a thermoelectric generator and thermal energy storage for a propane fueled SI engine

In this paper, an integrated waste heat recovery system consisting of a thermoelectric generator and a latent heat thermal energy storage system was constructed to convert the wasted heat energy in a spark-ignition engine into useful energy. The TEG used in the integrated system has a three-layer structure formed of two cold-side heat exchangers placed on the upper and lower surfaces of the rectangular mid-exhaust heat exchanger. A total of 2x12 = 24 pieces of TEM were used between the lower and upper TEG_ec_hex and mid-TEG_ex_hex. For LHTES, a 3-layer heat exchanger consisting of a vertical copper tube placed in the middle of two cylindrical coils in a cylindrical tank with a diameter of 280 mm and a height of 350 mm was used. Three different configurations (Case_1, Case_2 and Case_3) were designed for the integrated system, in which exhaust gases, engine coolant, and HTF are used in different combinations. As a result, while the TEG_power is 69.395 W in Case_1, it decreases to 64.375 W in Case_2 and 62.417 W in Case_3. The total energy generated in the TEG at 7200 s is 500.27 kJ, 463.99 W, and 449.97 kJ for Case_1, Case_2, and Case_3, respectively. The stored energy in PCM_hex at 7200 s is 1372.91 kJ in Case_1, but it increases to 2255.16 kJ in Case_2 and to 2559.39 kJ in Case_3. While the fuel energy recovered by the integrated system is 1.03% in Case_1, it increases to 1.49% in Case_2 and 1.66% in Case_3.