Improvement of volume controlled thermal energy storage system using phase change material for exhaust waste heat recovery in a SI engine


Gürbüz H. , Aytaç H. E. , Akçay H. , Cahit Hamamcıoğlu H.

JOURNAL OF ENERGY STORAGE, vol.53, pp.1-12, 2022 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 53
  • Publication Date: 2022
  • Doi Number: 10.1016/j.est.2022.105107
  • Title of Journal : JOURNAL OF ENERGY STORAGE
  • Page Numbers: pp.1-12
  • Keywords: SI engine, Exhaust waste heat recovery, LHTS system, Melting, Volume control, EXCHANGER, ENHANCEMENT, PERFORMANCE

Abstract

In this paper, the effect of volume control on the melting process of phase change material (PCM) in a latent heat storage (LHTS) system used for storing the exhaust waste heat energy of a typical SI engine is explored experimentally. In the LHTS system, paraffin wax, commercially known by the code RT55, is used. A closed-loop liquid circulation system with two heat exchangers is designed with one (exhaust heat exchanger-Ex_hex) mounted to the exhaust tailpipe of the SI engine and the other (PCM heat exchanger-PCM_hex) used in the storing and melting of the RT55. The PCM_hex is designed to have a cylindrical geometry and variable internal volume and is fabricated of optical material to monitor the melting process of the RT55. The cylindrical side surface of the PCM_hex is designed as two layers for vacuum insulation application. For volume control, the movable top surface of the cylindrical PCM_hex is controlled by a linear actuator with a 1000 N capacity. Experimental studies are performed under 1/2 throttle opening and 2800 rpm constant engine speed of a propane fueled SI engine for three different PCM_hex arrangements (i.e., free volume, constant volume, and volume controlled) during 7200 s (120 min). As a result, the melting process of the RT55 with the volume controlled PCM_hex is improved, and the energy storage capacity is increased by approximately 4.57%. At the end of 7200 s for 9.136 kg solid RT55, 85.2%, 85.7%, and 87.4% liquid fractions are obtained with the free volume, constant volume, and volume controlled PCM_hex, respectively. With free volume, constant volume, and volume controlled PCM_hex, 2339.9 kJ, 2355.9 kJ, and 2446.8 kJ of energy are stored as sensible and latent heat, respectively, while 37.2%, 38%, and 39.5% PCM_hex efficiency are obtained. In addition, the rate of fuel energy stored in PCM_hex is 3.97%, 4.01%, and 4.17%, respectively.