DIESEL ENGINE WASTE HEAT HARNESSING ORC DEVICE

asme-orc2015 Tracking Number 92

Use of ORC in waste heat recovery is widely seen as a viable and promising solution for increasing energy efficiency and emission reduction efforts. Recently, several of “on-board” vehicular applications have been patented and further development of similar systems is on-going [1]. Along attempts to control the costs, the quest for a safe and justifiable choice of a working fluid with appropriate thermodynamic performance continues. Flammability and toxicity are of primary concern, especially when exhaust heat is utilised, and further environmental issues may arise. Component design, size and costing are also under scrutiny. Superiority of mixtures over pure fluids has been documented in the literature. Zeotropic mixtures in particular are an attractive choice, as they provide a better thermal match due to the temperature glide they exhibit. A mixture can also offer improved thermodynamic behaviour, such as lower exergy destruction and extended temperature range [2]. We have studied use of several organic fluids in bottoming ORC systems in diesel-powered vehicles [3] and we are expanding our approach to diesel generators. Both pure fluids and their mixtures were considered, and their advantages and drawbacks were identified. Cycle operational parameters were optimised to allow for safe device operation while achieving satisfactory outputs. Selected working fluids were compared in terms of thermal and exergy efficiency as well as the required turbine size and power produced. In addition to fluid selection our approach is focused on design and safety elements compatible with common diesel generators. We comment on applicability of high-temperature working fluids, which diesel exhaust can thermally support, whilst taking in account practical risks associated with the use of flammable and toxic substances, as well as fluid stability, material compatibility and size limitations. REFERENCES 1. Capata, R. and C. Toro, Feasibility analysis of a small-scale ORC energy recovery system for vehicular application. Energy Conversion and Management, 2014. 86(0): p. 1078-1090. 2. Radulovic, J. and N.I. Beleno Castaneda, On the potential of zeotropic mixtures in supercritical ORC powered by geothermal energy source. Energy Conversion and Management, 2014. 88(0): p. 365-371. 3. Koelsch, B. and J. Radulovic, Utilisation of Diesel Engine Waste Heat by Organic Rankine Cycle. Applied Thermal Engineering, article in press.