Performance Improving of an Internal Combustion Engine for Ship Propulsion with a Bottom ORC

This work is part of a study aiming to achieve high efficiency and low emissions in a marine propulsion system. In order to significantly enhance the efficiency of a propulsion plant, it is possible to recover the exhaust gas heat normally rejected to the atmosphere and the heat of the cooling water usually rejected to the sea. The study examines the possibility of energy recovery applying ORC (Organic Rankine Cycle) technology; this technology is very effective for recovering waste heat from low temperature sources, both from the thermodynamic and the economic standpoint. When a "combined cycle" ORC-diesel engines set up is considered for this size of engines, an increase in power output of about 10% can be expect. In addition, a significant amount of heat is released at low temperature and could be used by other ship services, or by other thermal users, in case of land based applications. In the present study several possible thermodynamic cycles are simulated using the Aspen® code, considering also different working fluids. The results are evaluated in both thermodynamics and economics terms.