Improving the Efficiency of Marine Power Plant Using Stirling Engine in Waste Heat Recovery Systems

Abstract

Energy seems to be the subject at the heart of many of the greatest issues and debates facing the world today. Global warming is a huge issue that promises to change the face of the planet in unimaginable and irreversible ways. This alone is considered as a major driving factor in development of energy efficient technologies for various purposes including marine transportation for sustainable development. The predominant source of power in a ship is the Diesel engine which has evolved as a highly efficient means of generating necessary power for propulsion and auxiliary uses However it is widely recognized that about 30% of the total energy converted in a Diesel engine is rejected in the exhaust gas. On large ships some of this heat is recovered partly using exhaust gas boilers. However on a majority of small ships or on large ships on short voyage durations, there is no or limited mechanism to recover this energy. The recently mandated energy efficiency design index (EEDI) has the provision to deduct the power produced from any energy saving device thereby giving credit to the design. While some of the energy saving devices being contemplated, use wind and solar power, it is being recognized that some of the energy from the engine exhaust gases and cooling water can still be tapped to generate power resulting in improved energy efficiency of the plant.
One of the ways of utilizing waste heat without conversion to steam is to use a Stirling engine. A Stirling engine requires only an external heat source (such as external combustion chamber or waste heat) for its operation. For marine use this engine could be utilized to generate some amount of power from the exhaust gas. This paper advocates the use of heat balance studies for improving the efficiency of the marine power plant. An estimation of the power which could be generated from a Stirling engine is presented based on estimation of the power which could be produced from the exhaust gas of a high speed (560 KW) propulsion engine and expected savings in fuel.