Onboard Hybrid Propulsion and Sewage Treatment System Powered by a Stirling Engine Unit

At present, boats have to comply with very strict environmental regulations on emission production and sewage disposal. In the near future, new environmental policies on reduction of water pollution will also affect sailing boats. To reach environmental targets, a few models of new boats on the market are equipped with hybrid propulsion systems in which an electric generator is combined with a diesel engine. The electric generator, driven by the diesel engine, charges a bank of batteries which in turn powers an electric motor. The electric motor can operate in parallel with the main propulsion engine to provide more power output or on its own, when a quieter and more fuel-efficient operating performance is required during idling or docking. In this paper a Stirling engine is considered for the onboard application. The main advantage is that a Stirling engine can run continuously to charge the bank of batteries in the hybrid propulsion system or to supply power on request for onboard appliances, all whilst producing a very little noise. In addition, the heat discharged by the cooling system of the engine can be utilized for onboard sewage treatment. New environmental regulations limit the sewage disposal at ports thus making it necessary to store and treat sewage during navigation. In order to reduce sewage disposal, the engine’s thermal output is used to aid evaporation thereby reducing the quantity of waste disposed. In this work, the authors have studied the integration of hybrid propulsion and sewage treatment systems powered by a Stirling engine in order to meet these new environmental regulations and provide comfort during the navigation of sailing boats. It is anticipated that experimental tests will be carried out after once the design stage of the system has been completed.