Development of hybrid diesel - electric propulsion system for ships

Abstract

In our days, when environmental protection and low petroleum consumption are the top priorities of a marine engineer and a naval architect, the design and construction of fully optimized engines, smart installations and exploitation of the highest percentage of energy produced is required. As a result innovations, optimization, new concept design and simulation play a significant role in marine industry. Although 93% of the world’s trade is done by ships and by the year 2011 the emissions of CO2 will contribute to 4% of world’s CO2 emissions as well as 37% and 28% of NOx¬ and SOx emissions respectively, the marine sector is targeted.

The problem of high emissions exists, when the engine operates in the non optimum condition, a percentage relevant to engine’s MCR, tuned by the engine manufacturer. This means that in transient load (project SMOKERMEN, 2002; project HERCULES, 2007) large amounts of smoke, particle matter, NOx and SOx hazardous gasses are produced. Two stroke engines on board ships are directly coupled to the propeller using a rotating shaft. While ships operate in constantly changing environment and chartering commands change during voyage, propulsion unit have to adapt its speed and produced torque. Therefore engine loading changes to less efficient points and the SFOC is increased. Meanwhile, temperature of combustion and pressure differ from the most efficient and connected to them formulation of NOx increases along with increase in SOx, CO2¬ and smoke.

Our work is based on real operational data provided by a Greek maritime corporation with a fleet of 65 cargo ships. The obtained data contains information from 3 Post Panamax new built sister vessels, regarding fuel consumption, engine loading, weather and sea conditions along with bunker characteristics (e.g. Sulphur percentage). Phase one of the project is separated into 3 parts. The first part includes worldwide adopted methods for emission calculation. Project utilizes the “activity based method” (NTUA - Laboratory of Marine Transportations, 2008) which uses proper emission factors taken from relevant literature (VDMA Engines and Systems, 2008; MARPOL, 2005; EMEP/ CORINAIR, 2000). The second part, utilizes the voyage data of the vessels, correlates the consumption and engine loading with the weather characteristics. Furthermore, applies the assumption of constant loading of diesel engines and the existence of storage medium in order to estimate the fuel savings of the hybrid vessel. At the third part, industrial and market research was performed to find the proper storage medium. As first step, batteries were examined and different types were compared, judging by their energy density, weight, operational factors and restrictions. Also a proposal for sizing the alternative propulsion system was done and economical assessment was performed. Finally conclusions were discussed and they are summarized below:

Hybrid Technology has significant fuel savings that can be increased due to further optimization of Turbochargers and by the operation of engine in smaller margin. Furthermore emission reduction in NOx is successful due to lower combustion temperatures. Moreover, ship design and cargo capacity will be affected making the overall task difficult. Finally, Hybrid Technology is economically feasible and the Internal Rate of Return of investment varies between 4.7% until 20.7% depending on the storage medium type and the availability of kWh.

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Identifiers

ORCID for D.A. Hudson: orcid.org/0000-0002-2012-6255

ORCID for S.R. Turnock: orcid.org/0000-0001-6288-0400

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