The influence of propulsion system design on the carbon footprint of different marine fuels

Övrigt konferensbidrag, 2013

Rising environmental awareness and stricter environmental regulations have increased the interest in new fuels and energy efficiency measures in the shipping industry. Different fuels have different physical and chemical properties that affect the performance of internal combustion engines, e.g. the efficiency, the exhaust gas emissions, and the potential for energy recovery. This has an impact on the potential propulsion efficiency as well as on the life cycle environmental performance. The aim of this study is therefore twofold. First, to assess the potential for optimising the energy use of the propulsion system dependent on fuel choice and second, to assess the overall life cycle global warming potential of the optimised systems. Three fuels are compared, heavy fuel oil (HFO), marine gas oil (MGO), and liquefied natural gas (LNG), in combination with two exhaust gas cleaning technologies, scrubbers and selective catalytic reduction (SCR) units. Data from one year of actual operation with a product tanker are used as a base for the optimization. The results show that the solution with the lowest fuel consumption and carbon footprint is a two-stroke engine with waste heat recovery (WHR) powered by LNG. The synthesis of an optimization procedure for the propulsion system and an LCA approach leads to very interesting results. The different carbon content of different fuels, together with methane slip, leads to a better estimation to the carbon footprint of different propulsion systems. On the other hand, a better insight of the differences between different propulsion arrangements allows performing a more accurate comparison between different fuels. The potential for WHR has a particularly relevant influence on the final result.