Machinery Division in South Korea, backed LNG fuel as the best common solution for addressing all the environmental and efficiency challenges. He highlighted the two main options for LNG propulsion systems – low pressure using a pump and vaporiser, or a high pressure system. There are also several LNG tank options available, with development work continuing on LNG tank design and location onboard. “Owners need to look at the whole system design including the vessel’s operating profile,” he said. Christoph Rofka, senior general manager
at ABB Turbo Systems, outlined the benefits of enhancing the performance of engines using two technologies. “Although two-stage turbocharging is not new technology, it is new for marine applications,” he said.
Developing this for marine engines involves model development, with a doubling of pressure ratios up to 12 compared with single-stage turbocharging. This results in higher efficiency by more than 75 per cent and more compact two-stage systems can be developed. He also highlighted the use of advanced variable valve trains,
The CIMAC panel in Shanghai debated integration of propulsion systems featuring individual valve control for
closing, opening and lift height. Valves feature steep closing flanks, but with no increase in mechanical load. Variation from cycle to cycle replaces conventional control elements. “These technologies can be used in combination to enhance performance of medium speed diesels by up to 5-7 per cent with higher pressure ratios. For gas engines the potential is up to 10 per cent efficiency gain,” Mr Rofka indicated.
Further potential performance gains involved engine integration, standardisation and service- friendly designs such as integrated two-stage turbochargers, gas engines with diesel-like flexibility, improved diesel mode for dual-fuel engines and use of different operating modes. Yasuhiro Itoh, managing director Niigata
Power Systems in Japan, focused on hybrid propulsion systems, using an actual example of two tugs being operated in Japan by Tokyo Kisen in Yokohama. He pointed out that tugs require high powered engines but for 75 per cent of the time they operate at less than 20 per cent load resulting in energy being wasted. “Our idea is for main engine shutdown at low loads, using lithium ion batteries instead that can be re-charged while alongside the pier. Another option is a hybrid solution without batteries, using auxiliaries instead of the main engine when operating at low loads.” He described the first hybrid tug in Japan that went into service in March 2013, the Tsubasa, with a plug-in hybrid propulsion system using a battery. This system saves 32 per cent in fuel consumption. In October 2013 another tug, the Ginga, went into service using a hybrid system without batteries. “The challenge
www.mpropulsion.com
is balancing the higher initial cost of these systems, especially the battery, with the savings in operation,” Mr Itoh said. The hybrid system currently costs about 40 per cent more than a conventional propulsion system, he said. In answer to a question as to who should be the driver for such developments, engine makers or shipowners, Mr Itoh said that for these tugs Niigata supplied the engines and propeller using an integrated system it developed. “But there is also an important driver from co-operation with owners. It does not have to be the enginebuilder who is the driver.”
In tests, Niigata simulated the system and
achieved a 20 per cent saving, but he said that actual savings in operation are 30 per cent. “The tug captain wanted to use the battery for as long as possible and used it for more than expected and more than it was used in the simulation, so the operator involvement is also significant in optimising performance.”
He said that on hybrid propulsion systems, benefits from energy saving and emission reduction have been verified. But maximising the impact of hybrid propulsion with fuel and emission reduction depends on the actual operating engine load pattern. For example, Mr
be applied to ships operating for long periods under low load or idle speed and ships for which rapid loads are required – such as tugs, offshore support vessels and some ferries operating short distance shuttle services. For compliance with IMO Tier III, batteries can be used in emissions control areas, with gas engines driving generators. In the future, the batteries could be recharged using renewable energy, such as wind, solar and tidal power. Summarising the presentations Mr Müller said that they demonstrated there is still more potential for internal engine optimisation. “New solutions include gas engines and hybrid systems and operational aspects are also important.” He raised the issue of rules for exhaust
Itoh suggested, hybrid propulsion could
gas after-treatment systems and the need to monitor actual performance. “Class societies are still developing rules for after-treatment. Where rules have been developed they are mainly focused on safety aspects due to the chemicals involved, rather than performance.” Mr Wojik referred to WHR systems, commenting that there is a trade-off between the system cost and the fuel savings for each vessel, which would depend on its operating profile. Mr Rofke stressed: “We do not see that it is possible to meet upcoming emission regulations by internal engine modifications alone. We are seeking to optimise performance and reduce emissions, but this will also need external measures such as exhaust gas treatment systems.
Karl Wojik (AVL List): System efficiency is the next big challenge
He expressed concern that, with new systems, exhaust gas temperatures are getting lower and the requirement for exhaust gas to produce steam to heat the fuel will not be met and hence a requirement for an additional steam boiler. “So there is a need for all the consequences of such developments to be considered, he said.” Mr Wagen suggested that battery prices will reduce in the future and their capacity will increase. “We will see increased use of batteries and energy storage, even on conventional vessels.” MP
Marine Propulsion I April/May 2014 I 59
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