A review on regulations, current status, effects and reduction strategies of emissions for marine diesel engines

A review of emissions reduction technologies for low and medium speed marine Diesel engines and their potential for waste heat recovery

There has been mounting concerns over energy consumption and environmental impacts due to an increase in worldwide shipping activities. The International Maritime Organization has adopted regulations to impose limits on greenhouse gas emissions originated from fuel combustion of marine vessels. Such regulations are introduced in terms of energy efficiency design index and energy efficiency operational indicator. Extensive electrification of ship propulsion and shipboard power systems has been vastly proposed in the literature to make onboard energy systems more efficient. However, energy efficiency in the context of maritime transport is becoming even more stringent. Various technologies and operational practices therefore are being proposed to ensure full compliance with the tightening restrictions. The methods to increase energy efficiency and environmental performance of all-electric ships to satisfy such requirements involve integration of energy storage with a contribution of intelligent power management to optimize power split between various power generation sources; a tendency toward DC power distribution due to eliminating the need of all generators to be synchronized at a specific frequency; installation of unconventional propulsors for greater maneuverability requirements while keeping fuel consumption low; adoption of low carbon content fuel like liquefied natural gas for dual fuel diesel electric propulsion; establishment of onboard renewable energy systems for alternative clean power options; fuel cell integration in complementary operation with conventional diesel generators. This paper identifies promising technologies and practices that are applicable to onboard energy systems of all-electric ships and also reveals energy efficiency sensitivity of all-electric ships to different applications. The proposed strategies should be eventually combined with alternative technology-based and operational-based measures as implemented on conventional propulsion ships in order to realize full potential for energy efficient operation.

Energy efficiency of integrated electric propulsion for ships – A review

Alternative fuel options for low carbon maritime transportation: Pathways to 2050

The electric propulsion system as a green solution for management strategy of CO2 emission in ocean shipping: A comprehensive review

Vessel ozone depleting emission regulations are regulated in Annex VI of the MARPOL Convention, wherein the maximum levels of NOx, SOx and suspended particles are established These increasingly strict regulations, together with the increase in natural gas consumption and its price, have conditioned propulsion systems implemented on board vessels

This article reviews the different propulsion systems used on board vessels for the transport of Liquefied Natural Gas (LNG) The study describes the main characteristics of the propulsion systems, and the advantages and drawbacks that come along with these, from its very beginnings up to the systems installed to date The described propulsion systems include both gas and steam turbines, combined cycles, 2 and 4 stroke internal combustion engines, as well as reliquefaction plants, while encompassing mechanical, electric and Dual Fuel (DF) technology systems

The propulsion systems implemented have undergone continual alteration in order to adjust to market needs, which were always governed by both efficiency and the possibility of consuming boil-off gas (BOG), always in compliance with the strict antipollution regulations in force

The current direction of LNG vessel propulsion systems is the installation of 2-stroke DF low pressure engines due to their high efficiency and their possibility of installing a BOG reliquefaction plant Another great advantage of this propulsion system is its compliance with the IMO TIER III emission regulations, without the need to install any supplementary gas treatment system

Review of propulsion systems on LNG carriers

H-2 production by the steam reforming of excess boil off gas on LNG vessels

At present, LNG vessels without reliquefaction plants consume the BOG (boil-off gas) in their engines and the excess is burned in the gas combustion unit without recovering any of its energy content. Excess BOG energy could be captured to produce H2, a fuel with high energy density and zero emissions, through the installation of a reforming plant. Such H2 production would, in turn, require on-board storage for its subsequent consumption in the propulsion plant when navigating in areas with stringent anti-pollution regulations, thus reducing CO2 and SOX emissions. This paper presents a review of the different H2 storage systems and the methods of burning it in propulsion engines, to demonstrate the energetic viability thereof on board LNG vessels. Following the analysis, it is identified that a pressurised and cooled H2 storage system is the best suited to an LNG vessel due to its simplicity and the fact that it does not pose a safety hazard. There are a number of methods for consuming the H2 generated in the DF engines that comprise the propulsion plant, but the use of a mixture of 70% CH4-30% H2 is the most suitable as it does not require any modifications to the injection system. Installation of an on-board reforming plant and H2 storage system generates sufficient H2 to allow for almost 3 days' autonomy with a mixture of 70%CH4-30%H2. This reduces the engine consumption of CH4 by 11.38%, thus demonstrating that the system is not only energy-efficient, but lends greater versatility to the vessel.

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Ignacio Arias Fernández

Papers

Review of propulsion systems on LNG carriers

H-2 production by the steam reforming of excess boil off gas on LNG vessels

Generation of h2 on board lng vessels for consumption in the propulsion system

Energy efficiency and environmental measures for Floating Storage Regasification Units