Strict NO x emission regulations set for marine vessels by Tier III standard make ship owners/operators finding new efficient methods fulfilling these requirements. Utilization of LNG as main fuel at the moment is one of the most promising solutions with lean burn spark ignited (LBSI) engines and low pressure dual fuel (LPDF) ones being of primary choice. Technology provides not only low NO x levels, but also allows to reduce operational costs due to LNG currently being a cheaper fuel. The main drawback of low-pressure gas engines is rather high levels of methane slip, especially at low loads, as a result of poor fuel utilization due to low operational fuel-air ratios. Nevertheless, there are no standards that directly regulate methane slip for marine gas engines, but the topic starts to receive more and more attention due to the concerns associated with environmental effect of methane as well as due to ship operators analyzing ship data more thoroughly revealing substantial increase in gas fuel consumption at low loads. Presented study summarizes all gas engine technologies that are available for the maritime sector considering their current status and maturity and present a comprehensive measurement data summary for the main groups, namely LBSI and LPDF engines. The measurement data pool consists of both on-board and test-bed emission data revealing an interesting moments such as possible "overtuning" of engines for low NO x resulting in excessive levels of methane slip, importance of on-board measurements due to their more realistic nature, utilization of non-perfections, like

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A smooth transition to the use of gas engines instead of conventional engines in marine shipping is a logical pathway for compliance with tightening environmental regulations. Currently, five major gas engine concepts are applied in maritime sector. In this paper, a review of the marine gas engine concepts was performed with a focus on the control of combustion and emission. To assess all the contributors to combustion and the emission formation process, three main factors were outlined: design, operational parameters and fuel. The assessment of gas engines was conducted based on these factors. The present paper helps to provide an understanding of the current progress in development of marine gas engines towards improving of combustion efficiency and reducing the emissions. Moreover the knowledge gaps, particularly in four-stroke marine high-pressure gas engines, were identified.

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Environmental restrictions now favor cleaner fuels, and Natural gas (LNG) is one of the most promising alternative fuels. Highly efficient natural gas fuelled engines have been developed since around 1990. These engines are now entering maritime applications, offering significant emission reductions, both in a local and global perspective. Using LNG as fuel reduce NOx emissions by up to 90%, SOx and particulate matter (soot) are reduced by 95–100% and CO2 emissions are reduced by up to 25%, when compared to traditional marine fuels. These emission reductions are significant contribution especially in local and regional environments. Using LNG as a clean fuel also offers a significant increase in total energy efficiency. Combining power and heat generation, natural gas fuelled engines for on-shore power generation offer a total thermal efficiency of 80–90%, depending on the waste heat recovery rate. For liquid fuels exhaust heat recovery is limited due to the sulfur content, which may cause acid corrosion. Onboard ships, LNG fuelled engines have potential to utilize waste heat to obtain significant higher thermal efficiency than their diesel engine counterpart. LNG is mainly available from fossil sources, but now also increasingly from renewable sources as bio-gas. For storing and transportation LNG is preferred as less challenging compared to high pressure CNG. On the coast of Norway a LNG distribution system is now being built, supplying a fleet of more than 40 ships. LNG is transported by special designed small LNG carriers from the production plants to a series of main terminals along the coastline. From these main terminals the LNG is distributed by trucks to the local fuelling stations, or for direct fuelling of the ships. This paper will present the basic technology and experiences from this full scale LNG fuel system. The paper will discuss local and global environmental benefits, technical solutions, safety issues, and costs issues related to the distribution system and the on-board fuel installations.