ISO 23306:2020 pdf free download – Specification of liquefied natural gas as a fuel for marine applications.
Due to numerous economic and environmental factors, the use of liquefied natural gas (LNG) as fuel for marine applications has increased. The 0,10 % sulfur limit, in the sulfur emission controlled areas in Europe and the US, which entered into force on 1 January 2015 has been one of the major driving forces for using LNG as fuel for marine applications. The decision for the 0,50 % global sulfur limit from 1 January 2020 by the International Maritime Organization (IMO) might further increase the interest in LNG. The International Code of Safety for Ships using Gases or other Low-f lashpoint Fuels (IGF Code) was a response to the need of guidance in this emerging market. Since LNG-fueled vessels are likely to bunker LNG in different parts of the world, a common specification is needed for ship owners, ship operators and LNG suppliers. It would help engine manufacturers and ship designers and it is beneficial for the development of this new alternative marine fuel market.
In 2018, IMO adopted an initial strategy on reduction of greenhouse gas (GHG) emissions from ships. The strategy includes the objective to peak GHG emissions from international shipping as soon as possible, whilst pursuing efforts towards decarbonizing the sector as soon as possible in this century. It also includes the objectives to reduce the CO2 emissions per transport work and total annual GHG emissions from international shipping by 2050, with an interim target in 2030. Thus, LNG produced from renewable sources as biomethane that can reduce CO2 emissions when used as marine fuel is also addressed in this document.
LNG is produced in different locations in the world in liquefaction plants. Large scale production facilities are often dedicated to specific markets such as natural gas grids and large power plants that use their own standards. This document takes into consideration this major constraint for any adaptation to marine applications specificities/requirements.
C.1 Methane number
The ability of a fuel to resist engine knock for given conditions in the cylinder of an engine is referred to as its knock resistance. The knock resistance for a gaseous fuel is usually characterized using a methane number. The knock resistance of the fuel is an important parameter for engine operation; the maximum non-knocking power output of many marine engine types can depend on the methane number.
Originally, the methane number was derived in analogy with the octane number for gasoline; it is a measure for the specific knock intensity in a reference engine. The knock intensity for a given fuel is compared to a mixture of reference fuels. For the methane number, pure methane was assigned the value of “100’,, while pure hydrogen was assigned the value of “0”.
There are several calculation tools for determining the methane number, which often give different methane numbers for the same fuel composition. The same method can for some gas compositions overestimate the methane number and for other gas compositions underestimate it. The differences between the tools reflect different engine conditions for which the tools are intended (e.g., stoichiometric vs. lean-burn) and differences in how the methane numbers are derived from experimental, empirical and theoretical data. This results in different approaches for how the effects of higher hydrocarbons and their isomers, as well as the impact of inert gases, are incorporated in the tools.
NOTE In EN 16726:2015, the MWM method has been used to calculate the Methane Number.