The current standards for LNG for marine use (ISO 23306:2020) don’t define limits for Methane Number even though it is an important fuel characteristic that can vary with fuel source and the
The current standards for LNG for marine use (ISO 23306:2020) don’t define limits for Methane Number even though it is an important fuel characteristic that can vary with fuel source and the addition of bioLNG into fuel blends.
Power generation organization CIMAC’s Working Group 17 says Methane Number is like the Octane Number of gasoline in that it is a measure of the fuel’s resistance to auto-ignition or engine knock.
In diesel engine combustion, gaseous fuel in the cylinder is put under high temperature and pressure as the flame front advances. At a critical level, it will auto-ignite, causing a very rapid release of the chemical energy of the fuel. This is known as knocking as it causes ringing or a knocking sound.
Engines are typically tuned for the lowest Methane Number fuel they are expected to be operated on. For Western engines, that is typically 70-80; for Japan it is around 65.
Pure methane has a Methane Number of 100, and hydrogen has a Methane Number of zero. LNG mostly consists of methane but can also contain nitrogen and longer-chain hydrocarbons which reduce Methane Number. Boil-off gas from methane cargo, often used for fuel on LNG carriers, can have
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