When evaluating the combustion performance of the original
and modified fuel nozzles, methane fuel is tested instead of natural
gas for the following reasons: the composition of natural gas varies
with the season and regions, and these variations make it difficult
to obtain the exact measured combustion properties such as burning
velocity and auto-ignition temperature; on the other hand, the
combustion properties of methane are well-known and distinct;
and furthermore, methane can reflect the combustion characteristics
of natural gas since natural gas contains as much as 85% or
more methane. Thus methane instead of natural gas is selected
as a test fuel for a more precise and quantitative analysis of the
combustion test results by comparing the combustion properties
of methane with those of DME.