... inert % = % by volume of inert gases in the fuel (i.e. N2, CO2, He, etc.)
When the members of the group were discovered and identified they were thought to be exceedingly rare, as well as chemically inactive, and therefore were called the rare gases or the inert gases. It is now known, however, that several of these elements are quite abundant on Earth and in the rest of the universe, so the designation rare is misleading. Similarly, use of the term inert has the drawback that it often is applied to gases such as nitrogen and carbon dioxide to connote their nonflammability. In chemistry and alchemy, the word noble long has signified the passivity toward oxygen of a group of metals, such as gold and platinum; it applies in the same sense to the group of gases covered here.
Это интересно
The term "inert gas" is also used to designate one of the six gases comprising the extreme right-hand group of the periodic table, i.e., helium, neon, argon, krypton, xenon, and sometimes radon. The term "noble gas" is to be preferred for that other meaning.
