1-Methylnaphthalene defines the lower (zero) reference point of cetane number, a measure of diesel fuel ignition quality, as it has a long ignition delay (poor ignition qualities).

In contrast, cetane, with its short ignition delay, defines the upper reference point at 100.

[2] In testing, isocetane (2,2,4,4,6,8,8-heptamethylnonane or HMN) replaced 1-methylnaphthalene as the low cetane number reference fuel in 1962 for reasons of better oxidation stability and ease of use in the reference engine.

[3] With alkali metals, 1-methylnaphthalene forms radical anion salts such as sodium 1-methylnaphthalene.

Compared to its structural analog sodium naphthalene, sodium 1-methylnaphthalene is more soluble, which is useful for low-temperature reductions.