Oppure in motori di concezione arcaica come i Rotax 912 (boxer 4 cilindri doppia eccensione, carburatori Bing, per uso aeronautico sportivo), che nutro con la 100 ottani, utilissima poi se fai quota.
Volevo far notare il degrado di ottani all' "invecchiamento" del carburante, cosa che potrebbe erre un problema se i carburanti, compresi quelli speciali alla pompa non hanno un grosso smercio e rimangono spesso in cisterna oppure li tenete tanto nel serbatoio (fonte, officina aeronautica specializzata canadese):
"Some may have noticed that the Rotax manuals mention ratings of 90 and 95 respectively. These ratings are calculated based on the RON standards used in Europe and are equivalent to a rating of 87 and 91 under the AKI standards used in Canada.
In all cases, we recommend using as high an octane rating as possible, since fuel evaporates and quickly loses its octane rating by osmosis when it lays in your aircraft’s fuel tank or in a plastic jug. A “premium” fuel will see its octane rating reduced to unusable levels after as little as three weeks. Fuel with a lower octane rating would obviously have an even shorter usable life.
Too low an octane rating will cause pre-ignition and detonation which can damage the piston ring grooves, skirt and crown."