Who has Angel' mods installed can chance the fuel to liquid-ngl in the ingame-mod-options in the main menue.
(there are an converter in angel but the reciepe are methan and its a different think that the normal Angelgas. For me its better to get gas from a gasrecource as gas from oile.
Maybe the autor from transport drones make an: if angel is installed with petrolium than use liquid-ngl as fuel to? So The people dont must search for ID-names and options and reat text how it works.