andytk58 wrote: Straight run avgas is essentially a single refined component with a homogeneous evaporation point so has no trouble with this vapour/liquid device.
Mogas is a complex blend of all sorts of hydrocarbons all of which evaporate at different pressures and something about the swirl pot venting off the lighter fractions of mogas and/or vapour lock is the reason Mogas can't go through a Bendic mechanical injection system.
It was a while ago I read this and I have no idea of the publication it was in. Sorry.
If any, or all, of the above is bollox I'm sure someone will be along with the right explanation soon!
Sadly its mostly bollox, but its a shame that "straight run avgas" isn't a thing - would certainly simplify HF Alkylation and Reformer plant output in those refineries still producing Avgas
Reality is Avgas is a blended product, just as Mogas is. The components evaporate as per Raoult's law - essentially the composition of vapours produced will be dependant on the partial pressures of the components which in turn will depend on several factors including the proportion of each of these components in the liquid fuel. Generally (but not always), the vapour pressure of Avgas will be lower than that of Mogas at a given temperature.
But vapour pressure is not the whole story. As I've said numerous times before on here,, you won't get vapour lock if a net positive suction head is maintained. Fuel vapour pressure is only one component of the calculation of NPSH. However, the liquid head is a more significant factor, and thus the likely range of G's an aircraft will experience is a significant factor affecting NPSH. Mogas may not be suitable therefore for aerobatic use in certain aircraft, but it depends on the fuel system.