[Rob L]

I believe that 5% or less ethanol does not need to be declared, but willing to stand corrected.

[MikeW]

Not sure if your remark is aimed at Esso but his is what they say, it's pretty specific -

Esso super unleaded petrol (Synergy Supreme+ Unleaded 97) is ethanol free (except in Devon, Cornwall, the Teesside area and Scotland). We would therefore advise anyone who has concerns about the presence of ethanol in petrol to use Synergy Supreme+ – providing they do not fill up in Devon or Cornwall, the Teesside area or Scotland.

I understand even alcohol free fuel has to be labelled E5 at the pump as there isn't an E0 grade! E5 means up to 5%, including 0%. (There is a small distributor here in Sussex that does label their pumps E0 but I think that's a bit irregular!)

[Sooty25]

I've tested Esso synergy+ this week and it is ethanol free in East Anglia

[MikeB]

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!

Cheers

Andy

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.

[andytk58]

I knew you'd be along to correct me Mike

So, apart from octane, is there any reason the you couldn't run mogas through a mechanical fuel injection system.
Assuming NPSH is the critical issue at the suction inlet of engine driven mechanical fuel pump, all you would need to ensure is that you have an electric fail safe pump boosting the fuel from the tank to the engine pump so the pressure never falls below atmo.

Wish I could find that article!

Andy

[MikeB]

If NPSH is guaranteed, Mogas should have no inherent issues for mechanical fuel injection systems so long as the components of the fuel system can withstand Mogas constituents (not just the perceived antichrist ethanol).