Primarily for general aviation discussion, but other aviation topics are also welcome.
#1829178
I would be careful to ensure the aircraft in question is explicitly allowed to use MOGAS using ethanol.

GC No. 7, in CAP 747 (http://publicapps.caa.co.uk/docs/33/CAP747_Issue_4_Jan_2021_corr_27012021.pdf) states:
2 Introduction

2.1 Because of the difficulties experienced in obtaining Aviation Gasoline (Avgas), particularly
in small quantities, and the ready availability of Motor Gasoline (Mogas), CAA was
asked to consider permitting the use of Mogas in general aviation aircraft. This was
granted under the auspices of Generic Concessions (GCs) 2, 3, 4 and 5, published in
CAP 747 (previously Airworthiness Notices 98, 98A, 98B and 98C), which allow
microlights and certain light aircraft to use Mogas, subject to the conditions therein.

2.2 Since the publication of these documents, the composition and properties of some
Mogas fuels has changed and it is becoming increasingly difficult to obtain Mogas that
does not contain any alcohol. With the exception of microlights, the use of Mogas
containing alcohol is generally prohibited in aircraft.


2.3 This Generic Concession, by means of the attached Exemption against Article 33 of the
Air Navigation Order 2016 (as amended), permits the use of a new unleaded aviation
fuel, UL 91 Avgas, in Annex I aircraft, subject to the conditions stated in this Concession.


In my case I can't use UL91 - the manual explicitly states a minimum octane rating of 95.

OC619
#1829184
MikeB wrote:
As for E10 Mogas (which will be here from September) - the UK is sticking with 5% max ethanol for Super Unleaded for the time being, so that will remain an option for the Mogas fleet.


Quite a lot of E5 super unleaded is alcohol free, e.g. I have found my local Tesco's to be so far (but I will test every purchase), hope that continues. Can't get UL91 anywhere near me.

It's bad news. On hol in France in 2019, my car with latest generation VW 1.5L engine, was definitely not so good on E10 which was already the norm there.
#1829195
Having read on this Forum, about the availability of "Super" without Ethanol, I did a web-search and found the only Esso station within 10 miles. A month later, it no longer has Ethanol-free fuel of any grade. I expect this is as a result of reduced demand and refineries closing.

Electric-car adopters have a lot to answer for :twisted: law of unintended consequences strikes again!
#1829197
We need to know whose standard the engine manufacturer requires:

In Europe, the octane rating on the pump is simply the RON figure. America, by contrast, uses the average of the RON and the MON figures, called the AKI (anti-knock index). Thus, 97 octane “super unleaded” in Britain is roughly equivalent to 91 octane premium in the United States.
#1829218
skydriller wrote:Out of interest, does anyone know if its possible to remove ethanol from Mogas?

It comes out if you mix the MOGAS with water - but I suspect that's unhelpful!
patowalker, Nick liked this
#1829249
In the olde days engineers told me explicitly that using the Mixture control was not saving money....
Why did the engine - carburettor manufacturer fit it then?

As for petrol... When you read “Any good quality motor spirit of 71 octane...” for prewar engines, why would you put ‘unapproved’ leaded fuel in any engine designed in this period?

Go by the engine manual...

I remember pitching up at Damblain (tres naughty par moi) in a Rallye Club, G AVIN... They only had 80 octane Avgas, and some bright spark had marked the fuel caps 100LL!
But the O-200 loves 80 octane!
#1829270
MichaelP wrote:From memory the Rotax 912S has a 10.5:1 compression ratio which is higher than many Lycoming ‘high compression’ engines.

The 160bhp O 320 has to run on Avgas, but its compression ratio is 8.5:1 so there’s something odd about this argument.


Combustion chamber size. The speed of the flame front is determined by the octane rating.
Charles Hunt liked this
#1829294
cockney steve wrote:Having read on this Forum, about the availability of "Super" without Ethanol, I did a web-search and found the only Esso station within 10 miles. A month later, it no longer has Ethanol-free fuel of any grade. I expect this is as a result of reduced demand and refineries closing.

!


Are you sure about that?
If it's alcohol free it still has to be marked E5 which means "not more than 5%." There is no authorised mark for alcohol free.
Nick liked this