Primarily for general aviation discussion, but other aviation topics are also welcome.
#1843324
Forfoxake wrote:
MikeW wrote:It's SL912-016R2, not SI912-016...


OK, thanks. I wonder why Rotax have not updated SI 912 016?

I reckon they have: SI912-016R2 is Release 2 of the SI, isn't it?

It seems Rotax have further updates, too. A quick Google finds up to at least ...-016R10.
#1843336
MikeW wrote:It's SL912-016R2, not SI912-016. You can get it from the flyrotax site documentation section.

It says
"In general, the minimum RON 98 fuels significantly reduce the proneness to detonation
damage and increases engine longevity. The selection of proper fuels is one of the
main levers to prevent detonation damage, especially in the case of other contributing
factors being present (see the table in section 3.1). ROTAX®, therefore, recommends
a minimum of RON 98 fuels in case of uncertainties or doubts."

In fairness, it doesn't prohibit using RON95 but says you must be careful about operating conditions and detonation.

The RPM/MAP graph from the previous version of the SL is redrawn with separate curves for RON95 and RON98. With RON98 you can use WOT down to 4000rpm, with RON95 use of WOT is only allowed above 5200rpm.


Does this mean that UL91 (RON 95 minimum) is no longer recommended in certain installations?
#1843339
Dave W wrote:
Forfoxake wrote:
MikeW wrote:It's SL912-016R2, not SI912-016...


OK, thanks. I wonder why Rotax have not updated SI 912 016?

I reckon they have: SI912-016R2 is Release 2 of the SI, isn't it?

It seems Rotax have further updates, too. A quick Google finds up to at least ...-016R10.


You are right. I have found SI-912-16 R11 but it still specifies 95 RON minimum for the 912S/912ULS.
#1843365
Forfoxake wrote:
You are right. I have found SI-912-16 R11 but it still specifies 95 RON minimum for the 912S/912ULS.


I think the message is you can use 95 but be careful, better to use 98.

I suspect it's connected with ethanol too. Fresh E5 RON95 should be OK but it will degrade and lose octane rating quicker than ethanol free fuel if kept for a while. Note this is my theorising, Rotax don't say this!

I'm able to buy ethanol free RON95, I shall probably carry on with that. Alternative is 98 that may contain ethanol which I would much rather avoid. The devil and the deep blue etc!
Charles Hunt liked this
#1843369
Forfoxake wrote:So unleaded (or premium) 95 should be OK for a ULS. However some brands of super have the advantage of 0% alcohol whereas 95 has to contain alcohol unless it is from a low volume supplier (this concession is UK only I think.)

I have a niggle and it's based on no more than gut feel, that the length of time super unleaded lies in a tank with less throughput may come close to neutralising the benefits over using fresher regular unleaded. Particularly through covid times. At least in frugal Scotland! :wink:

I know there are other ways of checking ethanol, however the easiest is testing with an ethanol soluble dye. We used to have a kit with a purple dye on 'cotton buds'. Would anyone know of a source? :thumright:
#1843375
MikeB wrote:In my view, it would be a right faff testing every fuel purchase before putting it in the aircraft.

That's exactly what I did with the kit, absolutely no problem dipping a cotton bud in the newly purchased fuel. :D

MikeB wrote:If you are concerned about ethanol, run on 91UL or 100LL.

Don't have access to 91UL, wouldn't want to use 100LL in my Rotax.
Forfoxake, MikeW liked this
#1843391
Miscellaneous wrote:
Forfoxake wrote:So unleaded (or premium) 95 should be OK for a ULS. However some brands of super have the advantage of 0% alcohol whereas 95 has to contain alcohol unless it is from a low volume supplier (this concession is UK only I think.)

I have a niggle and it's based on no more than gut feel, that the length of time super unleaded lies in a tank with less throughput may come close to neutralising the benefits over using fresher regular unleaded. Particularly through covid times. At least in frugal Scotland! :wink:

I know there are other ways of checking ethanol, however the easiest is testing with an ethanol soluble dye. We used to have a kit with a purple dye on 'cotton buds'. Would anyone know of a source? :thumright:


I think I can save you the trouble. In my experience, all unleaded petrol in Scotland contains alcohol-it all comes from Grangemouth I believe.

Fortunately, it all appears to be E5 at the moment. It will be more of a problem if/when it switches to E10 but the test cotton buds will presumably not detect the difference- you will need to use the test tube method for that.

When E5 was introduced in Scotland, some super unleaded (super plus in the Rotax SI) remained alcohol free for a while eg at Esso Stations. Hopefully, this will happen again and we can use 98 RON with only 5% alcohol for a while. Otherwise, it will have to be Avgas until the LAA (if applicable) produces an E10 approval procedure and you carry it out on your aircraft. However, despite the fact that Rotax approve E10 in the 912 series engines, I am a bit reluctant to use it in my airframe so am looking to source a supply of UL91.

PS Glenrothes already have UL91, at a bargain price atm.
#1843395
Forfoxake wrote:I think I can save you the trouble. In my experience, all unleaded petrol in Scotland contains alcohol-it all comes from Grangemouth I believe.

When I was using the 'cotton bud' kit not all fuel was coming from Grangemouth. The depot in Inverness was supplied by sea from Immingham and at the time even the std unleaded did not have ethanol. As was confirmed by the test. It was relatively easy to find which petrol stations were supplied from the Inverness depot and use them.

I'm not entirely positive of the present situation regarding whether the fuel from Inverness is still ethanol free, however I am told the depot is still in operation. Last time I did the periodic water test on standard unleaded it was ethanol free. :thumright:

It is time to do another. :thumleft:
#1843399
Miscellaneous wrote:
Forfoxake wrote:I think I can save you the trouble. In my experience, all unleaded petrol in Scotland contains alcohol-it all comes from Grangemouth I believe.

When I was using the 'cotton bud' kit not all fuel was coming from Grangemouth. The depot in Inverness was supplied by sea from Immingham and at the time even the std unleaded did not have ethanol. As was confirmed by the test. It was relatively easy to find which petrol stations were supplied from the Inverness depot and use them.

I'm not entirely positive of the present situation regarding whether the fuel from Inverness is still ethanol free, however I am told the depot is still in operation. Last time I did the periodic water test on standard unleaded it was ethanol free. :thumright:

It is time to do another. :thumleft:


Interesting- I should have written Central Scotland! I do not normally top-up when I go to Easter or Dornoch but maybe I should. Please let me know the results of your research. It obviously a different country up there!
#1843406
Some goodish news from Auto Express in February:

"The DfT has not yet set a deadline for when UK petrol stations will be required to offer E10. It will not be offered alongside E5 unleaded at the same forecourt, though - once a fuel station has switched to E10, standard E5 will no longer be available there. Motorists whose cars aren’t compatible with E10 will still be able to purchase E5 petrol in super-unleaded form, though, with the DfT confirming the UK will maintain a supply of this fuel."

And from Esso fuels UK FAQs:

"What is the ethanol content of your fuels?
The majority of unleaded 95 Octane petrol sold in the UK contains up to 5% ethanol as required under the Government’s Renewable Transport Fuels Obligation (RTFO).

There is currently no requirement for renewable fuel (such as ethanol) to be present in super unleaded (97 and 99 grade petrol).

Esso super unleaded petrol (Synergy Supreme+ Unleaded 97 and Synergy Supreme+ 99 ) is ethanol free (Except in Devon, Cornwall, North Wales, North England 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, Cornwall, North Wales, North England and Scotland. The European standard BS EN228 covers the requirements for 0-5% ethanol unleaded petrol, the labelling requirement for zero % ethanol is E5 (as is up to 5%), a E0 label doesn’t exist."
#1843494
I've been following this thread with some interest as I fly a Rotax 912ULS powered aircraft. I live in North Somerset and have several Esso garages I can get fuel from enroute to my home base, so I've always used Esso Premium petrol. I've checked every batch for ethanol and never once found it in the fuel I've purchased since 2013. I use the water+fuel sampling technique which only takes a few minutes to test each batch after purchase.

I see that Esso have recently introduced Synergy Supreme+ 99 which, according to their web site, is ethanol free 99 octane fuel. https://www.esso.co.uk/en-gb/fuels/petrol
Considering that 100LL is 100 octane rating, I wonder what difference the 1 octane would make in real life operations in Lycarus type aircraft engines. Could Esso Synergy Supreme+ 99 be a good replacement for 100LL? I wonder if it's worth having this fuel analysed to see if it reaches the standards required for aviation use.

I dare say we have someone on here who may be able to provide the technical reasons why or why not this may be worth pursuing.

Any takers?
#1843501
Volare wrote:I've been following this thread with some interest as I fly a Rotax 912ULS powered aircraft. I live in North Somerset and have several Esso garages I can get fuel from enroute to my home base, so I've always used Esso Premium petrol. I've checked every batch for ethanol and never once found it in the fuel I've purchased since 2013. I use the water+fuel sampling technique which only takes a few minutes to test each batch after purchase.

I see that Esso have recently introduced Synergy Supreme+ 99 which, according to their web site, is ethanol free 99 octane fuel. https://www.esso.co.uk/en-gb/fuels/petrol
Considering that 100LL is 100 octane rating, I wonder what difference the 1 octane would make in real life operations in Lycarus type aircraft engines. Could Esso Synergy Supreme+ 99 be a good replacement for 100LL? I wonder if it's worth having this fuel analysed to see if it reaches the standards required for aviation use.

I dare say we have someone on here who may be able to provide the technical reasons why or why not this may be worth pursuing.

Any takers?


Again, interesting although the website you refer to also states:

"Although our pumps have E5 labels on them, our Synergy Supreme+ 99 is actually ethanol free (except, due to technical supply reasons, in Devon, Cornwall, North Wales, North England and Scotland). Legislation requires us to place these E5 labels on pumps that dispense unleaded petrol with ‘up to 5% ethanol’, including those that contain no ethanol, which is why we display them on our Synergy Supreme+ 99 pumps"

However, I have just had further confirmation from Orkney that not all unleaded petrol in the north of Scotland has alcohol in it! Will try to get further details.
Last edited by Forfoxake on Wed Apr 28, 2021 8:01 pm, edited 1 time in total.