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100UL (merged thread)

Interesting… I always assumed Kos had no avgas, and I don’t recall a time when it did. This summary doesn’t mention it. Samos has, and we will probably go back down there in 2014

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Shoreham EGKA, United Kingdom

At an airport not a million miles away from me, the manager has emailed all operators that a risk assessment is required for any engine run unless one is going flying.

I think he needs to seek treatment.

Both my aircraft have had auto fuel STCs for approximately 25 years but alcohol in auto fuel made the STCs useless many years ago. 100 LL smells a great deal better anyway, and when 100 UL replaces it I think people will fill up without cogitating much about the change.

Last Edited by Silvaire at 04 Dec 14:21

I posted this comment on another forum last night. Another reader of this forum sent me the thread and asked if I would post it here also.

Here it is as posted on flyer.

“I was searching the internet earlier today and found several articles on EN228 mogas and the thread on the Shell 100 UL avgas.

I thought I might offer my views, but first I will introduce myself as a newbie. I am a retired PPLA and PPLH and have owned both fixed and rotary aircraft( at the same time). I saw the Avgas problem coming in 2005 and decided to slowly exit my hobby of nearly 30 years.

My job is with a large chemical company and you could describe me as a petroleum chemist. I have worked in this industry for over 35 years both in refineries and petrochemical plants. I currently work on evaluating petrochemical feedstocks from refineries and gas plants. I talk to refiners, I talk with gasoline blenders, and also give presentations from time to time to industry conferences. Some of my work is on the internet. The company I work for is one of the biggest MTBE producers in Europe, producing over 500000 tonnes of MTBE each year. MTBE is an octane booster that was, and still is, used in gasoline blending in many parts of the world. We also produced ETBE until 2011 when it proved to be no longer worth producing and we switched back to MTBE.

Something like 3 years ago I wrote an essay on Avgas replacements which I offered to another magazine outlining a potential way to produce an unleaded high octane Avgas. The publication had an in-house expert who turned the essay down without even talking to me.

Technically, there are no real difficulties in producing a high octane un-leaded fuel but matching the 100LL in performance would be a little challenging, especially as Avgas is measured by Performance Number not octane number as with mogas.

This is not a plug for either MTBE or ETBE but my suggested blend included isopentane, alkylate, toluene, and xylene plus MTBE. Essentially the first 4 ingredients are the components of 100LL and the addition of the MTBE would boost the octane to above 100. Nothing really complicated as far as gasoline goes and running it through my blend model predicted pretty good correlations with 100LL

Price wise it was not too expensive at wholesale pricing. More than EN228 gasoline by about 25% and probably not far from the cost of Avgas (more expensive). The real problem comes from all the testing, segregation and special handling that Avgas demands. It is also not helped by the few certified refineries now left in Europe. There is now no UK refinery equipped to produce Avgas. Shell have one facility in Rotterdam, Total one in La Mede, and Esso one in Augusta. PKN produce Avgas in Plock, and there is the Swedish UL producer whom I believe is Preem.

It very much surprised me that Shell have gone to the trouble of launching this grade as in the scheme of things the market is so small, and so niche, that it incurs high cost. I evaluate projects in my job and I would have walked away from this on day 1. I wish Shell well in their new venture but it will not be easy for them to make any money. I fear the same applies to Total as well.

Moving on to EN228 and BS7800 I would make the following comments. Both grades are identical in all the key parameters: density, distillation, vapour pressure, aromatics, olefins and sulphur. The same alcohols and ethers are also permitted. The only difference is in the octane numbers and permitted oxygen content of the BS7800. EN228 covers three grades; 91, 95 and 98 octane and where ethanol is permitted up to 10% volume, there is a relaxation of the oxygen content to 3.7%. Otherwise the oxygen limit in EN228 is the same as BS7800 at 2.7% by mass. In the UK we do not have a EN228 98 RON grade so we have BS7800 97 RON grade. That is the only difference. In both cases as long as the fuel meets the specification there is no requirement to label if ethanol is present or not.

This is purely my opinion but the chances of finding a fuel on a UK forecourt without ethanol is slim. EU legislation essentially mandates it’s use under the nonsensical renewable fuels directive, which has only raised pricing, not only for fuels but foodstuffs as well, and enriched a few ethanol producers in foreign lands. (As an aside most biodiesel producers have lost their shirts. ) I do not hold much faith in the accuracy of some of the pocket alcohol test kits either. They are simply to inaccurate and prone to error.

Most European mogas is produced as Eurobob which stands for European gasoline before oxygen blending. That means that the addition of an oxygenate is required to be blended at the despatch terminal in order to meet the required octane. The point to note here is that if the oxygenate is removed, either intentionally or unintentionally then the octane will be lower by several octane numbers. The other noteworthy point is that the vapour pressure limits vary from summer to winter. Winter gasoline will be blended with butane to aid starting. Refiners like to blend as much butane as possible, and it will have a much higher vapour pressure. This is made worse if ethanol is blended as there is a further vapour pressure waiver allowance of 8kPa.

I think I will finish here but if the comments are favourable to my ramblings I might be prepared to write some more."

I have read some of the posts on the Shell 100 UL and would add the following.

The high compression and turbo charged sector is the most challenging and obviously tends to be the biggest consumer. Large thirsty engines. The testing of aviation gasolines i.e. 100LL is done in a different way than mogas so octane numbers are not exactly the same. Above 100 octane aviation gasolines are measured by performance number using the F3 to provide an octane knock rating under weak mixture conditions. the F4 method determines the knock limited performance of aviation gasolines under supercharged rich mixture conditions.

In terms of Mogas MON is the most important number and is indicative of an under accelerating under load. Typically it is around 10 octane numbers below the RON. In the UK RON numbers are posted on the pumps. In the US it is (RON+MON)/2 hence US pump numbers are about 5 octane number below the UK. All clear- probably not.

95 RON mogas in the UK must have a minimum 85 RON. To get to the 100 MON of the Shell 100 UL is one heck of a challenge. The choice of blending components is limited but I would suggest the following.

  MON RON
isopentane 91 93
C4 alkylate 96 97
p-xylene 127 146
MTBE 118 101

p-xylene octane numbers are the blending numbers in a 20% blend with 60 octane reference fuel , so some care has to be exercised in the interpretation of the values.

p-xylene is the most expensive component and could be substituted with an EB and o-xylene depleted solvent xylene mixture. This is chemist talk- sorry. p-xylene is used exclusively for the production of terephthalic acid which is used for producing PET polyester, films, resins, and yarns. p-xylene is heavy, It has a density of 0.87

MTBE will help with density, octane and vapour pressure.

Again I do not want to bore everyone to death so I will sign off. If the comments are favourable I might be persuaded to write some more.

[edited to format the values into a table]

Last Edited by Peter at 23 Jan 12:26

Very interesting, although i only understand 25%

Do you have a (personal) opinion on running big bore Contis on anything other than Avgas? I know people who did so for a couple of hours when they travelled through countries without Avgas.

@Rutan Pilot: very interesting reading, many thanks for posting. Though not all of it is clear to me, either, I certainly look forward to reading more of the same! You also confirm my thesis that, on internet forums, the best content is the best worded.

One phrase makes me scratch my hairs:

p-xylene is heavy, It has a density of 0.87

I should think anything lighter than water is “light” rather than “heavy” – and for me, water has a density of 1,00 (at 4 degrees C or so?) kg/litre. Were you referring to the other fuel components to call this product heavy, or do you use another unit than kg/litre?

Last Edited by at 23 Jan 14:29
EBZH Kiewit, Belgium

Avgas density is 0.72g/l so 0.87g/l is in comparison heavy. Making the fuel heavier without increasing the energy density is not something you want to do.

Rutan Pilot confirms that it is very difficult (if not impossible) to come up with an unleaded replacement of 100LL that can be applied in all situations where 100LL is used today. As this is not possible (or has not been achieved yet), we are faced with having to certify replacement fuels for each particular installation and cannot make a clear cut and phase out one for the other.

This certification is a very delicate subject. EASA have made a very bold statement, saying if the engine can handle the UL91 according to the manufacturer, so can the aircraft. That is a highly unfounded statement (the FAA does not share the opinion) and I am sure it will be revised one day — when we get the first accident where fuel pumps run dry because of vapor pressure.

I will never be a specialist in this topic, but I am somewhat sceptical when manufacturers are so strictly against new fuels. Take the ENDLESS MoGas debate. Until today fairy tales are told that MoGas is “bad for engines”, even for the ones that are certified for it. But my experience is otherwise: I am flying my Warrior on MoGas for 15 years now, up to FL130, which is the max it will climb anyway.

I never had the slightest problem. The only difference is that the spark plug fouling went away (even though i always leaned the engine on the ground) – and that I saved a lot of money for some years.

Of course this is different for the bigger engines, that’s why i was asking the specialist for a personal opinion on the matter. I KNOW peope who operated their IO-520s and IO-550s on car fuel when Avgas was not available. Worked fine, AFAIK.

This certification is a very delicate subject. EASA have made a very bold statement, saying if the engine can handle the UL91 according to the manufacturer, so can the aircraft. That is a highly unfounded statement

Why do you think so? It sounds logical.
UL91 supposedly is 100LL without the lead, so as long as the engine can handle the lower octane, there can be nothing in the fuel that could harm things like rubber tanks, seals, etc. UL91 is totally different than autofuel from the local petrol station.

Interested if you have any other (substantiated) information.

Last Edited by boscomantico at 23 Jan 15:10
Mainz (EDFZ) & Egelsbach (EDFE), Germany

Since no one else has mentioned it, about half the US states have banned MTBE, which would seemingly make it a non-starter for 100UL. That was how we got the universal use of alcohol in auto fuel, making it unusable for aircraft under existing STCs.

I think the issue with EASA’s approach to 91UL is that they contradicted the fuel requirements of the aircraft type certificates, creating the ambiguity that seems to be their specialty.

UL91 supposedly is 100LL without the lead, so as long as the engine can handle the lower octane, there can be nothing in the fuel that could harm things like rubber tanks, seals, etc. UL91 is totally different than autofuel from the local petrol station.

Not having TEL (the lead) changes its properties including the vapor pressure. The fuel system depends on the airframe, not the engine. Depending on how it is constructed, there can be problems when fuel characteristics change. The biggest problem is by far the danger of vapor lock in low wing aircraft. And even mild vapor lock can cause damage to the fuel pumps due to cavitation.

100UL was the first fuel with a very good and strict specification and it has made aircraft constructors become sloppy. Before 100UL fuel quality was not as uniform and the systems had to be more tolerant. Remember the Cessna 172N which suddenly required 100UL. Much easier for the constructor if you take high quality fuel for granted. You can observe the same with the high-tech car turbo-diesel engines from Europe that were problematic in the USA because their diesel specification was not as strict as the European.

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