Not having TEL (the lead) changes its properties including the vapor pressure.
Do you have a reference?
91UL is supposed to be exactly the same as 100LL, minus the TEL.
Mogas is the fuel which has vapour pressure issues but that’s because its composition is very different from avgas.
The fuel system compatibility is “just” (a) vapour pressure and (b) materials compatibility. Mogas can potentially have issues with both, and car forecourt petrol even more due to the alcohol in it. I have a 3kW generator at home (and another one at work) and the fuel gauges on both were basically eaten (dissolved) by the ethanol in the petrol.
It seems you are right about vapor pressure. Warter is very open with their fuel specifications. They show the same vapor pressure for 100LL and 91UL:
Still the fuels are different and it is a very bold claim by EASA that the airframe cannot be affected. I guess it mostly isn’t but how do they substantiate their claim? Why certify an aircraft when the EASA can just change the TC of about every airplane out there without any real data and while a much more competent body (FAA) thinks otherwise?
Still the fuels are different
But only in terms of octane, which is purely an engine issue.
Why certify an aircraft when the EASA can just change the TC
They are not doing that.
Isn’t 91UL basically dead?
I think it was a crude attempt by TOTAL France to push airfields into a corner and throw out 100LL and screw all the people who had to use it. It was a move which might be possibly expected by TOTAL, given that the French GA scene has almost no touring activity and most of its club aircraft can burn 91UL OK. They should have done some market research.
96UL is different, however. It is 91UL (i.e. unleaded avgas) with “some stuff” added so, in theory there could be material compatibility issues. And I think the same for any “100UL” fuel, since any possible formulation must have “stuff added” which is not present in 100LL.
QuoteBut only in terms of octane, which is purely an engine issue.
Really? The chemistry behind this is rather complex and how would you be able to say that they only differ in exactly one thing and that has generally no impact on the airframe and installation and no tests or certification have to be done?
They are not doing that.
The TC includes the list of allowed fuels thereby EASA give the power to Lycoming to change the TCs of any aircraft they see fit. That is very bold.
Don’t get me wrong, I’m all for it and I personally would even ban leaded fuel altogether for environmental reasons but to me EASA’s approach seems a bit premature. They think seatbelts need to be overhauled in the USA because European companies cannot do that but they just allow Lycoming to change the TC of any number of aircraft based on exactly what?
You will never achieve perfection, and the alternative is to test every engine/airframe combination, dismantle them, and check for degradation of materials. Of course you would need to start with fresh materials… It just isn’t going to happen. The way this is done is by looking at material compatibility data sheets. And 91UL has no issues which 100LL does not have.
Such testing is never going to happen. Look at how long Lyco took to do the 91UL engine tests.
My guess is that there is (for a change) somebody smart inside EASA who appreciates the gravity of the European fuel situation and decided to get a move-on with it. The FAA has much less incentive because 100LL is not under any real threat in the USA.
You may be thinking that the additives in 100LL prevent degradation which would take place in their absence. In theory that is possible but I am sure if it was the case, some chemist out there would have said something about it by now.
Type Certificates are “owned” by the certifying agency (FAA or EASA etc) not by the manufacturer of the aircraft or the engine. So the certifying agency has the power to permit, or ban, particular usage. They also have the power to require a “mandatory” SB to be disregarded, etc.
Really? The chemistry behind this is rather complex and how would you be able to say that they only differ in exactly one thing and that has generally no impact on the airframe and installation and no tests or certification have to be done?
We (pilots) cannot be totally sure, obvious. But the documentation seems to support that. I am sure EASA had something on their mind when they approved UL91 for aircraft that, according to their TC, were good for 91 octance fuel conforming to Avgas standards. But saying EASA=uninformed, FAA=the experts strikes me as a little too simplistic.
Many thanks to all those that made positive comments to my posting and the warm welcome that I received
To follow up my previous posting and try an provide an answer to some of the questions on the two forums that it was posted to, I am doing a general reply that will again be posted on both forums. In a private email I was asked about lead. The text of that email is below but in the meantime I am now in my home office and have more history at my fingertips.
To the best of my knowledge Innospec (formerly known as Associated Octel) is the only TEL producer remaining in the world( there are apparently some illegal Chinese producers- this is no surprise). I spoke with the CEO in 2012 at a European Fuels Conference and he said that Innospec would continue producing TEL as long as there is a market ( my view here that means as long as it is profitable). All the other TEL producers shut down production with the lead phaseout, and Octel emerged as the last am standing. The remaining lead demand is now very very small. It is difficult to know the exact avgas demand. The US is the biggest market by far, probably making up over 50% of the demand. The production for the US. 2013 is not available yet but in 2012 the US produced 4589 kbls of Avgas which is about 570 kta . An optimistic demand for avgas is up to 1 million tonnes per year, but it is falling as you can see by the drop in US demand from 2007 to 2012 of over 1 million barrels per year. (Follow the link at the bottom of the post.)
Put that into perspective with mogas and avgas is less than 0.1% of the global mogas demand. Doping the fuel at 0.5 g/ltr as lead (0.625 kg/mt) would give a demand of 625 mt of lead per year. That is peanuts. I have no idea what TEL costs these days but if it cost £10 k per tonne the value to Innospec would be a bit over £6 million per year. If it was £20k per tonne it would still be a small market. As I said for such a small market it is not worth re-investment.
I quoted the lead doping rate as lead which is how it is reported in the specification and the certificate of analysis that is produced with every batch. The actual lead additive is tetra ethyl lead, TEL, which is a dense oily liquid. In order to remove lead from the engine a lead scavenger is added. The scavenger reacts with the lead during combustion and produces a volatile lead compound which in theory leaves in the exhaust ( of course many of us know that is not always the case). For mogas the scavenger was usually a mixture of ethylene dichloride and ethylene dibromide, which formed lead chloride and lead bromide respectively. For Avgas only ethylene dibromide is used, as it appears that ethylene dichloride caused corrosion problems with aluminium.
I managed to find a typical formulation for the mogas TEL additive circa 1980’s
TEL 62%
EDCl 18%
EBr 18%
Solvents, Dyes, Antixoidant 2%
All units by mass. In other words that would mean to dope 0.5g of lead into Mogas would require about 1.5g of the TEL additive.
I also managed to find some pricing circa 2003. At that Time Octel were selling to the Iraqi regime at an inflated price of £10k per ton of additive. Apparently this was about 37% above the norm (sanctions busting). As recently as 2009 Octel/ Innospec were in the news regarding bribery allegations. They had been bribing the last six remaining countries still using TEL to continue using lead in gasoline. Those countries were Algeria, Iraq, Yemen, Afghanistan,Myanmar, and North Korea. It is difficult to obtain accurate gasoline consumption in those countries. It is likely though that the demand is at least as great as the global Avgas demand probably higher.
How TEL works has never been fully explained. The general theory is that the TEL decomposes and ethyl groups form free radicals that act as chain termination agents. When I was at University, a long time ago, I was taught by a lecturer called John Nicholas, whose speciality was combustion kinetics. He discussed low and high temperature combustion and cool flames. Trying to keep things simple the combustion process could under certain conditions lead to an explosion, due to degenerate branching reactions. These can be likened to chain reactions in nuclear explosions, where each reaction step releases further multiple reactive free radicals. If the concentration of free radicals is high enough the reaction rate runs away to explosion; in effect there is a minimum concentration of free radicals that is required to form a runaway rate of reaction that leads to explosion.. I cringe every time I here people describe an internal combustion engine and refer to the ignition step as an explosion. It is not an explosion; even when things go wrong it is more a deflagration than explosion. Typical flame speeds in a spark ignition engine are low- well under 20m/s which will surprise many folk. For those amongst us who remember the old points and distributor cap, timing of engines could be crudely done by advancing the ignition until the engine pinked and then back off. When switching to unleaded fuels the ignition timing had to be retarded, which actually made the engine run a little hotter MTBE works in a similar but less effective manner to TEL. The combustion step would generate some free radicals which would act as chain termination agents. like wise anyone who has burned ethanol in a lamp will notice how “docile” the flame is. Repeat it with gasoline(not recommended) and you will have a monster to deal with. What is significant is that high octane blending components usually have high autoignition temperatures. Low octane components such as strain run naphthas have low autoignition temperatures. The inverse applies to diesel fuel. Diesel fuels require components with low autoignition temperatures so that they readily ignite. These components can autoignite as low as 200 dec C. Jet A and Jet A1 typically have an autoignition temperature of 220 deg C which is why it can be used in an aircraft diesel. I have probably opened up a new debate here so I will go back to TEL and Avgas.
So in essence as the TEL market continues to decline all of the fixed costs of a manufacture, maintenance of plant, compliance,. etc have to be paid by a shrinking volume of product. At some point Innospec will call it a day, or the producers of Avgas will see volumes drop to a point where the refinery determines it is no longer profitable to continue production. This in fact happened to the sole UK Avgas producer which was BP when they operated the Coryton refinery. The refiner has exactly the same issues. To produce Avgas it must comply with all the testing, segregation, certification, traceability, and distribution requirements, and comply with the health and safety rules when handling a very toxic substance called TEL. Even if 100UL is finally approved all of the testing, segregation,certification, traceability and distribution costs will remain, so it will no be cheaper. My guess it will be at least the same if not more than 100LL
Someone will ask why does the west not buy TEL from the Chinese. The Chinese fuel standards are basically following the European standards which are increasingly seen as the global standard. In theory there should be no need for TEL in China, though they do use and produce Avgas. I suspect the illegal Chinese TEL producers are producing TEL for illegal blending into mogas. Our own experience in China has not been good, and we are not alone in this experience. If baby milk can be adulterated with melamine then anything in China can be adulterated, and it would be no surprise to learn that Chinese mogas had been boosted with TEL in order to upgrade low octane gasoline. For Avgas purposes it would not be possible since there has to be traceability of all the components back to the point of manufacture, and throughout the supply chain.
In my suggested suggested 100UL alternative I made reference to the the following components
Isopentane
C4 Alkylate
p-xylene
MTBE
In the posting to the euroga forum I made reference to p-xylene. This is a product from mixed xylene which is used for the production of terephthalic acid used for PET polyester production. On a global basis it is currently long in supply and around 40 million tonnes per annum are produced.
One question asked was would my fuel work in a large V8. I think it was a chevy. Of course it would with one proviso. The exhaust valve seat would need to be capable of the high temperature and loss of lubricity afforded by the lead. A bit of an overkill though.
Another place to look is at the Sunoco range of racing fuels. These make some interesting reading on how they have blended high octane fuels for challenging conditions.
Spec for p-xylene from here http://www.cpchem.com/bl/specchem/en-us/tdslibrary/xyleneparapuregrade.pdf
As an aside the total avgas demand could be met by ONE smallish refinery of about 5 million tonnes per year crude refining capacity. It would not actually be possible but it indicates just how small the avgasmarket is.
Here are some octane number and RVP (Reid Vapour Pressure) for various gasoline components.
MON RON RVP psiIsopentane 91 93 19.4
C4 Alkylate 96 97 4.6
p-Xylene 127 146 0.3
MTBE 101 118 9
Reformate 88 100 3.2
FCC gasoline 82 91 14.1
N-butane 92 93 52
Light Naphtha 61 66 11.1
Toluene 107 121 1
Ethanol 106 132 11
I normally work in kPa units but I know that this will confuse some and most literature value are in psi. The RVP, Reid Vapour Pressure is measured by adding the gasoline to a sealed vessel with a pressure gauge and immersing the vessel in a water bath at 100 F and measuring the pressure. 1 atmosphere pressure is 101.3 kPa.
I included MTBE in my proposal mainly due to its properties. It has a very good RON and MON and because of its vapour pressure it would allow the isopentane, the lowest MON component to be minimised. Isopentane is only included in Avgas for starting. Please note the above are literature values and actual may vary slightly, so treat them as indicative. The para xylene values are for a 20% blend in 60 RON gasoline.
Toluene could also be used instead of or with MTBE. If MTBE is used it would minimise the amount of toluene and para – xylene required, which will help with the finished density. More than one comment has been on the banning of MTBE in the US. I agree that this is an issue. You might be surprised to know that the US still produces a very significant amount of MTBE which is exported out of the US for gasoline blending. The problem with MTBE in the US is well documented. It is mainly an issue of very poor handling and storage which resulted in groundwater contamination. MTBE, and its homologues (ETBE, TAME) will taint drinking water concentrations as low as 5 parts per billion. That is about a teaspoon in a good sized swimming pool. In Europe we do not have issues with these ethers. I do not want to debate the US MTBE debacle, but it is sufficient to say that the were powerful agro producers involved. Anyone who is interested in ethanol as a fuel should google PAN’s (peroxyacyl nitrates) and have a read.
Though difficult, it might be possible to obtain a waiver for MTBE use in Avgas. After all it is highly unlikely that it would be used in ground vehicles due to the cost. If all else fails then replace MTBE with Toluene and maintain the isopentane concentration.
I have also included in the table some of the main gasoline components. Reformate and FCC gasoline are the main components in mogas. n-butane and light naphtha are also blended because they are cheap. Alkylate is frequently used especially in the higher grades. Reformate and FCC gasolines are limited by the aromatic and olefines limits in the fuel specifications. This is all driven by air quality issues.
As an aside the total avgas demand could be met by ONE smallish refinery of about 5 million tonnes per year crude refining capacity. It would not actually be possible but it indicates just how small avgas is.
In this link are the US Avgas production stats.. My skills with HTML are not that good and although I have an image of the table I need to post this image to a host to obtain a URL.
From the EIA website. http://www.eia.gov/dnav/pet/pet_pnp_refp2_a_eppv_ypy_mbbl_a.htm
Rutan Pilot, thanks for a very interesting insight. Now, what about the WWII approach to high-octane fuels? I am not sure about other countries, but Soviet fighters flew on blends up to 130 octane containing large amounts (potentially >50%) of aromatics, from benzene to xylenes, and possibly also naphthalene? Of course, such blends might be even more toxic on skin contact than leaded avgas, but they might circumvent the legal restrictions. Also, technical grade xylene (or xylene-toluene) mixture would probably be taxed at a lower rate than avgas/mogas.
For Ultranomad
As you can guess the weather is vile and I am at my computer. There is nothing new about this approach. You are absolutely correct that a blend of Toluene and Xylene will boost the octane to very high levels; it is called re-inventing the wheel. I am not sure about naphthalene as it has the habit of precipitating from solution at low temperatures. Technically it would be possible to run an engine on toluene or xylene with an appropriate adjustment to the mixture. Due to the higher density of aromatics, about 0.87 kg/ltr or 1150 ltrs per tonne the mixture would be a little rich. Normal avgas is around 0.73 density or 1370 ltr per tonne, and the carburettor will be set up to this density. A modern ECU would be able to manage this by looking at the oxygen level in the exhaust. But aviation does not use ECU’s so it would have to be a manual adjustment.
Honda, in their F1 days used a blend of 90:10 toluene: heptane to achieve the most unbelievable output form 1.5 ltr turbocharged engine at very high boost. In Europe the authorities see toluene, xylene , and just about any hydrocarbon as a fuel extender and tax it accordingly. There is no getting around it as ALL suppliers have to keep detailed records of who the product is supplied to and the use. The end user has to have approval from the authorities to receive the product, otherwise the product is supplied DUTY PAID i.e. the full rate of hydrocarbon duty applied. The customs and excise authorities have to be satisfied that the product is not being used, or can be used, for fuels.
15 years ago there was abig scandal about a product called D75 which was a type of unmarked, no dye or chemical tracer, that was used as an industrial solvent. It was a bit like a heavy whites spirit. It was a very good diesel fuel and one transport company figured it out. Needless to say customs and excise were not amused and everyone who used or supplied the product got a visit. I was responsible for the product in the company that I then worked for and to this day I can remember the unannounced visit from the customs and excise boys.
So will a T-X mixture be taxed differently. My opinion would be – not in my lifetime.
Another problem with aromatics is that they can swell rubbers. this might be an issue in some situations. In mogas aromatic concentrations are much higher. In the last 10 years it has been reduced from 45% to 38% by volume.
In the old days in what was called a hydroskimming refinery gasoline was essentially reformate, naphtha and butane. Lead was liberally added to boost the octane to the desired level. Toluene and xylene was also added if the price was cheap enough.
Over the years more refineries were equipped with fluid catalytic crackers (FCC), isomerisation units, and hydrocrackers. Not much has really changed. Its has been an evolution process driven by air quality issues. Now benzene is virtually eliminated from gasoline and aromatics, olefines and sulphur are controlled to improve tailpipe emissions and reduce the precursors for photochemical smog.
I am probably opening up a whole new line of discussion now. Must go as I have to run to the airport.
