Loss of Avgas

[bcfc]

I overhead a conversation this afternoon that sounds bizarre. Apparently, the use of Avgas 100LL will be banned in the year 2002 (next year if my watch is correct :eek: )

Anyone know if this is for real and isn't that going to be a bit problematic when my little Cesssna wants some go-juice?

[Kermit 180]

So run it on plain old Avgas 100. Its all you can get in some countries anyway. Fouls the plugs ocassionally but apart from that its ok. I heard a senior engineer comment that in another 10 years we'll all be flying small turbine-powered aeroplanes.

Kermie

[Skylark4]

Or diesels.
Sawq some interesting turbine projects at Oshkosh. One uses a `surplus` GPU and produces 300hp, too much for many but the cost compared with a Lytinental.
Similarly, several Diesels. The Zoche looks very nice but it is a purely ported two stroke and STILL hasn`t flown.
Was trying to find the latest situation with the Wilsch and cannot find anything on the WWWeb. Can anyone point me in the right direction?

Mike W.

[Fujitsu]

Found this on the Flyer website

Wilksch partners with DynAero

Wilksch Airmotive, the British company developing a diesel engine for light aircraft, has announced that it is teaming up with DynAero, the French kitplane manufacturer.

The WAM-120 engine has been tested in an MCR-4S aircraft from DynAero, and plans will continue to advance with the design of structural and aerodynamic modifications and airframe development and testing.

The first customer for the CITEC (Compression Ignition Turbo Exhaust Charged) MCR-4S will be M Serge Blanchard.

Christophe Robin, of DynAero, said "We see no technical barriers to the installation of the WAM engine and initial predictions indicate impressive cruise performance at altitude. We are excited about the cost benefits for European customers. We expect to take many more orders for the CITEC powered version of the MCR-4S".

More info on the Wilksch website at www.wilksch.com. (http://www.wilksch.com.) null (http://www.wilksch.com)

[Spiney Norman]

Skylark4.
I think you've hit the nail on the head there, Diesels are definately the way we'll be going, but unfortunately development seems to be very slow because it seems to be mostly driven by small companies in Europe cos we all know about the outrageous cost of AVGAS here. In the states both Continental and Lycoming are working on JETA1/Red diesel powered piston engines but mainly in the 200BHP plus range. I'm no engineer but I'd have thought that a certified, reasonably priced engine to replace the Lycoming 0-235 or Continental 0-200 to address the retrofit market would clean up! I'm definately keeping a close eye on the Wilksch but as I understand it there is no plan to certify the WAM120 in the near future. I reckon the possibility of reducing your fuel bills by around 60% would be something that most Flying training organisations would snap up.

[Skylark4]

No wonder I couldn`t find it, I missed out the `K` in Wilksch and therefore only picked up references on sites that had similarly mis-spelled it. There were quite a lot of them.
Wilksch is developing his engine for use in permit aircraft. When he has it FULLY sorted, then he will certify it. That way we do not get an unimproveable engine which isn`t quite right. Had a talk from them at our PFA Strut last year.
MikeW.

[Vfrpilotpb]

Good Morning Ppruners,

100LL is needed for most of the FW and RW piston engines, its all very well talking about the Diesels, but these are quiet a few years off yet, but what is going to be available fuel wise when 100LL is off menu possibly next year, or at the latest the year after will people use Mogas, or are all piston powered things going to sit on the apron, or are the fuels companies keeping quite to see what the could squeeze out of us piston types!!

[FlyingForFun]

The thing which concerns me about MoGas is not the actual fuel itself. I drive around 14,000 miles/year in a 24 year old car (with an engine block which was designed in the 1950s). It was perfectly happy when I converted it to unleaded fuel, and has been happy ever since. I know it's not a direct comparison because the construction/material of aircraft engines is very different to car engines, but with the correct tuning and other minor mods, our engines could run on just about any petrol you care to put in them.

The thing which concerns me about MoGas is quality control. I'm pretty sure we've all experienced a bad tank of fuel in our cars. You pull into the petrol station, everything is fine. You fill up, and 20 miles later you notice a little blip in the power which wasn't there before. Not enough to worry about, but you notice it. It gets worse over the next few miles, but then it settles down and you get used to it. You maybe think "I'll take it to the mechanic if it carries on." But that's not necessary, because it doesn't get any worse. Then, you fill up again, and within 20 miles of this fill-up everything is back to normal. "Hmm, must have just been a bad tank" you think to yourself, and that's the end of it. There's a theory that this is most common after the petrol station receives a delivery, because pumping all that fuel into their storage tanks stirs up the crap at the bottom of their tank. I'm not 100% convinced, but it's certainly possible.

Well, that's ok for cars. But not for aircraft. At least, not for aircraft that I'm flying in, nor my family and friends. Just as with the car scenario, you'd probably get by without it causing too much trouble. Certainly in the cruise it wouldn't matter too much. But then you go to put the power in for a go-around when some idiot lines up as you're at 50' on short finals and the engine splutters, just for a few seconds. Even in this situation you may get away with it, but I guarantee your heart would be beating a little faster once you've got a positive rate of climb.

Whatever we get, it must have the same level of quality control as what we currently have. If they can guarantee quality, I'll be happy.

FFF
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[bcfc]

I spoke with the bloke at the pumps this weekend about this. He'd heard about it but didn't know more than I did. What I did learn from him was that 100LL (low lead) has about 4 times the lead content of good old 4 star. :eek:

I'm no tree hugger but that don't sound too healthy to me.

[ 28 August 2001: Message edited by: bcfc ]

[Spiney Norman]

I was under the impression that 2002 was a target date for phasing out 100LL, but not one set in concrete. There's a lot of research going on at the moment that has resulted in 82UL fuel which is, I believe, in production in Sweden at the moment. This is fine for all of us at the lower end of the horsepower spectrum but useless for the sophisticated high horsepower engines like those in the Malibu etc. But as far as I've been informed both at where I work and my flying base there isn't going to be a cessation of supply next year.

[GWYN]

It so happens I read this after attending a Flight Safety Forum in Sydney today. One of the speakers was a petrochemist from Shell and I asked him about the future in store for all the aircraft piston engines as the high lead fuels are withdrawn.

To summarize, it is his considered opinion that the lower power engines, up to maybe 200hp will run OK on 80 Octane fuel. Higher power engines will simply not be operable, and the private / freight / charter operators will simply have to re-equip with turbines or diesels if available.

When I asked about the operators of vintage aircraft, such as we all like to watch at the airshows, his answer was effectively a shrug of the shoulders and a statement that they would not be able to be flown. He did add that there may be some sort of ‘synthetic’ possibly non oil derived fuel available in small quantities, but was not optimistic.

Not very encouraging at all really!

[mickypitch]

Its interesting that a mention was made of 100LL having more lead than four star, mainly because I read an article about the dangers of unleaded. Apparently the lead in four star and supposedly 100LL is ejected from the exhaust and falls to the ground and stays there. So unless you are standing with your nose to the exhaust pipe it is virtually harmless. Whilst flying this lead gets dispersed in the atmos.(and I should think light aircraft pollution compared to cars is not worth worrying about)
However the replacement chemicals used in unleaded to provide the lubrication are VERY carcigenic and do not fall directly to the ground. The fuel itself should not be sniffed (one of the things most people do during preflight)or allowed to touch the skin and you should avoid the fumes from the exhaust at all costs. Cars have cats to reduce this danger (but are no good until warmed up) but aeroplanes do not.
So leaded does not appear to be the great evil that the press made it out to be......

[Wile E. Coyote]

If these highly carcinogenic chemicals do get added to avgas then draining some of the fuel to check it is going to be damned dangerous unless precautions are taken, e.g. gloves, somewhere to dispose of the drained fuel etc... :mad:

[dirkdj]

One possible solution is to replace the (1920 tech) magnetos with an electronic ignition system that adjust timing in function of power required, fuel qualities etc.

Such a system is under development and is in the certification process. It will allow a lot of high power engines (IO550 etc) to run on MOGAS or 82UL without any power loss.

The designer says that the price will not be any higher than current magnetos (over the lifetime of the engine).

Have a look at the website www.gami.com (http://www.gami.com)

[FlyingForFun]

Krida,

I'm not sure of the wisdom of removing mags from our engines. Mags, imho, have one big advantage over both distributors and electronic ignition - they do not need an external power supply. That means that if you have an electrical problem in flight, your mags will keep going - not so with electronic ignition.

When my alternator packed up earlier this year, I was able to make it back to my home airfield with no serious concerns. Had I had electronic ignition, I would have been diverting to the nearest airfield.

(Also, this solution is not possible for non-electric aircraft, although this is unlikely to be a real problem because aircraft without electrics are generally sufficiently low-powered to be able to run off low-octane fuel without problems.)

I am surprised that the experts claim that high-performance engines won't work with lower octane fuels. I'm certainly not an expert in this area, but I don't understand why adjusting the ignition timing won't cure most problems. The most severe modification I can see that may be required is a re-profiled cam, but I'm not convinced that would be necessary. Sure, this will cost a bit of power, but surely it's not impossible?

Maybe it's just a ploy by the engine manufacturers to make all the high-perfomance guys (who, they believe, have loads of money) to buy new engines?

FFF
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[Edit coz I realised I was talking bo!!ocks]

[ 02 September 2001: Message edited by: FlyingForFun ]

[ 03 September 2001: Message edited by: FlyingForFun ]

[ShyTorque]

Problems with MOGAS for aviation:

1. Detonation / knocking. Due to the lower octane rating of MOGAS it may be impracical for use in some types of aircraft engine. Engines with a high compression ratio or large cylinder volumes may suffer from explosion, rather than smooth combustion of the fuel/air charge, irrespective of ignition timing adjustments. Piston overheating and severe damage (melted & holed pistons) may result. The debris thus caused may mean scrapping the engine due to bearing wear or worse (if it survives the engine-out landing). Unlike in car engines, knocking/pinging/pinking is difficult to detect in aircraft engines.

2. Vapour lock. MOGAS is more volatile than AVGAS. This means that it is more likely to form vapour in the fuel lines, resulting in engine fuel starvation with the associated rough running or engine failure. That is why the regs allowing use of MOGAS include an altitude limit.

3. Long term damage to valves and/or valve seats on 4-stroke engines. Lead compounds released from the combustion process of leaded fuels (AVGAS) coat the exhaust valves and valve seats. This acts as a protective buffer between them. Older engines relied on this (softer and cheaper materials could be used for valve seats). Use of a fuel without lead additives means that direct metal to metal contact occurs at exhaust gas temperatures, possibly resulting in partial welding together of the crystalline structure between valve and valve seat, only for them to be ripped apart again when the valve is forced off its seat on the next exhaust stroke. This results in valve seat recession, leakage and then burning out of the exhaust valves. Loss of compression and performance may result.

I have never actually seen any documented proof of public health improvements since the wider use of leaded petrol has declined. Bearing in mind the carcinogenic properties of unleaded fuels, I think we may have been duped into swapping one lot of health issues for another. I hope I am wrong because I would dearly like to buy 4 or 5 star petrol again without having to drive 25 miles each way to the pump.

ShyT

[FlyingForFun]

ShyT,

Thanks for pointing out the detonation problem, I'd completely forgotten about that! Shouldn't be too difficult to overcome, though - just replace the pistons with recessed pistons, or use shorter con-rods, to decrease the compression ratio if it turns out to be necessary. Or, if you don't want to tear the engine apart, put a spacer between the cylinder and the head.

I think it will actually be less of a problem in high-performance engines, because they are turbo-charged. I know very little about turbo-chargers in aeroplanes, but going on my knowledge from cars, the only thing which would be required would be to open the wastegate slightly.

As for your other points: I have never heard that lower octane fuel is more susceptible to vapour lock than higher octane. If that is the case, though, a bigger fuel pump should fix it?

And valve seat recession can be easilly cured using hardened valve seat inserts, exactly the same as it has been in hundreds of thousands (if not millions) of classic cars.


I'm sorry, but I really feel that some people are looking for a problem where there isn't one. And it is certainly in the interests of the engine manufacturers to do this. All piston engines are pretty much exactly the same - it's just that some are more tuned than others. And the lower the ocatane rating, the less you can tune the engine. Aviation engines are typically not very highly tuned anyway, because reliability is more important than performance.

I think I will post a link to this thread on the Tech Log forum. I can't speak for anyone else here, but most of my engine knowledge comes from car engines, which are not aluminium, so there could well be some issues I'm not aware of. It would be good to here from someone with some real expertise in this area.

FFF
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[Gaspasser]

This is a copy of an article written by an oil company aviation tech mananger on this subject.

The Future of G.A. Fuels

Currently the two principal types of fuel used in Aviation are Avgas 100LL and Jet A-1; Jet A-1 for turbine engines and Avgas for spark ignition piston engines. If you are a general aviation pilot, the one you are probably more familiar with is Avgas and it is this which we will concentrate on here.
As you may be aware, Avgas contains Tetra Ethyl Lead (TEL) - the additive which has recently been banned in automotive forecourt fuels in the European Union for environmental reasons. Although the total fuel volume used in aviation is less than 0.5% of that used in the automotive sector in Europe, there is considerable pressure from Environmental Lobbyists to remove or replace TEL in Avgas and produce an unleaded grade.
To understand what is involved, we first need to look at what benefits TEL has. As you may know from the problems with Automotive fuels, Lead compounds from TEL form a protective layer on the valve seat and prevents the soft valve seats from eroding. Without TEL small areas of a soft metal valve seat will fuse to the valve and be 'plucked' from the face of the seat. Once attached to the valve they form an abrasive surface which further damages the valve seat. This combination of actions is known as Valve Seat Recession (VSR) as the seat of the valve is worn away and recesses into the cylinder head. The solutions to this are to either use a VSR additive or fit hardened valve seats which are resistant to this action.
VSR additives are now commonly used in Lead Replacement Petrol on automotive forecourts, however for several reasons they are not yet approved for use in aviation engines. This means that the only current method of preventing Valve Seat Recession for aviation engines using unleaded fuels would be to fit hardened valve seats. This is common in new manufacture Avco Lycoming and Teledyne Continental engines, but some older engines would need modification.
The other more significant problem with unleaded fuels is that of Octane rating.
Octane rating is a measure of how resistant a fuel is to detonation or "pinking"; the higher the Octane rating, the more the fuel / air mixture can be compressed without detonation happening. To make this clear, octane rating is not a measure of the amount energy in the fuel, but is a measure of its resistance to detonation. The advantage or higher octane fuels is that a higher compression ratio or supercharging ratio can be used, which then leads to a higher engine cycle efficiency, which in turn means more power output for a given fuel burn. However, to confuse things further, there are four principal ways to measure Octane rating, RON, MON, Lean Mixture and Rich Mixture ratings.
Road fuels tend to be measured on a RON scale, for which unleaded fuels tend to be 95 - 98 RON but are only 85 - 87 MON. Avgas is measured on Lean Mixture (similar to MON) but also has a Rich Mixture Octane rating. The Lean Mixture rating is 100 octane (15 octane higher than the comparable 85 MON for unleaded Mogas) but Avgas also has a Rich Mixture rating of 130 which allows higher supercharger boost pressures to be used without detonation occurring. This is particularly a problem when using high power settings at low altitude, for example during take off.
As you can see TEL in Avgas makes a significant difference to the octane rating and without it Octane ratings would be back down to 80 - 85 Lean Mixture - the level for road fuels - instead of 100 / 130. This is not a problem for most typical modern normally aspirated engines as their compression ratios are quite modest and detonation would not be a problem with 80 - 85 Lean Mixture Octane fuel. However, for those aeroplanes with supercharged or turbocharged engines the use of low octane unleaded fuels would not be suitable. The only way to operate these turbo engines on current unleaded technology fuels would be to significantly reduce the boost pressure of the supercharging and massively de-rate the engines. This de-rating would be so severe that many of the engines would no longer be powerful enough for the aeroplane in question.
Modern aviation unleaded fuels are currently being developed, such as 82UL in the United States. This is an 82 Octane Lean Mixture rating fuel and is approved for use in modern non turbo Avco Lycomings engines amongst others. However, it is not yet available in Europe but also not everyone can use it - your aircraft manufacturer must raise a Aircraft Modification document to approve its use. Some new Cessnas are approved to use 82UL, but most aircraft types currently do not have manufacturer's approval. The potential quantity of Avgas piston engined aircraft world-wide that could use this grade is estimated to be around 60%, although some of these would probably need fuel system modifications prior to approval.
To date there are no additives available to replace TEL which increase the Octane rating - the additives used in automotive Lead Replacement Fuels only tackle the problem of valve seat recession and do not effect the Octane rating of the fuel. Therefore if Avgas 100LL were to disappear, the only other option currently available to owners with turbo or supercharged engines would be for the aircraft manufacturer raise a modification to replace their engine with either a turboprop or diesel engine.
This brings us on to the other recent advance in General Aviation engines; the development by several engine manufacturers of diesel engine technology. Shell is involved with all of the major prospective aviation diesel engine manufacturers and is working closely on these projects. These engines potentially offer several significant advantages over Avgas engines. They return up to 30% better fuel economy, use Jet A-1 rather than Avgas, and have the potential to be retrofitted to many light aircraft, replacing their current Avgas type engines. The downside will be the cost of engine replacement and aircraft modification and whilst some applications may be able to take advantage of this technology, this will not be a solution for everyone.
So in summary, Aviation engines present many unique challenges to the development of Avgas and as such there is yet no firm date to replace Avgas 100LL, but there can be little doubt that eventually Leaded Avgas will be withdrawn from use. However this does not seem likely until suitable fully developed alternatives are available; a situation that is likely to be several years into the future

[Kermit 180]

Interesting regarding the possible future of aircraft fuels and alternatives. Amazing to read that Avgas 100LL has several times more lead than some car fuels. In NZ there is no Avgas100LL (blue coloured) that I am aware of, its all Avgas100 of the green variety (so much for clean and green). The quality of Avgas has dropped noticeably in recent times. It now has more of a sulphur smell to it than it used to, and in recent times we have had many new problems with Avgas, from contamination scares to common every-day plug fouling. Maybe this is one way for the fuel companies to ruin our engines slowly and force us into new fuels later. Does anyone know why Avgas has a stronger sulphur smell today, than it did two years ago?

Kermie

[ShyTorque]

FfF,

As you rightly said, the problems of valve seat recession can be overcome with modification & expense. That is the easy bit. There are more, lesser known issues, such as the possibility of increased valve guide wear caused by the removal of TEL (tetra-ethyl lead) compounds from fuel, and the poor compatibility of aviation lubrication oils with MOGAS, resulting in an increase in general wear rates of all the engine parts. Yet another problem is the possible incompatibility of MOGAS and rubber parts such as fuel pump diaphragms and fuel lines etc.

Vapour lock is definitely a problem affecting unleaded fuels. It may or may not be cured by simply changing the fuel pump, it's an individual problem depending on the design of the whole aircraft fuel system. Vapour lock is not caused by changing the octane rating per se, but by the requirement to change the composition of the fuel recipe in order to regain an octane rating without the use of lead compounds. Adding lead was obviouly an easy answer!

Unleaded fuels may also be health damaging, they now contain higher levels of benzene (poisonous/carcinogenic) than leaded fuels. Benzene, a fuel in itself, has a high octane rating so the content in unleaded fuels has been increased. Unfortunately it is also very volatile, giving the increased vapour lock problem. BTW, this is the reason why unleaded fuel goes "off" quicker than leaded fuels. If a tank of MOGAS fuel is left standing for a period of time, the benzene content reduces through evaporation resulting in a reduction in fuel quality. This may be seen as a difficulty in engine starting and octane rating. This has obvious implications for aircraft not flown often, especially if the MOGAS they are filled with has come from a garage with a low turnover of fuel. It may result in pilots complaining of a "bad tank" of fuel.

Some areas of the USA have complex vapour recycling pumps at gas stations to reduce the possibility of human ingestion of benzene vapour. So even sniffing a whiff of this stuff may be dangerous! TEL might be less harmful overall; I don't know the pros and cons but have my suspicions as we don't seem to have been given much information on the long-term health issues, especially regarding Lead Replacement Petrol (LRP) contaning other metal compounds such as potassium.

The one engine problem that cannot be overcome at the moment on existing engines designed for high octane leaded fuels is the loss of performance caused by reduced compression ratios required if using a lower octane rated fuel. Again, it's an individual problem depending on engine design. Some engines may be affected very little but conversely, some GA aircraft were only marginally powered in the first place!

An engine using any form of forced induction actually needs a higher quality fuel because forced induction = higher compression pressures. This is also why intercoolers are fitted to forced induction engines, the charge is already heated by compression and is more likely to suffer from detonation once inside the combustion chamber due to the increased temperatures. Forced induction engines are designed with lower compression ratios (larger combustion chamber volumes) to compensate. They do tend to be less fuel efficient than a conventionally tuned engine producing the same power as the secret to high fuel efficiency is a high CR, like diesel engines...(aha - that's definitely the way to go, so watch this space we'll all want one soon!)

Aircraft engines are not generally highly "tuned" and are generally slow-revving but they DO have large cylinder and combustion chamber volumes which still makes them prone to detonation. What needs to be understood is that fuel air mixture burns very rapidly on a "flame front" out and away from the spark plug/s but it does NOT explode as some people seem to imagine. A piston can only transfer energy to the crankshaft in the form of a steady push, not in the form of a "knock". If the mixture does explode, that is detonation and the piston cannot tranfer this energy to the crankshaft which is why it is so damaging (imagine someone tranferring energy to yourself in the form of a firm push and then the same amount of energy as a kick. The kick hurts!). As combustion takes place on the flame front, the combustion chamber pressure increases very markedly so that unburned mixture may detonate, just like inside a diesel engine. Large cylinders, having more volume, take longer to burn a charge and the proportionate increase in compression chamber pressures is very high compared to smaller cylinders. This is why engines such as those used in F1 cars have very small cylinders, they burn the charge much quicker and there is less chance of detonation taking place, which allows a higher state of tune to be used. TEL works to increase the octane (anti-knock) rating because it forms incombustible dust particles which act as a buffer inside the combustion chamber, preventing detonation.

Go diesel! ;)

ShyT

[dirkdj]

FFF,

The proposed electronic ignition system I am talking about comes with a secondary 25 (or so) Amp alternator that fits on the back of the engine. This gives you two alternators and a battery.

This solution is a lot more practical for existing airframes than re-engining with diesels. The PRISM system is expected to be certificated early next year. The price may be somewhere between 5 and 10K$, a diesel engine would probably be 50 to 70K$ (300 hp turbocharged class).

Also, over here, MOGAS is about 40 % cheaper than AVGAS.

In the long run it will be diesels ... :p

[FlyingForFun]

Hmm, seems this is a far more complex issue than I'd imagined. Thanks for your input, guys!

FFF
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