Mogas

[ozbear]

What revs do you cruise at?

2800-2900 cruise

 

 

[ozbear]

If only we could be sure of the quality of mogas. Perhaps there is a simple test kit we could carry.What a bind for a greenie like me: use AvGas and save the engine, or use mogas and save the planet?

I'd be much happier burning pure ethanol, like the Brazilians do.

 

How much extra weight would it cost to convert to LPG?

LPG creates a lot of carbon as well and is hard on valves and seats stellite faced valves and welltite seats are an improvement

 

 

[Dafydd Llewellyn]

I'm glad I'm not an engine manufacturer, if what is being said on this thread is typical.

 

 

[Bob Llewellyn]

LPG creates a lot of carbon as well and is hard on valves and seats stellite faced valves and welltite seats are an improvement

That seems a bit odd - LPG is composed of shorter hydrocarbon chains, so there's less carbon and more hydrogen - proportionally - than petrol. As hydrogen burns around 2,800C (from memory), and carbon burns around 3,400C, the flame temperature should be considerably lower, giving much more resistance to detonation.

 

 

[ozbear]

That seems a bit odd - LPG is composed of shorter hydrocarbon chains, so there's less carbon and more hydrogen - proportionally - than petrol. As hydrogen burns around 2,800C (from memory), and carbon burns around 3,400C, the flame temperature should be considerably lower, giving much more resistance to detonation.

Somebody forgot to tell thehydrocarbon chains that .the trouble is impurities in the LPG cause a few problems the valves and seats in practice run quiet hot

 

 

[ozbear]

I'm glad I'm not an engine manufacturer, if what is being said on this thread is typical.

What do you mean Dayfydd ?

 

 

[Dafydd Llewellyn]

What do you mean Dayfydd ?

I mean, people here are ignoring the fuel that is specified in the engine TCDS. That's the fuel for which the engine detonation testing was done.

I have repeatedly pointed out that there is roughly a ten-point difference between MON (Motor octane number) as used in Avgas, and RON (Research octane number) as used for Mogas. So 91 RON is roughly equivalent (in regard to detonation) to 80/87 octane Avgas (no longer made, but some Lycomings were certificated for it). The old leaded "super" used to be a very close equivalent to 80/87 Avgas, but with a higher vapour pressure. Since that went off the market, there has not been a grade of Mogas that is anything like equivalent to 100LL. If there were, it would be called something like 110 RON.

 

If people persist in being so bloody-minded stupid about the fuel they use, they have no right to blame the engine manufacturer for the problems that result. The RON rating method was an advertising ploy introduced by the fuel companies to disguise the drop in fuel quality that resulted from the no-lead legislation.

 

(The no-lead legislation itself, was introduced so that catalyctic exhaust devices to clean-up the oxides of nitrogen (which produce brown smog) would not have their platinum catalyst "poisoned" by the lead bromide. The Rah-Rah about babies suffering brain damage from lead poisoning was political eyewash - the lead plumbing in British towns supplied far more lead than the vehicle exhausts.)

 

The message is: RTFM, you idiots.

 

 

[ozbear]

I use premium unleaded because I think it's a better fuel than avgas for me when you pull an engine down that has run on it the carbon left behind is minimum and soft andflakey unlikely to do damage not like left behind by avgas the engine runs fine and does not detonate or ping at all temps are in limits and plugs are clean but time will tell .if you recall a few years ago avgas was disolveing fuel lines

 

 

[Russ]

One time only, I filled my tanks with premium, my jab ran fine, but when I returned 4.....5 days later, opened my door, the jab reeked of fuel inside, I immediately thought "leak" but nothing was leaking, then I was told about fume leak from hoses etc, drained the fuel, refilled with avgas again, no fuel smells again, so.......staying on avgas.

 

 

[Bob Llewellyn]

I use premium unleaded because I think it's a better fuel than avgas for me when you pull an engine down that has run on it the carbon left behind is minimum and soft andflakey unlikely to do damage not like left behind by avgas the engine runs fine and does not detonate or ping at all temps are in limits and plugs are clean but time will tell .if you recall a few years ago avgas was disolveing fuel lines

2,2,4 trimethyl pentane is not a fuel line solvent; nor is tetra-ethyl lead, even with bromide added. I don't see how comparing contaminated avgas with uncontaminated PULP is valid. The soft flaky carbon is indicative of the high proportion of aromatics used to elevate the "octane" number of the PULP, and indicates combustion lag, with corresponding (slightly) reduced efficiency. If you can live with the low vapour pressure, and your supplier reliably meets your engine's octane requirements, fine and good. 100LL (iso-octane + TEL) does have a higher octane rating than PULP, and the combustion process typically yields a somewhat higher thermodynamic efficiency - if you need these, or your fuel system is sensitive to vapour lock, then PULP is not a substitute. Personally, I'd like to have enough money to do the fuel research the engine manufacturers didn't try... though I probably wouldn't spend it on that!

 

 

[ozbear]

There are a lot of cars running on pulp with very little problems engines now outlast their car bodies when did you last have to decarbonise your engine a common occurrence in the leaded days:)

 

 

[ozbear]

I mean, people here are ignoring the fuel that is specified in the engine TCDS. That's the fuel for which the engine detonation testing was done.I have repeatedly pointed out that there is roughly a ten-point difference between MON (Motor octane number) as used in Avgas, and RON (Research octane number) as used for Mogas. So 91 RON is roughly equivalent (in regard to detonation) to 80/87 octane Avgas (no longer made, but some Lycomings were certificated for it). The old leaded "super" used to be a very close equivalent to 80/87 Avgas, but with a higher vapour pressure. Since that went off the market, there has not been a grade of Mogas that is anything like equivalent to 100LL. If there were, it would be called something like 110 RON.

 

If people persist in being so bloody-minded stupid about the fuel they use, they have no right to blame the engine manufacturer for the problems that result. The RON rating method was an advertising ploy introduced by the fuel companies to disguise the drop in fuel quality that resulted from the no-lead legislation.

 

(The no-lead legislation itself, was introduced so that catalyctic exhaust devices to clean-up the oxides of nitrogen (which produce brown smog) would not have their platinum catalyst "poisoned" by the lead bromide. The Rah-Rah about babies suffering brain damage from lead poisoning was political eyewash - the lead plumbing in British towns supplied far more lead than the vehicle exhausts.)fydd

 

The message is: RTFM, you idiots.

Just back to what you were saying earlier Dayfydd jabiru specify that mogas min 95ron be used I'm not ignoring the specified fuel

 

 

[Dafydd Llewellyn]

Just back to what you were saying earlier Dayfydd jabiru specify that mogas min 95ron be used I'm not ignoring the specified fuel

Good for you! I did not say it HAS to be 100LL; I said, it is stupid to ignore what the engine was type-certificated for. And illegal to disobey whatever is written in the Flight Manual, BTW; RAA aircraft are NOT exempted from that regulation. So if you are following the Flight Manual, fine; it's not you I was talking to. I agree TCDS VE 501 issue 2 lists both 100LL Avgas and 95 RON mogas for the Jab 2200C.

 

 

[ozbear]

I also agree I just wasn't clear on who you were targeting.

 

 

[facthunter]

The only time I've used Mogas ( except in a 912 )was when I shandied it, and didn't use it on take off .Not in a Jab by the way. I know LAME's who just won't use it. ever. I've heard of Grumman Ag cats using it in a radial but also heard the gum deposits are excessive. This was 18 years ago. Perhaps the newer Mogas from Singapore is better but it varies in quality from time to time. IF there is any possibility the engine you use could suffer from preignition ot detonation, why use it at all? Avgas into the future is not assured and something else will have to be available . Some oil companies already make a racing fuel and if demand is there, aviation might get a look in. Sorry another several day old hold up in the posting Nev

 

 

[Bob Llewellyn]

There are a lot of cars running on pulp with very little problems engines now outlast their car bodies when did you last have to decarbonise your engine a common occurrence in the leaded days:)

...used to run Peugeot 404 & 504 engines with no de-cokes, on leaded, for ~150,000 miles, then change the rings and big ends - no decoke required. Yes, modern car engines have finally caught up with 1950s vintage french car engines... it's not a fuel issue!

 

 

[facthunter]

AH -ha another Peugeot nut. That makes at least 2 of us left.. A lot of the deposit is from dust. Talking of French car engine design. 1913 Delage( 3 made,) had large displacement 4 cyl full rollerbearing engine with 4 valve desmodromic head. Way ahead of much else. Reading the adds you would be lead to believe HONDA invented it all. Nev

 

 

[Bob Llewellyn]

The only time I've used Mogas ( except in a 912 )was when I shandied it, and didn't use it on take off .Not in a Jab by the way. I know LAME's who just won't use it. ever. I've heard of Grumman Ag cats using it in a radial but also heard the gum deposits are excessive. This was 18 years ago. Perhaps the newer Mogas from Singapore is better but it varies in quality from time to time. IF there is any possibility the engine you use could suffer from preignition ot detonation, why use it at all? Avgas into the future is not assured and something else will have to be available . Some oil companies already make a racing fuel and if demand is there, aviation might get a look in. Sorry another several day old hold up in the posting Nev

Let us suppose we have 2 liquid hydrocarbons, one with a Reid vapour pressure of (say) 0.8 bar, and the other with an RVP of 0.7 bar. Mix them together. The RVP of the mix will be less than 0.7 bar. Now take low-octane petrol, add triptane, toluene, and Methylcyclopentadienyl manganese tricarbonyl (MMT); the "octane" rating is now higher - probably about 95 RON - but the RVP is very low; which is why modern cars have sealed fuel tanks and the ECU is designed to cope with variable pressures and flows in the vapour return line. Indeed, it's also the reason most cars have a fuel pump in the tank (otherwise the suction would cause vapour lock). If you put such a fuel in an aeroplane with suction lift from the fuel tank, such as a Piper Cherokee, there is a good probability of vapour lock causing EFATO at ~100ft one summer's day.

If a conscientious fuel company pushes the RON up to 98 "octane" by dissolving some butane in the blend, the RVP plummets for a few days, until all the butane has evaporated and the anti-knock rating has fallen.

 

Now, the majority of the anti-knock hydrocarbons are slower-burning than aliphatics, so the combustion cycle needs to be adjusted to compensate; the difference is generally not huge at high manifold pressures, but car engines generally have quite sophisticated systems to allow sustained running at low manifold pressures. The issue here is that PULP can comply with the commercial standard, yet have a wide range of burning rates with varied additives. 100% iso-octane + TEL (100LL) is, however, 100% iso-octane + TEL, and burns like - you guessed it - 100% iso-octane + TEL.

 

Back to those octane-boosting additives - MMT decomposes under storage, quite rapidly in hot weather; and the byproducts of partial decomposition tend to trigger partial polymerisation of the aromatics, creating a varnish of quite pleasant light-brown colour. There's not very much of it, unless you really stew your fuel, but you don't have to varnish a fuel filter very much before the flow rate drops. (MMT is not the only culprit, but it certainly helps the process along).

 

We could drop the MMT and add a few % napthalene, but unfortunately it will condense out of the fuel at low temperatures, forming a substance with the initial texture of soft wax. try pushing soft wax through your fuel lines and pump...

 

If you have a supplier of PULP, whose base stock is of sufficient quality that no butane is added, and whose turnover is enough that the fuel is always fresh*, and you operate with always-fresh fuel off a coastal strip and don't climb above a few thousand feet, in an aeroplane with a gravity-fed fuel system, and a well-cooled engine, you will probably never experience a fuel-related problem. If any of the above parameters are not met, you should expect a problem at some time.

 

*Now it's not refined here, how fresh can it be?

 

Spark ignition requires a tightly controlled fuel for tightly-controlled results; and for spark ignition engines that climb and descend, RVP ultimately demands either a pure fuel or pressurised tanks. The steam engine is undoubtedly the future for aviation...

 

 

[Bob Llewellyn]

AH -ha another Peugeot nut. That makes at least 2 of us left.. A lot of the deposit is from dust. Talking of French car engine design. 1913 Delage( 3 made,) had large displacement 4 cyl full rollerbearing engine with 4 valve desmodromic head. Way ahead of much else. Reading the adds you would be lead to believe HONDA invented it all. Nev

...I thought Ernie Peugeot ran a 4-valve head in the 1912 GP? PS - Honda read Ricardo's "The High Speed Internal Combustion Engine"; the postie bike engine is designed straight out of the third edition!

Darn keyboard can't spell for nuts...

 

 

[Dafydd Llewellyn]

The only time I've used Mogas ( except in a 912 )was when I shandied it, and didn't use it on take off .Not in a Jab by the way. I know LAME's who just won't use it. ever. I've heard of Grumman Ag cats using it in a radial but also heard the gum deposits are excessive. This was 18 years ago. Perhaps the newer Mogas from Singapore is better but it varies in quality from time to time. IF there is any possibility the engine you use could suffer from preignition ot detonation, why use it at all? Avgas into the future is not assured and something else will have to be available . Some oil companies already make a racing fuel and if demand is there, aviation might get a look in. Sorry another several day old hold up in the posting Nev

I used the old leaded Super in my PA28-140 on occasion (the fuel system was legally modified to reduce the risk of vapour-lock - tho nowadays I'd have gone about it differently) because it had a low-compression Lyc 0-320 that was certificated for 80/87 Avgas. Seabird certificated the original 360 model Seeker for the same fuel, because it also used a low-compression variant of the Lyc 0-360. However, that grade of MOGAS had neither aromatic hydrocarbons nor alchohol in it; it was essentially similar to 80/87 AVGAS except for its higher vapour pressure (which makes it more prone to vapour-lock), 50 % higher methyl bromide to tetra-ethyl lead ratio, and a much less precise quality control requirement. In those days, when you purchased a drum of AVGAS, it came with a Release Note - and the distributor came & collected it if you had not used it within 3 months. A shandy of Super-grade Mogas and 80/87 Avgas worked pretty well in the low-compression engines, the main issue was vapour lock, except in high-wing aircraft with the fuel in the wings.

Those days are long gone; and the issue that most people are unaware of with motor fuels, is that they are all pumped through the one pipeline; the fuel companies pump one product for a while, then a different product for a while, etc - and the result is a slug of contaminated fuel where the two batches are mixed in the process. That slug of fuel ends up (mostly) in the 91 RON tank. But it means the precise QA of any of the fluids that are transported that way (and most of them are), is somewhat suspect - and well below AVGAS standards. The least-worst of them is almost certainly 95 RON.

 

Modern car engines cope with this variability by their "smart" electronic fuel injection systems, wish oxygen sensors and knock sensors etc. I do not know enough about fuel chemistry to comment on the reasons for the freedom from deposits that we enjoy nowadays - tho I suspect ashless dispersant oils have a lot to do with that. The issue of reliability of electronic ignition systems for aircraft use will have to be overcome - it's not an easy one - because it's obvious that the QA issue for aircraft is too small a concern for the fuel companies now that there are no airline or military users of the product, so it will have to be addressed by the machinery that uses the fuel, rather than by the supply system, in future. This SHOULD mean that the cost of fuel should come down, to compensate for the increased cost of the engines, which are NOT thumped out by the million. Wanna bet it will?

 

 

[facthunter]

Bob,...That's true. The bike was a vertical twin with gearbox integral and dry clutch. The metallurgy of the heads in particular was not up to it, so the story goes, but aircooled four valves have a difficulty with cooling between the exhaust valves , in general.

 

4 valve heads were used on the racing Indians in 1913 but the combustion chamber design was grim but they still performed well up to about 1923 where more highly developed SIDEVALVES often beat them. This seems remarkable but the reason was tied up with the fuel .Until tetra ethyl lead became available mainly demanded for aviation, the compression ratios were only around 4:1.. The lead was becoming available around the late 20's. releasing the potential for much more power, from higher compression ratios. Ricardo (Harry) was pre eminent in head design from the early 20's and there is a fair bit of his notes around. There was a Ricardo TRIUMPH built about 1924 which was only a four valve head on a pretty standard production bike and was unspectacular. Rudge produced "Four Valve Four speed " Bikes about 1925 till it's demise during the war probably due to being bombed. I did own and ride a 1935 "Ulster" (Bronze head with semi radial valves) but I sold it. I think the bike is now in a shop in Chapel Street, Prahran.. Nev

 

 

[Bob Llewellyn]

Let us suppose we have 2 liquid hydrocarbons, one with a Reid vapour pressure of (say) 0.8 bar, and the other with an RVP of 0.7 bar. Mix them together. The RVP of the mix will be less than 0.7 bar. Now take low-octane petrol, add triptane, toluene, and Methylcyclopentadienyl manganese tricarbonyl (MMT); the "octane" rating is now higher - probably about 95 RON - but the RVP is very low; which is why modern cars have sealed fuel tanks and the ECU is designed to cope with variable pressures and flows in the vapour return line. Indeed, it's also the reason most cars have a fuel pump in the tank (otherwise the suction would cause vapour lock). If you put such a fuel in an aeroplane with suction lift from the fuel tank, such as a Piper Cherokee, there is a good probability of vapour lock causing EFATO at ~100ft one summer's day.If a conscientious fuel company pushes the RON up to 98 "octane" by dissolving some butane in the blend, the RVP plummets for a few days, until all the butane has evaporated and the anti-knock rating has fallen.

Now, the majority of the anti-knock hydrocarbons are slower-burning than aliphatics, so the combustion cycle needs to be adjusted to compensate; the difference is generally not huge at high manifold pressures, but car engines generally have quite sophisticated systems to allow sustained running at low manifold pressures. The issue here is that PULP can comply with the commercial standard, yet have a wide range of burning rates with varied additives. 100% iso-octane + TEL (100LL) is, however, 100% iso-octane + TEL, and burns like - you guessed it - 100% iso-octane + TEL.

 

Back to those octane-boosting additives - MMT decomposes under storage, quite rapidly in hot weather; and the byproducts of partial decomposition tend to trigger partial polymerisation of the aromatics, creating a varnish of quite pleasant light-brown colour. There's not very much of it, unless you really stew your fuel, but you don't have to varnish a fuel filter very much before the flow rate drops. (MMT is not the only culprit, but it certainly helps the process along).

 

We could drop the MMT and add a few % napthalene, but unfortunately it will condense out of the fuel at low temperatures, forming a substance with the initial texture of soft wax. try pushing soft wax through your fuel lines and pump...

 

If you have a supplier of PULP, whose base stock is of sufficient quality that no butane is added, and whose turnover is enough that the fuel is always fresh*, and you operate with always-fresh fuel off a coastal strip and don't climb above a few thousand feet, in an aeroplane with a gravity-fed fuel system, and a well-cooled engine, you will probably never experience a fuel-related problem. If any of the above parameters are not met, you should expect a problem at some time.

 

*Now it's not refined here, how fresh can it be?

 

Spark ignition requires a tightly controlled fuel for tightly-controlled results; and for spark ignition engines that climb and descend, RVP ultimately demands either a pure fuel or pressurised tanks. The steam engine is undoubtedly the future for aviation...

Oops! got the RVP effect back to front - blending puts RVP UP, not down... the fuel commences to vapourise at a lower TEMPERATURE or a HIGHER pressure. Focus, grasshopper...

 

 

[Bob Llewellyn]

Bob,...That's true. The bike was a vertical twin with gearbox integral and dry clutch. The metallurgy of the heads in particular was not up to it, so the story goes, but aircooled four valves have a difficulty with cooling between the exhaust valves , in general.4 valve heads were used on the racing Indians in 1913 but the combustion chamber design was grim but they still performed well up to about 1923 where more highly developed SIDEVALVES often beat them. This seems remarkable but the reason was tied up with the fuel .Until tetra ethyl lead became available mainly demanded for aviation, the compression ratios were only around 4:1.. The lead was becoming available around the late 20's. releasing the potential for much more power, from higher compression ratios. Ricardo (Harry) was pre eminent in head design from the early 20's and there is a fair bit of his notes around. There was a Ricardo TRIUMPH built about 1924 which was only a four valve head on a pretty standard production bike and was unspectacular. Rudge produced "Four Valve Four speed " Bikes about 1925 till it's demise during the war probably due to being bombed. I did own and ride a 1935 "Ulster" (Bronze head with semi radial valves) but I sold it. I think the bike is now in a shop in Chapel Street, Prahran.. Nev

Ricardo's "turbulent" head, and then the "shock absorber" head, were - as far as I know - the ultimate sidevalve developments; 91 RON ULP is an argument to go back to them, except exhaust valve cooling is a challenge in an air-cooled application...

 

 

[Dafydd Llewellyn]

I also agree I just wasn't clear on who you were targeting.

I was trying to get a general message across to the readers of the thread.