Tetra-ethyl lead

[TMetzinger]

The engines can't run on mogas without the advanced fuel/air/ignition timing setups that autos have.

YES, you can make 400+HP on mogas - Various sports/supercars do it all the time.
Will those engines work for airplanes? Probably not well enough to make them appealing compared to existing Lycs and Continentals.

Now - make 100LL go away, and either GA will go away (mostly) with it, or we'll eventually see new airframe/engine combos that work for the new fuel(s).

 

[dmccormack]

The engines can't run on mogas without the advanced fuel/air/ignition timing setups that autos have.

YES, you can make 400+HP on mogas - Various sports/supercars do it all the time.
Will those engines work for airplanes? Probably not well enough to make them appealing compared to existing Lycs and Continentals.

Now - make 100LL go away, and either GA will go away (mostly) with it, or we'll eventually see new airframe/engine combos that work for the new fuel(s).

Must it be "new fuels" though? If so, it doesn't look good for GA.

 

[TMetzinger]

By new fuels I'm not eliminating mogas... but you have to remove 100LL as an option before economic forces will cause engines to change.

 

[Cap'n Jack]

I'm not arguing that it's simple -- just trying to understand.

Assume that 100LL will be outlawed, so far the only arguments in favor of 100LL over mogas rest on distribution and requirements of higher-compression engines.

Can't mogas can meet all the other requirements, given the use of auto fuel in a wide variety of climatic conditions and even certain a/c engines?

I didn't say anyone was arguing.

Mogas by itself isn't the issue. Avgas and Mogas are the same hydrocarbons. It's the antiknock additives that are the issue that some engines need. The question really is "What is the replacement for TEL?"

 

[dmccormack]

I didn't say anyone was arguing.

Mogas by itself isn't the issue. Avgas and Mogas are the same hydrocarbons. It's the antiknock additives that are the issue that some engines need. The question really is "What is the replacement for TEL?"

So -- oversimplifying, I'm sure -- if a TEL substitue was identified, the current 100ll distribution network could be replaced with unleaded mogas + some TEL replacement?

That would be ideal -- since engines which did not require TEL could operate more economically, while the overall price would go down, given the size of the overall mogas market.

 

[kyleb]

So -- oversimplifying, I'm sure -- if a TEL substitue was identified, the current 100ll distribution network could be replaced with unleaded mogas + some TEL replacement?

That would be ideal -- since engines which did not require TEL could operate more economically, while the overall price would go down, given the size of the overall mogas market.

Yes, IF someone resolved the storage stability, volatility, and chemical compatability issues with today's mogas AND added another set of tanks and pumps at every FBO AND worked through the certification issues for all the airplanes that could use mogas but are not certified to do so.

It is a big process.

 

[dmccormack]

Yes, IF someone resolved the storage stability, volatility, and chemical compatability issues with today's mogas AND added another set of tanks and pumps at every FBO AND worked through the certification issues for all the airplanes that could use mogas but are not certified to do so.

It is a big process.

Right -- but the options are:

• Continue with 100LL as is Not an option long term due to Lead concerns
• Mogas + for engines that require +, mogas for everyone else (requires all you described)
• New fuel, yet to be released (same drill, but far more costly given the small market size)

 

[wsuffa]

My engine (TO360) won't run on Mogas. The cost of replacing the engine with one that will would be more expensive than the airframe value.

 

[Ted]

Having two fuels does not make economic sense unless one of those fuels can be directly drawn from a batch that is already being produced (i.e. car gas), which at present it can't. It doesn't make sense to cater to the <20% of fuel purchased by aircraft with O-200s.

The engines that genuinely require 100LL do, in fact, require a fuel with those anti-knock properties at their rated power levels, fuel consumptions, compression ratios, spark timing, etc. If you make it run on something with less anti-knock capabilities, expect to have problems.

I know everyone wants the solution to be simple, but it's not. Don't believe me? I'm done.

 

[dmccormack]

Having two fuels does not make economic sense unless one of those fuels can be directly drawn from a batch that is already being produced (i.e. car gas), which at present it can't. It doesn't make sense to cater to the <20% of fuel purchased by aircraft with O-200s.

The engines that genuinely require 100LL do, in fact, require a fuel with those anti-knock properties at their rated power levels, fuel consumptions, compression ratios, spark timing, etc. If you make it run on something with less anti-knock capabilities, expect to have problems.

I know everyone wants the solution to be simple, but it's not. Don't believe me? I'm done.

So what's your proposal to handle the inevitable abolition of TEL?

 

[EdFred]

It's 90/10 with 100LL.

90% of the AvFuel is burned by 10% of the fleet. That 10% can't use anything else right now. Great, so 90% of the plans *can* burn Mogas. It doesn't mean squat, because whoopteefreakingdo you've only solved 10% of the problem.

The solution is going to be finding a TEL substitute, and guess what, you'll end up burning that too, because that is going to satisfy 90% of the industry.

 

[Missa]

I'm not arguing that it's simple -- just trying to understand.

Assume that 100LL will be outlawed, so far the only arguments in favor of 100LL over mogas rest on distribution and requirements of higher-compression engines.

Can't mogas can meet all the other requirements, given the use of auto fuel in a wide variety of climatic conditions and even certain a/c engines?

By new fuels I'm not eliminating mogas... but you have to remove 100LL as an option before economic forces will cause engines to change.

I would eliminate Mogas as a possible 100LL replacement.

The mogas you buy in Denver is not the same blend as the mogas you buy in New York City. The Mogas is blended for optimum performance at the location (and time of year, ie atmospheric conditions) that it is being sold at. By the time you change altitude/season enough to need a different blend of mogas, your car's tank will be empty (and so will the service stations tanks for seasonal changes.)

Mogas is a “dirty” fuel compared to Avgas. If you look at a petroleum distillation curve (and by god I can’t find one on-line to link to) you will see that mogas comes off earlier in distillation and contains more diverse chemistry. Avgas is on a very high part of the distillation curve and is more "pure". This allows it to be more stable both in atmospheric conditions and in time. Avgas does not need to be “stabilized” like mogas does if you put your vehicle away for the winter. This is also part of why it costs more, it takes more energy to distill avgas then it takes to distill mogas. Pure distilled avgas before adding lead is about 91UL. It takes the Lead to get to 100.

Mogas will work in engines and planes designed for lower octane levels, especially if you fly relatively close to the ground, and you fly often enough to rotate the fuel out of you tanks before it breaks down. Otherwise you are taking increased risks when you fly. Especially if it's been a while since you filled you tanks with mogas.

Future unleaded aviation fuel will still be Avgas, with some other additive to gain the 100 octane.

Why don’t they just make 80UL Avgas? Not enough demand. The fuel companies only run the distillation up to the avgas level once a year or so to make all the predicted needed fuel for that year. If you want you can get 91UL Avgas from the refinery (if you can convince them to sell it to you) but due to the demand issues of 91UL vs 100LL (the 90% of the fleet that can use it only accounts for 10% of the fuel sales) no one with the power to buy it wants to invest in the infrastructure to distribute it.

 

[Missa]

I didn't say anyone was arguing.

Mogas by itself isn't the issue. Avgas and Mogas are the same hydrocarbons. It's the antiknock additives that are the issue that some engines need. The question really is "What is the replacement for TEL?"

No, Avgas and Mogas are not the same, they both come from crude but they are not all the same hydrocarbons.

Mogas is a greater mix of hydrocarbons then Avgas is, which is why Avgas is more stable. If you continue to distill Mogas, you get Avgas (and a bunch of lower level hydocarbons).

 

[Ted]

So what's your proposal to handle the inevitable abolition of TEL?

Assuming that I had that information, how stupid would I have to be to post it on a public forum? You know what I do for a living...

 

[dmccormack]

Assuming that I had that information, how stupid would I have to be to post it on a public forum? You know what I do for a living...

I didn't think there was a link between the possible replacement for 100LL and your work, though I guess I shoulda thought of that.

 

[dmccormack]

I would eliminate Mogas as a possible 100LL replacement.

The mogas you buy in Denver is not the same blend as the mogas you buy in New York City. The Mogas is blended for optimum performance at the location (and time of year, ie atmospheric conditions) that it is being sold at. By the time you change altitude/season enough to need a different blend of mogas, your car's tank will be empty (and so will the service stations tanks for seasonal changes.)

Mogas is a “dirty” fuel compared to Avgas. If you look at a petroleum distillation curve (and by god I can’t find one on-line to link to) you will see that mogas comes off earlier in distillation and contains more diverse chemistry. Avgas is on a very high part of the distillation curve and is more "pure". This allows it to be more stable both in atmospheric conditions and in time. Avgas does not need to be “stabilized” like mogas does if you put your vehicle away for the winter. This is also part of why it costs more, it takes more energy to distill avgas then it takes to distill mogas. Pure distilled avgas before adding lead is about 91UL. It takes the Lead to get to 100.

Mogas will work in engines and planes designed for lower octane levels, especially if you fly relatively close to the ground, and you fly often enough to rotate the fuel out of you tanks before it breaks down. Otherwise you are taking increased risks when you fly. Especially if it's been a while since you filled you tanks with mogas.

Future unleaded aviation fuel will still be Avgas, with some other additive to gain the 100 octane.

Why don’t they just make 80UL Avgas? Not enough demand. The fuel companies only run the distillation up to the avgas level once a year or so to make all the predicted needed fuel for that year. If you want you can get 91UL Avgas from the refinery (if you can convince them to sell it to you) but due to the demand issues of 91UL vs 100LL (the 90% of the fleet that can use it only accounts for 10% of the fuel sales) no one with the power to buy it wants to invest in the infrastructure to distribute it.

Good summary of this complex issue. Thanks, Missa!

 

[steingar]

No, Avgas and Mogas are not the same, they both come from crude but they are not all the same hydrocarbons.

Mogas is a greater mix of hydrocarbons then Avgas is, which is why Avgas is more stable. If you continue to distill Mogas, you get Avgas (and a bunch of lower level hydocarbons).

Is that distillation in the normal chemical sense, i.e. capturing and condensing the vapor phase? Genuinely curious.

 

[Steve]

This mogas ain't all it's cracked up to be.....

 

[kyleb]

So what's your proposal to handle the inevitable abolition of TEL?

Dunno and not the issue I was addressing.

I was simply pointing out some of the reasons Mogas ain't a panacea.

 

[brcase]

Ted,

On a somewhat related topic, are you able to point us to any updated information on Lycoming approving Mogas for some engines. The information I have found is a couple years old.

http://www.avweb.com/avwebflash/news/LycomingAnnounces_AutoGasApprovalProgram_198039-1.html

Thanks

Brian

 

[Cap'n Jack]

So -- oversimplifying, I'm sure -- if a TEL substitue was identified, the current 100ll distribution network could be replaced with unleaded mogas + some TEL replacement?

That would be ideal -- since engines which did not require TEL could operate more economically, while the overall price would go down, given the size of the overall mogas market.

You're not oversimplifying. Without the additives, Aggas and Mogas are pretty much the same cut from straight-run distillation. Starting with branched C4s (4 carbon the longest chain if streched out) through C8 (not much of this) with most of the fuel being C5 and C6 chains.

Yes, IF someone resolved the storage stability, volatility, and chemical compatability issues with today's mogas AND added another set of tanks and pumps at every FBO AND worked through the certification issues for all the airplanes that could use mogas but are not certified to do so.

It is a big process.

It is a big process but it's only the additive that needs changed. Another set of tanks will probably not be needed since they are trying to make an additive useful for all aircraft engines. The issue isn't the fuel- it's the small amount of additive that is mixed in that gives us the antiknock charisteristics we desire or need. The issues you raised really apply to whatever additive we need, which needs to be compatible with the gasoline and flight- see my earlier post.

 

[Ted]

Ted,

On a somewhat related topic, are you able to point us to any updated information on Lycoming approving Mogas for some engines. The information I have found is a couple years old.

http://www.avweb.com/avwebflash/news/LycomingAnnounces_AutoGasApprovalProgram_198039-1.html

Thanks

Brian

Brian,

I can neither confirm nor deny anything that may or may not be going on in the walls of the hallowed building, only point you to press releases or other information that's already available. In this case, I think you've got it. Sorry I can't be of more help.

 

[Clark1961]

Is that distillation in the normal chemical sense, i.e. capturing and condensing the vapor phase? Genuinely curious.

To a degree, yes. The earliest "refineries" simply boiled the oil to separate the lighter molecules from the heavier molecules. Now they get all fancy with cat crackers (no, it's not pet food or food made from pets) and reformers and some such things. They end up with more product in terms of volume than they had when they started. I don't work that end of the industry so I really don't know the ins-n-outs but it is pure Chem E any more.

 

[Missa]

Is that distillation in the normal chemical sense, i.e. capturing and condensing the vapor phase? Genuinely curious.

To a degree, yes. The earliest "refineries" simply boiled the oil to separate the lighter molecules from the heavier molecules. Now they get all fancy with cat crackers (no, it's not pet food or food made from pets) and reformers and some such things. They end up with more product in terms of volume than they had when they started. I don't work that end of the industry so I really don't know the ins-n-outs but it is pure Chem E any more.

To tell the truth what I know I got from some Chem-E trying to explain it to me so I only know the Lay-mans explaination. Clark really has it. http://en.wikipedia.org/wiki/Petroleum_distillation This gives overall info on Distillation but the industrial secstion talking about Fractional Distallation is generally what I know about petroleum distallation.

 

[Missa]

You're not oversimplifying. Without the additives, Aggas and Mogas are pretty much the same cut from straight-run distillation. Starting with branched C4s (4 carbon the longest chain if streched out) through C8 (not much of this) with most of the fuel being C5 and C6 chains.

I don't agree. Mogas and Avgas are on the same end of the distillation but they are not the same. It's like saying Kerosean, Jet A, and Auto Deisel are the same just because they come off the distillation near each other. Sure if you fuel your jet with Auto Deisel it will run... for a while. But it's not the optimal fuel that the engine was designed for and you are taking risks by doing it. Mogas and Avgas are cousins as far as distillation and they can be used with some success in motors designed for the other fuel but they are optimized for the application. If you want to run mogas don’t run up at the high altitudes and make sure to run your tanks out on a regular basis. Mogas is not made to hang around for a years and still have the same octane rating nor is it made to be tolerant to changes in altitude and atmospheric conditions, Avgas is.

For me running mogas in an airplane is like taking off into 0/0... I'll do it if there is someone with a gun/large wave or natural disaster comming for me, but otherwise I'm not taking the risk. I will choose possible death over certian death, but I will not choose possible death over life.

 

[Cap'n Jack]

No, Avgas and Mogas are not the same, they both come from crude but they are not all the same hydrocarbons.

Mogas is a greater mix of hydrocarbons then Avgas is, which is why Avgas is more stable. If you continue to distill Mogas, you get Avgas (and a bunch of lower level hydocarbons).

What do you mean by "stable"? Neither one decomposed while sitting around.

I think they were different in the past, but since most gasoline is cracked from higher hydrocarbons, the difference has disappeared. One way to improve the octane rating is longer chain hydrocarbons, and they do this by optimizing the cracking for these molecules.

Is that distillation in the normal chemical sense, i.e. capturing and condensing the vapor phase? Genuinely curious.

Yes- Clark described it well. I remember this being the place where the term "theoretical plates" comes from in chromatography.
http://en.wikipedia.org/wiki/Theoretical_plate

I don't agree. Mogas and Avgas are on the same end of the distillation but they are not the same. It's like saying Kerosean, Jet A, and Auto Deisel are the same just because they come off the distillation near each other. Sure if you fuel your jet with Auto Deisel it will run... for a while. But it's not the optimal fuel that the engine was designed for and you are taking risks by doing it. Mogas and Avgas are cousins as far as distillation and they can be used with some success in motors designed for the other fuel but they are optimized for the application. If you want to run mogas don’t run up at the high altitudes and make sure to run your tanks out on a regular basis. Mogas is not made to hang around for a years and still have the same octane rating nor is it made to be tolerant to changes in altitude and atmospheric conditions, Avgas is.

For me running mogas in an airplane is like taking off into 0/0... I'll do it if there is someone with a gun/large wave or natural disaster comming for me, but otherwise I'm not taking the risk. I will choose possible death over certian death, but I will not choose possible death over life.

The terms are "kerosene" and "diesel"- and those those are different. Kerosene and Jet A are pretty much the same, but different levels of QC in prodution. Diesel and Jet A are close enough that bodiesel works seems to work well in both applications.

The differences in between Mogas and Avgas as sold are more a matter of quality control...but that isn't the topic at hand. One can apply the same levels of QC to a batch of material as appropriate for the application.

 

[Gary]

I
Mogas is a “dirty” fuel compared to Avgas. If you look at a petroleum distillation curve (and by god I can’t find one on-line to link to) you will see that mogas comes off earlier in distillation and contains more diverse chemistry. Avgas is on a very high part of the distillation curve and is more "pure".

Good explaination - minor quibble - Avgas distallation is run with a very tight distallation/pressure range compared to Mogas and will contain a higher proportion of lighter fractions (shorter carbon chains and more aromatics - carbon rings rather than chains, such as xylene, toluene and benzene). These actually come off first. The tighter range does lead to a "purer" mix.

No, Avgas and Mogas are not the same, they both come from crude but they are not all the same hydrocarbons.

Mogas is a greater mix of hydrocarbons then Avgas is, which is why Avgas is more stable. If you continue to distill Mogas, you get Avgas (and a bunch of lower level hydocarbons).

Agreed, they are similar, but not the same. You could indeed distill Mogas, but you wouldn't get Avgas.

Is that distillation in the normal chemical sense, i.e. capturing and condensing the vapor phase? Genuinely curious.

Simplifed - yes - but basically true.

I don't agree. Mogas and Avgas are on the same end of the distillation but they are not the same. It's like saying Kerosean, Jet A, and Auto Deisel are the same just because they come off the distillation near each other.

Correct, not the same.

Gary

 

[dmccormack]

For me running mogas in an airplane is like taking off into 0/0... I'll do it if there is someone with a gun/large wave or natural disaster comming for me, but otherwise I'm not taking the risk. I will choose possible death over certian death, but I will not choose possible death over life.

Ummm.. I was 100% with you until this -- a bit overstated, given that many airplanes can run perfectly fine for years and many hundreds of hours on mogas.

 

[Missa]

What do you mean by "stable"? Neither one decomposed while sitting around.

Not a Chem E so... When you put something in storage that you will not use all winter (boat, lawn mower, motorcycle) you can add a fuel stabilizer to it, or when you bring it out of storage it will tend to back fire, cough and not make full power(at least my jetski did on old fuel). Avgas is formulated so that you can fill you tanks and let it sit for 3-4 months and it still have relatively the same fuel.

The differences in between Mogas and Avgas as sold are more a matter of quality control...but that isn't the topic at hand. One can apply the same levels of QC to a batch of material as appropriate for the application.

It's a matter of QC but saying mogas and avgas are the same is like comparing the Geek in his parents basement playing D&D with greasey hair and pmiples who last showered sometime last month to the sucessful trim athletic well groomed Doctor and saying "well they are all human so they are the same." Uhm, no. They are very very diffrent.

 

[Missa]

Ummm.. I was 100% with you until this -- a bit overstated, given that many airplanes can run perfectly fine for years and many hundreds of hours on mogas.

Depends on the flying you do and what engine you have. It also depends on the level of risk you are willing to take. We all manage our risks to our own comfort level. I know pilots who would take off into 0-0. I'm not one of them. It's just where my comfortable level of risk is vs. others.

 

[Missa]

Good explaination - minor quibble - Avgas distallation is run with a very tight distallation/pressure range compared to Mogas and will contain a higher proportion of lighter fractions (shorter carbon chains and more aromatics - carbon rings rather than chains, such as xylene, toluene and benzene). These actually come off first. The tighter range does lead to a "purer" mix.

PLEASE CORRECT ME!!!! Thank you! I'm basing all my information off my understanding of a converdation I had about 2 years ago with someone who was a Chem-E for a oil company.

So basicly you are telling me I had it in my head backwards... longer chains are the heavier stuff at the bottem of the distallation... Duh that makes sense. Which is why you can crack it.

Ok, so can you explain (in layman's terms) why mogas octane will lower over time? I know that Mogas does (experiance with winterizing toys) and Avgas does not. Why?

 

[EdFred]

It breaks down.

 

[Missa]

It breaks down.

Ok smart @*(, How?

 

[brcase]

Brian,

I can neither confirm nor deny anything that may or may not be going on in the walls of the hallowed building, only point you to press releases or other information that's already available. In this case, I think you've got it. Sorry I can't be of more help.

Thanks, I didn't expect anything from within, Just thought you might be aware of newer public information about it.

Thanks Again

Brian

 

[EdFred]

Ok smart @*(, How?

Just like any other carbon based material (our bodies) do. It oxidizes, and the -H ions get replaced by -O or -OH ions forming a different compound. Probably still flammable, but not ideal. Also lighter molecules in the gasoline mixture will evaporate off, leaving the heavier molecules. Eventually, the stuff will just turn into a gooey, tarry material if left out long enough.

 

[Missa]

Just like any other carbon based material (our bodies) do. It oxidizes, and the -H ions get replaced by -O or -OH ions forming a different compound. Probably still flammable, but not ideal. Also lighter molecules in the gasoline mixture will evaporate off, leaving the heavier molecules. Eventually, the stuff will just turn into a gooey, tarry material if left out long enough.

Part one answered. How about part 2) I know Avgas is more stable then Mogas... What makes it that way?

 

[Gary]

PLEASE CORRECT ME!!!! Thank you! I'm basing all my information off my understanding of a converdation I had about 2 years ago with someone who was a Chem-E for a oil company.

Maybe it was me!

So basicly you are telling me I had it in my head backwards... longer chains are the heavier stuff at the bottem of the distallation... Duh that makes sense. Which is why you can crack it.

Yes.... Also, most refineries do cracking, there are a number of ways to do it.

Ok, so can you explain (in layman's terms) why mogas octane will lower over time? I know that Mogas does (experiance with winterizing toys) and Avgas does not. Why?

I'm not sure that Mogas loses octane ratings over time, unless they used MTBE, which is easily oxidized and has a short half-life. Since Mogas has more of the "heavier" stuff, as well as some of the cats and dogs that passed through the distallation process (since the distallation range is wider), the "loss" is as much a function of a greater concentration of this junk. Avgas isn't immortal either, it will still show a loss, however tetra-ethyl lead is pretty long-lasting. See Ed's post below!

Just like any other carbon based material (our bodies) do. It oxidizes, and the -H ions get replaced by -O or -OH ions forming a different compound. Probably still flammable, but not ideal. Also lighter molecules in the gasoline mixture will evaporate off, leaving the heavier molecules. Eventually, the stuff will just turn into a gooey, tarry material if left out long enough.

Gary

 

[Missa]

Avgas isn't immortal either, it will still show a loss, however tetra-ethyl lead is pretty long-lasting. See Ed's post below!

Gary

I understand that Avgas isn't imortal, but I was told it didn't breakdown as fast as Mogas.

So if I'm understanding you correctly, that is due to both the lighter more controlled nature of Avgas and the TEL additive being very stable.

This would mean if we were looking for a TEL substitue additive for avgas, we would have the added requirment that it needs to be very stable over time.

 

[Gary]

I understand that Avgas isn't imortal, but I was told it didn't breakdown as fast as Mogas.

True

So if I'm understanding you correctly, that is due to both the lighter more controlled nature of Avgas and the TEL additive being very stable.

Partly due to the stability of the TEL, it's not the only reason.

This would mean if we were looking for a TEL substitue additive for avgas, we would have the added requirment that it needs to be very stable over time.

Seems to be a good idea!

Gary

 

[Dan Thomas]

Good explaination - minor quibble - Avgas distallation is run with a very tight distallation/pressure range compared to Mogas and will contain a higher proportion of lighter fractions (shorter carbon chains and more aromatics - carbon rings rather than chains, such as xylene, toluene and benzene). These actually come off first. The tighter range does lead to a "purer" mix.

Oil refining isn't as simple as it used to be. It's not just distillation anymore. Various catalyzing and other processes such as unification and alkylation are employed to obtain the desired fuel properties. In essence, the molecules of the distillates are taken apart and reassembled into something not achievable by simple cracking.

See http://science.howstuffworks.com/oil-refining5.htm

Dan