Vapor Lock Issues Resolved For Now

[FlyingMonkey]

Running 93 octane ethanol pump mogas I have been struggling with vapor issues in my CTSW for a while now, but I wanted to work through them as far as I could without asking for help.  I ran this same fuel for ten years with no issues, and it came up after I changed my fuel system to include teflon-lined hoses. The symptom has been pretty consistent: intermittent power loss when the engine is hot and the deck angle is high.  This means I most often saw it on takeoff and climb out, sometimes at very low altitudes (not fun!).  The RPM would drop from WOT RPM (5200-5500 with the eProp) down to about 4000rpm, often surging up and down in 2-5sec pulses.  Reducing throttle and deck angle usually allows me to fly at 4000-5000rpm and land.

After this first happened I re-routed a fuel line to remove a potential vapor trap and the issue went away and was gone all Summer when it was hot so I assumed it was solved. Then I went to Tampa last fall to visit Bill Ince, and we were two up departing St. Petersburg and the issue happened again out over the water, two quick pulses and then it smoothed back out but we were both a little puckered up! The problem did not recur and we continued on the 15-20 miles back to Clearwater.  Before I went back to Georgia I topped off with 100LL and had no issues going back home.  After I got back home I went back to mogas and had no issues all winter, so I thought maybe a difference in Florida fuel blends vs Georgia could have been the cause, or just some bad gas in Florida.  Carbs were rebuilt in March, and I flew until mid-April with no issues.

The last few weeks it got warmer, but only in the 70s or so.  Quite suddenly I started getting the vapor issue on every flight.  I tried insulating all the AN connections on my fuel lines in case they were getting hot, but no joy.  Finally I switched to 100% 100LL fuel and the problem ceased immediately and has been gone for several flights.  I'm fine with running avgas if necessary, but I'm still a little confused over what exactly happened or changed.  I checked my gascolator screen and did a fuel flow test draining out the tanks completely and there were no issues.  My ideas are:

1) The new fuel lines are teflon, stainless braided, and with integral silicone firesleeve.  It's possible the new lines retain more heat than rubber hoses and lead to increased chance of vaporization of ethanol.

2) Fuel blends have changed.  I read that the EPA is working on changing the max ethanol in standard fuel from 10% to 15%...I'm wondering if suppliers have begun a stealth creep up of ethanol content or other additives.

3) I changed out my fuel pump when I did the hose change...perhaps my new pump is weaker than the old one?  The old one was well past replacement age and was an older revision pump, but I never had this issue until after it got changed out.  Maybe the new one is just a factory dud.

4) I had to make a new heat shield for my gascolator during the fuel system changes, but it's pretty much the same thickness aluminum material and the exact same shape as the old one if not slightly larger, plus it's more reflective so should bounce more heat. I guess I could beef that up or add additional insulation.  Here's what it looks like:

I'm certainly open to other ideas, recommendations, or wild speculation.  I know Corey recommends a boost pump installation, and I'd do that if 100LL ends up not totally curing the issue, but so far so good.  I miss the cheaper fuel, but it is more convenient to just pull up to the pump.

[Eddie Cesnalis]

Clear gas is easily available in Florence because of all the sand dunes.  Not as cheap but less than Avgas.  Try a fresh check of your area maybe someone is selling to atvs or boats.

Your problem is interesting.

[shiny.ice]

It sounds like part of the problem is winter gas blend when the temperatures warm up. The RV crowd has found you can mix in a ratio of 100LL and get protection against vaporlock, you might try 2:1 or 3:1 and see if it helps.

It’s remarkably easy to test your ethanol percentage. That might help dissuade that concern.

Ron’s presentation goes deep into these issues: 

 

 

[Madhatter]

I also went to teflon fuel lines but only on the engine and engine side of the gascolator, and have no issues. You checked fuel flow but I assume only from the gascolator. That leaves the carb and fuel bypass lines in play. And you never had the issue until you changed hoses which is the only significant variable changed. I know it’s a PITA but you might want to temporarily go back to original type hoses and see if it makes a difference. Maybe the bypass orfice is an issue as that was also changed. It would certainly be an issue if wrong size or blockage. 

[FlyingMonkey]

7 minutes ago, Madhatter said:

I also went to teflon fuel lines but only on the engine and engine side of the gascolator, and have no issues. You checked fuel flow but I assume only from the gascolator. That leaves the carb and fuel bypass lines in play. And you never had the issue until you changed hoses which is the only significant variable changed. I know it’s a PITA but you might want to temporarily go back to original type hoses and see if it makes a difference. Maybe the bypass orfice is an issue as that was also changed. It would certainly be an issue if wrong size or blockage. 

I imagine if I had a restriction, blockage, or wrong size orifice I would have the issue with both mogas and 100LL, right?

[FlyingMonkey]

40 minutes ago, shiny.ice said:

It sounds like part of the problem is winter gas blend when the temperatures warm up. The RV crowd has found you can mix in a ratio of 100LL and get protection against vaporlock, you might try 2:1 or 3:1 and see if it helps.

It’s remarkably easy to test your ethanol percentage. That might help dissuade that concern.

 

I have tested my gas in the past and it was around 5% ethanol, I have not tested recently. 

I don't really want to run a fuel mixture because you then get all the hassles of avgas AND all the hassles of mogas, and save hardly any money on fuel.  I'm only saving about 50 cents a gallon between 100LL and mogas as it is.

[Tommy Mc]

I posted an EASA study from 2008 on this subject.  It was long in the Tooth however the Executive summary was well worth the read.  It has been removed for some reason, if  anybody would like the 248 page .pdf just let me know.

0% Ethanol Fuel is ideal for Aviation.  No damage to fuel tanks and lines.  No damage to the Carbs when left in the Aircraft for longer periods.  No water as it is not Hydroscopic.  Oil change interval of 50 hours due to no Lead.  Not prone to Vapor Lock

These are just the main advantages of 0% Ethanol Fuel.

Avgas is next as it's main disadvantage when compared to 0% Ethano Fuel is, 25 hour Oil change and pumping Lead into the Enviroment.

Carb Icing charts are not relevent when it comes to Mogas,  0 accuracy

You are not suppose to use Mogas over 6K feet and  or Temps above 25 Degree Celcius as it is prone to Vapor Lock 

It is Hydroscopic. 

A fish Head stays fresh longer, having said that we are up to 10% now.... It's horrible Fuel for anything with a Carb unless straight out of the pump fresh.

Blending Fuels is a No No too.  Like Forests' Chocolates, just just don't know what you got.

I have Imported UL 91  from Poland to stay away from Mogas with Ethanol and Avgas with Lead. It is an expense however I flew my Aircraft for the first time in 5 months (Horrible winter) the fuel was perfect and my Engine runs like a dream

[Roger Lee]

Having a backround in HazMat (hazardous materials) and chemistry have some of these items in your post wrong especially about ethanol. People who have no chemistry backround are wrong many times. Not all publications have scientific accuracy. Too many things now days just get passed on from one group to another.

[FredG]

Roger, since you have expertise in chemistry, why not tell us what is correct and what is incorrect about the post (rather than just informing us that people with "no chemistry background are wrong many times")?

[FredG]

I think it is hard to get useful information about summer blend vapor pressure versus winter blend vapor pressure (other than the fact that they differ).  So, a change in fuel composition over time is on the list and hard to confirm or refute.  

Hard to know if teflon hose has poorer thermal insulation properties than rubber hose.  It is possible, since the rubber hoses are also equipped with a separate fire sleeve.  One approach is to find a length of old fire sleeve, slit it and wrap some (or all) of the teflon hose to see if the additional insulation helps.  Also, some auto supply vendors sell an insulating wrap for fuel hose (look up "hook and loop" and "fire sleeve" on the Summit Racing web site).  It may provide some additional insulation.  

Hard problem to solve, especially given its intermittent occurrence.

[FlyingMonkey]

I didn’t want to turn this into a Mogas v. Avgas argument.  I don’t have anything against Mogas and ran it with ethanol trouble-free in hot Georgia Summers for a decade.  But something has changed and I need to change with the situation.

Fred I don’t think the new lines are poorer at insulating the fuel from heat.  What I suspect is that the stainless steel braiding absorbs and retains heat, and potentially transfers it to the fuel and leads to higher chances of vapor formation.  It’s maybe a distinction without a practical difference, but I just want to be clear about what I think is occurring.

[Anticept]

A guy on one of the aircraft forums found that only a small mix of avgas is required to drop the reid vapor pressure considerably, and higher blends had dramatically reduced returns. There really isn't a need to put in much. He made his own reid test rig, it was slightly jank but it was accurate and repeatable enough, and tested various fuels. Reid pressure varies wildly with mogas, but is very consistent with avgas.

I would run about 10-20% avgas and never had a fuel pressure issue.

However, on my field, there is no self serve. So this wasn't viable to bother the fuel truck for 5 gallons of avgas.

Another thing: if the alarm goes off, increase airspeed (thus reducing nose up pitch). Increasing airspeed to 80 substantially reduced these occurrences.

The e-props are nice but the aggressive climb rate really aggravated this issue.

[Roger Lee]

We've posted numerous times about ethanol fuel and its properties. Plus you almost never see ethanol at its advertised concentration. Most states say up to 10% or 15%. People at my field with CT's have tested every batch of fuel for the last 15 years. We have up to 10% in AZ. The real number is 6 % - 7% and the highest we have ever seen is 8%. The people that jump up and down about ethanol being hydroscopic and water will come through the vents and saturate the fuel have no clue about the physics involved. I took one time in a CT and poured 6 oz. of water into a full tank and you know what happened. Nothing. Depending on the ethanol concentration it can suspend the water and just burn through the system. Is it as good as fuel without it, no, but it works and the engine just runs.  Can heating a fuel line cause some vaporization, yes, but it can be mitigated up to a point. They use up to 23% in South America.

One way to help reduce your under cowl temps is to use header wrap.

[FlyingMonkey]

7 hours ago, Anticept said:

A guy on one of the aircraft forums found that only a small mix of avgas is required to drop the reid vapor pressure considerably, and higher blends had dramatically reduced returns. There really isn't a need to put in much. He made his own reid test rig, it was slightly jank but it was accurate and repeatable enough, and tested various fuels. Reid pressure varies wildly with mogas, but is very consistent with avgas.

I would run about 10-20% avgas and never had a fuel pressure issue.

However, on my field, there is no self serve. So this wasn't viable to bother the fuel truck for 5 gallons of avgas.

Another thing: if the alarm goes off, increase airspeed (thus reducing nose up pitch). Increasing airspeed to 80 substantially reduced these occurrences.

The e-props are nice but the aggressive climb rate really aggravated this issue.

Thanks Corey I'll consider a mix.  I admit it would be nice to keep the avgas to 30% or less to take advantage of longer Rotax maintenance intervals.  I do have self serve on my field so that makes it easier.

I agree the deck angle makes a big difference.  Once the engine had issues, pitching down was often enough to clear it, but pitching down and reducing power always got it under control.  At its worst even making a consciously flat, shallow climb out wasn't enough to avoid the problem.

[FlyingMonkey]

20 minutes ago, Roger Lee said:

One way to help reduce your under cowl temps is to use header wrap.

I have avoided wrapping my pipes because I have had exhaust cracks in the past and want to be able to see the pipes to catch problems early.  But there have been no issues since you helped me out in Tucson and we set the exhaust correctly with no stress on the pipes like 8 years ago, so it might be time for me to revisit wrapping.  IIRC I have some header wrap in the hangar already.

[FredG]

Andy, my practical suggestion was to increase the insulation value of the fuel hoses by wrapping them in fire sleeve of some kind (either conventional sleeve that was slit to facilitate installation or aftermarket fire sleeve with velcro designed to be wrapped around existing hoses).  Assuming cool fuel is coming from the tanks, the less heat that transfers from hot air (or radiates from the exhaust) under the cowling through the fuel hose and into the fuel flowing in the fuel hoses, the lower the risk of vaporization.

Also, I assume you have the heat shields (aka, drip trays) in place under the carbs on your CT.  I suspect that heating of those uninsulated aluminum carb bowls could boil fuel.  A bit of header wrap for just a few inches of the header under the carbs might be enough to manage that problem, if it is occurring.    

I had vapor lock one time in my 912ULS powered RANS S20.  It was an unusually hot spring day and I had winter blend mogas onboard.  The airplane does have a boost pump and it was on.  In response, I insulated the teflon fuel hoses with fire sleeve (yes, redundant) and I run a blend of non-ethanol mogas and 100LL during the spring when temperatures may get hot and the mogas may still be winter blend.

[FredG]

When it comes to solving the problem of vapor lock, a question worth asking is whether ethanol blended gasoline (e.g., E10, etc) results in a greater tendency for vapor lock and the answer is yes, it does.  

See the section, "Ethanol’s Effect on Fuel Volatility" on the web page, https://www.eesi.org/papers/view/fact-sheet-the-consumer-and-fuel-retailer-choice-act#:~:text=While neat (pure) ethanol has,ethanol to more readily vaporize.

See also, from the same web page, the figure below.  The vapor pressure of an ethanol-gasoline mixture is greater than non-ethanol gasoline alone (ie, it has a greater tendency to form vapor) at 5%, 10%, 20% and 30% ethanol.  So, yes, ethanol blended gasoline does increase the potential for vapor lock in comparison to non-ethanol blended gasoline.

Also, the term for a tendency to absorb water is "hygroscopic", not hydroscopic.  

 

[GrassStripFlyBoy]

1 hour ago, Roger Lee said:

One way to help reduce your under cowl temps is to use header wrap.

Reading down the trail here I was about to suggest this.  It is a huge improvement in under cowl temps, and that suggests other benefits too, such as integrity of oil over time.  I understand the desire for root cause and placing your finger on the true problem, but if it's thermal in nature here - why fight the obvious.

[FlyingMonkey]

43 minutes ago, FredG said:

Andy, my practical suggestion was to increase the insulation value of the fuel hoses by wrapping them in fire sleeve of some kind (either conventional sleeve that was slit to facilitate installation or aftermarket fire sleeve with velcro designed to be wrapped around existing hoses).  Assuming cool fuel is coming from the tanks, the less heat that transfers from air under the cowling through the fuel hose and into the fuel flowing in the fuel hoses, the lower the risk of vaporization.

Also, I assume you have the heat shields (aka, drip trays) in place under the carbs on your CT.  I suspect that heating of those uninsulated aluminum carb bowls could boil fuel.  A bit of header wrap for just a few inches of the header under the carbs might be enough to manage that problem, if it is occurring.    

I had vapor lock one time in my 912ULS powered RANS S20.  It was an unusually hot spring day and I had winter blend mogas onboard.  The airplane does have a boost pump and it was on.  In response, I insulated the teflon fuel hoses with fire sleeve (yes, redundant) and I run a blend of non-ethanol mogas and 100LL during the spring when temperatures may get hot and the mogas may still be winter blend.

Yes, I have drip trays installed.  Good suggestion.  It sounds like header wrap keeps coming up as something to put in place.

[Tommy Mc]

17 hours ago, Roger Lee said:

Having a backround in HazMat (hazardous materials) and chemistry have some of these items in your post wrong especially about ethanol. People who have no chemistry backround are wrong many times. Not all publications have scientific accuracy. Too many things now days just get passed on from one group to another.

It is not my written Paper Roger it is a final report from EASA.  As I said there is a lot of information, if you would like to read the report and critique the Report be my be my guest.  I look forward to your response with reference to published papers casting doubt on the EASA report.   

For me every day is a School day.

I have attached the Report for your perusal.

Final_Report_EASA.2008-6-light-2.pdf

[FredG]

I am not a big fan of wrapping long segments of the headers because  it results in greater heat retention within the exhaust system and wrapping makes it hard to find cracks/leaks.  I use it header wrap over short-ish segments where the header comes close to something I want to keep cool, such as a hose.  

[Towner]

This is not to debate rubber vs Teflon, but I’m just curious if anyone has had suspected vapor lock problems with the rubber hoses? It’s only for my personal information since I still run rubber and gas with ethanol. 
 

When our Sheriff’s Department was flying a CTLS, the engine quit once and they landed at a nearby private runway. They never did figure out what the problem was and it seemed to run fine after that incident.

[Tom Baker]

Andy, post a picture of the top of your engine showing the fuel lines.

[procharger]

I had vapor lock one time in 8 years 93 degree day shut down for 10 min, started up taxied down

runway took off about 20 seconds later engine started to loose power backed off throttle and

engine came right back to normal. Thought I was going in for a water landing at First Flight Nags 

Head NC.

[Anticept]

I think two areas where it tends to develop vapor issues are the hard downturn to the gascolator, and in the fuel pump.

The fuel pump has the inlet on the TOP and outlet on the BOTTOM, which I think aggravates the issue. The hard rapid churning (prop RPM) of the plunger, and the fact that air has to move DOWN, makes me think it will foam up a bit before it is finally purged.

The old pier burgs never ever had an issue and I really want them back.