Alcohol induces vapor lock?

Bevan said:

Where it will drop to as low as 2psi in the nozzle lines (according to people on here smarter than I). Fortunately there's lots of cooling air here during flight but not so much when starting/taxiing.

Bevan

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So, what happens when the correct quantity of fuel is metered by the spider to each injector line, but it's fully or partially vaporized by the time it enters the intake runner?

The Ethanol subject certainly is always a lively one. I am no engineer, but some things that I do know:
My engine has changed in my EFI airplane, but the fuel system has not. It clocked nearly 600 Hours pre-lycoming without vapor lock issues running 91e10 almost exclusively. I have two high pressure automotive style pumps mounted below the tanks, that feed the 40PSI fuel rail for electronic injectors, a dueplex fuel valve, and a fuel return system. (very similar setup to all the cars cars on the road that regularly use 91e10 with the exception of a fuel valve). Now with about 675 hours on the airplane, the Subaru has been swapped out for Lycoming, which seems equally as happy to run on 91e10. I don't fly at FL230 in my RV, so I dont think that fuel freezing is an issue for me. I don't run my CHT's at 500 degrees either, so less octane inst a huge concern either. For extra safety margin, my ignition timing is set to 20-21 degrees for full power.
I live in a very wet coastal climate. My main concern with 91e10 would be letting it sit for an extended period of time. This comes from my observations on how quickly the Ethonol blend fuel goes bad in my lawn mower. That being said, my airplane flies several times a week. If I knew It wasn't going to be flown much, I might be temped to top it off with 100LL.

my .02c

Caleb

Norcalrv7 said:

The Ethanol subject certainly is always a lively one. I am no engineer, but some things that I do know:
My engine has changed in my EFI airplane, but the fuel system has not. It clocked nearly 600 Hours pre-lycoming without vapor lock issues running 91e10 almost exclusively. I have two high pressure automotive style pumps mounted below the tanks, that feed the 40PSI fuel rail for electronic injectors, a dueplex fuel valve, and a fuel return system. (very similar setup to all the cars cars on the road that regularly use 91e10 with the exception of a fuel valve). Now with about 675 hours on the airplane, the Subaru has been swapped out for Lycoming, which seems equally as happy to run on 91e10. I don't fly at FL230 in my RV, so I dont think that fuel freezing is an issue for me. I don't run my CHT's at 500 degrees either, so less octane inst a huge concern either. For extra safety margin, my ignition timing is set to 20-21 degrees for full power.
I live in a very wet coastal climate. My main concern with 91e10 would be letting it sit for an extended period of time. This comes from my observations on how quickly the Ethonol blend fuel goes bad in my lawn mower. That being said, my airplane flies several times a week. If I knew It wasn't going to be flown much, I might be temped to top it off with 100LL.

my .02c

Caleb

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Your $00.02 is appreciated. Yes, with regards to lawn equipment, letting it sit all winter long with E10, it does not always want to start and run the next spring. I use fuel additives in my mower, weed eater, tiller, etc. This really helps and almost negates the ethanol issue.

I wonder if anyone here with an RV has ever been tempted to use any type of fuel additive?

There are some folks who use Decalin religiously while burning 100LL in an auto conversion aircraft.

Another point to keep in mind is that the RVP is specified at 100F I believe. As the temperature of the fuel drops, so does the vapor pressure. I have experienced lowered fuel pressure as I climb high with warm fuel and pumps are having trouble pumping it due to cavitation - but as you climb up to cooler air the fuel in the tanks will pretty quickly drop in temperature, the vapor pressure drops, and the cavitation disappears. If you have 9.5 RVP fuel in the tanks and climb to the mid-teens when the fuel is at 90-100 on the ground, you will almost certainly experience this.

There are lots of horror stories about running Ethanol laced fuel in airplanes - but there are also a lot of us doing it. Those who say something is impossible should not be preaching to those of us who are actually doing it. A lot can be learned with first-hand experimentation and research versus listening to monsters under the bed.

The fuel age issue is something about which I've considered starting a separate thread.

Since I don't get to fly much these days, I've got a lot of experience with 'old' mogas. Since there are so many variables, I'll try to document all my specific conditions.

Carb'd 160 HP RV-4. I run *premium* *no-ethanol* mogas (E-free because of the very old E-vulnerable fuel pump, and very old tank sealant.) It's not unusual for the plane to go well beyond a month between starts.

For several years, I've had problems starting the plane after it's been sitting. I spent a lot of time blaming the mags & carb (I did find a couple of carb issues, which didn't help the hard starting issues). Frequently, I'd end up either running the battery down or flooding the engine. Then, the next day, I'd go to the plane and it would start right up. Finally, a light went on in my head. The next time I wanted to fly after a long hiatus, I went to the plane early, ran the boost pump to fill the float bowl, and then, with mags off & mixture at cutoff, I'd pump the throttle repeatedly to empty the bowl using the [edit] accelerator pump. After a long enough interval for all the puddled fuel to evaporate (overnight, the 1st time I did this), I went through a normal boost pump/prime/crank procedure. Fired right up. And it's worked every time, since. If the plane's been sitting for more than a couple of weeks, I 'purge' the float bowl like this an hour or so before the planned flight, and it always starts quickly now.

Now, to causes. We all have heard about the perceived issues with 'old' mogas, vs avgas. I'm not qualified to render a verdict, but my belief is that mogas (E, or not) has more and different 'volatile' chemicals that help it light off, than avgas. And my belief is that those chemicals, when in a small volume, high surface area place like a carb float bowl, can evaporate fairly quickly. The fuel in the tank seems much less affected; pumping the bowl dry and refilling with fuel from the tank solves the problem; at least for me.

As possible reinforcement to the theory, I've seen very similar, but worse, symptoms with my 2stroke lawn power tools. With those, not only are the volatiles gone, but the oil % goes up, too.

Note that I keep fuel in sealed 5gal gas cans, and I don't have issues with the fuel, even after months of storage.

Above is just offered as additional data points, and *my* theory of why the 'old gas' legend exists. I'm not an authority, and I didn't sleep in any hotel chain last night.

Charlie

Based on all of the info posted here, we are comfortable burning 93E10. Also, 91 octane E0 is available for us, albeit at a long drive.

The benefits of $$$ savings, plus a cleaner burning engine, with extended oil changes, make this worth it.

this thread makes some of us realize how lucky we are.
i live in n. wi. and at least 95% of the gas stations carry no ethanol premium. also , my airport carries swift no ethanol ''mogas''.
some comments have been made on sufficient octane rating. auto fuel is ''mon'' and avgas is ''ron'' 2 different ratings and ''converting'' mon to ron gives a higher number.

bobnoffs said:

this thread makes some of us realize how lucky we are.
i live in n. wi. and at least 95% of the gas stations carry no ethanol premium. also , my airport carries swift no ethanol ''mogas''.
some comments have been made on sufficient octane rating. auto fuel is ''mon'' and avgas is ''ron'' 2 different ratings and ''converting'' mon to ron gives a higher number.

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Yes, you are lucky and I envy you!

MON: Motor Octane Number
RON: Research Octane Number

In the US, it is usually expressed as (R+M)/2

This is how the anti-knock index (AKI) is formulated.

Well done Charlie. I think you have absolutely nailed it, and this completely reflects my experiences with gasoline engines. I always turn the fuel off an run my motorbikes until the carby is sucked dry, and leave the tank full and I've never had any stale fuel issues when I go to start them up six months or more later. I think the most important thing to keep in mind is not the fuel going "bad" in a sealed container (where are the volatile components going to crack off to if it is sealed anyway) but the fact that the auto summer and winter blends are going to be different. I think in our situations, we should be running summer blends all year round if possible, but definitely not winter fuels in summer. Running summer fuels in winter may make it a little tougher starting, but the lower vapor pressure should be less likely to cause vapor lock issues. I think ultimately it is probably prudent to run a reid vapor test or equivalent on our respective auto fuel batches.
I'm convinced Charlie spent last night at some type of swanky hotel chain.
Tom.

Here is something interesting, that I found on "another forum"...(yes, copy/paste)


Here is another reason to be paranoid...

Fuel for Rochester NY comes in a pipe. Not alcohol, it's incompatible with the steel in the pipeline, ( That is trucked in ) but gas, diesel, fuel oil. Same pipe. They just put a slug of water between petroleum products. There's a separator that deals with the contaminated fuel at the edges of the bolus of fuel. The middle part goes to the premium stations, and the edge stuff, after separation goes to the discount stations.

So it actually does make a difference where you buy gasoline. The stations I worked at dipped the tanks every morning, and most of them actually checked for water. ( the one that didn't was really only open 24/7 as a gas station because the taxes were far cheaper than being a parking lot, which was the main business. )

I'd take that account with a shovel of salt. The fuel has to meet posted specs at all gas stations. Same inspectors visit all the stations. You don't see cars stuck on the side of the road with water in their tanks, or engines damaged from water laced fuel.

And for the final nail, I'd be really impressed if there's enough 'contaminated' fuel at the beginning/end of each slug to supply all the independent stations out there.