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Definitive Mogas Thread

Mix mo & av

deej said:
Is anyone running 87 Octane mogas with a 160hp O320-E2D? I know 87 octane is fine with the 150hp O320-E2D with the 7.0:1 compression ratio. However, if upgrading an O320-E2D to 160hp 8.5:1 compression pistons, can you still safely use 87 octane, or are you now in the 91 octane realm? Thanks, -Dj
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Deej: In my 9A with an O-360, I mix av with unleaded, ethanol free 87 octane mo in my rite wing for takeoffs and landings. Once I am at altitude and below 65% power, I switch to unleaded, ethanol free mo (no av) w/o a problem.

I'm paying a buck a gallon less for the unleaded, ethanol free, 87 octane mo. I have learned that unleaded, ethanol free 91 octane mo is only 10 cents per gallon more. We buy it in 500 gallon lots and it can only be used in airplanes.
 
Std comp TCM IO-550 w/ Bendix mags, as used in a Cirrus. 100LL in the tank used for ground OPS, T/O, & landing. I switch to 93 octane E10 in cruise, or sometimes 87 octane. Doesn't seem to matter on the octane. Sometimes, with winter blend, I need to run the boost pump to keep the vapor demons at bay. If I remember to add about 20% 100LL to the nasty MOGAS, all is good - no vapor demons show up. In any case, the boost pump makes it all good.
I am careful to not store the ship for any length of time with E-anything in the fuel system - it is flushed out.
I do see differing flow numbers from the tanks - I suspect filter screen contamination, but I cannot point to any specific reason for this FF anomaly. Cleaning the filters seems to eliminate the problem, but I can't say why, as both are equally dirty (farm environment - DIRT).
Maybe the ethanol cleans the dirt out of the system (tanks) agressively?

Carry on!
Mark
 
IO-540

Using mogas 91 Octane E10 FOR 150 hours in the right tank for cruise.
Tested mogas for all flight regimens hot weather, cold weather full power take offs and climbs to 14000 feet without the boost pump.
Fuel system is an AFP boost pump and mechanical fuel pump with a constant flow (6GPH) return out of the mechanical pump. No vapor lock issues as tested at 101 F OAT heat soaked and full take off power.
Take off and landing normally on 100 LL and aircraft exercised at least once a week or twice sometimes more.
Most of my trips are a couple of hours long sometimes more and using the mogas tank only is inadequate for fuel consumption.
I generally use 4 tanks of mogas and fill up one tank of avgas and no mixing.
Planning to go to 87 octane E10 for more testing.
Engine is an Aero Sport IO-540 AFP injection one mag and one electronic ignition. One boost pump and one mechanical pump with constant flow return line to prevent vapor lock.
So far so good, no issues with vapor lock or detonation.
 
Thanks to those with the 6-bangers for chipping in on this. I'm planning for a RV-10 build and am very interested in mogas in the IO-540 in the future to help control flying costs.

I'm wondering if the electronic ignition might help the engine with the different fuel, as isn't it a more precise ignition system than the mags?
 
N427EF said:
Using mogas 91 Octane E10 FOR 150 hours in the right tank for cruise.
Fuel system is an AFP boost pump and mechanical fuel pump with a constant flow (6GPH) return out of the mechanical pump. No vapor lock issues as tested at 101 F OAT heat soaked and full take off power.
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Could you give us some detail as to how the constant flow return line system(6 gph) is made up? Is the constant flow return regulated just by a fixed oriface that flows based on pressure?

Does the return line go back to a tank? as opposed to the feed line. If so, does it dump into the first bay? Does it dump at the top or bottom of the tank?

Thanks

Bevan
 
I don't want to wander off on this thread, so here is a link to another thread
explaining my fuel system, see post #13.
http://www.vansairforce.com/community/showthread.php?t=87674&page=2&highlight=constant+flow+return

Could you give us some detail as to how the constant flow return line system(6 gph) is made up? Is the constant flow return regulated just by a fixed oriface that flows based on pressure?
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It is a fixed orifice (.020) tested at 25psi to return 6GPH.

Does the return line go back to a tank? as opposed to the feed line. If so, does it dump into the first bay? Does it dump at the top or bottom of the tank?
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Back to the tank via a fuel selector into the first bay.
1/8" NPT tank flange installed somewhere convenient in the upper half when I built the fuel tanks.
 
How much difference does it make running mogas or mix of ETOH and gasoline whether an engine is higher compression (say, 9.00:1), medium compression (8.50:1) or lower compression (7.00:1)?
 
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Just speaking in generalities, the higher the compression, the more likely to have detonation problems which require higher octane to control.
Don't forget av gas octane is "motor octane"; 91 "R + M/2" car gas has a motor octane around 87 or so.
 
Several folks have mentioned how they take off & land on 100LL and use mogas during flight. It's not clear to me why this is so - is there something particular about these phases of flight (other than being close the ground etc.) where 100LL is preferable?

I can only thing of cooling - does mogas actually run hotter?
 
Octane helps control detonation. Detonation is most likely at high manifold pressure (e.g., takeoff and climb). Hence use 100 octane for takeoff and climb, lower octane mogas at cruise power.
 
Several folks have mentioned how they take off & land on 100LL and use mogas during flight. It's not clear to me why this is so - is there something particular about these phases of flight (other than being close the ground etc.) where 100LL is preferable?
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I can't speak for others but for me it's a couple of things like the ethanol in mogas that supposedly eats up your rubber parts. (Diaphram in the mechanical fuel pump). Exposing those parts to ethanol for a relatively short period of time during cruise pretty much eliminates that possibility.
Carrying avgas in one tank allows you to have the aircraft sit with avgas in the system. While you have avgas in one tank you might as well use it for the most critical part of the flight, namely full power take offs and climb where detonation may be a concern.
The one thing I do believe about mogas is the fact that it gums up your fuel system when it sits around too long and although I get to fly once or twice a week there may be times when it will sit for awhile. I think three or four months would be maximum shelf life for mogas.
As far as engine temps, I cannot detect any difference between the two fuels
but I have seen from others a slight decrease in EGTs when switching to mogas in cruise.
 
BobTurner said:
Octane helps control detonation. Detonation is most likely at high manifold pressure (e.g., takeoff and climb). Hence use 100 octane for takeoff and climb, lower octane mogas at cruise power.
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The other issue is vapor lock. Avgas has lower vapor pressure than some* mogas. Lower vapor pressure means fewer bubbles in the lines and a reduced likelyhood of vapor lock. Vapor lock seems to be encountered most often during ground operations on hot days. It could ruin your day on takeoff.

Why do I use an askerisk with the word "some"? Because there are quite a few formulations of mogas. It is very hard to know exactly what you're getting out of the pump, especially during the transition between warm and cool weather.
 
Octane Numbers

This is what I've found about different fuel octane ratings. My sources are unofficial, Wikipedia and the likes, so take it for what it's worth.

Fuel MON RON
100LL 100 103
87 83 91
91 86 97
94 88 101
 
Kyle Boatright said:
The other issue is vapor lock. Avgas has lower vapor pressure than some* mogas. Lower vapor pressure means fewer bubbles in the lines and a reduced likelyhood of vapor lock. Vapor lock seems to be encountered most often during ground operations on hot days. It could ruin your day on takeoff.
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So my field has a 92UL (no ethanol) pump next to the 100LL. I'm tempted to try it due to the $1.20/gallon price delta, but frankly if it's too dangerous to use for any phase of the flight then I question why trust it at all.

Being ~35?F during the day here in wintery Minnesota, I don't think heat soaking the engine or hot climb outs would be of particular concern. I'm also not clear on how an injected engine along with it's high pressure boost pump would be as susceptible to vapor lock as a carb'ed engine would be. Wouldn't the boost pump simply push any vaporized fuel through the system?
 
ChiefPilot said:
So my field has a 92UL (no ethanol) pump next to the 100LL. I'm tempted to try it due to the $1.20/gallon price delta, but frankly if it's too dangerous to use for any phase of the flight then I question why trust it at all.

Being ~35?F during the day here in wintery Minnesota, I don't think heat soaking the engine or hot climb outs would be of particular concern. I'm also not clear on how an injected engine along with it's high pressure boost pump would be as susceptible to vapor lock as a carb'ed engine would be. Wouldn't the boost pump simply push any vaporized fuel through the system?
Click to expand...

Ernst is correct; proper fuel system plumbing is the key to being able to run MOGAS, not the gas itself.

N427EF said:
Your situation and symptoms are classic vapor lock indications
and end in many unexplained engine failures and crashes that can easily be avoided.
When I say situation and symptoms, I am refering to mogas users who have not made any modifications to their fuel sytem and symptoms exactly as you describe in you near disaster had it happened on a shorter runway.
The question is, are you willing to make some modifications to your fuel system that will immunize your fuel system against vapor lock?
FrankH has an all electric fuel supply system, he can explain it if he wants to.
Mine is electric/mechanical with a constant flow RETURN LINE.
As others have posted, the return line is key to this system, where a constant flow of cool fuel replaces hot fuel and vapor from the mechanical "boiler" fuel pump. You simply T into the exit line on the mechanical fuel pump and route the return line back to a tank. The return line must be orificed to allow an average of about 6 GPH.
Fuel metering and fuel pressure must be measured after this T fitting in the line.
A cool air blast tube directed at the fuel pump helps too but is in no way adequate without a return line.

A bypass line would also help where your electric fuel pump can bypass the mechanical pump in case it vapor locks. Your low pressure pump probably cannot overcome the vapor pressure build up in the mechanical pump, this is why you see no fuel pressure improvement with the electric pump on.
Of course this would not happen with a return line installed.

IMG_2462.JPG
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Page 2

Here is pg 2 in case you were wondering.
The second fuel selector can be an integrated Andair selector with supply and
return ports being selected with one handle or as I did, make use of the kit supplied selector for the return line and a nice Andair for the main supply.
While the 2 fuel selector pictures show normal operation for left or right tank use, it's easy to see how mixing and transferring fuel is limited only by your imagination.

IMG_0458.JPG


IMG_2746.JPG


IMG_2748.JPG
 
David Z said:
What ratio is required to solve the vapor lock issue?
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That depends on the aircraft, the fuel system, and a number of other factors. Vapor lock can occur with 100ll.

Pressurizing the fuel system at the source is the best cure, not the mixture of the fuel.
 
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No vapor lock issue!

I have no vapor lock issues, that problem was solved with the constant flow return line and installing everything behind the firewall that could be installed behind the firewall to keep it cool.
Pressurizing the fuel supply lines with the electric boost pump is yet another component of keeping vapor lock in check.
Again, it's the fuel system that should solve vapor lock problems not the kind of fuel you use.
I don't mix fuels.
I am simply pointing out that with a return line selector you have many options for fuel transfers and mixing if you so desire.
 
I'm with Ernest on the return plumbing, plus one more step;
I have automotive fuel injection, which is approx 40 PSI from the fuel pump across the top of the injectors then to the regulator. After the regulator, the unused fuel continues to the return selector valve then a fuel tank to cool.
Vapor lock should be nearly impossible in my system, so I hope to rate it for "Gasoline, ANY GRADE" I expect to run on E-mogas, pure mogas, 100LL Avgas, and Swift Fuel, if it ever becomes real.:confused:
Keeping the fuel pressure high, right to the electronic controlled fuel injector, and returning unused fuel to the tank is the key component to preventing vapor lock.
My next thought would be to build the fuel pump inside the tank with an access door on the top, just like modern cars & trucks.
When the time comes to change out a pump, I would be sitting on a stool in front of the wing, instead of standing on my head with my back bent over the spar.:D
 
Reply to post #69

Vapor Lock sensitivity is not a function of octane. It is a function of Reid Vapor Pressure (VPR). Based on my research 100LL has a RVP of 5.5 - 7. Car gas is currently 7 - 9. Car gas is producecd to be more volatile for winter cold starts.

According to Todd Peterson, who produced many of the MoGas STCs, mixing 25% 100LL with MoGas reportedly addresses the vapor lock issue.

When I started work at the Chrysler Proving Ground in 1976, a vapor lock issue had developed with Dodge trucks that was an unintended consequence of Federal crashworthiness roll-over standards. When the trucks were rolled upside down, fuel leaked through the check valves in the engine mounted fuel pump and the vehicles failed FMVSS 301. Higher spring rate check valves cured that problem, but caused vapor lock issues. Talk about the Law of Unintended Consequences!

35 years later all vehicles have fuel injection and almost all manufactures have gotten rid of mechanical fuel pumps in favor of tank submerged electrical fuel pumps - which is the hydraulically correct design. Many posters on this forum have converted their aircraft to hydraulically correct fuel delivery systems by eliminating the mechanical pump and installing individual electrical pumps in each wing root adjacent to the fuel tanks. You can find these threads by doing a search.

Larry Tompkins
N544WB - 6A
W52 Battle Ground, WA
 
Reply to Post #68

The link you provided is merely an algebraic calculator.

1) How do we know the algebraic average = chemical requirement?

2) One needs to know the Motor Octane Number for each type of fuel.

3) This still does not address the issue of what the actual octane requirement is for: a) various compression ratios in use (7 - 10:1)
b) ambient temperatures
c) cylinder head temperatures
d) power demanded
e) engine RPM
f) spark advance

Lycoming has certainly been no help with their knee-jerk 100LL response.

If someone has a suggestion for aircraft/engine combination testing, with a reasonable engineering basis, that is conservative enough to produce a gain without risking catestrophic destruction of the engine, I am open to their input.

Larry Tompkins
N544WB -6A
W52 Battle Ground, WA
 
LarryT said:
Many posters on this forum have converted their aircraft to hydraulically correct fuel delivery systems by eliminating the mechanical pump and installing individual electrical pumps in each wing root adjacent to the fuel tanks. You can find these threads by doing a search.
Click to expand...

Being a software & electronics guy, it's not immediately clear to me
how fuel pumps located at the wing root are significantly different (from a hydraulic point of view) than the high pressure boost pump mounted centerline just ahead of the spar.

Any insights into this would be very helpful for me and others I suspect...
 
Original poster Chris Hill

Wanted to know the following and got a long string of great answers of dozens of people using mogas. No one has reported an engine being blown up or a
failure. Some posters have used mogas for thousands of hours (Turbo). and described how and when they use it.
We'd all like to hear from someone with test results done on a
reasonable engineering basis
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but how much better can it get than pilots reporting real life field experience?
Anyway, I hope more people will post their mogas experience and describe theis systems.

Definitive Mogas Thread
If you have experience with Mogas, please post it here.

Include aircraft type, as many engine details as you feel pertinent, duration of use.

If you have used it successfully, please describe your "keys" to success such as mixing fuels etc.

If you have used it with negative results, please describe your results.

I'd like to avoid opinions in this thread and focus on actual experience people have had with operating on Mogas.
Thanks! Looking forward to your information.
Click to expand...
 
Reply to #75

Increased pressure increases boiling point temperature, suction lowers boiling point temperature.

A pump in the location you suggested is certainly way better than a heat-soaked mechanical pump on the engine at a higher elevation than the fuel tank.

Hope the above helps, there are threads with more detailed discussions.

Larry
 
ChiefPilot said:
Being a software & electronics guy, it's not immediately clear to me
how fuel pumps located at the wing root are significantly different (from a hydraulic point of view) than the high pressure boost pump mounted centerline just ahead of the spar.

Any insights into this would be very helpful for me and others I suspect...
Click to expand...

I don't believe being in front of the spar is an issue (other than simplicity? Im not a builder) I believe being behind the firewall is the point (segregated from the heat source) and the wing root has a possible added benefit of cooling airflow. Heat is the main, if not only cause (I'm reading this thread because I am still a student on the subject myself) for vapor lock.

I believe his point is mechanical fuel pumps, that are attached to a hot engine doing their ever lovin best to boil the fuel that goes through them, are less than optimal. The best fuel system is a short, insulated run from behind the firewall to fuel injectors, combined with a return line to allow stagnant, heated fuel, an opportunity to return to the tank to cool off. The way to do this is with electric pumps, and return lines, not mechanical ones attached to the big heater. The reason for injectors, instead of carb is to keep the fuel under pressure. Just like water, any given fuel blend will vaporize at a higher temp under pressure. Hence the hydraulic delivery comment.

I think of it this way; boiled water equals steam, Boiled fuel equals vapor. Vapor does not provide enough volume of combustible material to sustane engine operation. Engine won't start, or fail on takeoff, or other in opportune time.

The other factor that they are discussing here is the temp that fuel boils. Just like water under pressure, or with coolant added, boils at a different temp than unpressurized water (think car radiator) different blends of fuel boils (turns to vapor) at different temps. Mogas boils at a lower temp than 100LL. There are different blends of Mogas/ octane levels and their associated boiling points. That is where it really starts to get over my head.

Hope that helps, and by all means tell me if I got something wrong.

Mark
 
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Reply to post #77

Hi Ernst,

Unless I am mistaken, the OP did not ask for engine compression ratio information. Yes, I am convinced that MoGas is fine for CR of 8.5:1 or less based on field experience - which I highly value, as do you.

My engine has 10:1 pistons and that is my specific dilemma. I think I disclosed this in an earlier post, perhaps not the one you were responding to. The advantages are more power and better fuel economy. The disadvantages are shorter engine life and a requirement for higher octane fuel. Unfortunately, I don't feel that I specifically know what that octane requirement for an O-320 10:1 Lycoming is.

I hope I did a better job explaining my specific concern in this post.

Larry
 
Thomas Shpakow

offered to test some mogas combinations on his test stand.
See post #14

http://www.vansairforce.com/community/showthread.php?t=96596&highlight=mogas+testing+octane&page=2

FWIW:
A friend of mine is burning 91 Octane E10 in his RV-8 220 HP Franklin with 10:1 CR. Strictly for cruise.
2 electric fuel pumps and no return line.
Other than him I don't know of anyone using mogas in a 10:1 compression engine.
Larry, you can easily solve the vapor lock issue but detonation is more difficult to deal with. Keep your cylinders cool for starters. You could try one tank of 91 octane in cruise I am quite sure you won't be detonating anything.
A good engine monitor would be helpful in detecting detonation before damage occurs.
 
Franklin 220 HP 10:1

Ernst-

Isn't the Franklin a 6 cyl of about the same total displacement as a Lycoming. Therefore the individual cylinder diameter would be smaller and there would be lower detonation sensitivity.

I think I will try to sneak up on this with a 75% 100LL; cruise only. Then a 50/50 mix. I will keep good track to cylinder temps. I hope Thomas S. puts a 10:1 engine on his list.

When I was in engineering school 43+ years ago, we had a dyno cell with a variable compression ratio engine that was specifically designed for anti-knock fuel testing. They were pretty interesting experiments.

Thanks for your responses.

Larry
 
Good Plan

Good plan Larry.
The 220 Franklin is 350 cubic inches, a bit smaller than the IO-360 I guess.
Let us know how things work out.

All of us would like to hear from Thomas but I am sure he is busy and testing mogas is not how he makes a living.
 
my mogas experience

O-360, fixed pitch prop in RV-7A, I think the compression ratio is 8.5/1. 250 hrs. using mogas (93 UL 0% ethanol advertised 100% gasoline by the station and tested to show 0% ethanol). The station is located near a popular local boat ramp area.

I first tried using 10 gal mogas in left tank and 100% avgas in right tank. I held my breath on the first swing of the fuel selector from 100% avgas to 50% mogas at 7500'. No changes. The engine purred as before and I continued to my destination 3 hrs. away with no issues.

I gradually increased the percentage of mogas to full left tank for cruise and 100% avgas in right tank for takeoff & landing. My cross-countries are at least 2 hours long. After a half dozen flights and noting no change in operating with mogas, I started mixing the mogas and avgas in varying (non scientific) ratios.

I almost never fly local flights, my practice is to top off with mogas at home base and buy enough avgas to get back home. I've topped off with as much as 30 gallons of mogas and then flown as long as a 4 hr. outbound leg and topped off with 32 gal. of 100LL for the return flight. So, I guess you could say that I use mogas about the half the time, but it's never 100% of either fuel, because of the random mixing ratio.

Overall, no problems noted. I generally fly between 7500' & 11500', set 2550 to 2650 rpm, lean to 40 - 50 degrees F lean of peak, target an 8 gph fuel flow which yields a TAS of 155 kts.

Mike
 
I'm using mogas

Well a blend of mogas anyway. I have a 110 gallon tank and put in around 65 gallons of 87 octane no ethanol (it was 3.87 a gallon, 91 octane non ethanol is not available near here). I then top off the tank with 100LL. I like the idea of putting good ol Avgas in the Regular 87 to help stabilize it a touch. This gives me around 92-93 octane if I did the math right, for around 4.50 a gallon. Basicly I'm saving over a dollar a gallon on fuel, or every time I fill my big tank, I put a crisp hundred dollar bill in my pocket. I haven't seen any change in the engine monitoring but time will tell. I am running an 0-360, one mag one electronic ignition, fuel system per Vans specs. with a cooling blast shroud on the fuel pump. I use my left tank for 100LL only, all operations leaving or returning to the ground are made on the left tank, I then switch over to the right after I've made it off the ground a comfortable distance and reduced the throttle. As a data point, most of my flying is done at 50% or less power.

Randy
8A
 
required octane

Larry asked:
"Unfortunately, I don't feel that I specifically know what that octane requirement for an O-320 10:1 Lycoming is."

This has a variable answer.:eek:

The required octane varies with RPM and MP, and spark advance.:rolleyes: My experience says that my 550 with ~9:1 compression will run happily on 89 octane E10, at an MP of 30" and an RPM of 2700; boost pump ON. Spark has been reset to 24.5 from the factory setting of 22. Yes, I have to keep an eye on CHTs. A home-brewed ADI system keep that beast in its cage, as required.

I had a 9.5 Lyc in a previous ship, and it ran fine on the same fuel in cruise, but cruise MP was around 22" or less; RPM was around 2100-2200. 1 Rose Elec ignition/1 mag on that one - no issues at all.

My experience would suggest that cruising above 8000MSL will eliminate any worries about octane rating, due to the associated lower MP available.

Switch to a tank with at least 50% 100LL before entering the pattern, and use the boost pump for takeoff and landing. Any vapor pressure problems will show up as you taxi in with the boost pump off.

My bet would be that 50/50 100LL/premium MOGAS would be sufficient for any NA setup @ 10:1 or below, using a spark advance as recommended by Barrett Engines.

FWIW, an ADI System on a NA engine would reduce any octane worries to zero, not matter what fuel was in the tank.

Carry on!
Mark
 
I personally mix 30-40% av, the rest mo

We are able to get mogas and I personally mix 30-40% av, the rest mo. No problems with that combo @ 380 hours on a new engine. O-360, 7.2 compression pistons which should tolerate any octane.

The guv could make the enviro community happy if the feds would make ethanol free mo readily available for aviation. I know, getting the feds to make a smart decision will happen right after my hair grows back in.
 
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