Just tried MOGAS, didn't go well

[RV10inOz]

Originally Posted by Pittsartist

Some thoughts - not always directly related, but hopefully worth knowing.

1) Did you know that you can cheaply & easily test fuels for ethanol content yourself ?

- Get a tall, thin graduated glass container. Half fill with water, then top up to full with your chosen fuel. Mark the intersection line of the 2 fluids with a sharpie pen. Leave overnight and check for a movement of the intersection against the line. If movement is observed it is because the Ethanol in the fuel has absorbed some of the water. More movement = more ethanol.

2) The key problem with Mogas is its lower vapour pressure. In practice this means that you are MUCH more at risk of fuel vaporisation than with 100LL. Heating the fuel is the enemy and should be controlled at all costs.

3) Ethanol in motor fuels absorbs water (see "1"). Water is corrosive, Vans RV's have aluminium fuel tanks and fuels lines.

4) When you leave your aeroplane in the sun the fuel in the tanks is being warmed. Solar Absorptivity for Black = 0.94, Pure White = 0.12

5) Back to Vapour Pressure. If you dilute 100LL with mogas by even 5% the vapour pressure of the mixture becomes virtually the same as pure mogas.

(Apologies to the many on here who probably know all this)

My personal experience is that my RV was specified and built from the outset for (currently illegal) running on Mogas. For me this meant

- Use of ethanol tollerant components (In particular the Polymer fuel system parts)
- Purchase of a 160hp engine with an 8.5:1 compression ratio and latest generation cylinders
- A "2 tank" strategy - 1 always pure 100LL, 1 sometimes Mogas / Mogas Mix
- Always use "Shell V Power" Mogas (a UK brand) - Shell spec is nil or max 5% ethanol, 99 RON octane. It lacks the additives found in 100LL.
- Andair electric boost pump & Lyco Mech Pump, F.I. & no gascalator.
- Never run @ > 24" manifold or > 1250f EGT on mogas
- Never Run Mogas @ less than 1500' AGL
- Never take off or Land on Mogas
- Always run at least 5 mins on 100LL every time out (Valve stem lube in 100LL)
- I have minimised the amount of fuel "in the system" to make changeover of fuel types as fast as possible - I estimate that switching tanks takes about 20 seconds (0.3l system volume @ 45 LPH flow rate) to be effective ... provided the engine keeps running of course !

By and large this has worked well for me for about 60 hours. However, I have experienced fuel vapourisation problems on hot (at least by our standards) days.

MOGAS is in my opinion not without risk - you should only take risks that you fully understand and can afford to loose. (for instance - flying over water, adverse terrain, high ambient temps, high altitudes etc)

Time to kill some OWT's before anyone gets too carried away.

Items in RED

Avgas is a different fuel to mogas, it is not some special additive apart from TEL which dramatically improves the detonation characteristics (and nothing else). The rest of the fuel is a higher spec base alkalyte and it has different requirements for vapour pressure.

There is no valve guide lube?..biggest of the OWT's that get around. As for MP and EGT limits, those are a mystery.

Bottom line is ask yourself why the STC's for mogas are all carby engines?.as best I recall Petersens have never had one for an IO engine for good reason.

Stick to Avgas. Agressively lean on the ground and run WOTLOP whenever you can.

[RV10inOz]

Originally Posted by airguy

The pump is not behaving differently - the vapor pressure of the fuel is changing. 100LL has a lower vapor pressure than mogas, meaning that mogas will boil easier. Boiling occurs not only at elevated temperature, but also at reduced pressure. If you have restrictions of ANY kind in your fuel line, that will create a region of lowered pressure as the fuel flows through that restriction. If the fuel is warm enough, it can create its own vapor bubbles in the fuel, and the fuel pump does not do well at all with vapor. The fuel pump itself is bolted to that great big heating element up front, and the fuel will pick up heat in the pump itself as well, making the problem worse.

Keeping your fuel line routing as clean as possible with cooling air on your fuel pump will help, but it's going to be trial and error to eliminate the cause. You'll notice a difference between summer and winter fuel blends also, the winter blend will be more likely to cause the problem you are seeing.

Pretty good summation.

And as you climb past 7000' or there a bouts the issues of hot engine bay, low wings and sucking fuel up hill help promote vapour bubbles!

[ChiefPilot]

Originally Posted by RV10inOz

Bottom line is ask yourself why the STC's for mogas are all carby engines?.as best I recall Petersens have never had one for an IO engine for good reason.

Stick to Avgas. Agressively lean on the ground and run WOTLOP whenever you can.

Yep, out with the old wives tales and in with some new ones.

Peterson does in fact have an STC for an IO engine - the IO-470 in a Bonanza/Debonair.. I would not be surprised, however, to find out that such has more to do with the airframe and fuel system than it does the engine of course.

There is certainly a fair amount of anecdotal evidence and field testing among the RV crowd to suggest that there isn't anything inherently wrong with mogas and an IO engine; in fact, Superior and other engine builders specifically call it out (not just any car gas, of course - octane and no-ethanal restrictions apply).

[Subwaybob]

I use 87 from here in Texas with ethanol in it all the time. I had a rough engine once but determined that it was water in the fuel. I have had no problems aside from that 5 second burp, ever. By the way, I mix 87 and 100LL, use straight 87, pure 100LL, whatever I want. My engine runs like a sewing machine. A $30K ECI Titan sewing machine but still. Mine is injected BTW. Not sure if that matters.

[9GT]

I have been running one tank with 100LL and in the other 90 octane ethanol free "recreation fuel" I pick up at a local gas station as soon as I was out of Phase 1. I have found absolutely no difference between the two when I am cruising along and switch tanks. I planned to do this during the build so I put a shroud and blast tube on the mechanical fuel pump and doubled up on fire sleeve on the fuel supply hose from the pump to the servo, then wrapped that in reflective aluminum tape because it runs near the exhaust. I take off and land on the 100LL tank just to be safe. Lately I have been mixing the 90 rec fuel with 93 Premium auto fuel laced with 10% ethanol. That's required by law here in Michigan. Again no issues so far but that was a about a 30% 93 mix. I intend to increase that ratio a little at a time to experiment. I have done landings with the Recreation fuel and taxied back to the hanger on it. It does seem to boil out though and make a hot restart more difficult.

[Pittsartist]

Originally Posted by RV10inOz

Time to kill some OWT's before anyone gets too carried away.

Items in RED

Avgas is a different fuel to mogas, it is not some special additive apart from TEL which dramatically improves the detonation characteristics (and nothing else). The rest of the fuel is a higher spec base alkalyte and it has different requirements for vapour pressure.

There is no valve guide lube…..biggest of the OWT's that get around. As for MP and EGT limits, those are a mystery.

Bottom line is ask yourself why the STC's for mogas are all carby engines….as best I recall Petersens have never had one for an IO engine for good reason.

Stick to Avgas. Agressively lean on the ground and run WOTLOP whenever you can.

Hi David.

Here's an extract from the UK Light Aircraft Associations technical guidelines on fuel.

"With these engines, many of which were originally produced many decades ago, there have
been a variety of different valve seat and valve materials used over the years, and there is a
possibility that some combinations in the field might suffer problems with valve seat recession if
deprived of the dry-lubricating effect of tetraethyl lead in leaded fuels. To guard against this
possibility it is recommended that all users of Continental and Lycoming engines cleared for
Page 6 of 7
unleaded Mogas use should either use a fuel mixture with 10% 100LL in it or run a tankful of
100LL through the engine at least every 75 running hours to lubricate the valves and valve
seats."

The 24" max manifold effectively means that I cannot operate @ more than 80% of rated power on mogas. The max EGT is a cross check on not getting too lean (provided of course you are not already LOP). These measures are aimed at reducing the chance of detonation.

Regarding the F.I. setup, My company designs and makes automotive F.I. systems. We have also supplied aviation F.I. component parts and ignition systems for 40 years - This puts me in a good place to assess the suitability of component parts for ethanol bearing fuels. In my experience, a LOT of legacy aviation fuel systems are not ethanol fuel tollerant.

Just to be clear - My original post never said that "this would work" or suggested that others did the same, just describing what I do and why then sharing the results - "warts and all"

Regards,

Richard

[ronschreck]

Originally Posted by Elwell81

The only reason I installed the gascolator is I like the serviceable aspect of it. With the Andair gascolator, I can remove/clean/replace the filter element without undoing any fuel fittings. It gives me the opportunity to know what I have as far as contamination, and a simple inline replaceable filter doesn't do that.

As I said in previous post, I installed the gascolator in the cabin, under the fuel selector valve to prevent a heating issue.

Autogas is on the back burner now (no pun intended). I need to get my fuel pressure sorted out. I think trying the autogas just magnified an issue that I was already experiencing.

I ordered a new mechanical fuel pump to try out. Best case I get my fuel pressure back, worst case is I have a spare fuel pump. I'm finding it hard to believe there is a restriction problem upstream of the mechanical fuel pump causing this, but stranger things have happened. I'll update when I get the new pump installed.

I'm not convinced that your gascolator is not the problem even though it is on the cool side of the firewall. Unlike an in-line filter gascolators churn up the fuel just like 90-degree bends in fuel fittings. I replaced all 90-degree fittings in my fuel delivery system, have one in-line filter and a blast tube cooling my mechanical fuel pump. My injected Lycoming has been running on 100% 91 octane non-ethanol mogas for over 1200 hours. I occasionally get low fuel pressure during a long hot climb but turning on the boost pump brings the pressure back to 24 psi. (Many certified aircraft manufacturers recommend that the boost pump remain on during climb!)

IMHO gascolators should be accorded the same disposition as vacuum pumps and 8-track tape players.

[bjustus]

I remember times when flying one tank avgas and one tank auto gas in the past, I would enrich the mixture, switch tanks, then re-lean. I definitely had a different mixture setting for smooth operation with each type of fuel. If I just switched from one to the other without changing the mixture, I would usually get roughness until I fixed the mixture.

Not saying this is necessarily the cause of what you experienced, but maybe a factor to consider/eliminate as you sort it out.

[TThurston]

It probably isn't relevant, but some of the issues discussed seem related to the RV-12 design with it's always on boost pump and it's preference for high octane auto fuel.

[lr172]

Originally Posted by RV10inOz

Time to kill some OWT's before anyone gets too carried away.

Items in RED

Avgas is a different fuel to mogas, it is not some special additive apart from TEL which dramatically improves the detonation characteristics (and nothing else). The rest of the fuel is a higher spec base alkalyte and it has different requirements for vapour pressure.

There is no valve guide lube…..biggest of the OWT's that get around. As for MP and EGT limits, those are a mystery.

Bottom line is ask yourself why the STC's for mogas are all carby engines….as best I recall Petersens have never had one for an IO engine for good reason.

Stick to Avgas. Agressively lean on the ground and run WOTLOP whenever you can.

I would suspect the valve related OWT came from the lead issue. Pre-70's all engines, Lyc included, used regular steel valve seats. The lead from the burned gas would coat the valves and seats and provide insulation from the heat. One of the first thing the auto mfg's had to do in order to support lead free gas was to move to hardened valve seats to avoid cracked seats. There were many problems with older cars using unleaded gas once it became available and they were advised to use leaded gas (back when both were still being sold). This probably morphed into the above OWT.

Not sure what Lycoming has done about this, but many experts still recommend initial engine runs on 100LL to coat things as well as using 100LL every 3-4 tanks. Assuming they are in the know, Lyc still isn't using hardened seats, but I have no idea.

This is still a potential issue with Lycomings.
Larry