Running a Jabiru engine on Mogas?

[Guest Robw]

Hi,

 

Is anyone running a Jabiru engine on Mogas? We are flying J160 and currently run it on Avgas. But that is now up to 1.80 a litre. The difference in price with Mogas seems to increase. And with the new needles the engine is running a bit richer which reduces the risk for detonation. So maybe time to switch to mogas?

 

Cheers,

 

Rob

 

 

[Guest J430]

BP Ultimate

 

Caltex 98

 

Avoid the Shell.

 

remember the shelf life of PULP is very short, so basically use it or lose it. The octane boosting stuff evaporates readily leaving you with 91 or somewhere inbetween. If you dont fly for a couple of weeks buy fresh stuff, and pump out the old stuff into your car first.

 

Rings and pistons will be cleaner on PULP.

 

AVGAS is stable and has a long shelf life, months, and its less prone to vapour locks. AVGAS is tested and a known quality.....MOGAS is not.

 

I use the AVGAS 100% of the time, fuel is the cheapest part of your plane so why skimp.

 

;)Cheers

 

J

 

 

[geoffreywh]

As far as I could determine the BP and the caltex brands BOTH include an undisclosed amount (up to 10%) of ethanol/methanol. Shell unleaded however did not. I have been running my cont. 0-200 on unleaded MOGAS for some time, very clean plugs are a bonus...In my experience ( 50years in the motorcycle industry) Unleaded took somewhat longer to "go-off" than 2 weeks.I guestimate 6-12weeks MAYBE a shorter period might be valid in summer..I could not say about that....Geoff

 

 

[Guest brentc]

From memory the POH (and latest Jaba Chat newsletter) stipulates 95 ron minimum and from memory the fuel pump should remain on.

 

Interestingly my Mechanic told me not to run my Subaru on Caltex, but BP or Shell. At the time I assumed he was referring to ethanol.

 

 

[Guest disperse]

Bp ultimate and Shell optimax come out of the same refinery here in sydney just has a different sticker on it so to speak .......

 

in a good car thats all I used. But I don't know about ethanol content these days.

 

For a V-twelve jag motor made for leaded. we ran shell optimax with a "Pro-ma" additive.

 

there are other add's but "Pro-ma" is definitely good stuff.

 

 

[Whack777]

I've heard ethanol in the fuel can also disolve the coating used to line fibreglass tanks... don't know much about it... but might be worth researching.

 

 

[theoy]

Lead for stems

 

3 months ago i spoke with Don in Jabiru Engines about mogas and Jab engines. Mogas will shorten engine life, i think its to do with lead for valve stem lubrication. Best to ring Don. He also told me in Italy Avgas is $5/ L, I guess prices are on the move up .

 

Cheers

 

Theo

 

 

[Bigglesworth]

Ethanol dissolves the lining in the Jabiru tanks. This then gets caught in the fuel filter since Jab uses a very fine filter. And since the filter is also opaque, you won't see it being blocked, and next thing you know, the motor stops.

 

Or so I have heard, from pretty reliable sources.

 

 

[Harthy]

Lead in fuel provides a couple of functions:

 

-It provides lubrication for valve seats and stems and

 

-It prevents or reduces detonation in HIGH compression engines

 

Jabiru engines run between 8:1 and 8.5:1 compression ratio's, this is not classed as high compression. Combustion chamber design also has a hugh influence on on the combustion process which will also determine what fuel is required for the engine. Alot of cars on the road today run around 10:1 compression, some of these needing Premium and some will run very well on 91 unleaded fuel. This is all to do with combustion chamber design.

 

Now onto lubrication. With very few if any exceptions, all of our new cars these days have aluminium or should I say alloy cylinder heads. For them to operate without damaging the heads, they require hardened valve set inserts (stelite) valve guides and appropriate valves to match. These in most cases last very well, and are all operating without lead in the fuel for lubrication.

 

Jabiru cylinder heads are aluminium and there fore will have valve set inserts.

 

I know of a Pawnee used as a tug for gliders. It has been running on unleaded and 10% avgas for years with out any problems. maybe an option for Jabiru's running on mogas

 

The lead in fuel also causes more combustion chamber deposits which can in time reduce engine performance.

 

Unleaded fueled engines if tuned correctly, generally run cleaner.

 

This is all just a bit of food for thought.

 

Harthy

 

 

[Yenn]

I ran my original 1600 Jab engine on mogas as an experiment and found higher CHT. It wasn't excessive, but I switched back to Avgas and havn't tried mogas in the 2200 engine.

 

 

[Harthy]

Jabiru 2200 engines ignition run at 25 degrees BTDC. This also has an effect on the combustion process.

 

Low octane fuels burn faster and more uncontrolled then higher octane fuels. So if you were to run 91 unleaded in an advanced engine and because of it volatility, the fuel starts to burn when the spark occurs. and the fuel suddenly erupts or ignites and will obtain complete combustion before it reaches TDC. This will give you your pinging or detonation. High octane fuels burn in a more controlled manor which delays the combustion process and you don't have the problem of pinging engines. High compression influences the combustion process and this is also controlled by high octane fuels with thier more controlled burning rates.

 

There is a term called Thermal Efficency. This is the percentage of energy produced from the burming fuel that is used for useful work (turning over the engine and driving the prop or vehicle). In a petrol engine only about 25% to 30% of fuel energy is used, the rest of it is absorbed into the cooling system and goes out the exhaust system. So now if your engines combustion occurs early because of advanced ignition timing and is trying to turn your engine backwards so to speak. The heat energy then doesn't go into turning the engine in the right direction easily and is then absorbed into the engine and cooling system, which gives you your higher engine temps. This is probably why Jabiru recommend 95 or higher octane fuel if you decide to use mogas.

 

I hope this makes sense.

 

Harthy

 

 

[Guest disperse]

25 degrees BTDC is a big advance for 2800rpm.

 

If this is the difference between Mogas 8-12 degrees BTDC and Avgas then I would say a timming adjustment would be needed.

 

If I wanted the ducks n@#s in fuel. I would be looking for a High octane Mogas, with NO ethanol, and a good quality valve lubricant additive. And I would be adjusting my timming to suit.

 

The shorter advance would reduce Avgas performance. But you would have a much cleaner engine at pull down.

 

The one good thing about ethanol, is it's ability to combine with water. I always added a bit of metho to my outboard fuel. As it would mix with the water (if any) in the fuel and would still burn.

 

 

[glenns]

All, Maybe reading this service letter from Jabiru may help in the decision. http://www.jabiru.net.au/Service%20Bulletins/Airframe%20Files/JSL003-1(fuel%20tank%20sealent).pdf

 

 

[Yenn]

It would not be easy to change the timing on a Jab 2200 engine. It os all built in and the only adjustment is clearance between rotor and coils. It would take a complete redesign to change.

 

 

[geoffreywh]

25 degrees full advance is NOT much in the way of advance in modern engines. Modern motorcycle engines REGULARLY run 38 degrees of advance and 11-1 + compression ratio. Plus they do it on regular unleaded.(91 octane) I have not seen one worn out through normal use (racing or street) in many years....

 

 

[Guest disperse]

25 degrees full advance is NOT much in the way of advance in modern engines. Modern motorcycle engines REGULARLY run 38 degrees of advance and 11-1 + compression ratio. Plus they do it on regular unleaded.(91 octane) I have not seen one worn out through normal use (racing or street) in many years....

25 degrees advance is fairly common but not at 2700rpm ....... as far as I know anyway

 

 

[Harthy]

Most of the older cars on the road with distributors have variable ignition advance. Usually machanical and vacuum advance. These engines were set up with 4 to 10 degrees advance at idle depending on type, and as the engine speed is increased the ignition timing becomes more advanced usually up to 25 to 35 degrees at full throttle.

 

In high performance engines that produce high revs, they require more advance and can be up to 45 to 50 degrees. This is needed because as the engine speed increases the piston will travel further in the time it takes for combustion to occur. So if the timing were to stay constant, at high revs the piston could very well be moving down the cylinder when complete combustion occurs and therefore you would loose power.

 

Set timing engine are set up for the best ignition timing to suit there normal operating speeds were they will get there best efficiency for the use that they were set up for.

 

So it is unfair to compare a motor bike or car engine to an aircraft engine as there operating parameters are totally different.

 

I am not familiar with the Jabiru engine, but I think it has fixed timing (less to go wrong).

 

With the mogas topic. It is a number of things that have been discussed in this thread that determine the type and octane of fuel that is needed for an engine. So because engines are different, and are used in different applications they will need different settings. I am sure Jabiru in their production process have looked at all of these variables and have set the engines up to best suit there needs. They say Avgas or Mogas above 95. Then that is what is needed.

 

Harthy

 

 

[facthunter]

Gen.

 

Sensible comments Harthy. jabiru would know the optimum setting, Any engine dynamometer would confirm it straight away. The concept of considering large advance settings tending to make the engine run backwards, takes you nowhere. Multiple plugs reduce the advance required, but not by very much when they are close together as in the Jabiru. This is why there is not a marked rev drop when testing mags on these engines.( unless the remaining plug is inoperative). In my experience, there is not a great difference in the ignition advance required with avgas ( if there is any) and any other suitable fuel. (With sufficient anti knock capability). Nev..

 

 

[Yenn]

You can compare a motorbike to an aircraft engine when you can run the bike at full throttle, top gear, for 5 minutes, than 75% power for 3 hours or more, nil throttle for 1 minute and immediately full throttle top gear. I don't know where you will be able to do it and remember it is not only full throttle top gear but under load as well. If the bike engine will do 1000 hours of this it will be OK to drop into a plane.

 

 

[Guest Robw]

Hi guys,

 

Thanks for the advice. It sounds like if you fly regularly so the fuel doesn't sit in the tank forever, make sure you get mogas without ethanol then mogas isn't is problem. On one had it may reduce engine life due to less librucation of valves, but at the other hand, there are less deposits in the engine which is good for engine life. Only the increased risk for vapor lock would suggest that in the summer it probably is better to use avgas.

 

Cheers,

 

Rob

 

 

[Guest ROM]

We tried using MoGas in our Pawnee glider tug for a year or two but then went back to using AvGas.

 

At higher temperatures in summer and using MoGas the Pawnee used to regularly cough and splutter a couple of times as it was going out over the fence with a glider on tow.

 

Use to get the tuggies attention real quick!

 

Was not worth the risk for the few cents a litre saved so back we went to AvGas and have stayed there since with no vaporisation problems at the higher temps.

 

Should have added that there are no standards for mogas fuel quality in Australia.

 

 

[Modest Pilot]

Go to the B P Aust site and look for "Fuel Regulations in Australia".

 

Basic information dates from 2002 but is updated as of Jan 2006.

 

You will see that the stuff sold in QLD and WA is probably the best for aircraft.

 

 

[tangocharlie123]

Price of Avgas

 

Can somebody let me know what the price of Avgas is at the moment.

 

Brisbane NW Queensland and Lower NT

 

thanks Guys

 

peter

 

 

[Guest J430]

About $1.71 around Brisbane.

 

Be warned though.....bulk fuels are likely to have a 10c hike next week.

 

Avgas is generally adjusted monthly and somehow tied to the Singapore prices.....not sure why...they have no GA.

 

Anyway Mrs J430 has some inside knowlege, so expect the next price to be $1.80

 

J

 

 

[Guest Robw]

Around Adelaide it was $1.80 last week.