What is the best fuel (Mogas) for your engine

[Cosmick]

First lets start at Manufacturers recommendations - Rotaxservice.com -  The Rotax 912 A/F/UL engines require a minimum octane rating of 87 AKI, commonly referred to as “regular” while the Rotax 912 S/ULS/ULSFR and 914 F/UL require a minimum of 91 AKI (“premium”). Some may have noticed that the Rotax manuals mention ratings of 90 and 95 respectively.

Jabiru - AVGAS or Unleaded Automotive Gasoline above 95 Octane RON https://jabiru.net.au/wp-content/uploads/2018/05/JSL007-7_Fuel_Guidance.pdf

 

This article talks about the benefits for certain engines of increased octane fuels - https://www.mynrma.com.au/membership/my-nrma-app/fuel-resources/which-octane-petrol-is-best-for-you 

 

I have only had aircraft with 2 and 4 stroke Rotax and was advised at schools and by peers to use 98 Octane even in 2 strokes with of course only Rotax recommended 2 stroke oil. When up there we all want an efficient clean fuel system and is this the only (but very good) reason for the higher than recommended octane usage, do any Aircraft engines have Valve Timing to utilise the denser fuel.  

[facthunter]

Most aero engines are not high revving nor do they have to function efficiently over a large RPM range. from 70% to full power is where they have to run well.  Fuel at the servo is not controlled from being added to or  really quality assured. Avgas IS when the drum has not been interfered with (opened and left for any period not secure). 

 Aviation petrol (AVGAS) uses a different Octane reference and has a lean-rich double figure usually and 100LL octane would be above Mogas 98 by about 8 numbers.. It's also much less likely to vapour lock. Rotax don't recommend it  because the lead is an issue. as it runs too cold  to get the (exhaust)valve seat protection in the normal way..Nev

    

[skippydiesel]

Cosmick; The Rotax 9 (912/80 hp 912/100 hp & 914/115 hp) range of engines preferer to run on unleaded(ULP/MoGas)  fuel of 95-98 RON (Australian). 

 

They can run on AvGas (leaded aviation fuel) however you will have to halve the recommended oil change interval, from 100 hrs to 50 hrs and there is a gear box strip/clean/inspect required at (from bad memory) 900 hrs. The two requirements are  both related to lead fowling of the inside of the engine/gear box.

 

There is no performance benefit in using higher than 95 RON below 10,000ft AMSL.

 

Higher octane fuels (RON) do little if anything for engines not optimised to use them. I see a lot of people pulling up at the 98 RON bowser in vehicles that will run perfectly well on 91-95 RON. Use the fuel your vehicle/engine is designed to run on.

 

Facthunter/Nev's comments regarding quality control/assurance, AvGas V ULP, re absolutely correct . However I, along with most Rotax 9 drivers have never had a a problem with ULP. This may be due to following some simple common-sense rules when purchasing fuel:

 

• Use dedicated ( for your aircraft only) fuel containers - they must have air tight lids and preferably no tendency to internally rust or shed lining /paint.
• Purchase from name brand, high turn over servo,s - this minimises the chances of the fuel becoming adulterated and becoming "stale"
• Do not store fuel for more than 6 months and then only in a genuinely air tight container that is 75% or better, full of fuel (best to use fuel as soon as practical after purchase).
• I always refuel with a filter funnel - You can purchase a Mr Funnel - I dont much like them but they do work. I made my own for a fraction of the cost and it fits my vertical fuel filler point.
• Personally I prefer to purchase 98 RON on the basis that if there has been some adulteration/shandying, the actual RON is most likely to be 95 or better. This may be a bit of wishful thinking. There is a slight down side ;98 RON does not seem to have the shelf life of 95 but if stored as I have outlined you should not have a problem (Note: an aircraft fuel tank is not airtight so fueling just befor flight is a good practise - seems a good dollop of fresh 98, pretty much restores the in tank fuel to near 98 standards).

In 10 years I have never had a contamination (water/dirt)  problem with ULP - Years ago,  did fuel up with 95 from a no name brand establishment (only fuel place in town), engine definitely down on power, drained remaining fuel when I got home - smelt awful !!. refuelled with fresh and my engine delivered all that I expected.

[kgwilson]

In more than 50 years of buying Mogas I have never had a problem though I know others have had issues usually from servos in the middle of nowhere with low volume sales. I've used Mogas in my Jab 3300 since new and only use Avgas when I am away from home & it is all I can get.

 

Avgas may be quality controlled when the drum is unopened but most people fill up from the airport bowser so there is no difference from the car petrol bowser. The fuel could become contaminated at any point from pickup from the depot by the tanker to delivery from the bowser to the aircraft.

 

Originally I used BP 95 but they changed to 94 & added ethanol & I now use mainly Shell 98 as the servo is just around the corner from the aerodrome. The engine and plugs stay clean & leakdowns are all good. In the tank the aromatics evaporate off first as they are the lightest components. In a sealed full container they can't so fuel will last up to 6 months. In the tank after 5 or 6 weeks with a tank less than 1/2 full you may have starting problems but the RON number usually increases 2 or 3 points to 100 or thereabouts (based on a BP study in 2010).

 

You only need to add a couple of litres of fresh fuel to a 1/2 tank of 5-6 week old fuel to rejuvenate it to fresh again.

 

The longest time I have left Mogas in my tank between flights was about a month when the weather was poor. The engine started easily with no fresh added and ran perfectly for the flight.

 

I always use a Mr funnel & have never had any contamination. My Jerrycans are dedicated to the aircraft & plastic. 

[facthunter]

You do a good job but I'm not convinced that 2 litres added to half a tank will make much difference.  There's been many  changes in car petrol in the last 50 years. It was leaving a red coloured residue in the combustion  chamber at one stage. The Tankers carrying avgas would still be under a release note so it can all be traced in the event of an incident. 

  Accidently adding Avtur  to a piston plane has happened a few times. TURBO charged has been mistaken for turbine. . Nev

[turboplanner]

3 minutes ago, facthunter said:

You do a good job but I'm not convinced that 2 litres added to half a tank will make much difference. 

Yes it does, I've been successful binging a dead engine to life after finding half a litre and putting it in with about 30 litres.

 

[facthunter]

Most unlikely in such proportions but hard to prove either way. However rotten it is it will still burn and you could probably light Diesel with a flint gun in the right conditions if you try hard enough. Start Ya Bastard has ether in it but I would not use that on an aero engine.but it starts my Dexta at 1500 ft on a frosty morning in about one turn of the crank Saves batteries and starter motors. Nev

[skippydiesel]

16 minutes ago, facthunter said:

....................Start Ya Bastard has ether in it but I would not use that on an aero engine.but it starts my Dexta at 1500 ft on a frosty morning in about one turn of the crank Saves batteries and starter motors. Nev

Nev ! Nev ! As a confirmed diesel freak (your Dexta is a diesel ?), for at least the last 50 years, this (Start Ya bastard) is a blasphemes suggestion. I would only resort to such a perverse action/substance in a dire emergency such that I cant even conceive of (I have never owned a can of SYB). Does your Dexta not have cold start system/mechanism? 

[turboplanner]

Skippy he rides motor bikes...........

[spacesailor]

Iv,e used lots of SYB.

Everything from Peter single cylinder diesels to my half VW two pot motor.

Much beter than handcranking forever, trying to get the fuel or the spark to work.

Used a whole can getting a Ruston diesel motor to run Unassisted, huge thing, with the biggest cranking handle imaginable.

So I.m sold on it.

The old way of getting those old motors going was a bunch of petrol soaked rags, held infront of the induction pipe.

Anyone think they would enjoy holding flaming rags, without letting them get sucked down to the piston ,.

spacesailor

[walrus]

KG Wilson, BP Premium 95 does NOT contain Ethanol.

 

https://www.bp.com/content/dam/bp/country-sites/en_au/australia/home/products-services/data-sheets/premium-unleaded-95.pdf

 

....And another thing, Avgas has an SG of about 0.72 BP 95 ha an SG of 0.75. You should factor that into your W & B.

 

Furthermore Unleaded 95 has about 3% more energy than Avgas, so expect your fuel consumption to increase for the same power.

[kgwilson]

5 hours ago, walrus said:

KG Wilson, BP Premium 95 does NOT contain Ethanol.

 

https://www.bp.com/content/dam/bp/country-sites/en_au/australia/home/products-services/data-sheets/premium-unleaded-95.pdf

 

....And another thing, Avgas has an SG of about 0.72 BP 95 ha an SG of 0.75. You should factor that into your W & B.

 

Furthermore Unleaded 95 has about 3% more energy than Avgas, so expect your fuel consumption to increase for the same power.

I know it doesn't. The BP servos here changed to 94 RON and deleted 95 from the pumps. BP 94RON contains ethanol and this is what I said in my post and why I do not use it any more.

[facthunter]

 Skippy, SYB is only ether. Most diesels hate cold and altitude. With the right amount , the start action is gentle. The original electrical element vapourised diesel and doesn't survive long.. It's a 62 year of manufacture and I bought it when it was 8 years old. Since then It's done 4,000 more hours and has had NO  repairs other than hoses fan belt tappet adjustments (3) and a few steering rod ends and a tacho cable..Nev

[walrus]

1 hour ago, kgwilson said:

I know it doesn't. The BP servos here changed to 94 RON and deleted 95 from the pumps. BP 94RON contains ethanol and this is what I said in my post and why I do not use it any more.

Sorry, my apologies.

[Cosmick]

So out there you have the Skippys and the Turbs, KGs Nevs and Wals (sorry to take liberties) and others who will investigate the intricacies of fuels and then there is the rest of us who ask advice and get good feedback and some individual biases. Personally I use 95 like an Insurance cover that I know nothing bad should come of that fuel and I store in airtight metal containers (good condition jerry). Reading the above feedback does give us (me) the uneducated some satisfaction of good practice.

 

I think this guy is funny, sometimes too much and I tire of him but this Vid seems to cover technically.

https://www.youtube.com/watch?v=3Sl5KqF4AM8

[Yenn]

i recently tried BP super or whatever it is called in my Jab 2200. I didn't fly for a couple of weeks and had terrible trouble starting it. It would not run properly and no matter what I tried, the only way to get that motor going was to revert back to Avgas. NO more mogas for me.

[skippydiesel]

1 hour ago, Cosmick said:

So out there you have the Skippys and the Turbs, KGs Nevs and Wals (sorry to take liberties) and others who will investigate the intricacies of fuels and then there is the rest of us who ask advice and get good feedback and some individual biases. Personally I use 95 like an Insurance cover that I know nothing bad should come of that fuel and I store in airtight metal containers (good condition jerry). Reading the above feedback does give us (me) the uneducated some satisfaction of good practice.

 

I think this guy is funny, sometimes too much and I tire of him but this Vid seems to cover technically.

https://www.youtube.com/watch?v=3Sl5KqF4AM8

Your man (video) explains the fuel rating scale very well.

[skippydiesel]

 

5 minutes ago, Yenn said:

i recently tried BP super or whatever it is called in my Jab 2200. I didn't fly for a couple of weeks and had terrible trouble starting it. It would not run properly and no matter what I tried, the only way to get that motor going was to revert back to Avgas. NO more mogas for me.

Yenn -to have your start problem,  there must be something else going on - its not the unladed fuel (unless you got a bad drop), 

[kgwilson]

 

6 minutes ago, Yenn said:

i recently tried BP super or whatever it is called in my Jab 2200. I didn't fly for a couple of weeks and had terrible trouble starting it. It would not run properly and no matter what I tried, the only way to get that motor going was to revert back to Avgas. NO more mogas for me.

Your engine must be addicted to lead. There will be plenty on the heads and pistons. As I said earlier, after a month my 3300 started first time without adding any fresh fuel. I have also flown with an Avgas/Mogas shandy with no problems so your issues sound a bit strange to me.

[turboplanner]

35 minutes ago, skippydiesel said:

 

Yenn -to have your start problem,  there must be something else going on - its not the unladed fuel (unless you got a bad drop), 

BP Super hasn't been around since the BP Super Show featuring artists like Bob Dyer and Rolf Harris, so you need to be very careful to identify what you put in and whether it was a grade containing ethanol.

 

On this link click on the BP Ultimate 98 link. The starting problem after two weeks sounds like aromatics evaporating off.

Note that it is not recommended for aviation.

At the pumps it's also branded as "removing deposits" so that could also be a problem after avgas.

https://www.bp.com/en_au/australia/home/products-services/data-sheets.html

[rgmwa]

BP Premium 95 isn't recommended for aviation either, according to the data sheet.

[kgwilson]

Fuel companies are not going to recommend automotive fuels for aviation as if something happens and the finger gets pointed to the fuel they could easily be sued due to their recommendation. Jabiru recommends Avgas but advises that above 95 RON may be used if Avgas is unavailable. It is all about avoiding possible litigation. Jabiru has produced a service bulletin on the issues related to Avgas and Mogas. Most of what is discussed here is in this bulletin.

 

The link to the bulletin which like all of them can be downloaded is HERE

[walrus]

Rotax recommends unleaded 95 for my engine (912 iS). Starts every time.

[turboplanner]

7 hours ago, walrus said:

Rotax recommends unleaded 95 for my engine (912 iS). Starts every time.

How long between starts?

[walrus]

Between starts? One - two weeks.