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Fuel Degradation


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To make a long story short...

My PAP was lying up for approx. 2 months until the end of October. I knew the fuel in it would have gone stale but ran a little test out of curiosity (Yes I should have drained it...I didn't expect to be grounded for so long). The old fuel in it after 2mths was getting approx. 8400rpm (+/- 60rpm) according to my tinytach. Drained and refilled with regular 95 octane it was then getting approx. 9600rpm.

That's a 12% decrease in volatility in approximately 2 months.

So, after refilling 2 1/2 weeks ago the weather has been crap and its been sitting up again, this time for 2 1/2 weeks. Today I went out and was getting approx. 8600rpm.

That's a 10% decrease in volatility in approx. 2 1/2 weeks.

So therefore my fuel incurs 83% of its total 2 month volatility loss within the first 2 1/2 weeks. :shock:

What's worse, I found out today that in a 6-9mph headwind, that extra 1000rpm is the difference between me climbing out or just running aimlessly along the ground! :shock::shock:

So after a quick google trawl here's my questions...

1. Does anyone use premium 97/98 octane, super 98/99 octane or high performance 102 octane in their motor and what difference do you see in RPM?

2. Has anyone ever used a stabiliser in their paramotor fuel and how did it go?

3. General thoughts?

I need to get my hands on some premium unleaded to measure the rpm at 97 octane but it seems very few forecourts sell it anymore.

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Sound more like environmental difference to me. Did you try to tune your motor... I guess your on a two stroke ??

I always use good fresh fuel 98.. Especially for a record attempts.

Some people say higher octane fuel does not give you more power, But will make your engine run cooler enabling you to tune it higher for better RPM/Power. But you best ask some tech geek...

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Didn't know about the porosity of plastic to fuel vapour. That's very interesting.

Haven't tuned the motor, will do that after I've played around with seeing what difference the fuel alone makes.

Does anyone know if the manuals max 10250 rpm is realistic or what max RPM I should be expecting from a ROS125 with 120cm prop?

Thanks.

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Plastic ain't that porous, they make an awful lot fuel tanks out of it. :-)

My plastic jerry can ( like everyone else's ) is also UN approved for the movement of pretty much all dangerous goods. Very unlikely to leak liquid or vapour if used properly.

Sent from my iPhone using PMC Forum mobile app

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I don't want to get all technical as it's too early but... 'It depends on the type of plastic'

Most car tanks are made from 'Acetal' which is a plastic engineered for use with long term Petrol use.

Most cheep plastic cans are made from 'polypropylene' which is al all round good plastic and cheep to make things with. It WILL allow vapours to pass when under pressure which is why it cant be used for making cold moulds that are being used in a vacuum bag.

SW :D

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Basically the same and in fact both are used (and more) but as I said...

Can't be arsed to get all technical with you as it has taken me about 8 years to get all of this stuff out of my head LOL

SW :D

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A few points here:

1) To properly compare 'new' and 'aged' fuel, you'd have to test samples from the same batch using a calorimeter. The uncontrolled variables involved in measuring RPM of an engine driving a prop are too numerous to list.

2) It is difficult to know how long your 'new' fuel has already spent in the petrol station tanks, in a tanker on the road, in a holding tank, at sea, etc.

3) High octane fuels allow running with higher compression ratios without pre-detonation. Running higher octane does not, in itself, create more power.

4) If your fuel has been sitting in a stationary container for a while, give it a good shake up. Some of the lower density fractions may begin to seperate out over time, but they're still there and just need to be mixed in. This used to be compulsary practise with the old 2 stroke oils, which would settle into the bottom of the tank and carb, causing much frustrated kicking of BSA Bantams and the like.

5) Don't throw away old or degraded fuel. mix it in with a larger quantity for your car, bike, lawnmower or other inferior machinery. Probably best not to put any 2 stroke in your car if its one of the new fangled type with a catalytic CON verter.

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After a few hours of intense research and the the like a conclusion had been drawn .

If we use the fuel as intended and spend more time flying than pondering on the qualities of the slowly degrading fuel there will be no issues.

The question still remains, is it to early to eat last nights remaining curry. It has been in the fridge all night, but I failed to put a cover over it.

Sent from my iPhone using PMC Forum mobile app

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...If we use the fuel as intended and spend more time flying than pondering on the qualities of the slowly degrading fuel there will be no issues.

The question still remains, is it to early to eat last nights remaining curry. It has been in the fridge all night, but I failed to put a cover over it.

:lol:

Ok, so after more investigation and in the interest of not misleading anyone I'll swallow my pride and let you all know that this has turned out to be operator error. More accurately I've discovered that a few weeks ago I obviously made an arse of my throttle mechanism by tightening my throttle cable too much and damaging the throttle control piece! :oops:

My rpm are now back up to 9810.....at least until said throttle control piece slips due to said damage and everything goes awry.

I've emailed tim odlin in papparamotorsuk and will hopefully have her up and running again soon!

If your interested in wasting 45 seconds of your life feel free to view the video. Does it look like I just need to replace the rivet?

http://www.youtube.com/watch?v=gKqPVBymQuE

No more flying for me for a few weeks...serves me right...

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