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Is it safe to use lower octane gasoline?


fuzzybabybunny
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So the compression ratio of these engines seems to be anywhere from 10:1 to 12:1.

As far as I know, higher octane gasoline simply delays spontaneous detonation until higher compressions. That and it has some additives to clean fuel injectors and stuff.

But is 98 octane really necessary? Can I fill it with the same octane that my car uses, 91? During the first few weeks of owning the motor I didn't know any better and ran probably 20 liters of 91 octane fuel through it with no problems.

What about even lower octane like 87 or 85 that you can find in the US?

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You might get away with lower octane fuel for a limited time, but it's not a good thing. When you were running 91RON (Relative Octane Number) fuel, it may well have been pre-detonating when running at full power. During your first few weeks with the new motor, you may not have noticed this.

Note that when running with the throttle partially closed, the effective compression ratio of the engine is reduced, as the throttle restricts the volume of fuel / air mix which is admitted to the cylinder. Thus the effects of low octane fuel will not become apparent until the throttle is opened and the effective compression ratio is increased to a value at which pre-detonation occurs. The lower the RON, the lower the compression at which pre-detonation will occur.

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11 hours ago, ptwizz said:

You might get away with lower octane fuel for a limited time, but it's not a good thing. When you were running 91RON (Relative Octane Number) fuel, it may well have been pre-detonating when running at full power. During your first few weeks with the new motor, you may not have noticed this.

Note that when running with the throttle partially closed, the effective compression ratio of the engine is reduced, as the throttle restricts the volume of fuel / air mix which is admitted to the cylinder. Thus the effects of low octane fuel will not become apparent until the throttle is opened and the effective compression ratio is increased to a value at which pre-detonation occurs. The lower the RON, the lower the compression at which pre-detonation will occur.

Would you happen to know which octane ratings should be used for which compression ratios?

And I always thought that a predetonation would create a loud knock and just flat-out destroy the engine?

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1 minute ago, asquaddie said:

How many guys on here actually use hi Octane fuel for their motors???

Uh, well, everyone I know in New Zealand doesn't. 

For me it's just a question of chemistry. If the compression ratio my motor is capable of isn't going to predetonate, say, 92 octane, then I'm just going to save money and use that.

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me to use hi octane,momentum 99 from tesco.

reason are obvious,

most popular 95 are blended with terrible amount of water(instead of alcohol :D-ethanol)

more likely slurry-a lot less lubricating,a lot more carbon deposit(natural :$) on piston and cylinder head

if you not believe- try at home with care

put 1/4 liter 95 octane in jar and shake

do the same with 99 octane

and compare

because is to much water in 95 mixture after shake are milky white-not transparent or crystal clear

"you get what you pay for"-but not always

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On 9/14/2016 at 10:06 PM, fuzzybabybunny said:

Would you happen to know which octane ratings should be used for which compression ratios?

And I always thought that a predetonation would create a loud knock and just flat-out destroy the engine?

If you google "Octane compression ratio chart" you'll find plenty of data.

Predetonation is not 'all or nothing'. Predetonation will begin to occur as the temperature (generated by compression and residual heat in the engine) reaches the auto-ignition temperature of the fuel. Higher octane gives a higher auto-ignition temperature.

In normal operation, the spark plug ignites the fuel at the correct time, then the flame spreads through the combustion chamber at a speed determined by the heat and pressure generated. This process takes a finite time, so ignition is timed to occur before the engine reaches TDC and peak pressure occurs at or after TDC.

When auto-ignition occurs, most of the fuel will ignite and burn at the same time and the combustion process will be much faster. If this happens significantly before TDC, then you get a knock as it briefly tries to turn the crank in the wrong direction.

It follows that a low octane fuel may auto-ignite after the spark has fired but before the flame front would normally have spread through the combustion chamber. This causes peak pressure to occur earlier and is similar to running slightly over-advanced ignition. You won't notice a power loss and your engine will probably put up with it, until you are climbing flat out on a hot day.

 

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...it costs about 12p more per litre for high octane fuel.

at a burn rate of 4lph that's less than 50p per hour.

over 100hrs of flying, that's less than £50

engine costs around £2000

seems like a no brain decision to use the best fuel and oil to me?

 

 

 

Edited by Icarus
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I can confirm that in practical terms you will probably notice no difference in power as I have used both high and lower octane fuels, including flat out on  a hot day. I have never ever noticed a difference.

I use high octane if I can get it, mainly because it has less ethanol in it. Ethanol deposits in your paramotor are probably not a good thing so I try to avoid it, I have read that it produces sticky residues. I don't know if anyone has ever proven this on a motor though, other than just anecdotal stories? Ethanol in fuel might be more of a problem in the UK than in US or Australia - as the EU has a rule meaning a certain percentage of it now has to be ethanol (as it is considered more environmentally friendly). Consequently there is more ethanol in our fuels in the UK than previously.

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Ethanol in fuel is a hot topic among classic bike and car owners and has been the subject of much research and discussion.

Some of the basics about Ethanol:

Ethanol is hygroscopic, which means it attracts water. It draws in water from the air, which then sits inside your fuel system and corrodes parts which would normally be protected by their immersion in fuel. The combination of water, alcohol (i.e. ethanol) and dissolved oxygen will attack most of the materials used in traditional fuel systems, including steel, copper, brass, rubber and Mazak (carburetor bodies). Some of the plastics used in fuel systems are attacked and form a translucent, gummy deposit which is near invisible when immersed in fuel. I have dismantled petrol taps which have been entirely filled with this stuff.

Ethanol increases the octane rating of petrol. Some brands of 'premium' fuel contain more ethanol than the non-premium fuel of the same brand.

Ethanol has a lower energy content than petrol, so the reduction in power may provide some limited protection from overheating.

 

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7 hours ago, ptwizz said:

Ethanol in fuel is a hot topic among classic bike and car owners and has been the subject of much research and discussion.

Some of the basics about Ethanol:

Ethanol is hygroscopic, which means it attracts water. It draws in water from the air, which then sits inside your fuel system and corrodes parts which would normally be protected by their immersion in fuel. The combination of water, alcohol (i.e. ethanol) and dissolved oxygen will attack most of the materials used in traditional fuel systems, including steel, copper, brass, rubber and Mazak (carburetor bodies). Some of the plastics used in fuel systems are attacked and form a translucent, gummy deposit which is near invisible when immersed in fuel. I have dismantled petrol taps which have been entirely filled with this stuff.

Ethanol increases the octane rating of petrol. Some brands of 'premium' fuel contain more ethanol than the non-premium fuel of the same brand.

Ethanol has a lower energy content than petrol, so the reduction in power may provide some limited protection from overheating.

 

Thanks for the expert explanation.

I had no idea that there was more ethanol in higher octane fuels.

However I will still probably go and buy the higher octane rating if able - your predetonation argument is a good reason to.

 

Cheers,

Alex.

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  • 2 months later...

Just reading the discussion with interest And I read that 95 octane leaves deposits, as that is the only octane fuel sold locally near me, my question is there any additive that can be used in the mix to clean out these deposits and the frequency it can be used, such as on the top 80 engine.

 

 

 

 

 

 

 

 

 

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my advise.. iam a ex moto-x rider... and on the day of a mx race.. i buy high octane  fuel then.and use the fuel.  i do the same for paramotors. fresh  fuel on the day.. and i already know paramotors arent race engines.  the weather can have a effect too... hence why you should preflight checks.and  if needed.. check the color of the spark plug...    i went flying this sunday and as i started off to launch i noticed a blank in revs .. then those few secounds it was ok... ill be putting the video on this paramotor. video ...and youll be able to hear the blank in revs  then its ok... didnt have time to check.. due to the dark nights that settle in quick... i may need to open the high screw on carb?. a tab. or run engine as is .see if it does it agian ...  land then adjust...   always run engine a tab rich. then keep checking color of spark plug now and then... then youll know engine is good to go ;0)        my advise always use high octane fuel

Edited by TONYPARAMOTOR
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  • 3 weeks later...

I use AVGAS 100LL with my Fresh Breeze solo 210. It is what is recommended in the manual, and to be honest I think the cost difference is minimal per hour, only a few pence!. also it doesn't have any nasty hydroscopic additives like mogas to destroy rubber or suck moisture from the air, so it lasts ages and normally starts first pull. I have had all sorts of problems with mogas in the past and with it going off after only a few weeks. Only downside is the plug can clog from lead build up if at low rpm for prolonged periods. I don't know if it would suite all engines being leaded and 100 octane but personally it works great with mine.

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  • 5 weeks later...

 

This should be enough to convince anyone; a heat test. Ethanol burns HOT!!! Fast forward to 2:10 **/

On 9/19/2016 at 16:34, aljken said:

I can confirm that in practical terms you will probably notice no difference in power as I have used both high and lower octane fuels, including flat out on  a hot day. I have never ever noticed a difference.

I use high octane if I can get it, mainly because it has less ethanol in it. Ethanol deposits in your paramotor are probably not a good thing so I try to avoid it, I have read that it produces sticky residues. I don't know if anyone has ever proven this on a motor though, other than just anecdotal stories? Ethanol in fuel might be more of a problem in the UK than in US or Australia - as the EU has a rule meaning a certain percentage of it now has to be ethanol (as it is considered more environmentally friendly). Consequently there is more ethanol in our fuels in the UK than previously.

 

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On 2017-01-02 at 23:48, rob1980 said:

I use AVGAS 100LL with my Fresh Breeze solo 210. It is what is recommended in the manual, and to be honest I think the cost difference is minimal per hour, only a few pence!. also it doesn't have any nasty hydroscopic additives like mogas to destroy rubber or suck moisture from the air, so it lasts ages and normally starts first pull. I have had all sorts of problems with mogas in the past and with it going off after only a few weeks. Only downside is the plug can clog from lead build up if at low rpm for prolonged periods. I don't know if it would suite all engines being leaded and 100 octane but personally it works great with mine.

Yes! this should be great for any gasoline engine.

I use Aspen+ 98 octane alkylate and a premium 2-stroke oil, Maxima Formula K2. The oil is stable with different temperatures, perfect for flying or any motorsport when you need stable performance. Trim one time, and it always works. The fuel can be stored for long periods (not sure if it can be stored mixed for longer periods, contains bioethanol, so I keep an eye open on my carb filters). Problem is that this is like the most expensive fuel around, but my engine loves it. And the alkylate is clean so you won't get cancer from it. (if you believe the marketing).

AVGAS 100LL will soon be replaced. I guess that the lead free avgas might work just as well. I just stay away from mogas, there are too many problems involved with it.
The new Swift UL102 looks very promising. Might be the fuel solution for lots of things in the future. Maybe we know in 2018.

http://www.flyingmag.com/running-on-empty
https://www.flightglobal.com/news/articles/faa-selects-two-fuels-for-unleaded-avgas-testing-423621/
https://www.aopa.org/news-and-media/all-news/2016/september/13/swift-fuels-94ul-put-to-the-test

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