SV650.org - SV650 & Gladius 650 Forum



SV Talk, Tuning & Tweaking Discussion and chat on all topics and technical stuff related to the SV650 and SV1000
Need Help: Try Searching before posting

Reply
 
Thread Tools
Old 22-04-19, 04:27 PM   #11
SV650rules
Member
Mega Poster
 
Join Date: Nov 2016
Location: Shropshire UK
Posts: 1,357
Default Re: 97 Ron Fuel...?

Quote:
Originally Posted by glang View Post
hmmm I think if that was the case the car manufacturers would have to give varying engine power outputs and speed figures for different octane fuels and Ive never seen that.....
They specify engine power at their recommended octane, this varies across the world - in parts of Asia lower octane may be the norm, while in Europe 95 is standard. I have tried it in our cars and they are deffo smoother and perkier on 97 or 99 and the extra MPG can make it just about financially OK to pay the extra.
__________________
2016 SV650 AL7

Courage is resistance to fear, mastery of fear, not absence of fear - Mark Twain
SV650rules is offline   Reply With Quote
Old 22-04-19, 05:03 PM   #12
glang
Member
 
Join Date: Oct 2007
Posts: 535
Default Re: 97 Ron Fuel...?

in my manual the recommended fuel octane is 91 and presumably this is the fuel they used to get the rated power figure but it would have been much better marketing if they had used the power produced from 95 if as you say this would be higher......
glang is offline   Reply With Quote
Old 22-04-19, 06:25 PM   #13
Talking Heads
Member
 
Join Date: Jan 2017
Posts: 486
Default Re: 97 Ron Fuel...?

Higher octane numbers only provide benefits for engines designed to benefit from using them.
The number is an anti-knock index, higher = less volatile.
Higher octane absolutely doesn't guarantee higher power in fact it can reduce power and fuel economy.
And that is because..... higher octane fuel contains less energy.
Best to use whatever the manual says.
Talking Heads is offline   Reply With Quote
Old 23-04-19, 12:04 PM   #14
embee
Member
Mega Poster
 
embee's Avatar
 
Join Date: Jul 2003
Location: Warwickshire
Posts: 2,801
Default Re: 97 Ron Fuel...?

Rather a lot of "nearly right" comments being made. Just to try to clarify a few ……………

"Octane number" is indeed the measure of the tendency of a particular fuel to result in "knock" (aka detonation, pinking, pinging etc). NOTE that knock is different to "pre-ignition". As the name suggests, pre-ignition is where the burn starts before the spark, usually due to excessively hot items like a wrong grade spark plug or hot deposits. "Knock" occurs at the end of the burn process, normal combustion is a progressive burn, taking maybe 40 or so crank degrees from initiation, it is not an explosion. Knock has to be severe and extended for any real damage to occur (I've run engines in heavy knock to determine the effects, and one took 10hrs at full power knocking heavily until a ring land broke on a piston). Pre-ignition will destroy an engine in seconds due to massive heat input into pistons.

Fuels are assessed in specific test engines run at specific conditions, the tendency for the fuel to knock is then compared to a theoretical mixture of two specific hydrocarbons, iso-octane and n-heptane.

Iso-octane (usually 2-2-4 trimethyl pentane) is branched molecule and reasonably stable, defined as 100 "Octane". N-heptane is a straight molecule and breaks easily, and is defined as "zero octane". The test fuel is given a number which describes how it behaves compared to a mixture of the 2 reference fuels, so 95 octane bejhaves like 95% iso-octane and 5% n-heptane. IT IS NOT MADE OF THESE, but behaves like it. It has no DIRECT relation to volatility, that's a different characteristic. It is also not directly related to alcohol content, any commercial pump fuel is allowed to contain "up to" 5% alcohol without having to declare it, 10% or more must be labelled. Alcohol fuels have different octane ratings and content will affect how the fuel will behave, but it is the overall mix of constituents which determines the behaviour.

Different test conditions (speed/load/temperature) give rise to different numbers, one is "research octane number" RON, another is "motor octane number" MON.
MON is usually around 7 or 8 numbers lower than RON for most commercial petrol. In the USA they usually quote the average of the 2 ((RON+MON)/2), in Europe we quote RON. Thus USA "pump" numbers are usually about 4 lower than RON.


Knock is when a fuel/air mix is exposed to high pressure and temperature long enough for the fuel to break down into chemicals which will spontaneously react without the need for an ionisation source (flame/spark). It usually happens in the gas away from the plug where the mixture gets heated and compressed by the advancing flame front, and significant amounts of the charge can spontaneously react simultaneously resulting in a very rapid pressure rise, giving the metallic "knock" sound.

Commercial higher RON fuel tends to have slightly higher density and slightly higher calorific value than regular, but the difference is relatively small, of the order of 2-3%. This is down to the different constituents of the mix of hydrocarbons it contains.
95RON might be around 42.7MJ/kg and 0.74 kg/l, 98RON might be typically 43.5MJ/kg and 0.75kg/l. Since we buy fuel by the litre we usually get slightly more energy per litre for higher RON, but the effect is small.
The ignitability characteristics can be different, and this is often one aspect which you can notice. Combustion stability is measured as statistical variation in IMEP or the first 5 or 10% mass burned, and tests can demonstrate the effects of different fuels.

A higher octane number means a fuel can tolerate higher temps and pressures for longer, allowing the compression ratio to be increased (in simple terms). This improves the thermal efficiency (power and fuel economy). CR is selected according to what the commercially available fuel is in a specific market. In reality many manufacturers use a common spec for the engine for different markets, so the lowest common denominator applies.
At low speed and high load most engines are "knock limited", i.e. the ignition cannot be advanced to the point where the optimum output is achieved before knock is encountered. This is down to the choice of CR being to suit mid/high speeds where it can be optimised (often termed "best ignition" or "maximum brake torque" MBT ignition etc) in the interest of output and economy. Knock will happen at low engine speeds because the burn rates are low and cycle times long so the mix can be exposed to the high temps and pressures for longer and will reach the critical condition.

Running a higher RON fuel than the minimum recommended is not detrimental. Different speeds and loads will have different octane requirements in any given engine so the majority of the time the fuel rating is higher than actually needed.

It is a perennial topic, and I usually end up saying just try it. If you find it makes your engine run smoother or start easier etc then fine, if you can't tell the difference then don't bother. Some engines/operators are more sensitive that others to fuel characteristics. If your vehicle uses systems which optimise it for the use of higher octane fuels it will usually be worthwhile, but ultimately it's up to you.
__________________
"Artificial Intelligence is no match for natural stupidity"

Last edited by embee; 23-04-19 at 12:08 PM.
embee is offline   Reply With Quote
Old 23-04-19, 12:53 PM   #15
glang
Member
 
Join Date: Oct 2007
Posts: 535
Default Re: 97 Ron Fuel...?

Thanks that makes sense. I would have thought an engine with knock sensor might be able to take advantage of different octane fuels as the timing could be advanced until knocking starts so with a high octane fuel the timing could get closer to the optimum.
Bike engines dont have this presumably because they dont tend to operate at low revs/high loads - I certainly never heard of them having a knock problem....
glang is offline   Reply With Quote
Old 23-04-19, 12:56 PM   #16
Othen
Guest
 
Posts: n/a
Default Re: 97 Ron Fuel...?

Quote:
Originally Posted by embee View Post
Rather a lot of "nearly right" comments being made. Just to try to clarify a few ……………

"Octane number" is indeed the measure of the tendency of a particular fuel to result in "knock" (aka detonation, pinking, pinging etc). NOTE that knock is different to "pre-ignition". As the name suggests, pre-ignition is where the burn starts before the spark, usually due to excessively hot items like a wrong grade spark plug or hot deposits. "Knock" occurs at the end of the burn process, normal combustion is a progressive burn, taking maybe 40 or so crank degrees from initiation, it is not an explosion. Knock has to be severe and extended for any real damage to occur (I've run engines in heavy knock to determine the effects, and one took 10hrs at full power knocking heavily until a ring land broke on a piston). Pre-ignition will destroy an engine in seconds due to massive heat input into pistons.

Fuels are assessed in specific test engines run at specific conditions, the tendency for the fuel to knock is then compared to a theoretical mixture of two specific hydrocarbons, iso-octane and n-heptane.

Iso-octane (usually 2-2-4 trimethyl pentane) is branched molecule and reasonably stable, defined as 100 "Octane". N-heptane is a straight molecule and breaks easily, and is defined as "zero octane". The test fuel is given a number which describes how it behaves compared to a mixture of the 2 reference fuels, so 95 octane bejhaves like 95% iso-octane and 5% n-heptane. IT IS NOT MADE OF THESE, but behaves like it. It has no DIRECT relation to volatility, that's a different characteristic. It is also not directly related to alcohol content, any commercial pump fuel is allowed to contain "up to" 5% alcohol without having to declare it, 10% or more must be labelled. Alcohol fuels have different octane ratings and content will affect how the fuel will behave, but it is the overall mix of constituents which determines the behaviour.

Different test conditions (speed/load/temperature) give rise to different numbers, one is "research octane number" RON, another is "motor octane number" MON.
MON is usually around 7 or 8 numbers lower than RON for most commercial petrol. In the USA they usually quote the average of the 2 ((RON+MON)/2), in Europe we quote RON. Thus USA "pump" numbers are usually about 4 lower than RON.


Knock is when a fuel/air mix is exposed to high pressure and temperature long enough for the fuel to break down into chemicals which will spontaneously react without the need for an ionisation source (flame/spark). It usually happens in the gas away from the plug where the mixture gets heated and compressed by the advancing flame front, and significant amounts of the charge can spontaneously react simultaneously resulting in a very rapid pressure rise, giving the metallic "knock" sound.

Commercial higher RON fuel tends to have slightly higher density and slightly higher calorific value than regular, but the difference is relatively small, of the order of 2-3%. This is down to the different constituents of the mix of hydrocarbons it contains.
95RON might be around 42.7MJ/kg and 0.74 kg/l, 98RON might be typically 43.5MJ/kg and 0.75kg/l. Since we buy fuel by the litre we usually get slightly more energy per litre for higher RON, but the effect is small.
The ignitability characteristics can be different, and this is often one aspect which you can notice. Combustion stability is measured as statistical variation in IMEP or the first 5 or 10% mass burned, and tests can demonstrate the effects of different fuels.

A higher octane number means a fuel can tolerate higher temps and pressures for longer, allowing the compression ratio to be increased (in simple terms). This improves the thermal efficiency (power and fuel economy). CR is selected according to what the commercially available fuel is in a specific market. In reality many manufacturers use a common spec for the engine for different markets, so the lowest common denominator applies.
At low speed and high load most engines are "knock limited", i.e. the ignition cannot be advanced to the point where the optimum output is achieved before knock is encountered. This is down to the choice of CR being to suit mid/high speeds where it can be optimised (often termed "best ignition" or "maximum brake torque" MBT ignition etc) in the interest of output and economy. Knock will happen at low engine speeds because the burn rates are low and cycle times long so the mix can be exposed to the high temps and pressures for longer and will reach the critical condition.

Running a higher RON fuel than the minimum recommended is not detrimental. Different speeds and loads will have different octane requirements in any given engine so the majority of the time the fuel rating is higher than actually needed.

It is a perennial topic, and I usually end up saying just try it. If you find it makes your engine run smoother or start easier etc then fine, if you can't tell the difference then don't bother. Some engines/operators are more sensitive that others to fuel characteristics. If your vehicle uses systems which optimise it for the use of higher octane fuels it will usually be worthwhile, but ultimately it's up to you.


That was a good article.


Sent from my iPad using Tapatalk
  Reply With Quote
Old 23-04-19, 01:38 PM   #17
Biker Biggles
Member
Mega Poster
 
Biker Biggles's Avatar
 
Join Date: Jan 2005
Location: Barnet Herts
Posts: 5,067
Default Re: 97 Ron Fuel...?

I used BP ultimate once in a while in winter because I had problems with carb icing.(Old curvy Euro import with no carb heaters). I think it helped. I never found any other benefits.
__________________
On a clear day we stand there and look further than the ordinary eye can see.
Biker Biggles is online now   Reply With Quote
Old 24-04-19, 08:06 PM   #18
johnnyrod
Member
Mega Poster
 
johnnyrod's Avatar
 
Join Date: Jul 2003
Location: Doncaster, oop norf
Posts: 2,122
Default Re: 97 Ron Fuel...?

Embee knows his onions, no diggity. Biggles, carb icing is due to the carbs getting cold as the fuel vaporises. I'm a bit unclear TBH if there is any actual ice involved, or just the carbs get so cold the vaporisation is too feeble to run the engine. Anyway on old aircooled lumps there was always a nice stream of warm air from the engine, but on watercooled bikes there is either an electric heater of some sort (a plate between carbs and head, or little heater plugs in the bowls like the SV) or some engine water run around them (like on old Kwaks).
I've tried super unleaded on a few track days, in hindsight when you live at 7-10k it's probably a bit of a waste of time. Never noticed a difference, unsurprisingly.
johnnyrod is offline   Reply With Quote
Old 24-04-19, 08:28 PM   #19
SV650rules
Member
Mega Poster
 
Join Date: Nov 2016
Location: Shropshire UK
Posts: 1,357
Default Re: 97 Ron Fuel...?

There is less of the stuff that burns in higher octane but spark timing is the key to getting it to burn in a more controlled and efficient way inside the engine. If knock detectors are fitted and they detect knocking they retard ignition to stop knocking which reduces engine power. By clever design of combustion chamber and maybe twin spark plugs to 'light the fire in two places at once' higher compression ratios can be used on normal octane fuel, but an engine fitted with knock sensors and proper maps in ECU can make use of a range of octane ratings, and some can get good results on better fuel.

The formulation of petrol changes between winter and summer anyway, it is made more volatile in winter to make evaporation at lower temperatures better.
__________________
2016 SV650 AL7

Courage is resistance to fear, mastery of fear, not absence of fear - Mark Twain

Last edited by SV650rules; 24-04-19 at 08:33 PM.
SV650rules is offline   Reply With Quote
Old 24-04-19, 11:08 PM   #20
Talking Heads
Member
 
Join Date: Jan 2017
Posts: 486
Default Re: 97 Ron Fuel...?

Quote:
Originally Posted by johnnyrod View Post
Biggles, carb icing is due to the carbs getting cold as the fuel vaporises. I'm a bit unclear TBH if there is any actual ice involved, or just the carbs get so cold the vaporisation is too feeble to run the engine.
Carb icing is caused by water vapour in the intake air turning to ice and causing a blockage.
Talking Heads is offline   Reply With Quote
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
2008 SV650 Fuel Cap/Fuel Pump jwray4422 SV Talk, Tuning & Tweaking 3 26-06-18 06:27 PM
WTD, curvy fuel tap and fuel level sensor northwind Stuff Wanted 3 06-12-17 12:33 PM
Fuel rant whinge moans hate fuel prices bah Daimo Idle Banter 54 18-02-11 11:02 PM
Where is the fuel? Lifted fuel tank. BoomBoomBox Bikes - Talk & Issues 72 07-12-10 01:01 PM
Replacement fuel light / fuel tap riktherider SV Talk, Tuning & Tweaking 7 14-05-07 06:41 PM


All times are GMT. The time now is 10:56 PM.


Powered by vBulletin® - Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.