is premium petrol really necessary ?
#21
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Here ya go. Flex Fuel Station Finder |*Ethanol Retailer
Those Ford and GM vehicles with the little black badge with yellow lettering that read "Flex Fuel" are able to run on the more 'exotic' blends.
![](https://www.jaguarforums.com/forum/attachments/xj-xj6-xjr6-x300-26/74719-premium-petrol-really-necessary-flex_fuel_vehicle.jpg?dateline=1393818228)
#22
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Here ya go. Flex Fuel Station Finder |*Ethanol Retailer
Those Ford and GM vehicles with the little black badge with yellow lettering that read "Flex Fuel" are able to run on the more 'exotic' blends.
![](https://www.jaguarforums.com/forum/attachments/xj-xj6-xjr6-x300-26/74719-premium-petrol-really-necessary-flex_fuel_vehicle.jpg?dateline=1393818228)
Those Ford and GM vehicles with the little black badge with yellow lettering that read "Flex Fuel" are able to run on the more 'exotic' blends.
![](https://www.jaguarforums.com/forum/attachments/xj-xj6-xjr6-x300-26/74719-premium-petrol-really-necessary-flex_fuel_vehicle.jpg?dateline=1393818228)
#23
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![](https://www.jaguarforums.com/forum/attachments/xj-xj6-xjr6-x300-26/74787-premium-petrol-really-necessary-ethanol-4_3.jpg?dateline=1393885274)
In Shelby, Iowa, gas-station customers have choices of three ethanol blends not found at many pumps throughout the country: E20, E30 and E85.
![](http://ethanol.typepad.com/.a/6a00e553cd9c8588340133f1f80b13970b-500pi)
![](https://www.jaguarforums.com/forum/attachments/xj-xj6-xjr6-x300-26/74788-premium-petrol-really-necessary-ethanol_notexclusive_13896475439365.jpg?dateline=1393885760)
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![](https://www.jaguarforums.com/forum/attachments/xj-xj6-xjr6-x300-26/74788-premium-petrol-really-necessary-ethanol_notexclusive_13896475439365.jpg?dateline=1393885760)
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![](https://www.jaguarforums.com/forum/attachments/xj-xj6-xjr6-x300-26/74790-premium-petrol-really-necessary-08_11_19_biofuel_pump.jpg?dateline=1393885760)
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Last edited by Suede; 03-03-2014 at 04:29 PM.
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plums (03-03-2014)
#24
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All very true, except that high octane gas doesn't 'burn slower' than other fuels. It's simply less prone to 'self-ignition' or detonation. Changing the burn speed (flame front velocity) of a fuel would not prevent detonation and (in theory) provide more opportunity for detonation to occur.
I always believed the rate of combustion varied with the octane rating. Hence why some people in our Canuck Siberian climate use lower octane fuel in winter (and boy, I need a block heater in mine):
1. it's cheaper.
2. engine temps never reach the same levels as in summer, so there should be less chance for pre-ignition as the engine block will be colder, even if the combustion temps are the same.
3. we have 3 levels of fuel available, E10 87 AKI, E5 89 AKI, and pure gasoline 91 AKI. Ethanol can function as a gas line anti-freeze so some ethanol in our winters may be beneficial.
I usually don't vary my fuel use in winter, but I did use a tank of E5 89 AKI in my XJR this winter for the gas-line antifreeze effect. Even with the Andy Bracket installed my car ran the same. I didn't calculate the fuel consumption though.
#25
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Very interesting! Can you explain the chemistry in more detail please? I'd love to know the truth.
I always believed the rate of combustion varied with the octane rating. Hence why some people in our Canuck Siberian climate use lower octane fuel in winter (and boy, I need a block heater in mine):
I always believed the rate of combustion varied with the octane rating. Hence why some people in our Canuck Siberian climate use lower octane fuel in winter (and boy, I need a block heater in mine):
Normal combustion (deflagration) initiates at the point and moment when the spark plug 'fires'. The fuel droplets immediately in the path of the spark ignite and the flame spreads quickly to the adjacent droplets- not much different than the spark that lights a burner on a backyard BBQ but obviously at much, much greater speed, somewhere in the range of 20 to200 ft/sec depending on a multitude of factors. The key is that all times, the fuel is burning progressively and not 'exploding' as is commonly thought.
If all goes well, every droplet of fuel is burnt and maximum pressure has been exerted on the piston during the power stroke.
It is possible that subsequent to the spark igniting the fuel droplets, but before the flame has spread to all corners of the combustion chamber, some of the fuel mixture can spontaneously ignite, but instead of the desired progressive burning, 'explodes' not much different than dynamite. Instead of a flame speed of 20-200 ft/sec. the speeds can reach 2000-10,000 ft/sec setting of a shock wave again the same as a dynamite explosion. It is this shock wave that 'rings' the combustion chamber giving us the pinging/rattling sound and also what can destroy the engine itself.
To avoid detonation- the fuel must be modified to make it less susceptible to auto-ignition. In other words, keep it from exploding in the first place, not attempt futile efforts to slow down the 'shock waves'. Octane numbers are an expression of the fuel ability to resist self-ignition and no other factor. Originally tetraethyl lead (TEL) was added to achieve this. There are several members here who can advise what compounds, in addition to ethanol and toluene are blended into today's gas to achieve the desired octane numbers.
As to using lower octane in winter vs. summer, I can't explain why other than the engine is on the ragged edge of inducing detonation during the summer heat due to excessive coolant temps. The reduced inlet air temps won't make much difference.
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jvitez (03-03-2014)
#26
#27
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The Department of Energy, in partnership with the Oak Ridge National Labs, is also investigating the use of mid-level blends (up to E20) in regular, non-FFV vehicles. In their October 2008 report, Oak Ridge found the following:
These preliminary findings suggest that higher blends of ethanol fuel may be suitable for use in conventional gasoline powered cars. Additional testing is underway
- None of the vehicles displayed a malfunction indicator light (MIL) as a result of the ethanol content of the fuel.
- No fuel filter plugging symptoms were observed.
- No cold start problems were observed in 75°F and 50°F laboratory conditions.
- No fuel leaks or conspicuous degradation of the fuel systems were observed.
- Regulated tailpipe emissions remained largely unaffected by the ethanol content of the fuel
- With E20, the average reduction in fuel economy (i.e., the reduction in miles per gallon) was 7.7 percent compared to E0. A linear trend with increasing ethanol content
These preliminary findings suggest that higher blends of ethanol fuel may be suitable for use in conventional gasoline powered cars. Additional testing is underway
#28
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To demonstrate why flame front speed has nothing to do with avoiding detonation- it is essential to understand what detonation is.
Normal combustion (deflagration) initiates at the point and moment when the spark plug 'fires'. The fuel droplets immediately in the path of the spark ignite and the flame spreads quickly to the adjacent droplets- not much different than the spark that lights a burner on a backyard BBQ but obviously at much, much greater speed, somewhere in the range of 20 to200 ft/sec depending on a multitude of factors. The key is that all times, the fuel is burning progressively and not 'exploding' as is commonly thought.
If all goes well, every droplet of fuel is burnt and maximum pressure has been exerted on the piston during the power stroke.
It is possible that subsequent to the spark igniting the fuel droplets, but before the flame has spread to all corners of the combustion chamber, some of the fuel mixture can spontaneously ignite, but instead of the desired progressive burning, 'explodes' not much different than dynamite. Instead of a flame speed of 20-200 ft/sec. the speeds can reach 2000-10,000 ft/sec setting of a shock wave again the same as a dynamite explosion. It is this shock wave that 'rings' the combustion chamber giving us the pinging/rattling sound and also what can destroy the engine itself.
To avoid detonation- the fuel must be modified to make it less susceptible to auto-ignition. In other words, keep it from exploding in the first place, not attempt futile efforts to slow down the 'shock waves'. Octane numbers are an expression of the fuel ability to resist self-ignition and no other factor. Originally tetraethyl lead (TEL) was added to achieve this. There are several members here who can advise what compounds, in addition to ethanol and toluene are blended into today's gas to achieve the desired octane numbers.
As to using lower octane in winter vs. summer, I can't explain why other than the engine is on the ragged edge of inducing detonation during the summer heat due to excessive coolant temps. The reduced inlet air temps won't make much difference.
Normal combustion (deflagration) initiates at the point and moment when the spark plug 'fires'. The fuel droplets immediately in the path of the spark ignite and the flame spreads quickly to the adjacent droplets- not much different than the spark that lights a burner on a backyard BBQ but obviously at much, much greater speed, somewhere in the range of 20 to200 ft/sec depending on a multitude of factors. The key is that all times, the fuel is burning progressively and not 'exploding' as is commonly thought.
If all goes well, every droplet of fuel is burnt and maximum pressure has been exerted on the piston during the power stroke.
It is possible that subsequent to the spark igniting the fuel droplets, but before the flame has spread to all corners of the combustion chamber, some of the fuel mixture can spontaneously ignite, but instead of the desired progressive burning, 'explodes' not much different than dynamite. Instead of a flame speed of 20-200 ft/sec. the speeds can reach 2000-10,000 ft/sec setting of a shock wave again the same as a dynamite explosion. It is this shock wave that 'rings' the combustion chamber giving us the pinging/rattling sound and also what can destroy the engine itself.
To avoid detonation- the fuel must be modified to make it less susceptible to auto-ignition. In other words, keep it from exploding in the first place, not attempt futile efforts to slow down the 'shock waves'. Octane numbers are an expression of the fuel ability to resist self-ignition and no other factor. Originally tetraethyl lead (TEL) was added to achieve this. There are several members here who can advise what compounds, in addition to ethanol and toluene are blended into today's gas to achieve the desired octane numbers.
As to using lower octane in winter vs. summer, I can't explain why other than the engine is on the ragged edge of inducing detonation during the summer heat due to excessive coolant temps. The reduced inlet air temps won't make much difference.
So, it's misguided to think a lower octane fuel will provide better performance in cold winters. I guess the only proviso is that if a lower octane fuel can provide adequate octane, then the ECM will not need to significantly retard ignition timing, and then fuel consumption shouldn't be significantly reduced. A lot of what-if's though.
The other issue could be higher fuel consumption caused by the reduced energy content of ethanol. If E20 causes a 7.7% increase in consumption vs E0, then E5 should increase consumption by 2%. It would be interesting to try a tank of E0 91 vs E5 89 in winter and see if my consumption goes up by more than 2%. But I can't imagine any meaningful results with the wide variety of weather we've had this winter. The take home message is "Use premium."
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#30
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So, it's misguided to think a lower octane fuel will provide better performance in cold winters. I guess the only proviso is that if a lower octane fuel can provide adequate octane, then the ECM will not need to significantly retard ignition timing, and then fuel consumption shouldn't be significantly reduced. A lot of what-if's though.
The other issue could be higher fuel consumption caused by the reduced energy content of ethanol. If E20 causes a 7.7% increase in consumption vs E0, then E5 should increase consumption by 2%. It would be interesting to try a tank of E0 91 vs E5 89 in winter and see if my consumption goes up by more than 2%. But I can't imagine any meaningful results with the wide variety of weather we've had this winter. The take home message is "Use premium."![Smile](https://www.jaguarforums.com/forum/images/smilies/smile.gif)
The other issue could be higher fuel consumption caused by the reduced energy content of ethanol. If E20 causes a 7.7% increase in consumption vs E0, then E5 should increase consumption by 2%. It would be interesting to try a tank of E0 91 vs E5 89 in winter and see if my consumption goes up by more than 2%. But I can't imagine any meaningful results with the wide variety of weather we've had this winter. The take home message is "Use premium."
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I purchased a used Lincoln SUV a few months ago as a winter beater. Despite the instructions in the owner's manual and a sticker on the fuel filler door stating that only high octane fuel is to be used, the previous owner had used regular for many years. He was under the impression that the only difference was the amount of cleaning additives and since the vehicle ran just fine on regular, that fuel was adequate. I've been filling it with super to gauge performance and economy and will then try regular to see what, if anything, changes.
My Jag, like most others comes with a recommendation to use 95RON which is 91AKI. Despite the warnings of 'the sky is falling', I have used 87 octane extensively again to see what, if any, difference it makes. There is no clear indication at this point that fuel consumption suffers- I can easily average more than 30 mpg (US gallons) on the highway and using the hopelessly unreliable butt dyno, feel no difference in performance. I might have heard a brief rattle once from the engine during an urgent avoidance manoeuvre, but it lasted less than a second.
This suggests that our engines are not operating continuously on the ragged edge of detonation and that any brief periods of detonation are taken care of by the electronics which briefly retard the timing. It appears that the episodes where high octane fuel is actually required are so few and far between that it does not not show up in averaged fuel consumption.
The tests you've suggested above might reveal some differences, but the problem is there's two variables being changed at the same time- octane and ethanol content. It would be better to compare E0 of various octanes back to back, or 91 octane in both E0 and E10.
#32
#33
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A minor point but pre-ignition is a completely different condition than detonation. The two terms are NOT interchangeable. Detonation occurs subsequent to the spark as an 'explosion' wheres as pre-ignition occurs (as per name ) prior to the spark and is an otherwise normal combustion event with the fuel burning rather than exploding.
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I've installed an Andy Bracket, and mine is an XJR, so for safety's sake I should premium I assume. If there wasn't such a price spread between octane levels all of this would be moot. Though our cars were designed with E10 in mind, I do feel better not having all the ethanol issues with phase separation and hose degradation in an already 18 year old car.
Anyway, thanks again for your very helpful information.
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The phase separation issue is just more over the top 'sky is falling' hooey. It just doesn't happen on vehicles with sealed fuel systems like our Jags. 18 year old hoses might need replacing irrespective of ethanol.
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Samilcar (06-07-2016)
#35
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Hmmm, I guess I was transferring the warning about using high ethanol fuel with outdoor power products onto cars. Good point about sealed systems.
FWIW, here's the warnings about small engines and ethanol:
OPEI: PRICE is No Longer the Best Way to Select Gasoline
FWIW, here's the warnings about small engines and ethanol:
OPEI: PRICE is No Longer the Best Way to Select Gasoline
#36
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Note that they talk about fuel with higher ethanol content than E10.
"Most outdoor power equipment was not built, designed or warranted to run on fuel greater than E10,"
they've come a long way from just a few years ago when any ethanol would supposedly cause bad things to happen. Some of the brighter small engines manufacturers must have realized they could grab some market share by accepting the fact that E10 is probably here to stay and finally updated their products to be compatible.
"Most outdoor power equipment was not built, designed or warranted to run on fuel greater than E10,"
they've come a long way from just a few years ago when any ethanol would supposedly cause bad things to happen. Some of the brighter small engines manufacturers must have realized they could grab some market share by accepting the fact that E10 is probably here to stay and finally updated their products to be compatible.
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