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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.

 

Yes, E85 as it says in your picture. Where's the E20 fuel that you can fill your Jag with?

 

 

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):

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.

 

Thanks for posting those pics. That's certainly something I've never seen despite extensive travel around the US and Canada. I suppose the only vehicles that can use higher then E10 are 'flex fue'l factory designed for E85. There are no E85 stationa anywhere around here, despite us having a suspiciously large number of flex fuel vehicles (?)

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.

 

uh-huh

 

You definitely won't find it everywhere. Basically in the 'Corn is King' plains states, and in the 'Enviro' states.


This is the only actual study I know of. Apparentl E20 poses not serious risk to the general vehicle fleet. But that could just be the work of the powerful corn lobby.

 

I have never seen that before.

 

An excellent explanation! Many thanks for the details. I always assumed flame front propagation and pre-ignition would be occurring at the same velocity (a stable principle of burning gasoline) but I now see that's not the case. Interesting stuff.

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."

 

Suede: I certainly hope E20 never makes it to the Canadian prairies. Maybe there were "No cold start problems in laboratory conditions at 50°F," but what about -30°? If you have a FFV then it shouldn't matter, but no way would I want to start running E20 in anything else.

 

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.

The issue with modern cars is not knowing whether high octane fuel is required in the first place. In the old days it was easy to tell- listen out the window for detonation while lugging the engine up a hill in high gear. The choices were use even higher octane fuel, reduce the ignition advance the next time the hood was open or lift your foot now till it stops pinging. My old Corvette can be driven on 87 if I lift my foot slightly and avoid teaching punks in Civics a lesson. Otherwise, 91.

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.

 

The difference, in my experience with another vehicle, was the check engine light came on with lower octane, and went off when I switched back. Sorry to be technical on you guys.

 

Even more interesting. Thank you again! Precision in terms is extremely important when trying to learn new things. As opposed to Humpty Dumpty's statement of "When I use a work, it means precisely what I want it to mean, nothing more and nothing less."

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.

 

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.

 

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

 

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.