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Old 05-28-2012, 08:51 AM   #42
arghx7
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I went ahead and posted this on EvolutionM in their two big threads on this issue.

I am an engineer, and I have been following industry developments in alternative fuels. As I mentioned in an above post, GM had a production port injected turbo flex fuel engine all the way back in 2007. It was a Saab variant of the Ecotec engine family. Saab did extensive testing on a lot of boosted E85/Flex fuel issues and published some work on it. See Bergstrom, "The New ECOTEC Turbo BioPower Engine from GM Powertrain," 2007 and Bergstrom, "Alcohol Based Combustion Engines - Challenges and Opportunities," 2007. Deposit formation is one of the dirty little secrets of E85; another is pre-ignition.

GM found the exact deposit problems many of you are experiencing. I have read a lot of different ideas on here about the nature of the problem and I have read a lot of speculation about solutions for it. Here is what we know for sure about the deposit issue, based on GM's internal research.

Chemical Origins of the Deposits

The deposits primarily consist of "Poly Iso Butylene," or PIB, a cleaning additive in the gasoline portion of commercial E85 blends. As far as we know, the ethanol itself doesn't directly cause this type of problem with injector and valve deposits. This PIB additive was never designed for use in high ethanol concentrations.

PIB is designed to soften engine deposits, but below a certain concentration (by total fuel volume) it is actually counter-productive. What happens is that with insufficient PIB by volume, the normal valve deposits don't soften. The PIB actually combines with these normally occurring deposits and makes build up worse.

Running PIB-free E85 is basically impossible in a practical sense. GM engineers ordered special batches of PIB-free E85, but in the real world the E85 still becomes contaminated with PIB because the entire fuel refining and transport infrastructure has traces of it. Still, with this very low PIB concentration E85 deposits can still occur at similar rates.

A lot of people on here have speculated something along these lines.

Effect of Drive Cycle

Deposit formation is highly dependent on vehicle use and overall drive cycle. This whole issues is complicated, but aside from the makeup of the actual E85 blend, drive cycle is the #1 factor in these deposits.


Bergstrom, "The New ECOTEC Turbo BioPower Engine from GM Powertrain," 2007, Internationales Wiener Motorensymposium 2007, p. 29

On the left is a multi-hole type (not pintle type) fuel injector after 15,000 km running a GM in-house designed drive cycle to simulate major stop-and-go city driving. On the right is the same type of injector after 60,000km in a high-speed (mostly highway) drive cycle. Both engines were running the same commercial E85 blend in Sweden, consisting of 95 RON fuel and denatured ethanol.

Drive cycle variations may not explain absolutely everything but it is a reasonable hypothesis for why two vehicles running the same E85 blend can have such variability. This can also partly explain why somebody doing a lot of highway driving (rural driver or suburban commuter) who always runs E85 may never experience noticeable deposits.

Using Fuel additives and Normal Gasoline blends

There are a lot of fuel additive blends out there and they change all the time so I can't speak for all of the various formulations. What we do know based on GM's research is that PolyEther Amine or "PEA" , which can/used to be found in Techron products, cleans valve deposits but does not clean injectors with this problem. In fact, too much of fuel system cleaner could make the problem worse.



So how do we clean up the deposits if an engine is prone to them for whatever reason? Put "normal" gasoline blends in the tank and it will go away within 1 tank. You don't even need to pull the injectors.



Most of you already knew that. It's not really news; it just confirms with reliable sources what has been widely understood.

Conclusion

So yes, I didn't have any earth-shattering solutions to present, but I did clear up some of the mechanisms for this deposit formation. The deposits are caused by the gasoline portion of E85. The two biggest factors in deposit formation are the additive mix in the fuel and the way you drive the vehicle. Fuel system cleaner products are innocuous at best, counter-productive at worst. The type of injector or fuel system you run might matter some but they are not part of the mechanism of deposit formation.

So if you figure out that your engine is prone to these deposits, be mindful of stop-and-go traffic and put gasoline in your engine sometimes to clean it out.

Hope that helps.
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Last edited by arghx7; 05-28-2012 at 11:49 AM.
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