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1outlaw

Excellent Paper on High Compression/ High Ethanol Engines

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Eric (an superb E85 blowthru carb builder) posted this excellent research paper on another website. This paper was just released this Spring as an SAE paper- it details ethanol vs gas in various engine compression, valve timing, and other situations. EO regualr, EO high octane, E10, E50, and E85 blends were studied. Kinda dry and hard to follow unless you are an engineer. I found it very interesting ;)

 

http://delphi.com/pdf/techpapers/2010-01-0619.pdf

 

Clearly shows efficiency improvements are there for high compression E50-E85 engines-- as we all know already-- and has also been documented in numerous other studies like EPA did.

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Study keeps referring to need for backward compatibility with RG but with the number of new stations opening up this should not be a concern looking into the future.  Maybe DOE imposed this investigative requirement on them.  Nice analysis.  I learned a few more things.

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Thanks for that link. The paper started off what we all know....ethanol production is increasing within U.S., but older auto technology didn't capitalize on the fuels strength. Merely concerned with capability to burn the fuel. This is changing as supplies of ethanol blended fuel becomes more popular.

 

So, appears a 20% ethanol mpg penalty could be reclaimed with optimized operation conditions within modern vehicles. EPA emission requirement always in play and may erode improvements of mpg of either or both gasoline and ethanol fuels. 

 

It's both a blessing and curse to be blended with petrol. True easy access to fuel supply and ethanol makes petrol perform better at lower cost, yet the connection minimizes ethanols stand alone (or mostly alone) benefits with dedicated engine technology. Petrol can easily exploit and impugn ethanol and herd everyone over to their expensive premium blends. Also, the ability of E10 enabling low cost blend stock for oxygenate blending (BOB).  Can you imagine if diesel fuel and unleaded would have started out with similar blend paths? Gasoline would have been rated an inferior fuel with 30% mileage penalty. 

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Interesting the rate of change of octane improvements decrease proportional with high ethanol blends. This is common sense, but we overlook that point. Meaning a little ethanol makes petrol look good. Also, that may be ethanols most value as a fuel to make petrol produce more. At least with limited production of ethanol. Better to improve the whole fuel supply. Did petrol claim that advantage with strategy of low cost blend stock? Meaning an unfair handicap to make ethanol look bad and pure petrol high test look better. My best guess.....while utilizing ethanol to make cheaper grades of petrol look better and to limit vapor rate of blend....ethanol gets no credit for saving the motorist money. In fact they get blamed for the entire mpg loss. Remember, if ethanol blends were rock solid reliable fuel through out nation, auto technology would exploit the better fuel for mpg improvements. In fact this may be happening already within the E10 blend. Yet appears petrol will not allow anyone of power or wealth to divulge that fact.  Automakers need to make nice with wealth.

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As we know the turbocharger is ethanol best friend. The SAE didn't complicate testing with such device. Hot exhaust is free energy, something a hot turbine is most efficient in reclaiming. Utilizing turbine power is costly, yet a real boost to mileage and power.  Mechanical compression is not near as efficient and suffers from friction. The dynamics of high pressure intake appears not to inflict as much friction penalty and greatly decrease pumping energy loss.

 

The turbo hybrid combined with electric and generator flex should be a real boost to ethanol and diesel engines. Ethanol has dense/heavier exhaust stream as compared to unleaded and result able to pull turbo efficiency up.  Now, this is the turbo flex not the engine. Meaning the turbo actually generates electricity per cruising speed.  Actually, would guess a DI water injector could double up on this advantage. Inject water late into combustion cycle after max chamber pressure.  That would be interesting test. This should be better than hydrous ethanol.

 

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The 2012 post on Ford Focus....appears that 2.0L engine may be utilizing much of what the SAE test improvements of high ethanol blended fuel.  The variable double overhead cam apparently utilized for Atkinson cycle and tricks to limit compression ratio. Compression as high as 12:1, that would mean the compression is variable per valve timing.

 

Notice the SAE tests on advanced timing improving the engine efficiency. They limited advanced timing to engine knock.  Ethanol's burn characteristics allow more advanced timing which will always result in highest max chamber pressure...a good thing.  Now, max efficiency a compromise of engine environment and desired results. Often the max hp guys are talking a different game as compared to max mpg results. Also, the extreme high hp environment with turbo's and running rich to produce hp and warrant some engine protection will chose to take timing another direction.  This is not of concern with consumer desires of high mpg, long engine life, and forgiving stable engine operation. These the engines automotive companies produce, a max value, reliable, engine of better mileage and performance to increase sales.  Thus they like to report mileage with unleaded and state the car can operate with E85.  This is why the foreign auto like diesel as they can magically have higher mpg vehicles.  Promoting auto sales with ethanol technology is good, yet reporting low mileage numbers is bad.  Anytime your ad has to explain why a good thing to get lower mileage sounds like an excuse.

 

The SAE test discussion of ethanol's ability to increase engine torque and opportunity to design a better transmission to maximize ethanol mileage.  Problem is auto's currently designed around need of unleaded fuel.  Modern engine technology is adaptive within real time operation conditions and operator demands that helps a bunch.  Maybe the transmission can have variable drive ratio to boot.

 

The tests report on exhaust temps where engine operation conditions upon high efficiency....exhaust temps were lower. Usually the case and the reason a diesel warm up takes longer....the engine is more efficient. Ethanol fuel exhaust contains more moles per volume or more dense and able to transfer more heat as result. Good for a turbo, but easier to overheat converter.  If ethanol engine is operating efficient no problem, if not a potential converter overheat condition.   

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Thirty percent often spec’d as efficiency loss due to friction and resulting heat. Modern engines utilizing more roller bearings improve this, but the sliding piston only receives solutions of low friction coating (2012 Ford Focus) or better piston rings offering slightly lower sliding friction. Sliding friction increases with speed. Not good for high rpm engines unless the stroke is short. That is the leverage arm of crank in short and would apply least velocity upon piston at high rpm. This is not good for efficiency, especially for ethanol that appears to support burn of combustion longer and burns more efficient with high compression. In other word ethanol doesn’t explode, but burns. This fuel characteristic is good for building torque and not so destructive to mechanical engine. But the long stroke engine must severely limit it’s rpm due to piston velocity. Its one place a diesel loses efficiency ground to unleaded engine as diesel requires long stroke engine with resulting higher piston sliding friction.

 

HCCI combustion boosts engine efficiency as the fuel burns simultaneously throughout chamber. Burn energy is quicker. Longer stroke engines not required to harvest energy. Firemen are trained upon this phenomenon when heat and fuel explode into flame all at once. If ethanol could enter into this zone, maximum chamber pressure would improve dramatically. Probably improving ethanol more than unleaded fuel as ethanol doesn’t achieve as high max chamber pressures when compared. R&D is focused on utilizing variable compression tricks and most promising very hot EGR gas that make HCCI combustion more controllable. Turbo charging, also, minimizes the need for longer stroke engines while improving pumping efficiencies. An expensive piece of optional equipment, but gaining in popularity.

 

Once again, that OPOC engine should shine bright as the friction is halved merely by eliminating intake and exhaust strokes. This engine is designed around turbo charging.  Also, since two pistons simultaneously produce compression ratio, only half the effective piston stroke required. Finally, since the engine achieves stiff and balanced mechanical forces, this makes it possible to result in an ultra smooth two piston engine. Note: per piston sliding area, bigger pistons generate more power with less friction waste per cubic inch. Just simple surface area to volume math. Also, complete combustion achieved upon ideal zones of combustion such as center region of burn. Metal surfaces are a bunch cooler and promote inefficient combustion. Bigger combustion volume, more ideal burning volume conditions. Two cylinders will always beat same size four cylinder engine of same size as far as efficiency. Removing cold cylinder head will do so likewise.

 

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