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Originally Posted by hotrod
Part 3
What is your test history to date (6/2005) with E85 ?
I just tallied up my usage over the last 2 years, (the first year I was very cautious and did not use very much). I've put about 500 gallons of E85 and 100% fuel grade ethanol through the cars tank --- that's some where around 40 fill ups, or around 9,000 miles or so on high ethanol (ie greater than 10%) blend fuels.
I am intentionally running the E85 with no special fuel system modifications. In a few years or when ever problems crop up, I'll pull things apart and see what has happened. So far I have absolutely no evidence of ANY kind of degradation on my 2002 WRX. The only non-stock component I'm running in the fuel system at the current time is a walbro 255 L/hr pump, so I cannot absolutely tell you how the stock pump likes the stuff.
Why is E85 a better fuel ?
Ethanol is a very turbo friendly fuel for many reasons.
1. It has a much higher evaporative cooling power than gasoline so the intake air charge in the cylinder is significantly cooler that it is with a comparable mixture of gasoline --- that means higher VE.
2. Its octane as blended in E85 is about 100, its blending octane when added to gasoline is rated at 118, so it is a very cost effective octane booster.
3. Ethanol burns faster than gasoline but has a slightly longer ignition delay during the slow burn phase of combustion so the engine does not do as much negative work fighting rising cylinder pressures due to large ignition advances. The total ignition advance for E85 is almost identical to the ideal advance for gasoline so it does not cause the ECU problems when you mix them.
4. At proper mixture you actually are releasing more energy in the cylinder due to the higher quantity of fuel you can burn. ( Ethanol can burn effeciently at much richer mixtures than gasoline can) That means about a 5% increase in energy release all by itself.
5. Peak combustion pressures are actually lower for ethanol than for gasoline but the cylinder pressures stay higher longer, so you have more (longer) crank angle that is usable by the engine. This lower peak cylinder pressure also helps with detonaton control.
6. It will, at proper mixtures lower EGT's by around 200 deg F, but due to the higher quantity of exhaust gas products it produces you do not lose any spool up (in fact I would wager spool up is better).
7. It is much cheaper ( if you go to a station that is not trying to price gouge).
How much will my miles per gallon of fuel drop with E85?
The only negative to E85 is that it gives a lower fuel milage on a gallon for gallon basis to gasoline. The actual difference in energy content between straight gasoline and E85 is about 27%.
The drop in milage is not as significant as you would think based on that difference due to the higher effeciency of the ethanol as a high performance fuel. This winter I was getting about 92% of the fuel milage I would get on gasoline on 100% E85.
The lower milage is not really a big deal, ethanol has lower energy per gallon but your reduction in milage is not nearly as large as that difference would imply. Due to the higher torque,you use slightly smaller throttle openings to get the same level of preformance, and due to the greater quantity of combustion products (more moles of gas) per lb of fuel the engine effeciency actually goes up slightly. My long term fuel milage average is in the vicinity of 24.5 mpg, with pump gas, and with 75% ethanol blend, I was getting just over 23 mpg driven normally. Recently I have been flogging the crap out of the car to sort out new boost controller settings for my new turbo (went from a 13T to a 16G). Given I now have a larger turbo and all that is hardly a noticable fuel milage drop. I have gotten around 300 -345 miles/tank on straight gasoline when I was bone stock, and I expect to get from 280 - 310 miles per tank on the E-85 based on my notes of fuel consumption and accounting for the unusually hard driving I have been doing the last week working on the boost controller settings.
In very cold weather <20deg F I don't go above about 90% E85 to improve cold starting and speed up engine warm up a bit. Other than that the car loves E85 and so does my wallet ---- $1.89/gallon (6/2005) for 100 octane fuel is hard to argue with. It only drops my fuel milage a small amount. I get 93.76% of my gasoline milage when driving conservatively in my WRX with the larger injectors and high ethanol fuel blends.
will a wide band O2 sensor accurately read fuel air mixtures with E85 blends ?
To get an accurate AFR reading you need to switch the meter to Lambda or equivalence ratio setting rather than AFR. Most O2 sensors assume you are running gasoline and will report a stoichimetric mixture as 14.7:1 which is the proper value for gasoline. E85 has a Stoichemetric mixture of between 9.7 - 10:1 and a max power mixture of about 6.98-8.5:1 or so, where with gasoline it is 12.5:1-to 13.1.
If you must use an O2 sensor that only reports gasoline AFR information simply divide the numbers it reports by 1.47 - 1.50.
On gasoline, my ECU is supposed to give a mixture of 11.5:1 and on 100% E85 the dyno's wide band reported an AFR of 11.6:1. That means that my true AFR on the E85 was about 7.8:1 which is right in the middle of max power mixtures for E85.
Larry
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