Timing on ethanol blends will not change very much. MBT timing for both gasoline and E85 are very nearly the same at light to moderate engine loads. At high engine load the E85 will want just slightly more advance. The big difference will be fuel/air mixture. The E85 will give improved torque with much richer mixtures than gasoline. Both gasoline and E85 will give best thermal effeciency at about 15% rich of stoich, so the equivalent of 12.78:1 on gasoline would be about 8.5:1 on E85, but E85 will continue to give better torque numbers up to about +40% rich of stoich or 7:1 mixtures, so on a utec you would want to richen up your WOT high load cells and add a tweak of timing to get the most out of E85 from what I've read.
Just passing on what I've found in the various sources. Logically you are correct, but one source says simply that MBT timing is the same for E85 and gasoline, and another report says at low loads the E85 and gasoline like the same MBT timing but at high loads MBT timing for the E85 is slightly more advance.
I suspect this is due to them not running ideal max power mixtures but cannot confirm it. Burn speed for E85 changes quite a bit with mixture, so if they were just a little bit lean or rich of ideal the burn rate would be lower.
Lots and lots of variables not well covered in some of the sources and in general they are focusing on emissions issues not max power torque so that would incline them to use less than best power timing advance. In a couple of the reports they also had limited control authority over timing and may not have explored the extremes very thoroughly.
Just about a year ago (2003), I was finding conflicting information on alcohol fuel burn speeds and contacted The National Renewable Energy Lab here in Denver, they did a search and could only find a couple of references on it, one that showed ethanol fuels burn faster, so the literature is not very rich in data on the subject. Most reports are not entirely applicable to our needs like tests on lawnmower engines and alcohol fuels have some significant limitations
Still digging for info but that is my best information at the present time.
The report that mentioned the slight increased advance requirement on heavy load E85 fuels was :
"Final Report Control of Exhaust Emissions from Small Engines Using E-10 and E-85 Fuels"
http://www.michigan.gov/cis/0,1607,7-15 ... --,00.html
http://www.michigan.gov/documents/CIS_E ... 7915_7.pdf
On page 12 it says :
"Tests were conducted to assess the impact of MBT ignition timing on fuel economy and exhaust emissions. The spark timing was varied until the least advanced timing was achieved for the maximum torque for a given setting of the engine throttle. The A/F ratio was adjusted to achieve near stoichiometric operation. ... " The MBT timing for E-85 fuel was a few crank angle degrees advances compared to E-0 fuel when the engine was delivering high loads, typically 100 - 75%. Not much difference was observed at lower engine loads."
I'm assuming that this explains the timing change as they were using what would be closed loop fuel mixtures on the WRX. So in load cells that would continue to use closed loop fueling you would want to have slightly more ignition timing than you would with gasoline. In the case of WOT open loop fueling where your running a max power rich fuel mixture, I very strongly suspect the fuel burn speed would be noticably faster, and you would use less ignition advance than on gasoline and reap the benefit of less negative work on the late stages of the compression / early period of combustion prior to TDC.
In a power point presentation presented by the EPA at the SAE Government and Industry Meeting in Washington D.C. on May 13, 2003 titled:
"Ethanol-Gasoline Blends: Fuel Economy and Emissions Benefits"
http://www.epa.gov/otaq/presentations/g ... 051303.pdf
On page 9 of the presentation is a nice chart comparing laminar burn speeds of gasoline and Ethanol.
It shows the following burn speeds:
Mixture fuel/air---- 1:1 ------------ 1.1:1
Gasoline --------- 26 cm/sec ------- 30 cm/sec (max about 31 cm/sec)
Ethanol ---------- 41 cm/sec ------- 45 cm/sec (max value)
Clearly at +10% - +15% rich mixtures where ethanol shows max thermal effeciency it burns significantly faster than gasoline. Which could be quite important to a very over square bore engine like ours!!
what is the ideal fuel air mixture for E85
If you are tuning with a wideband O2 sensor you will want to switch it to Lamda mode to get valid fuel air mixtures with blended fuels.
Here are some comparisions of stoichmetric fuel mixtures for different fuel blends:
======== stoichmetric AFR ===== max power rich AFR
Gasoline ---------- 14.7:1 -------------------12.5
100% E-85 ------- 9.73-9.8:1 ------------- ~ 9:1 - 8:1
100% fuel ethanol - 9:1 ------------------- ~ 7.2:1
One source specifies that the proper fuel tune (stoich) for a VW Golf running 22% ethanol was 12.7:1 (this reference was probably from the Brazil tests)
Ethanol reaches max torque at richer mixtures than gasoline will.
Using a 99% ethanol mixture MEP increases with mixtures up to 40% excess fuel where with gasoline MEP is reached near 20% excess fuel. Over all thermal effeciency for both gasoline and ethanol is reached near 15% excess fuel.
E85 burns faster than gasoline at best mixtures so it is an inherently more effecient fuel. It also produces more exhaust gas for a give weight of fuel air mix giving higher average cylinder pressures inspite of lower EGT's. With streight E85 in a properly tuned car its good for about +5% power / torque increase. I suspect on a turbocharged car the benefit is larger.
My source lists stoich for E85 as 9.8:1 ( "Burn rates and emissions from ethanol gasoline blends" )
http://www.engin.umd.umich.edu/research ... 04.doc.pdf
Here's a little reference chart I whipped up when I was working out my dyno numbers.
Code:
Fuel AFRst FARst Equivalence Lambda
---- ----- ----- Ratio -----
=======================--====================================
Gasoline stoich 14.7 0.068 1 1
Gasoline Max power rich 12.5 0.08 1.176 0.8503
Gasoline Max power lean 13.23 0.0755 1.111 0.900
=======================--====================================
E85 stoich 9.765 0.01235 1 1
E85 Max power rich 6.975 0.1434 1.40 0.7143
E85 Max power lean 8.4687 0.118 1.153 0.8673
=======================--====================================
E100 stoich 9.0 0.111 1 1
E100 Max power rich 6.429 0.155 1.4 0.714
E100 Max power lean 7.8 0.128 1.15 0.870
=======================--====================================
Estimating fuel required on E85
Fuel injector, carburetor jet sizing, and fuel pump requirements can be estimated by using the following rules of thumb as a starting point. For a naturally aspirated (NA) engine (carbureted) on gasoline most need a brake specific fuel consumption (BSFC) for gasoline of 0.50 lb/(hp·h). On E85 the same NA engine would need a BSFC of about 0.65 lb/(hp·h).
Turbocharged engines typically need BSFC fueling of about 0.60 lb/(hp·h), a reasonable first guess for fueling required on E85 would be 0.77 lb/(hp·h).
For a simple conversion to replace gasoline with E85 take the current "flywheel horsepower" as a reference point. With E85, power should increase by about 5%, so the estimated E85 fueling would be:
(BHPgasoline x 1.05) x BSFCe85 = Estimated E85 fuel requirements.
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 and 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 13G 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.
Copied from Larry aka Hotrod Library article on awdpirates.net
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