Part 3
Where can I buy E85?
Distribution is currently a problem, it is most available in the mid western states, but there is a concerted effort to get an ethanol fueling infrastructure built, it just takes time, and recognition by the gasoline vendors that there is a market. Marathon oil has already added E85 to their formal product line so things are moving in that direction.
Current high fuel prices can only help that process, as will lots of people calling up gas stations and asking them when they plan on pumping E85 for FFV's.
E85 already contains inhibitors and such to minimize corrosion, and most of the problems with ethanol usage were solved 20 years ago when most of the country moved to ethanol addition to gasoline following the oil crisis in 1973 and high oil prices that continued up until 1981.
Where can I buy E85
For information on distribution points check out:
http://www.e85fuel.com/
How about fuel mixtures for E85 what is needed ?
It basically takes about a +30% increase in fuel flow to get the same equivalent mixture with E85 that you had with gasoline.
For example an adjustable fuel pressure regulator can increase your effective injector flow to partially compensate for the fuel changes.
As mentioned above, lean is still a bad thing, and with alcohol fuels due to the higher power levels a serious leanout is more lethal. With conservative mixtures alcohol actually burns so cool that on E85 FFV there is some concern about getting the cat to light off.
If you sneak up on a fuel blend slowly you should be just fine. I would venture to say for the near stock folks, up to 30% is probably safe as long as you give the ECU a few miles to make the major part of the fuel trim accommodation before you start beating on the car. You'll know when the ECU starts to get happy as the mid-range torque is noticeably better.
I also strongly suspect that a well tuned car with no cats can probably pass the emissions sniff test on high E85 blends.
How does ignition timing change on E85 ?
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 efficiency 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.
Quote:
Are you sure you don't mean that E85 will allow more advance?
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.
what data is available on combustion speed for E85?
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...0064--,00.html
http://www.michigan.gov/documents/CI...E-_87915_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 noticeably 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/presentation...mjb-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 efficiency 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. If you can only get gasoline AFR's, simply divide the gasoline AFR's by 1.5 to get the true AFR for 100% E85. If running a partial mixture you can make proportional changes based on the percentage of E85 in the mix.
Here are some comparisons 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 efficiency 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 efficient fuel. It also produces more exhaust gas for a give weight of fuel air mix giving higher average cylinder pressures in-spite of lower EGT's. With straight 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/resea...5-2004.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 0.10235 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
=======================--====================================
