Running E-15 (ethanol)

[InTruckDesign]

Just recently I have been noticing some pinging/detonation in the 4,000-5,000rpm range. The ecm tune has been unchanged for several months. I've been pulling my hair out trying to figure this out and for some reason decided to look at the % of ethanol in the fuel I am purchasing...I have found that the stations around me are all selling E-15 rather than the E-10 we have had here for years. My question is, what if anything needs/should be changed in a tune when the fuel changes in ethanol content by 5%? Thanks.

[WeathermanShawn]

Not sure of the specifics of your OS, but here was a thread I recently did about E-10 and what to change in a Tune: http://forum.efilive.com/showthread.php?16072-B3601-Ethanol-Fuel-Testing-Experiment&highlight=ethanol+gas+testing

Good Luck..

[samgm2]

A higher concentration of Ethanol will decrease your detonation problems NOT increase them.

Look somewhere else for the cause of the problem.

In any case, here is the formula for determining the stoichiometry of your burn.

For Gasoline:

C8H18 + 12.5 O2 -> 8 CO2 + 9 H2O

There are 3.74 Nitrogen Molecules for every O2 molecule in our Atmosphere. So the reaction for gasoline becomes:

C8H18 + 59.25 Air -> 8 CO2 + 9 H2O + 46.75 N2 (I am assuming n-Octane here - gasoline is a mixture of hundreds of molecules with an average carbon chain distribution centered around 8).

Stoichiometry by weight (what your vehicle computer requires since everything is based on mass: MAF, pressure across an orifice, etc)

1 Mole of gasoline: 8 * 12 + 18 = 114 grams of gasoline
59.25 moles of Air: 59.25 * 28.97 grams mole = 1716 grams of air

Dividing the two: we get about 15:1 A slight increase in the number of double bonds and aromatics will result in the stoich ratio being slightly lower (so the 14.7 in the literature is about right)

For Ethanol:

C2H6O + 3O2 -> 2 CO2 + 3 H2O

Once again, compensating for the fact that our atmosphere contains Nitrogen, we get:

C2H6O + 14.22 Air -> 2 CO2 + 3 H2O + 11.22 N2

Atomic mass of Methanol: 2 * 12 g / moles of carbon + 6 * 1 g / mole of hydrogen + 16 g / mole of Oxygen = 46 grams of ethanol.

Atomic mass of 19 air molecules = 14.22 * 29 grams / mole of Air = 412.4 grams of air

Stoich Ratio for ethanol: 412.4 / 46 = 8.96


If we have a 10% mixture of ethanol and 90% Gasoline, the stoich is as follows:

0.1 * 8.96 + 0.9 * 14.7 = 14.13

If we have a 15% mixture of ethanol and 85% gasoline, the stoch is as follows:

0.15 * 8.96 + 0.85 * 14.7 = 13.83

As you can see, it doesn't amount to a hill of beans of difference insomuch as it leans out your mixture and it pays back in a significant increase in octane which should allow to increase timing.

If you had adjusted your VE tables for the 10% mixture, then the change in air is 14.13 / 13.83 = 1.021 which is only a change of 2%.

If not, then you would be about 6% lean with the 0.15 mixture over pure gasoline tune. Still not very much but who knows maybe your timing is very aggressive.

Sam
Chemical Engineer/Research Scientist


Just recently I have been noticing some pinging/detonation in the 4,000-5,000rpm range. The ecm tune has been unchanged for several months. I've been pulling my hair out trying to figure this out and for some reason decided to look at the % of ethanol in the fuel I am purchasing...I have found that the stations around me are all selling E-15 rather than the E-10 we have had here for years. My question is, what if anything needs/should be changed in a tune when the fuel changes in ethanol content by 5%? Thanks.

[joecar]

But when it leans out you don't make as much torque... if you keep it from leaning out and you increase timing then you make even more torque.

[samgm2]

Anything that slows the reaction down will result in a more reversible reaction and thus increase power. That said, the use of a rich mixture to slow the reaction down will result in a drop of efficiency (You will need more fuel than you should to get that added torque and power). Adding ethanol to the fuel mixture slows the reaction down AND increases efficiency because Ethanol has slower kinetics. The use of higher octane fuels such as iso-octane (with more double bonds) or toluene (aromatic rings) that are composed of tougher molecules more resistant to rapid reaction also slow kinetics but without decreasing efficiency. There are several reasons that ethanol has lower kinetics. Primarily, it contains a non-reactive oxygen (this means that there are several molecular trajectory angles that will not result in a reaction taking place - Any O2 Molecule that hits the Oxygen end of the ethanol molecule will not result in a reaction during that collision event). A higher heat of vaporization for ethanol will result in a greater drop in combustion temperature leading to lower reaction kinetics (Arrhenius Equation).

In all cases, with a proper tune, E-85 results in increased power because of the more reversible reaction kinetics. E-15 is a bit low in ethanol to realize dramatic power increases but if he tunes his vehicle for the new fuel mixture, he can ultimately realize more power.

I will be releasing some spark tables for E-85 that are meticulously generated on our dyno in the near future (optimizing power and efficiency). These will be for e-85. I will also release a study of seals for several fuel alternatives over the next couple of months.


But when it leans out you don't make as much torque... if you keep it from leaning out and you increase timing then you make even more torque.

[joecar]

Some people have found on the dyno that:
- making peak torque rich (lambda 0.86) give the highest peak torque,
- leaning out a little on the way to peak power (lambda 0.88) gives the highest peak power;
their quarter mile ET/TS support this;
would this still be relevant to alcohol content fuel...?

[joecar]

What about the effect of using extra fuel to cool the combustion chamber and catalytic converter (what GM does)...?

Or does alcohol already burn cool...?

[joecar]

BTW: interesting topic... I'm full of questions... :)

[eficalibrator]

...As you can see, it doesn't amount to a hill of beans of difference insomuch as it leans out your mixture and it pays back in a significant increase in octane which should allow to increase timing.
Except you're forgetting that they re-normalize the blend to still only be the same (91 or 93) octane, even with the increase in alcohol fraction. If they add more high octane ethanol, it lets them blend it with (cheaper) lower grade gasoline and still deliver a final mix that is on target (91 or 93 again). You don't magically get 95 R+M/2 out of the deal.

Anything that slows the reaction down will result in a more reversible reaction and thus increase power. ...
Unless that longer, slower reaction also results in an increase of compression work prior to TDC. You need to account for more than just the chemistry here. The pyrolysis is only one part of the total picture. It's the net difference in pressure integrals (with respect to volume) that delivers useful positive work to the crankshaft.

I've had lots of cases where a faster reaction (due to improved charge motion) allowed me to run LESS ignition advance along with a more rapid rise of pressure and still have a good CA50 number and location of peak pressure relative to TDC. The result is more net torque because I've freed up losses on the compression stroke, yet still delivered good pressure on the expansion stroke. This is a case of getting closer to Otto Cycle. (Constant volume heat addition)

Bottom line: "91 octane" is still "91 octane" regardless of the mix. Burn temps may change slightly and stoichiometric ratio will certainly change, so there is still room for calibration changes. They're usually just more fueling based than spark and I don't expect more power as a result.

Oh, and fuel economy will drop slightly as ethanol content increases...

[samgm2]

Possibly, but it is not definitive and is likely unnecessary. By altering lambda you are changing the concentration of the fuel with respect to the oxidizer (air). For a particular fuel / oxidizer combination, there are two variables that affect reaction kinetics (the rate at which a reaction will proceed). The first is concentration, the second is temperature (where temperature is an expression of molecular motion (vibratory, rotational or intermolecular)).

When you alter lambda, you are affecting concentration. By increasing the ratio of fuel to oxidizer, you are increasing the likelihood of a gasoline molecule colliding with another gasoline molecule (resulting in a non reactive collision - a slower reaction). The result of this DELAY in reaction will play a role in the power generated BTDC and the power generated ATDC.

There is a lot going on here and the assertion that simply decreasing lambda always results in greater torque, is likely inaccurate for all conditions.

A better statement would be that given the timing table used in the particular test that was performed, a lower lambda resulted in more torque. A great deal more testing and characterization would be required to make the assertion that this is always the case (and I suspect that it is not). Still, the general statement that a slower reaction is more efficient for power conversion that a faster one is accurate.

While it may well be that this will be true for gasoline, it may not be true for alcohol and even if it is, the realization of more recovered useful work for non-useful heat energy may be negligible.

In any case, I will be able to answer that definitively during the next few weeks.


Some people have found on the dyno that:
- making peak torque rich (lambda 0.86) give the highest peak torque,
- leaning out a little on the way to peak power (lambda 0.88) gives the highest peak power;
their quarter mile ET/TS support this;
would this still be relevant to alcohol content fuel...?

[Chevy366]

Subscribed .
Interesting thread , my months of tuning with E-fuels 3 years ago might be justified .
I do agree with samgm2 .

[GMPX]

Oh, and fuel economy will drop slightly as ethanol content increases...
Talking metric here, I see an increase of about 3 Litres per 100KM on a 3.0L engine running E85.

[samgm2]

Please private email me regarding this. I would like to know more about your experiences with E-85 and flex fuel.



Subscribed .
Interesting thread , my months of tuning with E-fuels 3 years ago might be justified .
I do agree with samgm2 .

[InTruckDesign]

Wow, lots of good info here, alot is over my head, but I am learning. I did notice a small decrease in mpg's, generally 1-1.5mpg over the course of 26 gallons. I am still verifying that there is no mechanical issue.