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07-02-2013, 11:02 PM #1
What Is The In Cylinder IAT Drop With e85?
I justspent the last hour and a half searching high and low for a concrete answer tothis and I’m pretty surprised, I came up with nothing that makes me all warmand fuzzy.
I’mgetting closer and closer to jumping on the e85 bandwagon, but there is a pieceof the puzzle that I would like an answer too. And that is how much does e85lower your IAT’s?
The wayour IAT sensors are set up we can’t get a true reading of how much e85 dropsour IAT’s. Our IAT sensors are before where the e85 is injected, so they don’tread that temp reduction.
I’m aboutto jump on the e85 thing for all of its advantages. But the number oneadvantage that has me sold is the reduction in IAT’s and my ability to raisethe threshold where the ECU starts pulling timing. For example:
Right nowmy blue car starts pulling timing in my 93 tune at 136deg IAT, which doesn’ttake long to get too, especially when it is hot out. But, lets say that e85reduces IAT’s by 100deg (I think it’s higher though). If that were the case Icould set the threshold where the ECU starts pulling timing at 236deg and havethe same safety margin I have now because in theory a 236deg IAT with e85 addedtoo it is 136deg. And therefore safe.
Does thatlogic track?
Of coursethere are all the other advantages to running e85. More timing, more boost andtherefore more power. Which I will be more than happy to take advantage of. Butwhat I really want is for the car to make the same power heat soaked on a 90degday as it does in a controlled environment like the dyno cell.
What I amlooking for is having all of my power, all of the time.
But toset the tune up to do this I need to know how much the e85 drops the IAT’safter the IAT sensor so the “correction factor” can be built into the tune.
Anyonehave this data? I google’d my tail off and only came up with half answers. Someof these “half answers” are below with links to the source material.
Thanksfor your help!
A paperwritten by a MIT student in 2010.
The knocklimit for e85 is shown as being at a IAT 110deg C (230deg F) higher than gas.
Section6.1.2Peak Cylinder Pressure
Maybesomeone smarter than me can figure this worksheet out. I’m getting a IAT dropof 253deg F. That seems high, but not far off the results from the firstreference.
FastForward Superchargers Forum
Another fact is that the latent heat of E85 in thecorrect AF ratio compared to gasoline is four times as great. This means fourtimes the temperature drop. Since gasoline at a 12:1 AF ratio will drop the airtemp about 50 deg F, this means that E85 at the corresponding lambda for E85, would drop the air temp about 200 deg... or an additional 150 deg F tempdrop. FWIW, that is about as good as an Air/Air IC running 15psi of boost withthe MP62...
07-03-2013, 01:48 PM #2
The below came from black2003cobra in another thread where I asked a similar question. It doesn't completely answer your question, but you get a ballpark idea...ΔT just from evaporation of pure methanol, pure ethanol, and typical gasoline at an equivalence ratio of 1.25 below.
Methanol - 212 °C, 382 °F
Ethanol - 117 °C, 210 °F
Gasoline - 30 °C, 54 °F
07-03-2013, 04:37 PM #3
Do you have a link to were that came from. With no context I'm lost.
07-03-2013, 05:10 PM #4
What the link is saying is that with an equivalence ratio of 1.25 (which is around 11.7 AFR on gasoline) that there is an intake air temp drop of 54 degrees F using 100% gasoline. On 100% ethanol, the temp drop would be 210 degrees F.
07-03-2013, 05:29 PM #5
e85 would have a temp drop of about 178 deg F (85% of ethanol).
Subtract the temp drop of gas from e85 and you get a drop of 124 deg F. And that is pretty close to the data provided by Fast Forward Superchargers.
Lets just say for safety's sake you only built 100 deg of additional "e85" IAT cooling in (opposed to 124-150deg) to your timing threshold, that would give you a 230 deg threshold, which is a LOT! I'd be happy with 200deg!
07-04-2013, 10:52 AM #6
07-04-2013, 03:27 PM #7
- Join Date
- Jul 2006
Has anybody seen exhaust temperature changes with e85? I would think you could actually see measurable data there. Since your IAT sensors cant see exactly what the e85 is doing inside the runner/combustion chamber.
07-04-2013, 10:05 PM #8
- Join Date
- Jul 2009
You can research this til youre blue in the face.
Bottom line? E85 works and make a whole lot more power.
The only drawback is reduced MPG.
07-05-2013, 12:05 PM #9
- Join Date
- Jul 2006
07-05-2013, 12:34 PM #10
07-28-2013, 06:12 PM #11
Sorry I didn’t see this thread earlier.
DOD – It is very straightforward. The energy required to evaporate the fuel is pulled out of the air (as heat), which in turn, reduces its temperature. It is easy to show that by assuming an isobaric process and constant latent heat of vaporization (Lv), that the drop in air temperature (ΔT) from the evaporation of the fuel is given by the simple expression,
ΔT = (Lv/cp,a)/AFR
where cp,a ~1 kJ/kg.°C is the constant-pressure specific heat of air, and AFR is, as you know, the air-to-fuel ratio. This is how I determined the numbers I gave to Eric B.
For E85, I calculate Lv = ~770 kJ/kg and AFRs = 9.8. (AFRs = stoich air-to-fuel ratio). So for an equivalence ratio of 1.25, (equiv ratio = 1/lambda), the change in charge temp would be,
ΔT = 770/(9.8/1.25) = 98.2 °C
To convert to a change in temperature in °F, multiply by 1.8, (but don’t add 32!), so 178 °F, which is what you got.
In a DI engine, all that temp drop will occur within the cylinder. In a port injected engine, however, the fuel pools up behind the intake valve, where it will start to evaporate and cool the air within the intake manifold, which is where your IAT2 sensor is located. But since it does not all evaporate there, your computer won’t “see” the full effect. Most of the evaporation will be within the cylinder, in fact. Additionally, this air charge cooling is somewhat mitigated by the fuel coming in contact with various metal surfaces, which is shown/discussed in the MIT paper you referenced. (Nice paper, by the way. As an aside, I would direct people to Table 5.1 on p. 30, which compares energy content of the fuels. It clearly shows that ethanol does not contain more energy than regular gasoline.)
So yes, the charge cooling effect of alcohol fuels is quite significant, and greatly helps reduce the risk of detonation. (Its energy balance, etc., are another matter.)
gt347mustang - Good question. I would certainly expect so, since the drop in temperature should be reflected throughout the cycle. It would be nice to see some data! Oldbones saw this with methanol injection, although I don't recall the numbers or other details. It's over in the Terminator section somewhere.
07-29-2013, 11:45 PM #12
the IAT's are unaffected by using E85. Fuel doesnt have enough time to puddle and evaporate while the engine is running. And even if it did it wouldnt have enough time to reduce the intake air temp before the air and fuel mix is sucked into the chambers. the cooling effect comes from a lower combustion temperature. would be more informative to look at the exhaust gas temperatures
07-30-2013, 09:48 PM #13
There actually is some amount of cooling of the air within the intake, and it is measurable. Eric B. can give you some numbers. Most of the fuel is evaporated before combustion starts, in fact. Modeling shows that peak cylinder temperature is lower with E85.
08-01-2013, 09:32 AM #14
Is this 178deg of cooling in addition to how much gas cools the incoming air charge. Or does lets say gas (I’m guessing a number here) cool the IAT 50deg so when switching to e85 you get a net cooling effect of 128deg?
Right now I have the ECU pulling timing at 136deg. That isn’t going to cut it for the standing mile stuff I am setting up for though. The runs are way too long to keep the IAT’s under 136deg without the use of meth, ice chest, nitrous, etc. Which are all things I don’t want to use.
I was thinking that since the e85 lowered the actual intake air charge (post IAT sensor) I could build a correction factor into when the ECU starts pulling timing. I was thinking of setting up the ECU to start pulling timing at 200deg which should still give me a good size safety margin.
Assuming that e85 cools the IAT’s 178deg in addition to gas:
Set the ECU to pull timing at 200deg which would only be 64deg “into” the cooling effect offered by the e85. Should still be very, very, very safe (leaves 114deg of cooling on the table).
But if gas cools the IAT’s 75deg all by itself that leaves a safety margin of just 39deg (just an imaginary example). That may be a little close.
08-01-2013, 09:38 AM #15
A friend of mine is running a nearly identical setup to what I was last year, a 2.6L KB blower spinning 18,000rpm. My car, which has the most effective intercooler system of any S197 on the planet (I’m not kidding when I say this) would run at 145-150deg IAT on surface streets under normal driving conditions with ambient temps in the 75-85deg range.
My friends car, on e85 under the same conditions has IAT’s in the 115-120deg range. You can even touch his intake manifold and feel the difference with your hand.
There is absolutely no doubt in my mind that the e85 in the intake runners is sucking heat out of the manifold/cylinder heads.
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