Calculate the cooling effect of E85
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Launching!
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From: Dayton, OH
Calculate the cooling effect of E85 I've searched and found general discussion but not found specifics.
How do you calculate the cooling effect of E85 in the cylinder? IAT is the temp before E85 is introduced, that is measured.
A long time ago I calculated the temperature increase of the air/fuel charge when it is compressed and the temperature for different compression ratios. Now I am looking to calculate the decrease in IAT if the fuel is E85.
Thanks!
How do you calculate the cooling effect of E85 in the cylinder? IAT is the temp before E85 is introduced, that is measured.
A long time ago I calculated the temperature increase of the air/fuel charge when it is compressed and the temperature for different compression ratios. Now I am looking to calculate the decrease in IAT if the fuel is E85.
Thanks!
I am not sure, but the only real way that makes sense, is EGT. I haven't leaned on anything hard enough to worry about it. I know there are others in here, with more experience in this particular situation.
TECH Addict
Joined: Oct 2016
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From: PDX-OR-USA
A thermocouple on the head will show it fairly quickly. On the car I was working on the machinist that did the heads drilled a CHT hole for a thermocouple in the head to get the sensor very close to the bore of the sparkplug hole. Sorry to say that car is long gone.. but that was how we did it..
On VW air cooled midgets they just use the sensor that replaces the spark plug washer.
On VW air cooled midgets they just use the sensor that replaces the spark plug washer.
Joined: Apr 2006
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From: Grand Rapids, Michigan
This is an academic paper, but it has a lot of useful info. See the last paragraph on page 6 into page 7:
https://www.nrel.gov/docs/fy15osti/63091.pdf
https://www.nrel.gov/docs/fy15osti/63091.pdf
It can be estimated using heat transfer theory, 3rd year mechanical engineering. It's been too long and my skills are too rusty to help you but if we keep bumping the thread then somebody will find this and help you with the math and necessary fluid properties. 
I’d say the simple short answer is… you can’t. Not without some serious equipment none of us have. Thermocouples spit out false information when saturated with fluid and are 100% useless.
If we make a lot of assumptions and some educated guesses you can semi-sort-of come up with a number based on power gained NA vs NA back to back dyno runs with a fuel switch only. With nothing more than 30% fuel added to the fuel map, It’s common to see 15-20% at the crank simply by switching to E85. More so if you were knock limited with timing prior.
Of course not all of the gains are from a cooler CC. Much of the gains are from quicker flame travel which leads to more cylinder pressure and more power. But you ca solve the basic formula of cooler air VS hp and get a round about answer to how much cooler the charge would have had to of been to gain “X” amount of HP.
If we make a lot of assumptions and some educated guesses you can semi-sort-of come up with a number based on power gained NA vs NA back to back dyno runs with a fuel switch only. With nothing more than 30% fuel added to the fuel map, It’s common to see 15-20% at the crank simply by switching to E85. More so if you were knock limited with timing prior.
Of course not all of the gains are from a cooler CC. Much of the gains are from quicker flame travel which leads to more cylinder pressure and more power. But you ca solve the basic formula of cooler air VS hp and get a round about answer to how much cooler the charge would have had to of been to gain “X” amount of HP.
I guess my questions are, why, and if you could what would you do with that information? There is no formula that can be applied to every combo that says with x amount of cooling from E85 you can an add x amount of timing. Ultimately you give each combo what it wants and it can differ wildly.
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Thread Starter
Launching!
Joined: Sep 2008
Posts: 222
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From: Dayton, OH
I guess my questions are, why, and if you could what would you do with that information? There is no formula that can be applied to every combo that says with x amount of cooling from E85 you can an add x amount of timing. Ultimately you give each combo what it wants and it can differ wildly.
As @QwkTrip said, It can be calculated. Not simple, but it is a college level chemistry question and not rocket science. The term is "Latent Heat of Vaporization". Latent heat is defined as the heat or energy that is absorbed or released during a phase change of a substance. It could either be from a gas to a liquid or liquid to solid and vice versa. Latent heat is related to a heat property called enthalpy.
No way to measure it. Head temp is an inferential measurement and severely lagging so not useful. EGT may provide some insight but still a lagging measurement and is mixed with other factors.
Sidebar, pre-ignition occurs when the temperature of the gas/air charge in the cylinder exceeds the autoignition temperature of the fuel. The autoignition temperature of 93 is higher than that of 87 and the autoignition temperature of E85 is much higher. We understand the result even if we don't do the calculations.
The calculations involve the temperature of the incoming air, the temperature increase due to compressing the air/fuel mixture, the heat gained from exposure to the hot cylinder wall, piston, head and valves and the heat removed when the fuel changes state from a liquid to a gas in the cylinder. This is what I am interested in.
Back to the main topic, People are running FI engines on E85 without an intercooler. Since the IAT's are higher than if they were running an intercooler which results in lower intake air density and reaching autoignition temperature sooner, are they giving up power and if so, how much?
How much additional power can be produced by changing from an A2A to an A2W?
How much power can be gained by adding mechanical refrigeration or ice to the A2W system?
Does running E85 overshadow the intercooler system improvements. That is the question I am looking to answer.
Last edited by SteveJewels; Sep 28, 2025 at 09:41 AM.
Thread Starter
Launching!
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From: Dayton, OH
From "Handbook on Bioethanol: Production and Utilization";
Heat of Vaporization
At a stoichiometric 9:1 air:fuel weight ration, ethanol's charge-air cooling effect would be about 77 deg C on the intake air compared to 7 deg C from gasoline.
77 degrees C = 170 degrees F!
Maybe the people running E85 with no IC have a point.
Heat of Vaporization
At a stoichiometric 9:1 air:fuel weight ration, ethanol's charge-air cooling effect would be about 77 deg C on the intake air compared to 7 deg C from gasoline.
77 degrees C = 170 degrees F!
Maybe the people running E85 with no IC have a point.
I wish it worked like that! All kinds of holes in that theory and how it would apply to us.
You would have to rule out the 7* the gas normally does. So, they are saying you can pull 70*c or 158* more from the air charge temp than with gasoline?
So if the turbo was pumping 250*. The E85 would cool the charge down to 92*? That’s clearly not happening. Proven by non-intercooled race gas VS E85 setups on race gas. Also proven by intercooled cars VS non intercooled setups. Cooling the air charge 158* is worth X amount of HP. If E85 could replicate intercooler like effects, then we would see the same gains we see when an IC pulls 158* from the charge temps. but we don’t. Non intercooled setups make much less power per pound. E85 wont’ col the charge temps anywhere near as well as an intercooler. Its less knock prone in the CC.
Also you wouldn’t calculate stoich AFR, but peak rich power AFR. With boost, the charge would be more dense, so I’d think other factors would come into play there as well.
How much time is needed to pull 158* from the charge temps? Would this happen when fuel is sprayed at the valve with FI? Or just on a Carb?
Also you can’t really cool much past the vaporization point of the fluid. The phase change is where all the heat pulling work is done. Ethanol’s boiling point is 172*.
You would have to rule out the 7* the gas normally does. So, they are saying you can pull 70*c or 158* more from the air charge temp than with gasoline?
So if the turbo was pumping 250*. The E85 would cool the charge down to 92*? That’s clearly not happening. Proven by non-intercooled race gas VS E85 setups on race gas. Also proven by intercooled cars VS non intercooled setups. Cooling the air charge 158* is worth X amount of HP. If E85 could replicate intercooler like effects, then we would see the same gains we see when an IC pulls 158* from the charge temps. but we don’t. Non intercooled setups make much less power per pound. E85 wont’ col the charge temps anywhere near as well as an intercooler. Its less knock prone in the CC.
Also you wouldn’t calculate stoich AFR, but peak rich power AFR. With boost, the charge would be more dense, so I’d think other factors would come into play there as well.
How much time is needed to pull 158* from the charge temps? Would this happen when fuel is sprayed at the valve with FI? Or just on a Carb?
Also you can’t really cool much past the vaporization point of the fluid. The phase change is where all the heat pulling work is done. Ethanol’s boiling point is 172*.
Last edited by Forcefed86; Jan 18, 2023 at 01:43 PM.
Thread Starter
Launching!
Joined: Sep 2008
Posts: 222
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From: Dayton, OH