I decided to make a short post on how to do your own calculation for making E30 or other Ethanol mixes (skip to the end if you just want the simplified equations).
I was trying to be lazy and find an equation online but couldn't seem to find anything other than calculators so i decided to figure out the equation myself. Being a scientist who works with dilutions and making chemical mixes all the time, I was not satisfied just by using an online calculator--I had to figure it out myself. I hope someone finds this useful or at least interesting.
Lets start with one of the most commonly used equations in laboratory science : V1*C1=V2*C2
(Volume 1 * concentration1 = volume2*concentration 2)
Now this is all we would need and the calculation would be super simple.. but there is 10% ethanol in the gas you are diluting your E85 with so it makes it a little more difficult.
Lets take the previous equation and modify it a little bit to fit better with what we are doing. Replacing C1 with %Ethanol of your E85 (E85%), V1 with the amount of ethanol you are to add (Ev), C2 with your desired ethanol percent (%E_final), and V2 with the total volume you are trying to make (Fv).
variables so far:
%E85 = actual % ethanol of the E85
Ev = amount of E85 to add
%E_final = desired final ethanol %
Fv = final volume you are trying to make
New equation = %E85*Ev = %E_final*Fv
But like i said earlier, you have to take into account the 10% Ethanol in the gas you are diluting with. So the equation should be modified to contain the ethanol percent in gas (%Egas) and the volume of gas you are to add (Gv).
New equation = %E85*Ev + %Egas*Gv = %E_final*Fv
As it is now, this equation is impossible to solve because Ev and Gv are related but you cant figure one variable out without figuring the other one out. So you need to find the relationship between the two--and that is actually very simple if you realize that the volume of E85 + the volume of Gas = your final volume.
So Ev + Gv = Fv
Rearranging this equation you get Gv = Fv - Ev ( Gas volume = Final volume - Ethanol volume)
Now take this equation and plug it back into the original equation substitutin (Fv - Ev) for Gv because Gv = Fv - Ev
%E85*Ev + %Egas*(Fv - Ev) = %E_final*Fv
Now you have everything you need to solve the equation for the one unknown variable: how much E85 to add (Ev). But lets simplify the equation slightly to make it simpler for future use:
%E85*Ev + %Egas*(Fv - Ev) = %E_final*Fv (multiply parentheses)
%E85*Ev + %Egas*Fv - %Egas*Ev = %E_final*Fv (combine your two Ev values %E85*Ev - %Egas*Ev)
(%E85 - %Egas)*Ev + %Egas*Fv = %E_final*Fv (subtract %Egas*Fv)
(%E85 - %Egas)*Ev = %E_final*Fv - %Egas*Fv (divide by (%E85 - %Egas))
Ev = [%E_final*Fv - %Egas*Fv]/[%E85 - %Egas] (pull out Fv from the numerator)
Ev = [Fv(%E_final - %Egas)]/[%E85 - %Egas]
Thats it! So now lets do a typical example using typical percentages.
Your %E85 ended up actually being 85% -- %E85 = 85
Typically ethanol in gas is 10% -- %Egas = 10
desired Final ethanol percent is 30% -- %E_final = 30
lets say you want to make 13 gallons of the E30 -- Fv = 13
Ev = 13(30 - 10)/(85 - 10)
Ev = 3.47 galons of E85
And of course the amount of gas to add is 13 - 3.47 = 9.53
If you are always running E30 and your gas is always assumed to be 10% Ethanol you can simplify the equation further to
Ev = 20*Fv/(%E85 - 10)
And if you are too lazy to actually measure your E85% you can further simplify the equation to
Ev = 20*Fv/75
Now if you already have 2 gallons of regular gas in your tank and want to fill your 13 gallon tank with E30:
Just subtract 2 gallons of gas from the calculated regular gas to add:
Ev = 3.47 gallons
add 3.47 gallons of E85 and 11 gallons of gas (13 - 2)
If your gas tank is only 13 gallons i would recommend doing the calculations for a little bit less--maybe 12.5 gallons. Or in the fiestas' case: our tank is 12.4 (i think) so i wouldn't calculate for more than 12. You don't want to add one component then go to add the other and your tank is actually full before you can add all you need.
Use your Cobb AP to determine the Percentage of gas in your tank and multiply it by the total tank size.
% gas in your tank = 74
.74*12.4 = 9.176 gallons are currently in your tank
This all works for gallons or liters (or any other volume measurement) as long as you keep the units consistent in the equation.
In summary (also TLDR)
To make E30:
Volume of E85 to add = 20*desired final volume / (Actual E85% - 10 )
Volume of Gas to add = desired volume - volume of E85 to add
To make E40:
Volume of E85 to add = 30*desired final volume / (Actual E85% - 10 )
same as above
To make any other E mix:
Replace the first number in above equations with desired % - 10
I was trying to be lazy and find an equation online but couldn't seem to find anything other than calculators so i decided to figure out the equation myself. Being a scientist who works with dilutions and making chemical mixes all the time, I was not satisfied just by using an online calculator--I had to figure it out myself. I hope someone finds this useful or at least interesting.
Lets start with one of the most commonly used equations in laboratory science : V1*C1=V2*C2
(Volume 1 * concentration1 = volume2*concentration 2)
Now this is all we would need and the calculation would be super simple.. but there is 10% ethanol in the gas you are diluting your E85 with so it makes it a little more difficult.
Lets take the previous equation and modify it a little bit to fit better with what we are doing. Replacing C1 with %Ethanol of your E85 (E85%), V1 with the amount of ethanol you are to add (Ev), C2 with your desired ethanol percent (%E_final), and V2 with the total volume you are trying to make (Fv).
variables so far:
%E85 = actual % ethanol of the E85
Ev = amount of E85 to add
%E_final = desired final ethanol %
Fv = final volume you are trying to make
New equation = %E85*Ev = %E_final*Fv
But like i said earlier, you have to take into account the 10% Ethanol in the gas you are diluting with. So the equation should be modified to contain the ethanol percent in gas (%Egas) and the volume of gas you are to add (Gv).
New equation = %E85*Ev + %Egas*Gv = %E_final*Fv
As it is now, this equation is impossible to solve because Ev and Gv are related but you cant figure one variable out without figuring the other one out. So you need to find the relationship between the two--and that is actually very simple if you realize that the volume of E85 + the volume of Gas = your final volume.
So Ev + Gv = Fv
Rearranging this equation you get Gv = Fv - Ev ( Gas volume = Final volume - Ethanol volume)
Now take this equation and plug it back into the original equation substitutin (Fv - Ev) for Gv because Gv = Fv - Ev
%E85*Ev + %Egas*(Fv - Ev) = %E_final*Fv
Now you have everything you need to solve the equation for the one unknown variable: how much E85 to add (Ev). But lets simplify the equation slightly to make it simpler for future use:
%E85*Ev + %Egas*(Fv - Ev) = %E_final*Fv (multiply parentheses)
%E85*Ev + %Egas*Fv - %Egas*Ev = %E_final*Fv (combine your two Ev values %E85*Ev - %Egas*Ev)
(%E85 - %Egas)*Ev + %Egas*Fv = %E_final*Fv (subtract %Egas*Fv)
(%E85 - %Egas)*Ev = %E_final*Fv - %Egas*Fv (divide by (%E85 - %Egas))
Ev = [%E_final*Fv - %Egas*Fv]/[%E85 - %Egas] (pull out Fv from the numerator)
Ev = [Fv(%E_final - %Egas)]/[%E85 - %Egas]
Thats it! So now lets do a typical example using typical percentages.
Your %E85 ended up actually being 85% -- %E85 = 85
Typically ethanol in gas is 10% -- %Egas = 10
desired Final ethanol percent is 30% -- %E_final = 30
lets say you want to make 13 gallons of the E30 -- Fv = 13
Ev = 13(30 - 10)/(85 - 10)
Ev = 3.47 galons of E85
And of course the amount of gas to add is 13 - 3.47 = 9.53
If you are always running E30 and your gas is always assumed to be 10% Ethanol you can simplify the equation further to
Ev = 20*Fv/(%E85 - 10)
And if you are too lazy to actually measure your E85% you can further simplify the equation to
Ev = 20*Fv/75
Now if you already have 2 gallons of regular gas in your tank and want to fill your 13 gallon tank with E30:
Just subtract 2 gallons of gas from the calculated regular gas to add:
Ev = 3.47 gallons
add 3.47 gallons of E85 and 11 gallons of gas (13 - 2)
If your gas tank is only 13 gallons i would recommend doing the calculations for a little bit less--maybe 12.5 gallons. Or in the fiestas' case: our tank is 12.4 (i think) so i wouldn't calculate for more than 12. You don't want to add one component then go to add the other and your tank is actually full before you can add all you need.
Use your Cobb AP to determine the Percentage of gas in your tank and multiply it by the total tank size.
% gas in your tank = 74
.74*12.4 = 9.176 gallons are currently in your tank
This all works for gallons or liters (or any other volume measurement) as long as you keep the units consistent in the equation.
In summary (also TLDR)
To make E30:
Volume of E85 to add = 20*desired final volume / (Actual E85% - 10 )
Volume of Gas to add = desired volume - volume of E85 to add
To make E40:
Volume of E85 to add = 30*desired final volume / (Actual E85% - 10 )
same as above
To make any other E mix:
Replace the first number in above equations with desired % - 10
