Ethanol/ULP Mixes and Mileage Equivalence

[LaurieAG]

I have a car that, when purchased, ran for 400 kilometres on one 37 litre tank of Un Leaded Petrol (ULP). Since then the Australian government has introduced laws which allow up to 10 percent of Ethanol to be added to the ULP Mix.

 

This car had a tune and service with a full tank of ULP from a Major (non US) Multinational around 2 months ago, so I was interested to see how my mileage would go now. After reaching the half way mark on the fuel gauge my trip meter read 165 kilometres. I thought that this was a bit low so, when the tank was down to 1/4 full (a week after fuelling), I went back to the same Major Multinational, refilled my tank completely with ULP and reset the trip meter. This ULP was consistent with the first tanks trip meter reading of 165 kilometres at half a tank. I was thinking that something was going really screwy because the car seemed to be running better than it had been running for quite a long time.

 

One week later I went to another Major Multinational (US) and filled the tank with ULP when it was down to 1/4 full. This half tank gave me 190 kilometres on the Trip Meter and the next half tank was 195 kilometres with the next 3 all being between 190 and 195. I thought to myself, this was a lot more like the mileage I'd expected to see, allowing for the amount of Ethanol (10% by law Max?) in the mix. As I wasn't certain about what the mileage difference was between pure Ethanol and the previously unadulterated ULP, I decided to try a few different possibilities and see what I could get out of the two different sets of fuel consumption and mileage data, and also see what amount of distance lost could be attributed to the ethanol in the mix at 10, 25, 35 and 70 percent in Ethanol+ULP mixes with 75, 50 and 25 percent Ethanol mileage Equivalents.

 

The second Major Multinational gives a loss of 5 kilometres per 1/2 tank of ULP fuel (200 kms - 195 kms), the equivalent distance 'travelled' on Ethanol = Y where Y = 20 kms on 10 percent Ethanol, (i.e. 75% effectiveness to equivalent ULP, Y = 20 kms and is 10 % of 200, 15 kms are actually travelled and the 5 kms (Y/4 = 20/4 = 5) is lost). The first Major Multinational consistently gave a loss of 35 kms on half a tank of "ULP", 35 = Y/4 at 75% mileage equivalence so Y = 140 and Y/4 = 35 kms lost. At 50% 35 = Y/2, 5 = Y/2 and at 25% 35 = Y3/4, 5 = Y3/4.

 

This is what I came up with

 

if Ethanol is 25% mileage Equivalent to the same amount of ULP

(1) The first ULP Mix has 25 percent Ethanol mixed in with ULP

(2) The second ULP Mix has 3.5 percent Ethanol mixed in with ULP

 

If Ethanol is 50% mileage Equivalent to the same amount of ULP

(3) The first ULP Mix has 35 percent Ethanol mixed in with ULP

(4) The second ULP Mix has 5 percent Ethanol mixed in with ULP

 

If Ethanol is 75% mileage Equivalent to the same amount of ULP

(5) The first ULP Mix has 70 percent Ethanol mixed in with ULP

(6) The second ULP Mix has 10 percent Ethanol mixed in with ULP

 

 

Does anybody know what the actual mileage equivalent of ethanol in ULP mixes is?

[CraigD]

Does anybody know what the actual mileage equivalent of ethanol in ULP mixes is?

This wikipedia article gives the energy densities of gasoline, ethanol, and a 90/10% mix as:

Gasoline: 46.9 MJ/kg / 34.6 MJ/L;

90/10% gasoline/ethanol mix: 43.54 MJ/kg / 28.06 MJ/L;

and

pure ethanol: 30 MJ/kg / 24 MJ/L

 

From this, ethanol should be about 64% energy equivalent to an equal mass of gasoline, and about 69% equivalent to an equal volume.

I have a car that, when purchased, ran for 400 kilometres on one 37 litre tank of Un Leaded Petrol (ULP). Since then the Australian government has introduced laws which allow up to 10 percent of Ethanol to be added to the ULP Mix.

 

This car had a tune and service with a full tank of ULP from a Major (non US) Multinational around 2 months ago, so I was interested to see how my mileage would go now. After reaching the half way mark on the fuel gauge my trip meter read 165 kilometres.

This seems about right for a mix of slightly less than 10% methanol – about 83% gasoline equivalent, vs. the listed 81% gasoline equivalent energy density of a 10% “gasohol” mix.

 

I can’t vouch for the wikipedia article’s accuracy, and am puzzled that “10% ethanol” appears, based on the energy density give for it, to be closer to 20% by mass (43.54 = 46.9a + 30(1-a) -> a = 13.54/16.9 = ~ .8). It would be wise, I think, to validate (and possibly discuss and correct) the wikipedia data with some independent sources.

 

Assuming correct energy density figures, my guess is that there’s little difference in an engines thermal-to-mechanical efficiency burning from pure gas to pure alcohol, so there should be a pretty linear relationship between percentage by mass of gas and vehicle mileage, from roughtly 64% usual for pure ethanol to 100% for pure gasoline.

 

As I recall, calculating the volume of a gasoline/methanol mixture is tricky, as [math]\mbox{volume_{mixture}} \not = \mbox{volume_{gas}} + \mbox{volume_{alcohol}}[/math], due to the smaller ethanol molecules “filling the cracks” in a liquid of larger gasoline molecules.

[LaurieAG]

This wikipedia article gives the energy densities of gasoline, ethanol, and a 90/10% mix as:

Gasoline: 46.9 MJ/kg / 34.6 MJ/L;

90/10% gasoline/ethanol mix: 43.54 MJ/kg / 28.06 MJ/L;

and

pure ethanol: 30 MJ/kg / 24 MJ/L

 

From this, ethanol should be about 64% energy equivalent to an equal mass of gasoline, and about 69% equivalent to an equal volume.This seems about right for a mix of slightly less than 10% methanol – about 83% gasoline equivalent, vs. the listed 81% gasoline equivalent energy density of a 10% “gasohol” mix.

 

I can’t vouch for the wikipedia article’s accuracy, and am puzzled that “10% ethanol” appears, based on the energy density give for it, to be closer to 20% by mass (43.54 = 46.9a + 30(1-a) -> a = 13.54/16.9 = ~ .8). It would be wise, I think, to validate (and possibly discuss and correct) the wikipedia data with some independent sources.

 

Assuming correct energy density figures, my guess is that there’s little difference in an engines thermal-to-mechanical efficiency burning from pure gas to pure alcohol, so there should be a pretty linear relationship between percentage by mass of gas and vehicle mileage, from roughtly 64% usual for pure ethanol to 100% for pure gasoline.

 

As I recall, calculating the volume of a gasoline/methanol mixture is tricky, as [math]mbox{volume_{mixture}} not = mbox{volume_{gas}} + mbox{volume_{alcohol}}[/math], due to the smaller ethanol molecules “filling the cracks” in a liquid of larger gasoline molecules.

 

That's all well and good Craig but can you relate these figures to mileage loss as a result of the Ethanol component in the mix, for the two different mixes described as in my calculations.

 

From the 64% (to 69%) figure you give (compared with my 75% mileage equivalence calcs) I get between 50 and 60 percent Ethanol in the first mix from the first non US multinational and between 7 and 8 percent Ethanol in the second mix from the US multinational.

 

Do you think it would be correct to say that while the US multinational is operating within the constraints of Australian law (10% Ethanol Max), the non US multinational is engaging in criminal conduct or at the least failing to ensure that it's contractors and franchisers are not engaging in criminal conduct?

[LaurieAG]

I filled up my petrol tank last week and realised that I wasn't getting the full tank mileage out of my (rough) calculations. I had 303 kms recorded for 22.25 liters which means that my total mileage is very close to 500kms from 37 liters not 400.

 

It's just a little bit disturbing as the ACCC (Australian Competition and Consumer Commission) is just starting to monitor basic petrol pricing (the price went up 20c per liter when they stopped monitoring) let alone do anything about these new ethanol mix shenanigins.