Ethanol vs Gasoline

[Bojingles]

We will be talking about the energy output of fuels such as Methane, Gasoline, Diesel, and Ethanol and how they play in industry as far as usage as a fuel. I did this as a benefit to me as an engineering student and for those cretins on strafeRight. This information is my study on the value of Ethanol as a fuel source. Note I will not be talking about the environmental effects of this fuel in either it's E85 form or as a mixture with 90/10. I did this study for fun and will not be receiving a grade on it. Hopefully you'll find some beneficial information from this. As well I did not attempt to figure the amount of loss from 90/10 Gasoline. I may do that later if I get enough requests for it. Hope you enjoy!


The following are Higher Heating Values (HHV) basically the amount of output a fuel can produce if there was 100% combustion of the fuel.
Methane: 55,530 kJ/kg
Gasoline: 47,300 kJ/kg
Diesel: 46,100 kJ/kg (note this is light diesel and their is a form of heavy diesel)
Ethanol: 29,670 kJ/kg

You can see that Ethanol produces the smallest amount of energy per kg of fuel used, this also would explain why vehicles using Ethanol requiere more fuel to transfer the same distance as a normal gasoline vehicle would. Because of the addition of 10% Ethanol to much of the Gasoline we use today you can expect an overall decrease in MPG and a decrase in total HP and Torque since you cannot provide the same amount of energy in the motor as 100% gasoline. Is ethanol worth it though?

An average car consumes about 5L of gasoline a day and on average has a fuel tank of about 50L. Density of gasoline is 0.68 - 0.78 kg/L. Density of ethanol is .790 kg/L. We will use the Lower Heating Value(LHV) of Gasoline and Ethanol to accomidate for incomplete burn rates and possible contamination of the fuel. So..

Gasoline LHV: 44,000 kJ/kg
Ethanol LHV: 26,810 kJ/kg

The mass of gasoline used per day is:
m = (pV) = (0.75 kg/L)(5L/day) = 3.75 kg/day

Energy supplied by gasoline to the car per day:
E = (m)(LHV) = (3.75 kg/day)(44,000 kJ/kg) = 165,000 kJ/day

Amount of mass per day of ethanol to equal gasoline:
E = (m)(LHV)
m = E/LHV = 165,000 kJ/day / 26,810 kJ/kg = 6.15 kg/day

Amount of liters of ethanol used per day to equal gasoline:m = (pV)V = m/p = 6.15 kg/day / .790 kg/L =7.78L/day

We can see that it takes 7.78 L/day of ethanol to be able to travel the same amount as gasoline which only takes 5L/day. Are the savings worth it? Lets find that out.Average cost of ethanol in peak season of August 2008: $3.08 per gallon
Average cost of gasoline in peak season of August 2008: $3.74 per gallon

Convert to Liters:
$3.08 per gallon x gallon / 3.785 L = $0.81 per liter of ethanol
$3.74 per gallon x gallon 3.785 L = $0.99 per liter of gasoline

Cost per day:
$0.81/L x 7.78 L/day = $6.30 per day of ethanol
$0.99/L x 5L/day = $4.95 per day of gasoline

Looks like ethanol is actually more expensive!

[Fish111]

Welcome to like 6 months ago

Nah youre right tho

[CoffeeShark]

I generally skip to the conclusion when faced with math.

But yeah, that has been proven, plus the added cost of food crops being diverted to fuel instead of people, driving up prices of both.

[Bojingles]

I know the math has been done before but I wanted to do the study myself.

[Teck]

Nice

[BuddhistSoldier]

Down with ethanol... people need to eat before driving.

[FuzzyLogik]

isn't it ironic? i mean, the thing that's supposed to be so awesome doesn't work nearly as well as they say it does. I do hear though, that Ethanol made from sugar is supposed to be much better than made from corn...right? i don't remember exactly. but yeah. follow the money :P

[CoffeeShark]

Yes, I believe the Brazilians have been on sugar ethanol for a while.

[DennyCrane]

It's fine for a vehicle to be flex-fuel- that simply means it has a fuel sensor that can detect the percentage of ethanol in the mix and adjust the injector pulse width, spark timing... and even the valve event timings... to optimize performance. There's no reason we can't streamline crop farming dedicated to fuel use. It's just one more piece of the energy indepenence puzzle. It won't solve anything alone, but used along with the T. Boone Pickens plan, it can help keep us off foreign oil
~
And strictly from a performace standpoint, the more ethanol added to gasoline results in higher octane. Octane is the fuels ability to resist combustion and the higher the octane, the more mechanical compression and spark advance you can run without spark knock (detonation, pinging, etc). And that translates directly to more horsepower. As stated though, it takes more ethanol to achieve the same power. Running on pure alcohol, you need roughly a 2:1 ratio over gasoline. Electronic engine controls can compensate with larger injectors and a reprogrammed engine control computer, and carburetors require rejetting.
So, ethanol is not a total negative, it's just not a magic silver bullet by itself.

[Koniec]

We would need to take up 40% of the worlds usable agricultural land to create just 10% of the gasoline we use, I guess a year. Not going to happen.