Ethanol Versus Petrol: The Basics

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By John Cadogan | June 08th, 2010

There’s been a lot of controversy, but ethanol in petrol is here to stay. Holden will have E85-compatible engines here very soon in an attempt to get fuel companies to supply even higher ethanol blends than are currently available. Amid all the anti-ethanol hysteria and fuel-company hype, not very much has ever really been explained about the key differences between the two fuels.

NOT FOR EVERY CAR

Most cars can run E10 – a 10 per cent blend of ethanol in petrol. To check compatibility with your car, contact the manufacturer. Ethanol doesn’t destroy engines, but it can eat into the materials used in incompatible fuel systems (sealers and linings; that kind of thing) and the byproducts of that corrosion can block fuel injectors, which can be costly.

WHAT’S ETHANOL?

It’s a basic alcohol, the same stuff as in beer, wine and spirits. It can be made by fermentation of a variety of different energy-dense foods. In Australia, the majority of ethanol is produced from wheat. It can also be made from sugar and many other starchy crops – as well as from industrial, domestic and agricultural waste using chemically engineered microbes.

ENERGY

Petrol contains more energy than ethanol. If you burn one litre of ethanol you get 23.5 million joules of energy. If you burn one litre of petrol you get 33.5 million joules. That means there’s about 30 per cent less energy in a tank full of ethanol, compared with the same volume of petrol. And that means there’s about three per cent less energy in E10 compared with regular petrol. And that means fuel consumption goes up by three percent if you use E10. So if it’s not at least three per cent cheaper than regular petrol, you’re ripping yourself off. It also means if you ran a car on 100 per cent ethanol, fuel consumption would increase by more than 40 per cent. (Although it’s not advisable to do that. Car engines don’t like to start in the cold on E100. Which is why E85 is pretty much the upper limit for ethanol/petrol blends.) You need to burn 1.4 litres of ethanol to get the same energy as one litre of petrol. (Cruising range drops on E10, too – something long-distance drivers need to consider.)

GREENHOUSE

One litre of ethanol produces 1.5kg of CO2 when you burn it. One litre of petrol emits 2.2kg of CO2. But since 1.4 litres of ethanol and 1.0 litre of petrol contain the same amount of energy, maybe that’s a better CO2 yardstick comparison. And 1.4 litres of CO2 emits 2.15kg of CO2 – so, joule-for-joule, there’s not much in it from a greenhouse perspective.

HOW ENGINES WORK

The elephant in the room here is the engine itself – which is invariably optimised for petrol, not ethanol or ethanol blended fuel.

Engines don’t just burn fuel – they compress the air around it first. Compressing the fuel/air mix prior to combustion allows the expansion to occur over a greater range than just burning it out in the open, increasing the efficiency of the operation. More efficiency means more of the 33.5 million joules in every litre of petrol get converted into torque at the crankshaft. Less is lost out the exhaust pipe as waste heat.

So, the more the compression, the more the efficiency. Only there are physical limits to the amount of compression the fuel/air mix will tolerate before it begins to burn autonomously (think: pinging/knocking).

Octane rating is a measure of a fuel’s resistance to combustion (self-ignition or auto-ignition, and also knock/pinging) when compressed. So, higher-octane fuels resist auto-ignition better; they can be compressed more. So they can produce more torque and have greater efficiency. But if you run a high-octane fuel in an engine designed for low octane, there’s no benefit. This is essentially what you’re doing when you run an ethanol blend in a petrol engine.

A common misconception is that high-octane fuels have more energy in them. That’s crap. They allow greater compression, delivering more torque at the crank via increased thermodynamic efficiency.

Octane is a carbon chemical (eight carbon atoms and 18 hydrogens) which petrol approximates. The chemical with an octane rating of 100 (to which the 91, 95 and 98 fuels commonly onsale compare in percentage resistance to pinging terms) is an isomer of octane called 2-2-4 tri-methyl pentane, which is a specific architecture of eight carbons and 18 hydrogens. They all have the same amount of energy on offer in the various arrangements of the atoms, just the resistance to pinging (or knock) changes.

Ethanol offers a greater octane rating than petrol. So putting an ethanol blend in an engine designed for petrol means in theory it could handle more compression (produce more power and operate more efficiently). Only the compression ratio is set at the factory (it’s a function of piston sweep and combustion chamber shape, including piston crown shape). And that’s usually set for petrol.

This means ethanol blends won’t be as thermally efficient in most engines, compared with straight petrol. (Modern engines adapt slightly to higher octane fuels by increasing the spark advance, but the benefit is tiny compared to increasing the compression to suit the octane rating.) The only real way to solve this problem is to vary the compression, and the only real way to do that is via variable-boost turbocharging, where the effective compression ratio can be varied to suit the fuel’s octane rating by changing the pressure of the post-turbo inlet air mix.) E50 can tolerate something like 19:1 compression, with the right additional controls in place. Ordinary petrol likes 10.5:1 or thereabouts – slightly more with direct injection.

Subject to all these caveats the bottom line is that, broadly, to perform the same job as an equivalent volume of petrol, you’d need to burn about 40 per cent more pure ethanol, and it would emit the same (or very similar) amount of CO2. And if the blend of petrol and ethanol varies, hi-tech turbocharging will be required to exploit the fuel to the best effect.

Frenchie

Well you proven that pound for pound that ethanol blend fuel is not economically better than petrol. There are two things you have failed to mention.
That ethanol is a renewable fuel if grown from a crop(using up CO2) and/or can be created from green waste.
The other factor that you assume is that the price of ethanol blend to petrol cost are close. Once petrol starts to increase E85 will end up being more benifical.

AB

Firstly, great article John

Frenchie,
Growing crops for Ethanol production has proven to create more environmental issues than it solves – with an outcome similar to that outlined in the ‘Palm Oil awareness’ campaign (Huge scale land clearing)

Also, the crops only remove CO2 from the atmosphere while they are growing, and will subsequently release the captured CO2 as they are processed – its the same with a decaying tree.

As far as I’m aware, grass is one of the only plants that absorbs & process’s CO2 and does not release it once it dies.

Generating Enthanol from waste however appears to be a much more viable method once made efficient.

AB

Also, regarding supply, dont forget that growing ethanol is only cost effective while land is cheap & is also subject to the same climatic risks associated with all crop growth.

Ethanol crops also compete for the same growing areas as Food Crops.

I believe in Brazil where ethanol production is large scale the local food crop prices increased significantly due to decreased supply of land for food crops

Frenchie

“Ethanol crops also compete for the same growing areas as Food Crops”.

This is true but at least the farmer has two options to sell their crops. Hopefully this will give them a better gate price perhaps.

“Growing crops for Ethanol production has proven to create more environmental issues than it solves”.

Definitely true for developing countries. For Australia it would provide farmers who cannot sell produce because of cheap imported food to switch to ethanol production.

Shak

SO is this article promoting Ethanol or not? because the way i see it, even if the consumption rises slightly, we need to get off oil, foreign or not. We need to stop burning the Dino juice and start using our endless supply of VB. And besides its a nice marketing tool for Holden and the like.
Karl

Thanks for the article John, its good to see a decent technical article to give people some food for thought.
Hopefully this will give people a better understanding of the actual pros/cons of ethanol, rather then a pile of half-truths.
JooberGTi

Theres always two sides to the story in any case with ethenol vs petrol, and I think this article prooves its no golden goose.

Frenchie is right, its the supply potential which is the positive over petroleum, but if you look at the other side then ethenol production will compete with food production, and with growing and growing population sacrificing capacity to produce ethenol can be a problem. Secondly doesn’t ethenol require water? which may cause problems if water shortage looms.
http://www.facebook.com/profile.php?id=1435885244 Yani Hendriawan

that picture just looks like fog to me
Anthraxx66

Interesting article. The good thing is that most of it is understandable to the average person in the street.

There are positives and negatives for both Ethanol and Petrol… the only negative for ethanol in my eyes is that my bike is not designed to run on it, and the price of it here in country Victoria is still not low enough to make it economically viable.

The only real message I get out of this is that both fuels have negative impacts on the environment, so use less!
ABMPSV

Article forgot to tell you that since ethanol food prices went up. So the rich can drive and the poor must pay more for the food. In US they use corn and check the corn prices is up. Corn was 193 in year 2000 before financial crisis was 625 and now around 375. That is still 7% pa increase.

timmy201

In the US they have a huge import tax on the sugar cane ethanol from Brazil and other South American countries. The are too proud and stupid to accept that corn isnt the most efficient way of producing ethanol.

The other problem is, it cannot be transported via pipeline, as it eats out the seals. It must be moved by trucks, which isnt ideal.
Matt

In Mexico they had riots over the increase in corn-based foods, I believe the government had to step in to help out.

One of the drivers behind deforestation of the Amazon is more land to grow sugar cane for ethanol for the flex fuel cars.

I’m all for ethanol from waste materials but not from food crops – thats a hoax

MK

How about Bio-Diesel-Blend?
Shak

The whole point of the new tie up between Holden and Coskata is not to use food sources but wasted bio mass. that way we get pretty much Ethanol from Garbage, and we dont have to jack food prices up.

JEKYL & HYDE

spot on,

think of a perfect world where the blood-sucking city councils PAY YOU for taking your rubbish away.ethanols future is quite literally GARBAGE.other thing not mentioned is that,at least from overseas experience,ethanol boosts performance.think 10-20%.didn’t the v8 supercars which over last year.should be real interesting when holden bring out ve2 with e85…
Huh?

“…the new tie up between Holden and Coskata…”

Cant really see that partnership taking off unless they change their name, as it is now both comapanies sound the same:
Coskata and Coksuckas!

Tony M

A very informative piece. I can only conclude that LPG and Ethanol as alternate fuels are in the same basket, although I think LPG is better. I have a problem using land that grows food for us and export being used to produce fuel for cars. Recently I saw a show (Top Gear) where a Honda in America was electically driven and powered by a fuel cell. This was a production vehicle which you could fill up with liquified hydrogen, just like our LPG. As this is a production car I believe this will be where we will be going, not ethanol which I believe will be a short cycle in fuel alternative.
John Collins

Don’t people read newspapers these days? The Australian government has recently closed down many highly productive sugar cane properties and their attendant mills. Sugar is probably the most efficient way to produce ethanol! We don’t have to take food from the starving Africans. And as for “Holden will soon release a car capable of running on e85 … guess who produces a Chev badged car for the Brazillian market, capable of running on 100 per cent ethanol?

Jack

And knowing how good excess sugar intake is for the human body (it’s not!), all that sugar cane would be better burned in an engine!
Simon

“Holden will soon release a car capable of running on E85.”
Gotta ask the question, to who?
Can’t see any purpose when you can’t get it filled up at your local.
I think it’s pure hype in the order of Toyota’s fairy tales.

Smithy

“In Australia, the majority of ethanol is produced from wheat” – well not quite!

Australia currently has 3 commercial ethanol plants and CSR claim to supply over 50%, so sugar cane WASTE is the primary source of ethanol in Australia.

Addittionally all 3 plants use predominantly waste product (be it from grain or sugar crop production) to produce ethanol – so virtually no impact on food crops.

Any argument on food/fuel crops just does NOT stack up in Australia.

AB

Smithy,
No arguments with Enthanols origin is Australia, but would it be fair to say that if Ethanol was to be produced on a larger scale here, there simply wouldnt be enough Sugar Cane waste to supply it?
Therefore dedicated Ethanol Crops would be required?

themarvel

Great job.
One point I think isn’t quite right: re running higher octane fuels & compression ratio – in a petrol engine the fuel – air ratio is also contingent on how the mix burns, and the point at which auto-ignition occurs. A higher octane fuel allows for a leaner mix (less fuel) in the ratio. So a properly configured electronically controlled engine will see better economy running ULP 95 over 91, as it can lean out the mix to gain the same power result. So it is conceiveable that despite the energy density differences, an E10 fuel (with 95 octane) can deliver equal economy to ULP 91.

Tony M

Can you pass that onto the V8 Supercar boys who use 85 ethanol because they seem to complain that their consumption is higher.
John Cadogan

My understanding is that engines these days run stoichiometric air-fuel ratios. It’s possible to produce more torque by leaning them out even beyond this, but dirty emissions results. All the combustion professionals I’ve ever interviewed (and my lecturers at uni) speak to the fundamental relationship between compression and octane rating…
John Cadogan

Tony M

How much energy do we consume (CO2 by product) in producing ethanol?

Smithy

Not sure, but I’m willing to bet that it’s less than producing and shipping petrol from overseas.

Folks check out:
w w w . ethanolfacts . com . au/home

Tasso M

A major point of this issue in Australia is that GM Holden, the Victorian government and two other companies have entered into a joint venture to produce ethanol from waste rather than grown crops. This is a very significant development as it removes the food versus fuel debate from the issue completely. As mentioned by other posts, the CO2 emitted by ethanol (or the % of ethanol in the mixture) is for all practicable purposes neutral (as the green waste to produce the fuel has absorbed that level of Co2 during its life-cycle).

LPG emits around 15% less than petrol, but E85 will have a huge positive impact to the environment and hopefully to Australian industry as local production will take the lions share away from oil based fuel being imported.

A better environment, locally produced renewable fuel from waste (rather than food crops) and cheaper fuel though lower excise levies are all positives for this technology, not to mention new jobs and industry.

Holden will be the first local manufacturer with the Holden Commodore later this year and Saab already have these engines on the market. With Caltex now committed to providing at least 100 locations with E85 by December 2011, this is indeed a major shift away from being an oil dependant nation. There is quite a way to go, but this along with EV technology is great for the industry and the country as a whole.

A bright future awaits…

AB

Well said

Dave

Well done Tasso. someone informed made a comment.

JEKYL & HYDE

and the really good thing is the new holden motors will happily drink straight unleaded,but will work on e85 as well.win,win…..
Jack

If I could have pressed ‘+’ twice I would have Tasso. Spot on.

http://Audi ManualsOnly

The other important advantage of ethanol over petrol is the lack of toxic emmissions, low or non-existent nitrous oxides, sulphides and all the x-ene compounds that have to be trapped by the catalytic converter etc. Due to there being no complicated benzene compounds involved ethanol has very clean exhaust (excluding the CO2/CO of course).
Yonny

Good article John. I’m personally divided on the use of ethanol in petrol, because, to quote you, “if it’s not at least three per cent cheaper than regular petrol, you’re ripping yourself off”, and almost everywhere I look the price difference between standard petrol and E10 is only 2 cents a litre. People using E10 must indeed be ripping themselves off.

Of course, because standard petrol is being phased out soon people will only have 2 options – to use E10 (and rip themselves off) or use premium and pay extra.

I have no real argument with being forced to move to a more sustainable fuel source (debatable though that is, given the current ethanol industry) but surely the government could ease off the tax a bit on E10 so that at least you don’t get ripped off when you use it.
Jabba the Hut

Nice article. Algae plants are the future for ethanol. Soucing the fuel from sugar and wheat is not economical. It’s great for the farmers but not for world food supply. Currently there are testing stations growing algae for future needs. Algae produces a higher volume of ethanol than any food crop and can be grown faster in the right environment.
Shak

I still think the little bug that Coskata produced is the solution. The bug is anaerobic so if it comes in contact with air it dies. It feeds off waste and cellulosic by products, and then produces Ethanol as a waste product. Win win. City wide waste is reduced, and our reliance on imported oil is reduced. It should also be chepaer in the long run.
dave

still a stock standard and now outdated BF/BFII XR6 Turbo manual beats 90% of cars on the market.
MrQuick

Great article

Another awesome aspect of E85 fuels is tuning, especially in forced induction engines.

There is a cooling effect e85 it has due to the cooler intake charge temps, this cools the cylinder pre-ignition.
Not only that, but the higher octane rating is great, its a pretty cheap way of getting your fuel octane boosted.

Both the cooler intake charge and much higher octane rating means high compression, which means more power (thats good) and its just costs as much, if not cheaper, to run your car weekly on this stuff as it does to run it on ULP (even better).

Think about it, more power, same running costs, brilliant!

Only problem is sourcing it, I think in Sydney only a couple of independent servos sell it at the moment.
Jack

Hey John, a great article.

Some other interesting points about Ethanol:

1) Henry Ford designed the Model T to run on it. The idea was that US Farmers could produce their own fuel, and increase their independence and the country’s wealth at the same time.

2) When a Japanese Zero fighter (Mitsubishi A6M3, now there’s a Mitsu!) was captured by the Allies in 1944 I think, they were stunned to find out how it could rev so high: it was using ethanol fuel!

3) 100% ethanol can be mixed with water and burned in an engine! Indeed, distilled at home, it may contain some anyway: a reflux still is capable of producing 190 proof (95%) alcohol. This creates ‘water injection’ to the engine (as used in Allied aircraft in World War II). Water and petrol don’t mix, so you’d have to make sure your ethanol was 100% for E85.

John,

Your point about the ideal compression for ethanol being 19:1 makes me think. That’s diesel territory… Not to go into turbocharging, can anyone advise how increasing compression can result in a dedicated ethanol/water engine? I’m thinking old school, take a Holden 186 and put a 161 head on it, maybe a dedicated cam, harder valves, dedicated timing, and different jets in the carby.

Cheers
Andrew M

I still think LPG is a better option.

LPG is still cleaner and cheaper.

Ethanol blended fuels wont save $ at the bowser, LPG will.
LPG also produces less green house gasses.

LPG delivers more torque

LPG works well with turbochargers which are pretty common now days.

Infrastructure for LPG is here right now, why develop something that isnt as good??

If ethanol blends are all thats available in a few years, ill be looking at making an LPG vehicle purchase
Blitzkrieg

The article states that ethanol offers a greater octane rating than petrol.When E10 first came out a while back i noticed it was all rated at 94 octane,but now all the servos i’ve been to the E10 is only ever rated at 91 octane.Feels like a swiftys being pulled by the oil companys.Why bother using 91oct E10 when i might as well put regular 91oct petrol in.