Comment by credit_guy | Hacker News Reader

Comment by credit_guy | Hacker News Reader

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Petroleum contains many hydrocarbons, with chains of different lengths. Octane (C8H18) is one. Refineries separate various hydrocarbons. In principle a refinery can separate pure octane. If sold at the pump, that would be by definition gasoline with 100 octane rating. The majority of the hydrocarbons are worse than octane, but some are slightly better. So you could have gasoline without any additives that has an octane rating slightly higher than 100. The problem is that most chains have octane rating significantly lower than 100. What do you do with them? You throw them? Of course not. People create different blends, and add some additives so they can sell as much of the original petroleum as gasoline with a decent octane rating.

Yes, there are some other octane boosters. The main ones today are 3: ethanol, MTBE and ETBE. MTBE and ETBE are derived from methanol and ethanol respectively [1]. I don't know if there is anything wrong with MTBE or ETBE, but the ethanol lobby managed to push the idea that ethanol is good, so it is widely mixed in gasoline in the US.

According to the DOE [2]:

  Lower-octane gasoline is blended with 10% ethanol to attain the standard 87 octane.

[1] https://en.wikipedia.org/wiki/Methyl_tert-butyl_ether#Altern...

[2] https://afdc.energy.gov/fuels/ethanol_fuel_basics.html

You’re missing the chemistry involved, refineries don’t just separate out the constituents of oil as their name suggests. They manufacture the specific hydrocarbon blends using heat, catalysts, steam, and solvents that maximize the value of that oil.

EX: https://en.wikipedia.org/wiki/Cracking_(chemistry)

it's not the hydrocarbons or the fact that ethanol provides higher octane that I'm disagreeing with, it's this:

> and so less efficient engines, and fewer mpg

ethanol, while providing a higher octane rating (which if you drive a car that requires a higher octane rating for its immediate power might matter), actually lowers the mean mpg quite a bit, since it has much lower energy density.

that, and the fact that we're literally burning food, are some of my issues with ethanol.

I drive a car that knocks if I put less than 91 octane in, but if that octane is obtained from ethanol, it reduces the mpg by 25% (for 10% ethanol, higher if the ethanol percentage is raised). that's a problem. sure, I too want to get off of hydrocarbons that produce co2 for energy, but making that energy less efficient is not the way to do it, especially when we're burning our food and destroying the soil to achieve that.

No, ethanol has a lower energy density, but not that much lower as to make a huge difference.

Wikipedia has a handy table with the energy density of various fuels used in tranportation [1]. The net energy density per liter of regular gasoline is 32.2 MJ (megajoules). For gasoline with alcohol (which they call gasohol) it is 31.3 MJ. So gasohol has an energy density about 2.7% lower than regular gasoline, not 25% lower.

[1] https://en.wikipedia.org/wiki/Gasoline#Comparison_with_other...

> No, ethanol has a lower energy density, but not that much lower as to make a huge difference.

This isn't correct. It does make a huge difference in 4-stroke and an even larger difference in 2-stroke. Any engines that are being used for capacity / load will showcase the differential in a very significant way. Even according to the US Department of Energy they state that: "Denatured ethanol (98% ethanol) contains about 30% less energy than gasoline per gallon." [0]

If you've never towed in a vehicle that can use E-10 or E-15 and compared, I'd suggest you give it a shot. Be prepared for upwards of over 25% difference in gas mileage alone, not to mention reduction of power.

[0] https://afdc.energy.gov/fuels/ethanol_fuel_basics.html

Well, as someone else replied in the thread, if pure ethanol (98% is basically pure) has 30% less energy density than gasoline, then a mix of 90% gasoline and 10% ethanol has 3% less energy density.

I'm not sure what you mean by E-10. Basically all gasoline that is sold in the US is E-10. You have to look hard to not get E-10. I doubt you have performed the experiment you described, for the simple reason that it's hard to find gasoline that's not mixed with ethanol. I just googled, and apparently gasoline without ethanol is called "recreational gasoline", or REC-90 [1].

[1] https://en.wikipedia.org/wiki/REC-90

IME, the gas stations that sell ethanol-free gasoline seem to exist around farms or places where people use off-road gas powered equipment, though I don't have many data points. It stores for longer than ethanol blends (which absorb water over time), so it's better for filling up gas cans used to fill equipment, or infrequently used vehicles.

Around here every station has non-oxy premium but only one station has ethanol free regular unleaded 87.

Ethanol also has a nasty tendency to eat various portions of the fuel systems in older vehicles that don't have gaskets and hoses made of material specifically formulated to withstand it.

REC-90 is a very specific blend, which isn't sold in many states for the simple reason that they have others available.

Hell, just read the first sentence of the second paragraph of that wikipedia page:

> Unlike most stations in the plains states which carry ethanol-free 87 octane unleaded alongside 10% ethanol 87 octane unleaded, ...

As a midwest resident of a non-plains-state, I can confirm that there are plenty of gas stations that sell no-ethanol gas, either 87 or 93 octane (usually the higher, since it's a premium product anyway).

> I'm not sure what you mean by E-10. Basically all gasoline that is sold in the US is E-10. You have to look hard to not get E-10. I doubt you have performed the experiment you described, for the simple reason that it's hard to find gasoline that's not mixed with ethanol.

It's not really productive to make assumptions. Where I live I can buy non-oxygenated gas at almost every station. And, yes, I actually do this experiment all the time given I'll drive to places with a trailer where I'm forced to run an ethanol blend.

I realize my comment conflated two things: the reduction of performance and the difference in power per straight gallon. My point is that even with a minimal blend you can lose significant mileage / power. The easiest layman's way to measure that is in MPG. And, yes, there is a significant drop in both power available and MPG.

And for reference [0]: "Due to ethanol's lower energy content, FFVs operating on E85 get roughly 15% to 27% fewer miles per gallon than when operating on regular gasoline, depending on the ethanol content. Regular gasoline typically contains about 10% ethanol."

The above is in normal driving. So, no, I'm not making my statement up.

[0] https://www.fueleconomy.gov/feg/ethanol.shtml

it's called "clear" gas around here. there's a website that tracks places to buy it in all 50 states: https://www.pure-gas.org - but I've noticed that it doesn't track every location and is often wrong about prices, at least in my area.

I've never seen "REC-90" and had never heard of it before your posting. clear gas in my area is 92 octane, with up to 110 available in select locations.

most everyone I know who drives a performance vehicle, or a motorcycle can tell you where their closest gas station that sells clear gas is.

> I doubt you have performed the experiment you described, for the simple reason that it's hard to find gasoline that's not mixed with ethanol.

I've performed it many times over the last 17 years I've owned my current car. the results are always the same: 25% better gas mileage with the clear gas.

I keep track of my mpg, and am able to quickly see any difference between gasoline grades. I typically drive in my car's "power band", staying between 5000 and 6700 RPM.

If roughly pure ethanol has has 30% less energy than gasoline, going from a blend of 90/10 gasoline/ethanol to a 85/15 blend shouldn't decrease mileage by 25%.

It does [0].

"Due to ethanol's lower energy content, FFVs operating on E85 get roughly 15% to 27% fewer miles per gallon than when operating on regular gasoline, depending on the ethanol content. Regular gasoline typically contains about 10% ethanol."

[0] https://www.fueleconomy.gov/feg/ethanol.shtml

That link is about E-85. E-85 is 85% ethanol (actually 60%-85% depending on the season and the gas station). Ethanol has 30% less energy density than pure gasoline, so E-85 has 0.3*0.85=0.255 less energy density than pure gasoline. That is why E-85 gets 25% lower gas mileage.

"Standard" E-10 gasoline contains between 0% and 10% ethanol. E-15 is 15% ethanol. So E-15 has at most 4.5% less energy density than standard gasoline. You would not see a 25% decrease in gas mileage between standard gas and E-15.

> lowers the mean mpg… energy density

And that's why we don't quantify energy efficiency using just MPG. You adjust for the density to get some sort of mile per gallon-energy-equivalent.

> Making that energy less efficient

I have no idea at all how this could happen, except to say that your very rough numbers do suggest a reduction in energy efficiency. EtOH is supposed to have 34% less energy per volume, so for E10 the reduction should be around 3.4% (IGNORING VOLUME CHANGES WHEN MIXING). This matches well with the "up to 2.8%" claim of Wikipedia citing[1], but certainly not what your engine is doing.

[1]: https://web.archive.org/web/20070609142818/http://www.raa.ne...

> the fact that we're literally burning food

We are all minions of corn. The hope has for a long time been on grass and other stalks full of waste cellulose digestible only by microbes in ruminants and fermentation plants, but these just keep on not delivering.

Isobutanol was supposed to be a more gasoline-like biofuel too. Nobody figured out how to make it cheaply enough to burn either.

MTBE/ETBE is banned in many places due to groundwater contamination. But ethanol-less gasoline wouldn't be a disaster either, it would mean the refiners would have to do more processing (alkylation, reformation etc.) to increase the octane of the gasoline, which would increase costs. But OTOH without an ethanol mandate there might be less cost via agricultural subsidies etc., so it wouldn't surprise me if the total cost to society would be less.

There are also some other octane boosters that could be used (which aren't environmental disasters like lead, or arguably corn ethanol), like aromatic amines.

MBTE is a persistent ground water contaminant. Ethanol is definitely a better oxygenate.

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