this post was submitted on 01 Jul 2024
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54
why do a bunch of gas stations have 88 octane cheaper than 87? (lemm.ee)
submitted 4 months ago by [email protected] to c/[email protected]
42 comments fedilink hide all child comments
 

I figured it was a marketing gimmick to get you to buy 88 and then they would finally raise the price, but it's been years. are they adding extra ethanol or something?

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[–] [email protected] 3 points 4 months ago (2 children)

If anything, it would make sense to have gasoline with ethanol content in summer because ethanol is more knock-restistant, which you are more prone to if tempereatures are warmer.

[–] [email protected] 1 points 4 months ago (1 children)

Ethanol usage in the summer creates smog and other pollution which is why it's normally only for winter usage. Except this year, they allowed it to be used longer in an attempt to give Biden a boost in the polls

[–] [email protected] 2 points 4 months ago (2 children)

I googled a bit and the web said that ethanol does indeed burn cleaner which makes sense since there should be less contaminants and more oxygen is available. Ethanol also absorbs more heat then vapourized so there should be less heat in the combustion chamber resulting in less NOx emmissions. Do you have any sources for your claims? I would like to read about it because clearly i don‘t know everything about burning ethanol.

[–] [email protected] 3 points 4 months ago

“Adding ethanol to gasoline is known to increase smog pollution in hot weather, but research has shown little difference between E15 and the more-widely available E10 blends.”

https://www.reuters.com/business/energy/us-epa-allows-temporary-expansion-higher-ethanol-gasoline-blend-this-summer-2024-04-19/

[–] [email protected] 1 points 4 months ago* (last edited 4 months ago) (1 children)
[–] [email protected] 2 points 4 months ago (1 children)

Afaict from reading that (and one of the sources, and its source) it boils down to the fuels’ “RVP levels” (which have an impact on volatility and the amount of VOCs given off) being past a particular threshold. E10 is also past that threshold, but it has an exception that E15 doesn’t have. However, by that same measure, E15 is less volatile than E10.

The author also expressed concern about expanding corn production as a result of expanded E15 and that there haven’t been sufficient studies on the impact of E15 on the environment (particularly in the summer months). But that’s also paired with a statement saying that “consumers don’t want E15,” which detracts from the previous arguments; if true it means their impacts, if any, would be minimal.

I didn’t read every link from that page but none gave a better reason.

My takeaway is that it sounds like we don’t have any data showing that E15 is worse than E10, so the obvious move is to actually start funding those studies.

I also found https://foe.org/blog/2012-05-understanding-e15/ which is very anti-E15; however I wasn’t able to verify their claims because none of the linked articles loaded for me.

[–] [email protected] -1 points 4 months ago (1 children)

I mean the proof is in the pudding with this one as you must also ask yourself why E15 is banned during summer months in the first place. If you can answer that question you'll likely find the information you're looking for.

[–] [email protected] 2 points 4 months ago

the proof is in the pudding with this one

It isn’t.

as you must also ask yourself why E15 is banned during summer months in the first place.

I did. And I shared that in my comment above.

Your source doesn’t share any data on the topic, even just as a summary, but it links to summertime smog, which links to “smog-causing pollutants”, which says:

Section 211(h)(1) of the Clean Air Act prohibits the sale of gasoline that has a Reid Vapor Pressure greater than 9.0 psi during the “high ozone season,” which runs from June 1 to September 15. (RVP is a measure of volatility; high-RVP gasolines release more volatile organic compounds into the troposphere where those VOCs contribute to ozone formation.) Gasoline-ethanol blends below E50 are more volatile than straight gasoline and cannot readily meet the 9.0 psi RVP requirement. Congress created a “one-pound waiver” at Section 211(h)(4) that increases the RVP limit from 9.0 psi to 10.0 psi, but—and here’s the catch—the waiver is only available to “fuel blends containing gasoline and 10 percent denatured anhydrous ethanol.” That is, only E10 can take advantage of the one-pound waiver. Although E15 is slightly less volatile than E10, its RVP still exceeds 9 psi. It needs a one-pound waiver to meet Section 211(h)’s RVP limit in the same way that E10 does, but it is not eligible for one under current law.

The article’s justification for why E15 isn’t legally permitted is that there’s a law against it, which is circular logic. From the environmental protection perspective, it doesn’t sound like there is data suggesting that E15 on its own is worse for the environment than E10. If the only argument is a legal one, it’s not a good argument.

If you can answer that question you'll likely find the information you're looking for.

I did, and I shared that answer in my comment above, too - but it’s not the answer you seem to think it is.

[–] [email protected] 1 points 4 months ago (1 children)

Knock resistance is related to octane and not ethanol content directly I thought

[–] [email protected] 3 points 4 months ago

You are correct. Ethanol does have a higher octane rating though so a blend of gas and ethanol will have a higher octane rating and hence knock resistance.