Announcement

Collapse
No announcement yet.

Octane

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Octane

    Does adding ethanol to fuel increase or decrease the octane you see advertised on the pump?
    Follow up, did refineries change their formulas to account for the change in octane that adding ethanol would affect gasoline? or, is the octane rating just for the gasoline portion and no one knows what ethanol did to the octane ratings?
    Doing it all wrong since 1966

  • #2
    I wish I could figure it out too. My son is leaning towards the side where the e-85 is higher octane, but you need to open up jets or injectors, so you end up using close to twice as much, or in our case, 2 tank fill ups per week. I am running all stainless fuel lines this time just in case.

    Comment


    • #3
      Okay, so RCW 119.112.020 says it can be either or.

      But my bet - and I'm going to look more because I'm curious - is they rate it before they add ethanol because if they didn't, they'd have to change the stickers on the gas pump every time they went from a winter to a summer blend....the sticker says "contains up to ___% ethanol".... because the octane rating would change with the blend, they'd have to change the sticker when they got different rates. They cannot get in trouble if the rating is higher but the penalties are severe if it is less than the sticker on the pump....

      And my gut feeling - I've found that the variance in fuels would make one tank knock like a woodpecker and the next not at all in the 90s just doesn't seem to be as likely anymore.... sure, better refining.... but

      still waiting for our resident professionals to weigh in (like what I did there?).
      Doing it all wrong since 1966

      Comment


      • #4
        Octane is overrated. I'm sticking with cetane.

        Dan

        Comment


        • #5
          Originally posted by DanStokes View Post
          Octane is overrated. I'm sticking with cetane.

          Dan
          always the contrarian, shall we get off your lawn too?
          Doing it all wrong since 1966

          Comment


          • #6
            First let's define octane; It is a number arrived at either in the research mode or motor mode, each of which is a method of operating a fing big one cylinder research engine (and no we didn't have one at EPA...). The number corresponds to the percent of Iso-octane, assumed to be 100 on the octane scale, in a total mixture of Iso-octane and heptane, heptane being the 0 end of the scale.

            So if the research engine just operates without preignition, ping knock, with say 87% Iso-octane, then its an 87 octane fuel. But wait a minute, is that motor or reasearch? The answer here in the US is both. The engine will have been operated on both modes to get the 2 numbers, R and M let's call them. Then using a simple formula: octane = (R + M)/2 we get the average of those 2 numbers.

            The problem is some engines will detonate on a fuel with ahigh researchnumber but a low motor number, and vise versa (has to do with combustion chamber shape, fuel mixing, quench, air temperature, compression ratio, cam timing, and a few other factors thrown in for good measure).

            Now we get to the question as asked: Does ethanol affect the octane rating? Yes and no. I know, not a good answer.

            Yes the fuel mixture is adjusted to some lower octane without the ethanol. When ethanol and the fuel comingle, there is a rise in the apparent octane rating. The fuels people have redefined some of these terms when using alcohols. Ethanol has an apparent octane rating, or as the renaming goes, octane number (tricky right???), of about 110. Methanol has an apparent octane rating of 130-ish. I don't remember the next 2 up alcohols numbers, Isopropyl and Butyl alcohols, but they are lower, but still good for fuels.

            So why the different terminology? Combustion differences and heat of vaporization. If you have used methanol as a race fuel, on a hot humid summer day, there will be ice forming on your fuel injectors. Neat to see, lowers the air/fuel charge temperature significantly and inhibits preignition and slows burning, both good things for high compression engines. All of the alcohols have higher latent heats of vaporization, but as the molecule gets closer to a big hydrocarbon chain, it gets harder to vaporize. As a visual in your mind, think gasoline and diesel fuel. Which one vaporizes easier? And lights easier when you are getting fire extinguisher training on a cold day behind your test labs. Dan may remember between Dan Ray Oulette and myself, we improvised a flair on the end of a length of conduit so the experts (who couldn't light a fire) had fire for us to put out in a barrel of diesel.

            The final thing: the comingling effect isn't linear. Also alcohols tend to be hygroscopic, meaning they will suck moisture up right out of the air, and at some point the bond or more correctly the aziotrope, is broken and the alcohol and water, fully mixed and happy separates from the hydrocarbon portion of the fuel. I hesitate to call it gasoline these days, as it isn't what we all grew up with, and also the real experts in the industry call it fuel these days, so...

            So as a closing note. If you need some alcohol-free fuel for an older small engine, and it's not available in your area, here's how to "make" it. In a clear container of a useful size, say a gallon, put in 1/2 gallon of the highest octane fuel in your area. Now take a half gallon of water, well you don't need that much, it just makes the results easier to work out, put some blue or green food coloring in and mix well. Now mix the colored water with the fuel, shake lightly (it doesn't take long or much to make this happen). The colored water will make a chemical bond with the alcohol, breaking the aziotrope, and turning that mixture whatever color you used. It will settle to the bottom. The upper portion will be hydrocarbon fuel (gasoline???) of about 3 to 5 octane numbers lwer than listed on the pump. Pore it off carefully so as not to make salad dressing, and dispose of the water environmentally (don't drink it, as even tho it's ethanol, it will have traces of benzene and other nasty chemicals...).

            Comment


            • #7
              Originally posted by SuperBuickGuy View Post

              always the contrarian, shall we get off your lawn too?
              Yes! Little ba$t....... Hell, when I was a boy we had RESPECT for our elders blah blah blah.........

              Dan

              Comment


              • #8
                Originally posted by DanStokes View Post

                Yes! Little ba$t....... Hell, when I was a boy we had RESPECT for our elders blah blah blah.........

                Dan
                Dirt hadn't been invented yet when you were a boy! If I am 2 days older than dirt, and you are waaaayyyy older than me, then...

                Comment


                • #9
                  Originally posted by DanStokes View Post

                  Yes! Little ba$t....... Hell, when I was a boy we had RESPECT for our elders blah blah blah.........

                  Dan
                  I never realized that people existed when you were a kid... well I'll be...
                  Doing it all wrong since 1966

                  Comment


                  • #10
                    So SBG did that help? Sometimes I get a little wordy...

                    Comment


                    • #11
                      Originally posted by dave.g.in.gansevoort View Post
                      So SBG did that help? Sometimes I get a little wordy...
                      it does help - thank you.... especially the how-to-get the alcohol and water out. That's pretty cool
                      Doing it all wrong since 1966

                      Comment


                      • #12
                        For Two Days Older.......
                        He sure Learned a lot in them TWO DAYS......
                        Just Saying........
                        SBG,
                        I'm So Old, they Discontinued My Blood Type...
                        LOL
                        Captain
                        Superhero BangShifter
                        Last edited by Captain; April 10, 2021, 07:15 PM.

                        Comment


                        • #13
                          Originally posted by dave.g.in.gansevoort View Post

                          Dirt hadn't been invented yet when you were a boy! If I am 2 days older than dirt, and you are waaaayyyy older than me, then...
                          And I have 2 (count 'em TWO) older brothers!

                          Dan

                          Comment


                          • #14
                            Originally posted by DanStokes View Post

                            And I have 2 (count 'em TWO) older brothers!

                            Dan
                            And one is a plumber like Dan... Weebles wobble, but you can't flush them down! I still love that story

                            Comment


                            • #15
                              Originally posted by dave.g.in.gansevoort View Post

                              And one is a plumber like Dan... Weebles wobble, but you can't flush them down! I still love that story
                              about time we had someone here to keep Dan in line...ish.
                              Doing it all wrong since 1966

                              Comment

                              Working...
                              X