John N. Packard

Vapor Lock

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JIGGERS !!!! Here come the Octane Police ! I have to run and hide ! While I am gone , please read the short paragraph above the distillation curves shown in the bottom pic. This from "Marks' Mechanical Engineers' Handbook" , 2nd. Ed. , 1924. Also from "Marks'......." 3rd Ed. , 1930 , shown in the middle pic, please read the paragraph to the left of the distillation curves. This will explain the degradation of gasoline from the mid or late 'teens , and finally a recovery similar to the very good gasoline available until the mid 'teens. The distillation curves in the top pic are from "Marks'......." 6th Ed. , 1958 . Now , octane in 1920 was around 40. By the end of the '20s , around 50. Engines of the time were perfectly matched to the gasoline available , as the Octane Police will teach us. Low compression long stroke engines must use LOW octane gasoline because it burns FASTER ! Huh ? Yup ! HERE THEY COME ! Gotta lay low for a while. Let me leave you with this : Octane refers to flamefront propagation rate under standard conditions. The higher the octane , the slower the flamefront propagation rate.  Hiding out , - Carl

 

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Edited by C Carl
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13 hours ago, Spinneyhill said:

Does vapor lock occur more or less readily using fuel containing ethanol?

 

It is my understanding that adding ethanol to gasoline raises the vapor pressure, that is it makes it more likely to vaporize and thus more likely to cause delivery issues in a low pressure carburetor type fuel system. https://duckduckgo.com/?q=effect+of+ethanol+on+gasoline+vapor+pressure&bext=msl&atb=v45-6&ia=web

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I thought Octane referred to a fuel's ability to resist knock, or pre-ignition, hence the higher the compression, the higher the octane required.

??

 

jp 26 Rover 9

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I thought Octane referred to a fuel's ability to resist knock, or pre-ignition, hence the higher the compression, the higher the octane required.

??

 

jp 26 Rover 9

 

-------------------------------------------------

 

Yes, it is.

 

For additional info on that look up what the term "anti knock index" means.  Sometimes seen on gas pumps as "AKI".

 

There's lots of info on octane rating verses flame propagation speeds, too. Here's just a bit of some of the explanation available.

https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=967599

 

Paul

Edited by PFitz (see edit history)

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BRAVO , PAUL !! Thank you very much for alerting us/me to the Gasoline FAQ. Reading all 4 parts is extremely interesting. I have already learned quite a bit , but this will require considerably more study on my part. Have any of you guys read all of this ? Are any of you engineers ? I already have two major conflicts between prior knowledge and what I have learned so far. I have been curious about aspects of octane/flamefront propagation rate for decades. I cannot reconcile previous long held understandings with this marvelous new information. Very difficult to argue with anything in this well written document. Therefore, as with any learning process, this has stimulated questions brewing up in my mind. I hope you guys will be able to answer what I may not be able to answer myself. I think that will be the only way the Octane Police will let me make bail ! By the way : are any of you guys old flight engineers going back 50 years or so to the days of recip power ? Also , Paul , do you have any other links to octane/flamefront rate ? Thanks again for the fascinating read !  - Carl

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C Carl.

 

Your welcome. There is a lot of info if you do a web search using the search term, "octane and flame front propagation".

 

Keep in mind that todays gasoline is not the same as that from decades ago.

 

With all the additives there is not much "gasoline" in today's gas.  And additives can not only change octane rating, they can affect flame front propagation. So discussions of flame front based on old texts are not really relevant  to what we can get at the gas pump, except to have a debate to chew on. :) 

 

Plus, octane rating is not the only thing that affects flame front propagation. Turbulence inside a combustion chamber, plus combustion chamber shape can also affect how a flame front can react. 

 

I would love to have some drums of fresh 57 octane gas from the late 1920's, plus some 1930 Sunoco Blue 70 octane, to try out on my customer's cars to see what they really ran like when new. We can restore them mechanically to showroom new, but we can't restore what comes out of the gas pumps. And that has a big affect on how they were originally designed to run.

 

As you know, a lot has changed in the automotive chemical world in 90-100 years. Some things still apply and some don't. The trick is in don't assume everything they knew back then was the end-all be-all of automotive engineering knowledge.  And conversely, don't assume that all "advancements" we've made are across the board best for antique cars.  ;)   

 

Paul  

Edited by PFitz (see edit history)
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I had a 1935 Oliver Hart Parr 70 tractor.

Designated 70 because it was rated to develop its horsepower with 70 octane gasoline.

The Continental 6 cylinder engine had fairly high compression for the time.

I skidded quite a few logs with it and it needed to work pretty hard going up hills in our woods.

I never used anything other than 97 octane gas in it and it ran perfectly.

If I had to guess it probably ran better than it would have with 70 octane gas.

I DO know it dynoed 30 horsepower so....... :P

Edited by cahartley (see edit history)
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