Why does mixing fuel change octane linearly?

Let's say we have pine saw dust (flash point 300c) and oak saw dust (360c) . If we mix equal parts, I wouldn't expect the flash point to be 330c.

What does fuel work differently? What is the mechanism for this? Bonus points for a technical answer.

 

I technically don’t know

But I suspect it has to do with how they bind to each other.

I don’t think mixing wood dust physically changes the properties of each. Where as mixing gas physically changes each.

 

I’ll give it a whirl…

Octane isn’t an ingredient in fuel. It’s technically an Octane Rating…. meaning a comparison of how likely a fuel is to spontaneously combust vs Octane (which gets a rating of 100). Mixing fuels with a high and low octane rating gets you a mixture with an octane rating in the middle. Doesn’t tell you anything about the energy in the liquid, just how likely it is under a certain pressure to explode without an ignition source. It’s probably not perfectly linear

Been a while since engineering school and I’m not going to look up the curves

Flash point is a little different because it’s the lowest temperature a liquid will form a vapor that’ll ignite - not spontaneously combust. So the flash point is an absolute number deals with the surface and evaporation characteristics of a liquid while octane rating is a relative number and deals with the internal characteristics of a liquid mixture.

edit: alright this got me thinking - no way it’s linear. And turns out it’s not:

https://www.e-education.psu.edu/fsc432/content/octane-number-blending