According to https://en.wikipedia.org/wiki/Top_Tier_Detergent_Gasoline you're getting at least the EPA minimum amount of detergent additives even in low-octane fuel, and many brands participate in the Top Tier standard that requires even more additives, again with the requirements applying even to low-octane fuel. So I wouldn't bother paying extra for premium fuel for the sake of additives when the higher octane rating isn't needed. Which gas station you go to will probably affect that more than which grade of fuel you select at the pump.

Although stations buy from a lot of suppliers so how could you even know?

There is generally one refinery that all stations in a given town buy from. Shipping fuel from a different refinery would be enough more expensive that you wouldn't be competitive.

Sometimes stations have their own additive package.

Go to a station that sells one brand. Like a Shell or Exxon (Esso) station.

If you want the cleaning additives you can just buy them separately and pour them in, i.e. Chevron Techron.

You're getting them anyway, but sure in the sense that you're getting part-premium. I don't know many, if any in the US, that have actual USTs full of midgrade and don't blend the two more common ones at the dispenser.

Priming has nothing to do with cleaning. It’s higher octane fuel. If your car Isn’t designed for higher octane fuel it will run like garbage. The whole point of high octane fuel is that it requires a higher temperature to ignite. If your car Isn’t designed for it it’s most likely only going to partially burn the fuel.

No, the main point of high octane fuel is to be resistant to higher compression ratios so it doesn’t pre-detonate. Spark plugs have no issues igniting it.

What op is referring to is additives that are added in by some gas dealers to the high octane fuel to upsell you. “Techron” is one I recall seeing at Chevron IIRC.

You can sometimes buy the additives separately. e.g. for Techron: https://amzn.to/33LH1RN

The parent comment is right. It's not just the spark; heat and pressure are also part of what ignites your air/fuel mixture.

Not with gasoline. A gas engine can ignite at temps well below 0F and low compression.

You might be thinking of diesel. Diesel depends on compression to combust and has heater coils to ensure minimum temps as well.

This is more obvious when you read engine specs and they have minimum octane ratings, not specific ratings.

High-octane fuels will not burn poorly. It just isn't necessary to increase octane further once the threshold of knocking/self-ignition at the target compression and cylinder temperature is reached.

Plus you missed the point: In many places the premium fuel is the same octane number as regular (e.g. 95), but premium is with additives for <insert vague marketing>.