I think 89 is the usual midgrade, but the EIA says 89–90, so that’s what I ran with. As for why it’s higher in Europe, I don’t know for sure. It obviously improves fuel economy and emissions, but the actual “why” seems like an interplay between European regulation and industry from a long time ago that I wouldn’t know the half of.
That’s actually not correct. Fuel grades have to do with the fuel mixture’s ability to resist premature ignition. High performance engines look for higher octane fuel so that they can compress it further and more tightly control timing. Lower grade fuel will combust under higher compression and cause knocking in engines that require more compression and timing. The ECU will then try to adjust to alleviate the knocking reducing the cars rated performance.
The only relationship to efficiency and fuel octane is that when you’re not using the octane expected by the engine in question you could reduce your MPG which in turn may lower your fuel efficiency.
Okay, yes, sorry, I should’ve been more clear: the engines need to be designed for it to have this effect.
However, my overall point being that higher compression ratios improve efficiency in Otto cycle engines, and those engines with higher compression ratios require higher-octane fuel to reduce knock. Thus it’s not “the only relationship to efficiency”, because that need for knock reduction is a consequence of a more efficient engine.
Great paper actually but my point still stands. It’s not the fuel itself that creates more efficiency, it’s the fuel that is required to help these legacy cars achieve such efficiency.
Thus, these vehicles realize an improvement from increased octane rating in accordance with their ability to spark advance to take advantage of a fuel with a higher octane rating.
It’s the engine tuning not the fuel. If you just take higher octane fuel and put it into a legacy engine you’ll have no difference in your efficiency. The ECU must be programmed, if capable.
Fuel has two octane values: research and motor. The value you’d see at the pump in the US is the average of research and motor.
The spec for AI-95 is 85 motor and 95 research. I.e., this would be midgrade fuel – you’d see a ‘90’ in the US.
Ahh thanks. I was wondering why they needed damn near race fuel for their cars.
Also, if 90 is mid-grade, know that 91 is considered premium here.
I think 89 is the usual midgrade, but the EIA says 89–90, so that’s what I ran with. As for why it’s higher in Europe, I don’t know for sure. It obviously improves fuel economy and emissions, but the actual “why” seems like an interplay between European regulation and industry from a long time ago that I wouldn’t know the half of.
That’s actually not correct. Fuel grades have to do with the fuel mixture’s ability to resist premature ignition. High performance engines look for higher octane fuel so that they can compress it further and more tightly control timing. Lower grade fuel will combust under higher compression and cause knocking in engines that require more compression and timing. The ECU will then try to adjust to alleviate the knocking reducing the cars rated performance.
The only relationship to efficiency and fuel octane is that when you’re not using the octane expected by the engine in question you could reduce your MPG which in turn may lower your fuel efficiency.
Okay, yes, sorry, I should’ve been more clear: the engines need to be designed for it to have this effect.
However, my overall point being that higher compression ratios improve efficiency in Otto cycle engines, and those engines with higher compression ratios require higher-octane fuel to reduce knock. Thus it’s not “the only relationship to efficiency”, because that need for knock reduction is a consequence of a more efficient engine.
Great paper actually but my point still stands. It’s not the fuel itself that creates more efficiency, it’s the fuel that is required to help these legacy cars achieve such efficiency.
It’s the engine tuning not the fuel. If you just take higher octane fuel and put it into a legacy engine you’ll have no difference in your efficiency. The ECU must be programmed, if capable.
Thanks for the clarification, the difference between us and us been buggin me for ages.