The Oil Drum

173 comments on The Mythical Ethanol Threat

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Starship Trooper on May 29, 2007 - 9:15am

Yes, it depends upon region but it really is a function of altitude. You don't need 87 octane in Sante Fe, NM or Denver, CO because the already less dense atmosphere does not require higher octane. The compression ratio is the same at altitude but the absolute pressure reached during the compression stroke of the 4-cycle spark-ignited engine does not require the high octane rating to avoid knock from predetonation in the cylinders.

In the Four Corners region of NM you can run straight-run gasoline at 79 octane and have no problems. But it seems that most of the gasoline I saw in Colorado and Wyoming last year was 83 octane. Just don't take your vehicle below 2000 feet above MSL with that 79 octane gas in your tank.

Eastern Nebraska is about 1200 feet above MSL. Western Nebraska is at 4000-5000 feet, But most of the region within normal driving range is well-suited to the lower octane gasoline.

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Antoinetta III on May 29, 2007 - 3:17pm

Just what is "Octane" anyway? By the way, I remember, back when I was a kid in the '60s, with my parents in the car, when we went to the gas-station, signage on some of the pumps proclaimed "100+ Octane." Yet now I never see any references to Octane levels above the low 90s. What does Octane do, and what happened to the 100+ stuff?

Antoinetta III

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Mriswith on May 29, 2007 - 7:40pm

Octane is a measure of the ability of gasoline to withstand compression without spontaneously igniting.
Back in the old days, preignition in gasoline-engines was a major problem. This phenomenon, known as knocking, affects performance, but has largely been eliminated in modern gasoline engines. Today, high octane is mostly desired by high-performance engines, such as gasoline turbo engines.

Supposedly, the availability to the RAF during WW2 of tetra-ethyl lead, was one of the factors that won the battle of Britain. Tetra-ethyl lead, the blending component which is added to make leaded gasoline, was able to give the british aircraft engines the extra performance they needed to outfly the Luftwaffe.

This is as far as my knowledge goes... Hope it helps.

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jbl on May 30, 2007 - 2:44pm

Yes, the allies steadily increased the octane rating of their avgas during the war. At the end of the war they were using 115/145 (lean/rich) octane avgas. Or to be pedantic, when the number is >100, it's called "performance number" instead of octane, due to a different way to determine it (basically % power increase vs. 100 octane).

These high ratings were achieved mostly by ridiculous amounts of TEL.