TCM Tackles the Fuel Problem


During Continental’s press conference summarizing its fuel research into a replacement for 100LL, I had the odd feeling of waking up from a bad dream. As we reported this week, Continental’s idea is that maybe the industry can get by on a fuel called 94UL-essentially 100LL minus the lead. They’ve embarked upon a series of tests to find out if the supposition will fly, so to speak.

The bad dream part is that for nearly three decades we’ve been writing stories about the difficult struggle to find an octane enhancer as good as lead and now here comes TCM to say, well, never mind. It reminds me of that classic headline about World War I: “Archduke Found Alive; War a Mistake.”

I’m happy to see Continental take on this research and happier still to see them talking about it. The engine companies have tackled this critical problem only in fits and starts and Continental’s last run at the problem, its PowerLink FADEC, has been met with disinterest in the market.

Nonetheless, I think Continental is going to have its hands full proving that 94UL has sufficient octane to keep high-power turbocharged engines from detonating under worse-case conditions. Previous efforts at running lower octane fuels in such engines haven’t been encouraging. The problem is that in that tiny slice of the envelope that represents high power, high temperatures and high altitude, cylinder head temps head for the mid-400s. In a perfect world, if the factory got the baffling right and if it stays right after a few years of mediocre maintenance, maybe the cylinders will stay cool enough. I’ll believe it when I see it.

There are various ways to address the lack of octane. One is to throw more fuel at the engine-the old gas-is-cheaper-than-valves approach. Another is to throw more air at it, in the form of faster climbs or lean-of-peak operation or both. Retarding the timing a few degrees can also help. All of these exact a performance penalty and Continental concedes the point. It also concedes that the 94UL solution won’t necessarily require FADEC, an encouraging nod to market reality.

Even if it turns out that 94UL won’t work for turbocharged engines-or at least all turbocharged engines-it would be nice to have it available. For the vast majority of airplanes, it has more than enough octane.