Continental: Maybe 94 Unleaded Fuel Will Fly
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Teledyne Continental said on Wednesday that it has just completed a round of flight and test-cell trials that suggest that 94UL may be an adequate replacement for 100LL, whose existence is threatened by continued availability of tetraethyl lead. TCM says it will push for approval of 94UL as the leading replacement for 100LL. 94UL is essentially 100LL without the TEL additive. It meets vapor pressure and other avgas specs, but without the lead, it doesn't match 100LL's octane, which is typical about 103 straight from the refinery.
But is 94 sufficient octane to avoid detonation on a hard, hot climb on a summer day? Teledyne said in a press conference that it hasn't expanded its testing into all corners of the flight envelope but four flight tests in a normally aspirated A36 Bonanza have revealed no cooling or detonation issues thus far. The company also said it doesn't think Full Authority Digital Engine Control (FADEC) will be required to make the engines run properly on 94UL.TCM has not, however, conducted a standard FAA climb-cooling test, which is the regime in which detonation usually occurs. Further, said Continental, it's not opposed to autofuel as a replacement for 100LL provided that certain standards are in place to assure consistent specs with regard to octane, vapor pressure and especially oxygenate additives such as ethanol. Although pure ethanol has been approved for limited use in modified aircraft engine in Brazil, it's considered a bad actor for aircraft use because it's strongly hydrophilic, lacks the energy content of avgas and causes corrosion in aluminum parts and degradation of soft seals and gaskets. High-octane autofuel does, however, meet basic octane requirements for normally aspirated engines. Owners who use it are finding it increasingly difficult to find autogas without ethanol blended in.
What about Continental's large-displacement turbocharged engines, such as the TSIO-520 and -550 series? Will 94UL work for them? TCM says stay tuned; it hasn't done the flight testing to confirm that. Others who have, however, have had difficulty passing the climb cooling barrier without encountering at least light detonation. TCM began its alternate fuel testing about a year ago and it plans to push for ASTM approval of 94UL as the transparent replacement for 100LL. That application will be submitted in a few weeks and could be approved as early as next fall. However, that's just the beginning of 94UL's journey to becoming a certified fuel, if it ever does. It will still require FAA certification and approval and at least a paperwork shuffle so that owners can legally use it in some airplanes. TCM's testing took place in an IO-550-B powered Bonanza, but it has done test-cell work with the 200-series engines, the O-470 and O-520 series.