An analysis of ethanol/automotive gasoline blends for use in general aviation aircraft

Considering the rising cost and diminished availability of 100-octane, low-lead (100 LL) aviation gasoline, owners of aircraft certified for 100 LL may be forced to find an alternative fuel in the near future. This study proposed a blend of 200-proof anhydrous ethanol ($1.70 per gallon) and automotive gasoline ($1.05 per gallon) as a replacement for aviation gasoline ($1.75 per gallon). The research program included materials compatibility tests. Cooperative Fuel Research (CFR) engine tests, static thrust tests, and a flight test to determine the feasibility of such a blend as a fuel for an unmodified aircraft engine.

Throughout all tests, blends burned as well as aviation gasoline. Exhaust gas temperatures and cylinder head temperatures were hotter for the blends than for aviation gasoline. The static thrust tests indicated that a blend of 35% ethanol/65% automotive gasoline yielded the maximum thrust output. Fuel separation seemed to cause no engine problems. The materials tests revealed metals to be unaffected by contact with the blend fuel; the urethane elastomers showed signs of deterioration, but the nitrile elastomers seemed to perform satisfactorily. More research is needed in the area of materials compatibility. Fibrous growths were discovered in the blend and in the automotive gasoline samples.