FAA Releases Findings of Initial Swift Fuel Study
August 24, 2010 —The FAA has released findings of a 150-hour engine endurance test of unleaded aviation fuel produced by Swift Enterprises that was conducted earlier this year. The report states that the test engine, a Lycoming IO540-K, showed normal engine wear, light engine combustion deposits, light fuel system deposits, and very light oil system deposits. The FAA conducted the testing at its Hughes Technical Center Aviation Fuel and Engine Test Facility (AFETF), in Atlantic City, New Jersey. Testing conditions were described as “severe,” largely spent at “maximum-rated power under maximum engine and oil temperatures.” (See full report here.)
“There was no indication of excessive wear on any of the high-contact, high-stress parts of the engine, and the engine oil analyses showed minimal fuel dilution,” the report reads. “There was no evidence of excess fuel nozzle deposits or fuel maldistribution. Cylinder combustion deposits, including spark plugs, valves, and piston face deposits, were light. Varnish and sludge buildup were light.”
Two issues that will require further testing include cold-starting difficulty and material compatibility. The report states that the cold-starting difficulty occurred when the engine was left to sit overnight, while starting with a warm engine was immediate. In this case “cold starting” does not refer to cold weather operations such as winter temperatures but rather to normal starting of an engine. Traditional remedies for cold start issues in aviation gasoline has included the addition of petroleum components that often result in lowering the octane or anti-knock characteristics of the fuel.
The FAA tests noted stretch marks or creases on the fuel secondary pump diaphragm leading to recommendations for further materials compatibility testing. No noticeable creases, softness, or brittleness were noticed in the fuel-metering unit and distribution valve diaphragms or the throttle and mixture o-rings. The test conducted was on an engine in an instrumented test stand and did not consider the potential impact on airframe fuel system components. The evidence of stretch marks on the pump diaphragm reinforces the need to determine how any proposed unleaded fuel formulations will behave in existing aircraft from the standpoint of materials compatibility.
The fuel used was a Swift binary blend, manufactured in a refinery and not in bio-process, to determine whether there were any initial major engine performance-related findings that would prevent further research into the use of a Swift binary blend of these components. Having found none, the FAA recommended further testing by Swift Enterprises on their blend made from their biomass process and conforming to an approved commercial ASTM fuel specification.