Ich kann nicht verstehen, warum die Hersteller da so zögerlich sind. Quelle hier.
The Continental TSIO-550-K was primarily designed for use with 100LL leaded avgas, but there is evidence it was engineered with future unleaded fuel compatibility in mind. When Cirrus and Continental developed the TSIO-550-K for the SR22T, they specifically chose this engine to prepare for a possible transition to lower-octane, unleaded fuels like 94UL, which was already being discussed as a "backstop" or future fuel at the time. The engine was optimized for performance and integration, and its selection was partly motivated by the need to ensure adaptability to a variety of fuels globally, including unleaded options.
Industry sources confirm that Continental has been preparing its engines, including the TSIO-550 series, for unleaded avgas, and 94UL has been a focus for future compatibility
. However, it is important to note that while the engine was designed with unleaded fuel compatibility as a goal, actual certification and approval for specific unleaded fuels (like 94UL or others) depend on ongoing testing and regulatory approval processes, which are not yet complete for this engine.
In summary, the TSIO-550-K was designed with the intention of being able to use unleaded fuel in the future, but as of now, it is not certified for unleaded fuel use.
When operated on unleaded fuel-specifically 94UL, which has a lower octane rating than 100LL-the TSIO-550-K experiences a small reduction in performance. According to Cirrus and Continental, the engine was designed with lower-compression cylinders (7.5:1) to allow safe operation on 94UL, resulting in about a 2% reduction in cruise performance compared to 100LL, though some engineers suggest the decrease could be slightly greater. For example, reducing power from 85% to 75% (as might be necessary to maintain detonation margins with 94UL) would lower maximum cruise speed from roughly 214 knots to 203 knots.
Other operational impacts include:
: No reduction in performance is expected during takeoff and climb, since these phases use full-rich mixtures, providing maximum detonation margins.
: At typical cruise settings, running on 94UL may cause a negligible increase in exhaust gas temperatures (EGTs) and no significant change in cylinder head temperatures (CHTs) compared to 100LL.
: To avoid detonation at high power settings with lower-octane fuel, ignition timing adjustments (retarding spark to about 20° BTDC from the usual 24° BTDC) may be required. This can raise exhaust and turbine inlet temperatures, potentially leading to operating limitations that some pilots may find restrictive.
: In test flights, the TSIO-550-K powered SR22T performed well on 94UL, with good power output and cooler operation in some scenarios, though limitations may be needed at high altitude and high power.
In summary, the TSIO-550-K’s performance with unleaded fuel like 94UL is slightly reduced in cruise, with minimal operational differences in most flight regimes, but may require power or procedural limitations to manage detonation risk at high power settings
