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MBT Ignition Timing vs Ethanol Content

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in your video , u show MBT live on dyno for 60 Kpa with ethanol vs gasoline and as not expected (for me) MBT was 32.7 degree for gasoline and 28.9 for ethanol

when it comes to fuel burning rate , gasoline is faster than ethanol , so , we need much advance when using ethanol than gasoline

that`s why MBT should come with higher ignition advance for ethanol vs gasoline

or am i missing something here?1

Ethanol is faster burning than gasoline, at least under most part load conditions. So it takes less spark advance to get to MBT. See attached file. It's from a paper that Saab published about 10 years ago about their flex fuel engines. Each cell indicates the spark change due to E85. The dark gray areas on the left side (lower loads) indicate spark retard due to the faster burning of Ethanol.

Attached Files

G'day Ahmed.

My experience with E85 is pretty limited, but the way I understand it, in areas where the engine was not previously knock limited, and you were already at MBT, you'll end up retarding the timing to stay at MBT.

The converse is true for areas where the engine was previously knock limited. The knock resistance of the ethanol allows you to run more advance to get to MBT, but this amount of extra advance you require to reach MBT might not be as much as you'd think, because of the faster burn rate.

thank you guys

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