Big ignition advance at high rpm/low load

I need to explain this ignition map (picture attached).It is from a Ducati motorcycle, which looks similar on all older models up to about 2015 (I haven't had the chance to do the newer ones yet...)

The blue line is approximately acceleration, the green deceleration. In the yellow circle, on some models, under certain conditions, engine knocking occurs, e.g. when 1- adding gas without load, 2- gradual acceleration, 3- maintaining a constant speed.

My main question, why is there such a big ignition advance in the red circle I marked?

Please try to attach your image again, I'm not seeing an attachment.

Maps

Because fuel burning is time based. Lower density mixtures burn slower so that takes more time, and with very high RPMs (9-10k) there isn't a lot of time. Therefore the ignition lead in degrees has to be much more advanced.

BTW if they don't do that, you will find really high Exhaust Temps. This could also hurt the exhaust valves.

Math:

Let's look at how much time 60deg @ 9000 RPM takes.

9000 RPM / 60 (sec/min) = 150 revolutions / sec = 360 deg/rev x 150 rev / sec = 54000 deg/sec. 1 Sec / 54000 deg = 0.018 milliseconds / deg. 60 deg * 0.018 ms = 1.1 ms. This is a pretty typical burn time for complete combustion.

I kind of know and understand it, but according to that there should also be such a big advance at full throttle in this case 81% it is only 38° compared to 60° at 6-12% TPS.

The thought occurs to me, since there is such a large advance of the ignition in the area of deceleration, whether it has an effect on the engine brake?

This difference at full throttle, is there is more total mass (air & fuel) and therefore density is much higher. This makes the burn happen faster and you need less ignition lead. Notice when forced induction is used how the ignition timing is retarded as the density is increased.

yes you can tune engine braking with the ignition timing as well in the overrun areas.

As David says, timing is a function of the cylinder filling which affects the speed of the burn, and the rpm which affects the time available for it, and the balance between MBT (where the best torque is found) and detonation limits (where "pinking") may occur.

If I understand your question, yes, the amount of advance on over-run may affect the burn and the compression/expansion around TDC. How much, though, is the question?

In addition to those great comments, a lot of what you're seeing is the product of an engine that seems to require a lot of timing advance in general.

There's no set disparity between cruise and full throttle timing that works on all engines, but timing being 25 degrees more advanced at cruise vs. at full throttle on an NA engine is not an oddly large amount. Some engines run 30-40 degrees more timing at cruise vs. full load at a given RPM.

Thank you for the useful answers, I will take them into account.

I will also share the ignition map I have from my bike, it is the same type of Ducati engine that I have a race ECU on that has been tuned by a tuner in the past. It is interesting that in the area of deceleration (the green line and especially in the critical area the red circle) there is no longer such a large lead of 60 deg as in all ignition maps from the manufacturer

Note: the map is implemented on the contrary, the x-y axes are changed.

A lot of race maps look that like. They don't care about engine performance off throttle. So it makes less torque, the racer will just open the throttle more.

By reducing advance at low/mid throttle further, and not employing decel fuel cut off, you reduce engine torque more. This is done to give the driver/rider a broader range of torque output they can control. It's like making throttle a volume knob that goes from 10-100 vs. 30-100 (numbers just for the sake of illustrating the point), and helps modulate torque to the available grip better.

On a street bike you're more concerned with fuel economy and emissions so you want the additional low load timing to get the most out of those areas.

After these two answers, it is more clear to me. Thanks guys 🙂