Closed loop spark advance and it's effect on abnormal combustion.

chayced

Recently I read about Saab's experiments at closed loop spark advance, and it got me wondering. If you are controlling spark advance to maintain a constant peak pressure position of 20 deg after TDC is it possible to get into a situation where detonation or pre-ignition is possible. It seems to me that as cylinder temperature starts rising it will push the peak pressure closer to TDC which should drive the controller to retard timing before any abnormal combustion can occur. Any thoughts?

http://www.max-boost.co.uk/max-boost...rpretation.htm

Fahlin Racing

Apart from not reading the article yet, if your fuel amount changes for some reason, or, if there is mechanical seperation of air/fuel within the chamber. Having the amount of monitoring capabilities & adjustability we have today, its much more difficult to get into the abnormal areas. Doesn't rule out the detonation or pre-ignition possibilities IMO. All it takes is a hot spot ahead of the flame front with a little coagulation of fuel, heat and pressure from mechanical and approaching flame front. If we can harness the best possible process we could influence in the chamber we can prevent to a point, damaging combustion.

chayced

Thanks! Guess I will be using knock detection as well at least as a safeguard.

Fahlin Racing

Well, I would read more than that article to make a choice of how you maintain good combustion efficiency and prevent abnormal combustion. Numerous ways have been done and there are still more ways out there. They just haven't been found yet.

chayced

The problem I am facing is that there is little research on closed loop ignition control. Using ecu timing curves does not allow for changing timing as combustion itself changes, it only allows for limited changes based on known variables like ECT or IAT. I think I did find the answer though, by looking at several different sources for combustion pressures during knock. The first stages of knock happen without shifting the peak pressure. So relying on peak pressure alone is dangerous.