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

In summary: The second stage of knock happens when peak pressure is shifted, however the air/fuel mixture within the chamber has already started to combust. So, relying on peak pressure to prevent detonation or pre-ignition would be very dangerous.
  • #1
chayced
157
0
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/internet_articles/Spark-Advance%20Control%20by%20Ion-Sensing%20and%20Interpretation.htm
 
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  • #2
Apart from not reading the article yet, if your fuel amount changes for some reason, or, if there is mechanical separation 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.
 
  • #3
Thanks! Guess I will be using knock detection as well at least as a safeguard.
 
  • #4
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.
 
  • #5
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.
 

1. What is closed loop spark advance?

Closed loop spark advance is a system used in internal combustion engines to control the timing of spark plug firing. It uses sensors to monitor the engine's performance and adjusts the ignition timing accordingly.

2. How does closed loop spark advance work?

Closed loop spark advance works by using sensors to measure various parameters such as engine speed, load, and air/fuel ratio. This data is then sent to the engine control unit (ECU) which calculates the optimal timing for the spark plug to ignite the air/fuel mixture in the cylinder.

3. What is the purpose of closed loop spark advance?

The purpose of closed loop spark advance is to improve engine performance and efficiency. By continuously adjusting the ignition timing, the engine can operate at its most efficient level, resulting in better fuel economy and lower emissions.

4. How does closed loop spark advance affect abnormal combustion?

Closed loop spark advance can help prevent abnormal combustion, such as knocking or pre-ignition, by ensuring that the spark plug fires at the right time and in the right amount. This helps to maintain the stability of the combustion process and avoid any potentially damaging effects.

5. Are there any limitations to closed loop spark advance?

While closed loop spark advance is an effective system for controlling ignition timing, it does have some limitations. For example, it may not be able to adjust the timing quickly enough in certain situations, such as sudden changes in engine load. Additionally, the system relies on accurate sensor readings, so any malfunction or faulty sensor can affect its performance.

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