Method to enchance light load HCCI combustion control using measurement of cylinder pressures

1. Method for controlling an amount of fuel reforming in an internal combustion engine configured to selectively operate in a homogeneous charge compression-ignition combustion mode with an exhaust recompression strategy, comprising:

monitoring in-cylinder pressures during a current combustion cycle;

utilizing monitored in-cylinder pressures to project reforming required in a next combustion cycle; and

controlling the next combustion cycle based on the projected reforming required in the next combustion cycle;

wherein the monitoring in-cylinder pressures comprises monitoring a pressure ratio through a recompression period.

2. The method of claim 1 , wherein utilizing monitored in-cylinder pressures to project reforming required in the next combustion cycle comprises:

projecting a pressure ratio through the recompression period for the next combustion cycle corresponding to the reforming required in the next combustion cycle based upon the pressure ratio through the recompression period in the current cycle; and

estimating the reforming required in the next combustion cycle based upon the projected pressure ratio through the recompression period for the next combustion cycle.

3. Method for controlling an amount of fuel reforming in an internal combustion engine configured to selectively operate in a homogeneous charge compression-ignition combustion mode with an exhaust recompression strategy, comprising:

monitoring in-cylinder pressures during a current combustion cycle;

utilizing monitored in-cylinder pressures to project reforming required in a next combustion cycle; and

controlling the next combustion cycle based on the projected reforming required in the next combustion cycle;

wherein monitoring in-cylinder pressures comprises monitoring a pumping mean effective pressure.

4. The method of claim 3 , wherein utilizing monitored in-cylinder pressures to project reforming required in the next combustion cycle comprises:

projecting a pumping mean effective pressure for the next combustion cycle corresponding to the reforming required in the next combustion cycle based upon the pumping mean effective pressure in the current cycle; and

estimating the reforming required in the next combustion cycle based upon the pumping mean effective pressure for the next combustion cycle.

5. The method of claim 3 , wherein effecting control comprises modulating an injection timing calibrated to effect said reforming required in said next combustion cycle.

6. Method for controlling an amount of fuel reforming in an internal combustion engine configured to selectively operate in a homogeneous charge compression-ignition combustion mode with an exhaust recompression strategy, comprising:

monitoring in-cylinder pressures during a current combustion cycle;

utilizing monitored in-cylinder pressures to project reforming required in a next combustion cycle; and

controlling the next combustion cycle based on the projected reforming required in the next combustion cycle;

wherein controlling the next combustion cycle based on the projected reforming required in the next combustion cycle comprises:

determining a combustion stability based upon the reforming required in the next combustion cycle;

determining a NOx emission level for an equivalent flame propagation event based upon the reforming required in the next combustion cycle; and

balancing between reforming fuel and flame propagation in the next combustion cycle based upon the combustion stability and the NOx emission level.

7. Method for facilitating operation of an internal combustion engine configured to selectively operate in a homogeneous charge compression-ignition combustion mode with an exhaust recompression strategy at low engine speeds and loads, comprising:

monitoring in-cylinder pressures;

determining a desired fuel mass to be reformed for a next combustion cycle based upon the monitored in cylinder pressures;

predicting a combustion stability based upon the desired fuel mass to be reformed;

predicting a NOx emission level for equivalent flame propagation based the desired fuel mass to be performed;

determining a stability NOx tradeoff based upon the predicted combustion stability and the predicted NOx emission level; and

balancing between reforming and flame propagation for the next combustion cycle based upon the stability NOx tradeoff.

8. The method of claim 7 , wherein monitoring in-cylinder pressures comprises monitoring a pressure ratio through a recompression period.

9. The method of claim 7 , wherein monitoring in-cylinder pressures comprises monitoring a pumping mean effective pressure.

10. The method of claim 7 , wherein determining the stability NOx tradeoff comprises:

comparing the predicted combustion stability to a threshold combustion stability; and

limiting use of fuel reforming in the next combustion cycle if the predicted combustion stability is below the threshold combustion stability.

11. The method of claim 7 , wherein determining the stability NOx tradeoff comprises:

evaluating the predicted combustion stability based upon acceptable levels of combustion stability;

evaluating the predicted NOx emission level based upon acceptable levels of NOx emissions; and

selecting use of fuel reforming and flame propagation in the next combustion cycle based upon the evaluated predicted combustion stability and the evaluated predicted NOx emission level.

12. Apparatus for controlling an amount of fuel reforming in an internal combustion engine configured to selectively operate in a homogeneous charge compression-ignition combustion mode with an exhaust recompression strategy, comprising:

a sensor monitoring in-cylinder pressures within the engine in real-time; and

a control module configured to

monitor the in-cylinder pressures during a current combustion cycle,

utilizing the monitored in-cylinder pressures to project reforming required in a next combustion cycle, and

controlling the next combustion cycle based on the projected reforming required in the next combustion cycle;

wherein monitoring the in-cylinder pressures comprises determining a pressure ratio through a recompression period.

13. Apparatus for controlling an amount of fuel reforming in an internal combustion engine configured to selectively operate in a homogeneous charge compression-ignition combustion mode with an exhaust recompression strategy, comprising:

a sensor monitoring in-cylinder pressures within the engine in real-time; and

a control module configured to

monitor the in-cylinder pressures during a current combustion cycle,

utilizing the monitored in-cylinder pressures to project reforming required in a next combustion cycle, and

controlling the next combustion cycle based on the projected reforming required in the next combustion cycle;

wherein monitoring the in-cylinder pressures comprises determining a pumping mean effective pressure.