Active combustion control based on ringing index for reducing homogenous charge compression ignition (HCCI) combustion noise

1. An engine control system, comprising:

a ringing index (RI) determination module that determines at least one RI based on at least one pressure in at least one cylinder; and

an exhaust gas recirculation (EGR) control module that actuates an EGR valve based on the RI.

2. The engine control system of claim 1 wherein the EGR control module actuates the EGR valve based on the RI when a homogenous charge compression ignition (HCCI) engine system is operating in an auto-ignited combustion mode.

3. The engine control system of claim 1 wherein the EGR control module actuates the EGR valve based on the RI when an HCCI engine system is in a steady-state operating condition.

4. The engine control system of claim 3 further comprising a steady-state determination module that determines whether the HCCI engine system is in the steady-state operating condition based on a desired torque and a mass of airflow into an intake manifold.

5. The engine control system of claim 1 wherein the EGR control module actuates the EGR valve when at least one running average of the RI is greater than at least one threshold of the RI.

6. The engine control system of claim 5 further comprising an RI diagnostic module that determines the threshold based on a cylinder number of the RI and a number of samples for which the running average is determined.

7. The engine control system of claim 1 wherein the EGR control module actuates the EGR valve based on the RI when a combustion timing is less than a maximum combustion timing.

8. The engine control system of claim 7 wherein the maximum combustion timing is predetermined based on a maximum engine speed and a maximum engine load allowed when an HCCI engine system is operating in an auto-ignited combustion mode.

9. The engine control system of claim 1 wherein the EGR control module increases an amount of exhaust gas that flows through the EGR valve based on the RI.

10. The engine control system of claim 1 wherein the EGR control module increases an open position of the EGR valve based on the RI.

11. A method of operating an engine control system, comprising:

determining at least one RI based on at least one pressure in at least one cylinder; and

actuating an EGR valve based on the RI.

12. The method of claim 11 further comprising actuating the EGR valve based on the RI when a homogenous charge compression ignition (HCCI) engine system is operating in an auto-ignited combustion mode.

13. The method of claim 11 further comprising actuating the EGR valve based on the RI when an HCCI engine system is in a steady-state operating condition.

14. The method of claim 13 further comprising determining whether the HCCI engine system is in the steady-state operating condition based on a desired torque and a mass of airflow into an intake manifold.

15. The method of claim 11 further comprising actuating the EGR valve when at least one running average of the RI is greater than at least one threshold of the RI.

16. The method of claim 15 further comprising determining the threshold based on a cylinder number of the RI and a number of samples for which the running average is determined.

17. The method of claim 11 further comprising actuating the EGR valve based on the RI when a combustion timing is less than a maximum combustion timing.

18. The method of claim 11 further comprising increasing an amount of exhaust gas that flows through the EGR valve based on the RI.

19. The method of claim 11 further comprising increasing an open position of the EGR valve based on the RI.