Systems and methods for controlling engine combustion stability

1. A control system for an engine, the control system comprising:

a first module that determines an oxygen concentration within an intake manifold of the engine; and

a second module that regulates a flow of exhaust gas recirculation (EGR) into the intake manifold based on the determined oxygen concentration,

wherein the engine is a homogeneous charge compression ignition (HCCI) engine, and

wherein the second module selectively disables an HCCI combustion mode of the HCCI engine when the EGR valve is closed based on the determined oxygen concentration.

2. The control system of claim 1 , wherein the second module regulates the flow of EGR into the intake manifold by controlling an EGR valve based on the determined oxygen concentration and an oxygen concentration target.

3. The control system of claim 2 , wherein the second module increases an opening of the EGR valve when the determined oxygen concentration is greater than the oxygen concentration target.

4. The control system of claim 2 , wherein the second module decreases an opening of the EGR valve when (i) the determined oxygen concentration is less than the oxygen concentration target and (ii) the EGR valve is not closed.

5. The control system of claim 2 , further comprising a third module that determines the oxygen concentration target based on engine speed and engine load.

6. The control system of claim 5 , wherein the third module determines the oxygen concentration target further based on an engine temperature parameter.

7. The control system of claim 6 , wherein the engine temperature parameter is based on at least one of intake air temperature (IAT), engine coolant temperature (ECT), and engine oil temperature (EOT).

8. The control system of claim 1 , wherein the first module determines the oxygen concentration within the intake manifold of the engine based on measurements from an oxygen sensor in the intake manifold.

9. A control system for an engine, the control system comprising:

a first module that determines an oxygen concentration within an intake manifold of the engine; and

a second module that regulates a flow of exhaust gas recirculation (EGR) into the intake manifold by controlling an EGR valve based on the determined oxygen concentration and an oxygen concentration target,

wherein the second module decreases an opening of the EGR valve when (i) the determined oxygen concentration is less than the oxygen concentration target and (ii) the EGR valve is not closed, and

wherein the engine is a homogeneous charge compression ignition (HCCI) engine, and wherein the second module disables an HCCI combustion mode of the HCCI engine when (i) the determined oxygen concentration is less than the oxygen concentration target and (ii) the EGR valve is closed.

10. The control system of claim 9 , wherein the second module disables the HCCI combustion mode by (i) controlling spark plugs and (ii) adjusting at least one of fuel injection quantity and fuel injection timing.

11. A method for controlling an engine, the method comprising:

determining an oxygen concentration within an intake manifold of the engine;

regulating a flow of exhaust gas recirculation (EGR) into the intake manifold based on the determined oxygen concentration,

wherein the engine is a homogeneous charge compression ignition (HCCI) engine; and

selectively disabling an HCCI combustion mode of the HCCI engine when the EGR valve is closed based on the determined oxygen concentration.

12. The method of claim 11 , further comprising regulating the flow of EGR into the intake manifold by controlling an EGR valve based on the determined oxygen concentration and an oxygen concentration target.

13. The method of claim 12 , further comprising increasing an opening of the EGR valve when the determined oxygen concentration is greater than the oxygen concentration target.

14. The method of claim 12 , further comprising decreasing an opening of the EGR valve when (i) the determined oxygen concentration is less than the oxygen concentration target and (ii) the EGR valve is not closed.

15. The method of claim 12 , further comprising determining the oxygen concentration target based on engine speed and engine load.

16. The method of claim 15 , further comprising determines the oxygen concentration target further based on an engine temperature parameter.

17. The method of claim 16 , wherein the engine temperature parameter is based on at least one of intake air temperature (IAT), engine coolant temperature (ECT), and engine oil temperature (EOT).

18. The method of claim 11 , further comprising determining the oxygen concentration within the intake manifold of the engine based on measurements from an oxygen sensor in the intake manifold.

19. A method for controlling an engine, the method comprising:

determining an oxygen concentration within an intake manifold of the engine;

regulating a flow of exhaust gas recirculation (EGR) into the intake manifold by controlling an EGR valve based on the determined oxygen concentration and an oxygen concentration target;

decreasing an opening of the EGR valve when (i) the determined oxygen concentration is less than the oxygen concentration target and (ii) the EGR valve is not closed,

wherein the engine is a homogeneous charge compression ignition (HCCI) engine; and

disabling an HCCI combustion mode of the HCCI engine when (i) the determined oxygen concentration is less than the oxygen concentration target and (ii) the EGR valve is closed.

20. The method of claim 19 , further comprising disabling the HCCI combustion mode by (i) controlling spark plugs and (ii) adjusting at least one of fuel injection quantity and fuel injection timing.