HCCI engine combustion control
An exemplary method of controlling a gasoline engine operating unthrottled with homogeneous charge compression ignition (HCCI) combustion includes operating the engine with predetermined values of external EGR and internal EGR settings, and burned gas fraction set points for intake and exhaust gases. Repeated adjustments are made to the external EGR and internal EGR settings to move the exhaust and intake gases burned gas fractions toward their state set points. Effects of disturbances in actual operating conditions are thereby minimized.
1. Method of controlling an internal combustion engine operating unthrottled with HCCI combustion, the method comprising:
operating the engine with a predetermined external EGR setting;
providing a desired burned gas fraction set point for intake gases;
repeatedly determining burned gas fraction values of the intake gases and calculating differences from the corresponding desired burned gas fraction set point for intake gases; and
repeatedly applying adjustments to the external EGR setting to move the burned gas fraction values of the intake gases toward the desired burned gas fraction set point for intake gases.
2. The method as in claim 1 further comprising:
operating the engine with a predetermined internal EGR setting;
providing a desired burned gas fraction set point for exhaust gases;
repeatedly determining burned gas fraction values of the exhaust gases and calculating differences from the desired burned gas fraction set point for exhaust gases; and
repeatedly applying adjustments to the internal EGR setting to move the burned gas fraction values of the exhaust gases toward the desired burned gas fraction set point for exhaust gases.
3. Method of controlling an internal combustion engine operating unthrottled with HCCI combustion, the method comprising:
operating the engine with a predetermined internal EGR setting;
providing a desired burned gas fraction set point for exhaust gases;
repeatedly determining burned gas fraction values of the exhaust gases and calculating differences from the desired burned gas fraction set point for exhaust gases; and
repeatedly applying adjustments to the internal EGR setting to move the burned gas fraction values of the exhaust gases toward the desired burned gas fraction set point for exhaust gases.
4. The method as in claim 3 wherein the engine is operated in an exhaust recompression mode and said adjustments to the internal EGR setting are made to a negative valve overlap setting.
5. The method as in claim 3 wherein the engine is operated in an exhaust rebreathing mode and said adjustments to the internal EGR setting are made to an exhaust valve lift reopening setting.
6. Control for an internal combustion engine operating unthrottled with HCCI combustion, the method comprising:
an open loop control providing external EGR and internal EGR settings; and
a closed loop control providing desired burned gas fraction set points for intake and exhaust gases and adjustments to external EGR and internal EGR settings based on differences between actual burned gas fractions of intake gases and exhaust gases and the desired burned gas fraction set points.
7. The control as in claim 6 wherein the engine is operated in an exhaust recompression mode and said adjustments to the internal EGR setting are made to a negative valve overlap setting.
8. The control as in claim 6 wherein the engine is operated in an exhaust rebreathing mode and said adjustments to the internal EGR setting are made to an exhaust valve lift reopening setting.
9. The control as in claim 6 further comprising:
said closed loop control providing a desired cylinder combustion phasing set point and adjustments to the desired burned gas fraction set point for intake gases based on differences between actual combustion phasing and the desired cylinder combustion phasing set point.
10. The control as in claim 9 wherein cylinder combustion phasing is with respect to location of peak pressure (LPP) in the cylinders.
11. The control as in claim 9 wherein cylinder combustion phasing is with respect to location of combustion of one half the fuel supplied for each cylinder cycle.
12. Method of controlling an internal combustion engine operating unthrottled with HCCI combustion, the method comprising:
operating the engine with predetermined external EGR and internal EGR settings;
providing desired burned gas fraction set points for intake and exhaust gases;
repeatedly determining current burned gas fraction values of the intake and exhaust gases and calculating differences from the corresponding desired burned gas fraction set points; and
repeatedly applying adjustments to the external EGR and internal EGR settings to move the burned gas fraction values of the intake and exhaust gases toward their corresponding set points.
13. The method as in claim 12 wherein current burned gas fraction values of the intake and exhaust gases are determined from selected engine operating values.
14. The method as in claim 12 wherein said adjustments to the external EGR setting are made in response to feedback based on the difference between the current burned gas fraction value of the intake gases and the desired burned gas fraction set point for intake gases.
15. The method as in claim 12 wherein said adjustments to the internal EGR setting are made in response to feedback based on the difference between the current burned gas fraction value of the exhaust gases and the desired burned gas fraction set point for exhaust gases.
16. The method as in claim 15 wherein the engine is operated in an exhaust recompression mode and said adjustments to the internal EGR setting are made to a negative valve overlap setting.
17. The method as in claim 15 wherein the engine is operated in an exhaust rebreathing mode and said adjustments to the internal EGR setting are made to an exhaust valve lift reopening setting.
18. The method as in claim 12 further comprising:
providing a desired cylinder combustion phasing set point;
repeatedly determining current combustion phasing values and calculating differences from the desired cylinder combustion phasing set point; and
repeatedly applying adjustments to the desired burned gas fraction set point for intake gases to reduce differences between current combustion phasing values and the desired cylinder combustion phasing set point.
19. The method as in claim 18 wherein a determined combustion phasing value is location of peak pressure (LPP) in the cylinders.
20. The method as in claim 18 wherein a determined combustion phasing value is location of combustion of one half the fuel supplied for each cylinder cycle.