System and method for selective cylinder deactivation
Embodiments for operating an engine with skip fire are provided. In one example, a method comprises during a skip fire mode or during a skip fire mode transition, port injecting a first fuel quantity to a cylinder of an engine, the first fuel quantity based on a first, predicted air charge amount for the cylinder and lean of a desired air-fuel ratio, and direct injecting a second fuel quantity to the cylinder, the second fuel quantity based on the first fuel quantity and a second, calculated air charge amount for the cylinder.
1. A method, comprising:
operating an engine according to a skip fire schedule, including activating fuel injection to fire at least one cylinder and deactivating fuel injection to skip at least one cylinder, while maintaining spark ignition to all cylinders, where activating fuel injection to fire the at least one cylinder includes port injecting and direct injecting fuel to the at least one cylinder; and
adjusting the skip fire schedule if combustion is not detected in a cylinder without deactivated fuel injection.
2. The method of claim 1 , further comprising detecting if combustion occurs in the at least one cylinder with activated fuel injection based on feedback from an ionization sensor.
3. The method of claim 2 , wherein adjusting the skip fire schedule comprises activating fuel injection to a cylinder scheduled to not be fired in the skip fire schedule.
4. The method of claim 1 , wherein the commanded firing order is based on an original firing order of the engine during a non-skip fire mode, the selected number of skipped cylinders, and further based on which cylinders of the engine were skipped in a previous engine cycle.
5. The method of claim 4 , wherein the at least one cylinder that is skipped follows the at least one cylinder that is fired in the original firing order of the engine.
6. The method of claim 1 , further comprising, selectively actuating each intake valve and each exhaust valve of the at least one cylinder that is fired, and selectively deactivating each intake valve and each exhaust valve of at the least one cylinder that is skipped.
7. A method, comprising:
for a given engine cycle of an engine operating in a skip fire mode,
selecting a number of cylinders of the engine to skip combustion based on engine load;
setting a commanded firing order of non-skipped combusting cylinders of the engine, the commanded firing order including scheduling at least a first cylinder to be fired and at least a second cylinder in which combustion is to be skipped;
determining if combustion occurs as not commanded in the second cylinder;
if combustion does occur in the second cylinder, adjusting the commanded firing order to skip combustion of a cylinder next in an original firing order during a non-skip fire mode of the engine after the second cylinder of the engine.
8. The method of claim 7 , wherein the commanded firing order is based on the original firing order of engine during a non-skip fire mode, the selected number of skipped cylinders, and further based on which cylinders of the engine were skipped in a previous engine cycle.
9. The method of claim 7 , wherein determining if combustion occurs in the second cylinder comprises determining if combustion occurs based on feedback from an ionization sensor of the second cylinder.
10. The method of claim 8 , wherein the second cylinder follows the first cylinder in the original firing order of the engine.
11. The method of claim 7 , further comprising, if combustion does not occur in the second cylinder, proceeding to fire a subsequent cylinder scheduled to be fired in the commanded firing order.
12. The method of claim 11 , wherein during firing of the first cylinder, the method further comprises:
port injecting a first fuel quantity to the first cylinder, the first fuel quantity based on a first, predicted air charge amount for the first cylinder and lean of a desired air-fuel ratio; and
direct injecting a second fuel quantity to the first cylinder, the second fuel quantity based on the first fuel quantity and a second, calculated air charge amount for the first cylinder.
13. The method of claim 7 , wherein the first cylinder and second cylinder are located on a same cylinder bank, and wherein the second cylinder is fired after the first cylinder in the original firing order.
14. The method of claim 7 , wherein the first cylinder and second cylinder are each fluidically coupled to a common catalyst.
15. The method of claim 7 , further comprising resuming combustion in the original firing order after skipping combustion of the cylinder next in the original firing order.
16. A system, comprising:
an engine having a plurality of cylinders;
a port fuel injection system to port inject fuel to each cylinder of the plurality of cylinders;
a direct fuel injection system to direct inject fuel to each cylinder of the plurality of cylinders;
a spark ignition system to initiate combustion in each cylinder of the plurality of cylinders, including one or more ionization sensors to detect occurrence of combustion events in the plurality of cylinders; and
a controller including non-transitory instructions to:
determine a commanded firing order of the engine during a skip fire mode, where at least a first cylinder of the plurality of cylinders is scheduled to be fired and at least a second cylinder of the plurality of cylinders is scheduled to be skipped; and
determine if combustion occurred in the second cylinder via feedback from the one or more ionization sensors;
if combustion does occur in the second cylinder, adjust the commanded firing order to skip combustion of a cylinder next in an original firing order during a non-skip fire mode of the engine after the second cylinder of the engine; and
if combustion does not occur in the second cylinder, maintain the commanded firing order.
17. The system of claim 16 , wherein the controller includes further instructions to:
adjust the commanded firing order to fire the second cylinder if combustion does not occur in the first cylinder.
18. The system of claim 16 , wherein the commanded firing order of the engine is based on the original firing order of the engine in a non-skip fire mode, a number of cylinders to be skipped during the skip fire mode, and which cylinders of the plurality of cylinders were fired in a previous engine cycle, where the number of cylinders to be skipped is based on engine load.
19. The system of claim 16 , further comprising a valve actuation system to selectively actuate each intake valve and each exhaust valve of the plurality of cylinders, and wherein during firing of the first cylinder, the controller includes instructions to activate the valve actuation system to actuate an intake valve and an exhaust valve of the first cylinder.
20. The system of claim 16 , wherein when the second cylinder is skipped, the controller includes instructions to deactivate the port and direct fuel injection systems and deactivate the valve actuation system for the second cylinder, to prevent fuel injection to the second cylinder and maintain an intake valve and exhaust valve of the second in a closed position.