Method for operating and internal combustion engine
In a method of operating a supercharged internal combustion engine in which exhaust gas is retained in the combustion chamber during a charge change, wherein the engine is operated with compression ignition or with spark ignition depending on the operating point and in which a charge pressure can be established for the fresh air supplied to the combustion chamber, and the exhaust gas is compressed during the charge change, and a first fuel quantity is optionally injected into the retained exhaust gas and a second fuel quantity is subsequently supplied to the combustion chamber, such that a homogeneous fuel/air mixture is formed in the combustion chamber, the retained exhaust gas quantity in the combustion chamber is corrected in such a way that the center of the combustion is displaced in the direction toward a set point value when the center of the combustion deviates from the set point value because of a change in the charge pressure of the fresh air or because of a change in the temperature of the fresh air.
1. A method of operating a supercharged internal combustion engine having a cylinder, a cylinder head including inlet and outlet valves, a piston movably disposed in the cylinder and defining a combustion chamber between the cylinder head and the piston, to which fresh air is supplied by an air supply device whose air charge pressure can be controlled for supplying fresh air to the combustion chamber of the engine under a controllable pressure, said method comprising the steps of:
operating the internal combustion engine selectively in a compression ignition or in a spark ignition mode of engine operation depending on the engine operating point, and, in the compression ignition mode,
retaining exhaust gas in the combustion chamber which is compressed during a charge change, optionally injecting a first fuel quantity into the retained exhaust gas,
subsequently supplying a second fuel quantity to the combustion chamber together with fresh air so that a homogeneous fuel/air mixture is formed in the combustion chamber,
combusting the fuel/air mixture over a period having a center of combustion, and
correcting the amount of the exhaust gas quantity retained in the combustion chamber when the center of combustion deviates from a set point value because of a change in the charge pressure of the fresh air or because of a change in the temperature of the fresh air in such a way that the center of the combustion is displaced toward the set point value.
2. The method as claimed in claim 1 , wherein an auto-ignition time for the fuel/air mixture, which is formed from the first and second fuel quantities, is established as a function of a quantity ratio of the first fuel quantity and the second fuel quantity.
3. The method as claimed in claim 2 , wherein the quantity ratio of the first fuel quantity and the second fuel quantity is between 1:100 and 2:1.
4. The method according to claim 3 , wherein the quantity ratio is between 1:5 and 1:3.
5. The method as claimed in claim 1 , wherein the center of combustion is established by injecting a third fuel quantity, the third fuel quantity being injected after completion of the injection of the second fuel quantity and before the piston has reached its top dead center position.
6. The method as claimed in claim 5 , wherein a combustion duration is established as a function of the third fuel quantity and the injection timing for the third fuel quantity.
7. The method as claimed in claim 1 , wherein the first fuel quantity is 0% to 30% of the total fuel quantity, and the second fuel quantity is 40% to 100% of the total fuel quantity.
8. The method as claimed in claim 5 , wherein the third fuel quantity is 10% to 30% of the total fuel quantity.