Method for operating an internal combustion engine with direct fuel injection

1. A method of operating an internal combustion engine with an injection device, comprising:

feeding combustion air to a combustion chamber via an inlet port;

injecting fuel into the combustion chamber using a fuel nozzle arranged in the combustion chamber;

igniting a formed fuel/air mixture at a certain ignition point using a spark plug arranged in the combustion chamber; and

during the starting of the internal combustion engine, selecting a high-pressure or a low-pressure start as a function of a minimum fuel pressure built up in the injection device within a defined number of cycles, wherein the minimum fuel pressure and the number of cycles are selected as a function of a combustion-chamber temperature, and wherein the injection of the fuel into the combustion chamber takes place in a timed sequence during the starting operation.

2. The method as claimed in claim 1 , comprising, during the starting operation, injecting fuel into the combustion chamber in up to three partial quantities.

3. The method as claimed in claim 2 , comprising, during a low-pressure start, injecting the up to three partial quantities into the combustion chamber before the ignition point, and, during a high-pressure start, injecting one or two of the up to three partial quantities into the combustion chamber before the ignition point and one partial quantity is injected into the combustion chamber after the ignition point.

4. The method as claimed in claim 3 , comprising determining the ignition point during the starting operation as a function of the combustion-chamber temperature and a difference between an actual speed and an idling speed.

5. The method as claimed in claim 4 , comprising, during a high-pressure start, if the fuel pressure drops below a defined minimum pressure in the injection device, changing the operation over to the low-pressure start.

6. The method as claimed in claim 5 , comprising recording combustion-chamber temperature using a temperature-measuring device at the combustion chamber or with reference to a coolant temperature of the internal combustion engine.

7. The method as claimed in claim 6 , comprising effecting a low-pressure start at a coolant temperature of less than −15° C. or greater than 90° C., effecting a high pressure start at a minimum fuel pressure, built up in the injection device, of at least 10 bar and at a coolant temperature of between −15° C. and 90° C.

8. The method as claimed in claim 1 , comprising determining the ignition point during the starting operation as a function of the combustion-chamber temperature and a difference between an actual speed and an idling speed.

9. The method as claimed in claim 1 , comprising, during a high-pressure start, if the fuel pressure drops below a defined minimum pressure in the injection device, changing the operation over to the low-pressure start.

10. The method as claimed in claim 1 , comprising recording combustion-chamber temperature using a temperature-measuring device at the combustion chamber or with reference to a coolant temperature of the internal combustion engine.

11. The method as claimed in claim 1 , comprising effecting a low-pressure start at a coolant temperature of less than −15° C. or greater than 90° C., effecting a high pressure start at a minimum fuel pressure, built up in the injection device, of at least 10 bar and at a coolant temperature of between −15° C. and 90° C.