System for determining the start of combustion in an internal combustion engine

1. A method for determining the start of combustion of a mixture in the combustion chamber of an internal combustion engine, comprising the following step:

determining a start of injection,

continuously measuring form said start of injection the pressure in the combustion chamber, and

determining the start of combustion by reference to the continuously measured pressure, wherein said start of combustion is determined when a value derived from said continuously measured pressure exceeds a pre-defined threshold.

2. The method as claimed in claim 1 , further comprising the following steps:

determining the volume of the combustion chamber and

determining said value by reference to the measured pressure and the determined volume.

3. The method as claimed in claim 2 , further comprising the following steps:

calculating the heat released in the combustion chamber by reference to the determined volume and the measured pressure and

determining said value from the calculated released heat.

4. The method as claimed in claim 3 , further comprising the following steps:

calculating an integral of the released heat and

determining the value by reference to the integral of the released heat.

5. The method as claimed in claim 4 , wherein the integral of the released heat is calculated between the start of injection and the end of combustion.

6. The method as claimed in claim 4 , further comprising the following steps:

determining a mainly stationary starting value for the integral of the released heat,

determining a mainly stationary end value for the integral of the released heat and

assuming the start of combustion when the integral of the released heat exceeds a predetermined limit value which is between the starting value and the end value.

7. The method as claimed in claim 6 , wherein the starting value is calculated as the average value of a plurality of starting values for the integral of the released heat or for the released heat.

8. The method as claimed in claim 6 , wherein the limit value is adjustable.

9. The method as claimed in claim 6 , wherein the limit value is above the starting value by a predetermined percentage of the difference between the starting value and the end value.

10. The method as claimed in claim 2 , further comprising the following steps:

determining the heat release rate and

determining the start of combustion by reference to the calculated release rate.

11. The method as claimed in claim 10 , further comprising the following step:

assuming that the start of combustion occurs when the calculated heat release rate exceeds a predetermined limit value.

12. The method as claimed in claim 11 , further comprising the following steps:

determining a tolerance range for the calculated release rate having an upper and a lower limit and

establishing the predetermined limit value as the upper limit of the tolerance range.

13. The method as claimed in claim 12 , wherein the tolerance range is determined from the fluctuation of the release rate during a combustion-free period and/or during a period before the start of injection.

14. The method as claimed in claim 1 , wherein the following steps:

determining the ratio between the pressure measured in the combustion chamber and a corresponding pressure at the same operating point of the internal combustion engine without combustion,

assuming that the start of combustion occurs when the pressure ratio (α) exceeds a predetermined limit value.

15. The method as claimed in claim 14 , wherein the measured pressure is corrected by an offset value.

16. The method as claimed in claim 15 , wherein the offset value at the start of injection is calculated as the difference between the combustion-free pressure and the measured pressure.

17. The method as claimed in claim 14 , wherein the curve of the pressure in a combustion-free combustion chamber is a stored pressure curve.

18. The method as claimed in claim 14 , wherein the curve of the pressure in a combustion-free combustion chamber is determined while the internal combustion engine is operating.

19. The method as claimed in claim 3 , wherein the start of combustion is determined as a function of the calculated release rate and/or as a function of the calculated released heat and/or as a function of the pressure ratio between the measured pressure in the combustion chamber and a corresponding pressure at the same operating point of the internal combustion engine without combustion.

20. The method as claimed in claim 1 , wherein the start of combustion is determined while combustion is still taking place or before the next start of injection.

21. The method as claimed in claim 1 , wherein the quantity of a recirculated exhaust gas is influenced as a function of the determined start of combustion.

22. The method as claimed in claim 1 , wherein the start of injection and/or the injection period of a pre-injection, a main injection and/or a post-injection in the combustion chamber is influenced by reference to the determined start of combustion.

23. An engine controller for determining the start of combustion of a mixture in the combustion chamber of an internal combustion engine, comprising:

means for determining a start of injection,

means for continuously measuring the pressure in the combustion chamber from said start of injection, and

means for determining the start of combustion by reference to the continuously measured pressure, wherein said means for determining are operable to determine the start of combustion when a value derived from said continuously measured pressure exceeds a pre-defined threshold.

24. A method as claimed in claim 1 , further comprising the step of using an engine controller for performing the method.