Method for operating an internal combustion engine with a fuel detection

1. A method for operating an internal combustion engine with detection of the fuel used for injection, comprising:

determining an elasticity modulus E1 of the fuel to be injected, at a first injection pressure p1;

determining the elasticity modulus E2 of the fuel to be injected, at a second injection pressure p2;

forming a difference between the two determined elasticity modulus values and relating the difference to a pressure difference in order to obtain a difference value DW according to the equation

DW

=

E

⁢

⁢

1

-

E

⁢

⁢

2

p

⁢

⁢

1

-

p

⁢

⁢

2

;

defining a differentiation value for the difference value; and

detecting a first type of fuel if the difference value is above the differentiation value, and a second type of fuel if the difference value is below the differentiation value.

2. The method as claimed in claim 1 , wherein the first injection pressure and the second injection pressure are at least 1500 bar apart from one another.

3. The method as claimed in claim 1 , wherein said method is carried out at a constant initial temperature.

4. The method as claimed in claim 1 , wherein the method is carried out to differentiate between diesel fuel EN509 and biodiesel fuel.

5. The method as claimed in claim 1 , wherein the difference value is determined during operation of the internal combustion engine, on the basis of a plurality of natural operating points.

6. The method as claimed in one of claim 1 , characterized in that the difference value is determined on the basis of a plurality of artificial operating points.

7. The method as claimed in one of claim 1 , further comprising, while the internal combustion engine is operating, determining an elasticity modulus profile plotted against pressure and each pressure difference is assigned a difference value which is compared with a difference value which is determined in advance, in order to differentiate between fuels.

8. The method as claimed in claim 1 , wherein the first type of fuel is diesel fuel and the second type of fuel is biodiesel fuel.

9. A method for detecting a type of fuel used in operating an internal combustion engine of a vehicle, comprising:

determining an elasticity modulus value of the fuel to be injected into an internal combustion engine, at a first injection pressure;

determining the elasticity modulus value of the fuel to be injected, at a second injection pressure;

determining a difference value by dividing a difference between the determined elasticity modulus values by a difference between the first injection pressure and the second injection pressure; and

detecting a first type of fuel if the difference value is above a differentiation value, and a second type of fuel if the difference value is below the differentiation value.

10. The method of claim 9 , further comprising determining the differentiation value.

11. The method of claim 10 , wherein determining the differentiation value comprises extracting the differentiation value from a plurality of stored differentiation values.

12. The method of claim 9 , wherein the difference between the first injection pressure and the second injection pressure is at least 1500 bar.

13. The method of claim 9 , wherein one of the first injection pressure and the second injection pressure is 2000 bar and the other of the first injection pressure and the second injection pressure is 350 bar.

14. The method of claim 9 , wherein the first type of fuel is diesel fuel and the second type of fuel is biodiesel fuel.

15. The method of claim 9 , wherein the first type of fuel is EN590 diesel fuel and the second type of fuel is biodiesel fuel.

16. The method of claim 9 , wherein said method is carried out at a constant initial temperature.