METHOD AND DEVICE FOR DETERMINING LOW TEMPERATURE PROPERTIES

Abstract

In a method for determining the low-temperature properties of a paraffin-containing fuel, the fuel is conducted from a storage chamber through a measuring cell provided with a sieve, the measuring cell is cooled by means of a cooling device, the temperature of the fuel in the measuring cell is measured, and a fluid pressure representing the flow resistance occurring on the sieve is measured, and the temperature occurring at a defined fluid pressure set point is determined and output as a result of the method, wherein, for the pressure measurement, a defined sample amount of the fuel is abruptly delivered from the storage chamber in order to obtain a pressure pulse.

Claims

1. A method for determining the low-temperature properties of a paraffin-containing fuel, comprising: conducting the fuel from a storage chamber through a measuring cell provided with a sieve, cooling the measuring cell by means of a cooling device, measuring a temperature of the fuel in the measuring cell, measuring a fluid pressure representing a flow resistance occurring on the sieve, and determining a temperature occurring at a defined fluid pressure set point and outputting the determined temperature as being assigned to the defined fluid pressure set point as a result of the method, wherein for the fluid pressure measurement, a defined sample amount of the fuel is abruptly delivered from the storage chamber in order to obtain a pressure pulse.

2. A method according to claim 1, wherein the measuring of the fluid pressure occurs during the cooling of the measuring cell and is repeated at a number of different temperatures of the fuel in order to obtain a series of measured values, and wherein, for each fluid pressure measurement, a defined, identical sample amount of the fuel is abruptly delivered from the storage chamber in order to obtain a pressure pulse.

3. A method according to claim 2, further comprising: establishing a characteristic curve of the fluid pressure as a function of the temperature from the series of measured values, and wherein the temperature assigned to the defined fluid pressure set point in the characteristic curve is determined and output as a result of the method.

4. A method according to claim 2, further comprising using a maximum of the fluid pressure occurring at a pressure pulse as the fluid pressure measured value.

5. A method according to claim 1, wherein the measuring of the fluid pressure occurs upstream of the measuring cell and is used as the measured fluid pressure representing the flow resistance occurring on the sieve.

6. A method according to claim 1, further comprising outputting a cold filter plugging point of the fuel and/or a pour point of the fuel as a result of the method.

7. A method according to claim 6, wherein a first fluid pressure set point is specified, which is decisive for the cold filter plugging point, and wherein a second fluid pressure set point is specified, which is decisive for the pour point.

8. A method according to claim 1, wherein the temperature of the fuel in the measuring cell is stepwisely reduced in steps of 1 C., and wherein the measuring of the fluid pressure is performed after each cooling step.

9. A method according to claim 1, wherein the temperature of the fuel in the measuring cell is continuously reduced, and wherein the measuring of the fluid pressure is each performed during passage of defined temperature steps.

10. A method according to claim 6, further comprising determining a cloud point, a freeze point, or both of the fuel in the measuring cell by an optical measuring method.

11. A method according to claim 10, wherein the optical measuring method comprises a transmitted light measurement.

12. A method according to claim 10, wherein the fuel respectively present in the measuring cell is cooled, and the cloud point is determined during a first cooling step and the cold filter plugging point, the pour point, or both, are determined during a second cooling step.

13. A method according to claim 12, wherein the fuel respectively present in the measuring cell is reheated after cooling, and the freeze point is determined during heating.

14. A device for carrying out a method according to claim 1, comprising a storage chamber for the fuel to be tested, a measuring cell in fluid-connection with the storage chamber, said measuring cell being designed as a flow cell and provided with a sieve, a delivery device for delivering fuel from the storage chamber through the measuring cell, a cooling device for cooling the measuring cell, a temperature sensor for measuring the temperature of the fuel in the measuring cell, a pressure sensor for measuring a fluid pressure representing the flow resistance occurring on the sieve, and a control unit to which the measured values of the temperature sensor and of the pressure sensor are fed, wherein the delivery device is configured to abruptly deliver a defined sample amount of the fuel from the storage chamber so as to obtain a pressure pulse.

15. A device according to claim 14, wherein the delivery device comprises a piston delimiting the storage chamber and operable by a driving device.

16. A device according to claim 15, wherein the driving device comprises a stepper motor.

17. A device according to claim 14, wherein the delivery device comprises a micropump or a piezo pump.

18. A device according to claim 14, wherein the pressure sensor is arranged to measure the fluid pressure prevailing upstream of the measuring cell.

19. A device according to claim 18, wherein the pressure sensor is integrated in the piston of the delivery device.

20. A device according to claim 14, wherein the control unit cooperates with the cooling device and with the delivery device to actuate the same as a function of the measured values of the temperature sensor and of the pressure sensor, and that the control unit is arranged to repeat the measurement of the fluid pressure during cooling of the measuring cell at a number of different temperatures of the fuel thus obtaining a series of measured values, and to abruptly deliver, for each measurement, a defined, identical sample amount of the fuel from the storage chamber.

21. A device according to claim 14, wherein the control unit comprises an evaluation circuit to which the measured values of the pressure sensor and of the temperature sensor are fed and which has optionally stored the series of measured values, said evaluation circuit determining, and outputting as a result of the method, the temperature occurring at a defined fluid pressure set point.

22. A device according to claim 21, wherein a maximum of the fluid pressure occurring at a pressure pulse is used as the fluid pressure measured value in the evaluation circuit.

23. A device according to claim 21, characterized in wherein that the evaluation circuit is arranged to establish from the series of measured values a characteristic curve of the fluid pressure as a function of the temperature, and to determine, and output as a result of the method, the temperature assigned to the defined fluid pressure set point in the characteristic curve.

24. A device according to claim 14, wherein the control unit cooperates with the cooling device for stepwisely reducing the temperature of the fuel in the measuring cell in steps of 1 C., wherein a measurement of the fluid pressure is performed after each cooling step.

25. A device according to claim 14, wherein the control unit cooperates with the cooling device for continuously reducing the temperature of the fuel in the measuring cell, and that a measurement of the fluid pressure is each performed during the passage of defined temperature steps.

26. A device according to any one of claim 14, wherein an optical measuring device for measuring a cloud point, a freeze point, or both, of the fuel is associated with the measuring cell.

27. A device according to claim 26, wherein the optical measuring device operates according to the transmitted light method and preferably comprises a light source disposed on one side of the measuring cell and a light sensor disposed on an opposite side of the measuring cell.

Description

[0037] In the following, the invention will be explained in more detail by way of an exemplary embodiment schematically illustrated in the drawing. Therein, FIG. 1 illustrates a device according to the invention for determining the cloud point and the cold filter plugging point of a paraffin-containing fuel.

[0038] In FIG. 1, a storage chamber for the fuel to be tested is denoted by 1, accommodating a sample 2 of the fuel. The storage chamber 1 is formed in a hollow cylinder 3, which is closed on one side by an axially displaceable piston 4. The piston 4 comprises a piston rod 5 cooperating with a displacement drive (not illustrated) for the piston 4. The displacement drive may, for instance, be comprised of a stepper motor. On the side opposite the piston 4, the storage chamber 1 is closed by a valve block 8, in which the supply line 9 and the discharge line 10 are formed. The supply line 9 comprises a valve 11 and the discharge line comprises a valve 12.

[0039] With the valve opened, the discharge line 10 connects the storage chamber 1 to the measuring cell 13, which is designed as a flow cell and provided with a sieve 14. As soon as the piston has abruptly delivered a defined sample amount of the fuel from the storage chamber 1, the sample amount reaches the measuring cell 13 via line 10. The sample flows through the measuring cell 13, thus leaving the same on the side opposite the supply line via a discharge 15. A pressure value representing a flow resistance generated on the sieve 14 is determined by a pressure sensor, which in the present case is integrated in the piston 4. Alternatively, a pressure sensor disposed in the supply line 10 or at any other point upstream of the measuring cell 13 is also conceivable.

[0040] A cooling device is provided for cooling the measuring cell 13, the measuring cell 13 along with the cold side of the cooling device being thermally insulated as schematically indicated by 16.

[0041] It is further apparent from FIG. 1 that the measuring cell 13 comprises a glass window 17 each on two opposite sides. The thermal insulation 16 also comprises corresponding glass windows, or suitable optical passages 17, all optical elements 17 being in mutual alignment. On, one side of the measuring cell 13 a light source 18 such as a laser, and on the opposite side a photodetector 19, are disposed in such a manner that the light emitted from the light source 18 passes through the glass windows 17 and the measuring cell 13 and can be detected by the photodetector 19. Such a transmitted light method may be used to determine the cloud point of the sample.

[0042] Furthermore, a control unit 20 is provided, to which the measured values of a temperature sensor detecting the sample temperature within the measuring cell 13 and of the pressure sensor are fed and which controls the cooling performance of the cooling device. The cooling device for the measuring cell 13, for instance, comprises a cooling stage in contact with the measuring cell 13 and including a Peltier element 22. On the hot side of the Peltier element 22, a copper plate 21 equipped with a cooling body may be provided. In the copper plate may be formed bores or channels, through which a cooling fluid may be conducted.