Fuel dispensing unit with on-board refueling vapor recovery detection

1. A vapor recovery system for recovering fuel vapor from a vehicle tank during dispensing of fuel into the vehicle tank at a fuel dispensing flow rate, said vapor recovering system comprising a vapor recovering line for transporting a stream of fuel vapor, and a controller, wherein a flow meter is arranged in or adjacent to the vapor recovery line for indicating the flow rate of the stream of fuel vapor, a heated element is arranged in the vapor recovery line, and the controller is configured to:

detect a cooling exerted on the heated element by the stream of fuel vapor,

determine a correction for the detected cooling by weighting said cooling with the flow rate of the stream of fuel vapor to compensate for an increase in cooling as the vapor flow rate increases, and

decrease or stop the stream of fuel vapor, if after correction, the detected cooling is smaller than a predetermined level.

2. A vapor recovery system according to claim 1 , wherein the correction for the detected cooling comprises increasing said predetermined level as the flow rate increases.

3. A vapor recovery system according to claim 1 , further comprising a temperature sensor operatively connected to the controller and arranged to measure the temperature of the stream of fuel vapor, the controller configured to determine a correction for the detected cooling by weighting said cooling with the measured temperature.

4. A vapor recovery system according to claim 3 , wherein the correction for the detected cooling comprises decreasing said predetermined level as the temperature increases.

5. A vapor recovery system according to claim 1 , wherein the flow meter comprises a fluid oscillator for providing an oscillation of at least a party of the stream of fuel vapor.

6. A vapor recovery system according to claim 5 , wherein the fluid oscillator is configured to provide a frequency oscillation which increases with an increased vapor flow.

7. A vapor recovery system according to claim 5 , wherein the heated element is arranged at least partly in the oscillating part of the stream of fuel vapor.

8. A vapor recovery system according to claim 1 , wherein the heated element is supplied with an electrical current for providing the heating of the heated element, said cooling being determined by the voltage across, and electrical current through, the heated element.

9. A vapor recovery system according to claim 1 , wherein the controller is configured to estimate any of the density and the hydrocarbon content of the stream of fuel vapor, based on the cooling exerted on the heated element.

10. A vapor recovery system according to claim 1 , wherein the heated element is supplied with an electric current for providing the heating of the heated element and the controller is configured to detect the cooling exerted on the heated element by the stream of fuel vapor by determining a voltage value across the heated element at a constant current.

11. A method of regulating a vapor recovery system when recovering fuel vapor from a vehicle tank during dispensing of fuel into the vehicle tank at a fuel dispensing flow rate, said method comprising the steps of:

transporting a stream of fuel vapor through a vapor recovery line,

detecting a flow rate of the stream of fuel vapor by a flow meter arranged in or adjacent to the vapor recovery line,

detecting a cooling exerted on a heated element by the stream of fuel vapor,

determining a correction for the detected cooling by weighting said cooling with the flow rate of the stream of fuel vapor to compensate for an increase of cooling as the flow rate increases, and

decreasing or stopping the stream of fuel vapor, if after correction, the detected cooling is smaller than a predetermined level.

12. A method of regulating a vapor recovery system according to claim 11 further comprising supplying an electric current to the heated element, wherein detecting a cooling exerted on a heated element by the stream of fuel vapor comprises detecting a cooling exerted on the heated element by the stream of fuel vapor by determining a voltage value across the heated element at a constant current.

13. A fuel dispensing unit including a vapor recovery system for recovering fuel vapor from a vehicle tank during dispensing of fuel into the vehicle tank at a fuel dispensing flow rate, said vapor recovery system comprising a vapor recovery line for transporting a stream of fuel vapor, and a controller, wherein a flow meter is arranged in or adjacent to the vapor recovery line for indicating the flow rate of the stream of fuel vapor, a heated element is arranged in the vapor recovery line, and the controller is configured to:

detect a cooling exerted on the heated element by the stream of fuel vapor,

determine a correction for the detected cooling by weighting said cooling with the flow rate of the stream of fuel vapor to compensate for an increase in cooling as the vapor flow rate increases, and

decrease or stop the stream of fuel vapor, if after correction, the detected cooling is smaller than a predetermined level.