Various methods and system are described for a fuel system which includes a fuel composition sensor and a fuel lift pump disposed upstream of the sensor. The system may be operated in each of three different modes of operation. In each of the modes, a fuel lift pump voltage is adjusted responsive to
Various methods and system are described for a fuel system which includes a fuel composition sensor and a fuel lift pump disposed upstream of the sensor. The system may be operated in each of three different modes of operation. In each of the modes, a fuel lift pump voltage is adjusted responsive to a fuel capacitance output by the sensor, while a variable such as sensor temperature or fuel pump pressure is maintained depending on the mode of operation.
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1. A method for a gasoline direct injection engine system, comprising: monitoring fuel capacitance via a fuel composition sensor arranged in a fuel passage between a fuel lift pump and a higher pressure pump;determining a fuel vapor pressure and an amount of ethanol in the fuel based on the fuel cap
1. A method for a gasoline direct injection engine system, comprising: monitoring fuel capacitance via a fuel composition sensor arranged in a fuel passage between a fuel lift pump and a higher pressure pump;determining a fuel vapor pressure and an amount of ethanol in the fuel based on the fuel capacitance;based on the fuel vapor pressure, adjusting the fuel lift pump to a selected pressure within a threshold range above a fuel vaporization point; andif the system has been operating for greater than a threshold duration and no change in capacitance has been detected, temporarily reducing pressure at the fuel lift pump until fuel vaporization is detected by the fuel composition sensor, and then adjusting the selected pressure based on the fuel lift pump pressure at which fuel vaporization was detected. 2. The method of claim 1, wherein the higher pressure pump operates at a higher pressure than the fuel lift pump. 3. The method of claim 1, further comprising, responsive to the fuel capacitance exceeding a threshold capacitance, adjusting the fuel lift pump pressure. 4. The method of claim 1, further comprising, in a second mode, maintaining a temperature at a predetermined temperature at a location where the fuel capacitance is obtained, and adjusting the fuel lift pump pressure responsive to an indication of fuel vaporization. 5. The method of claim 1, further comprising, in a third mode, responsive to an indication of fuel vaporization, increasing the fuel lift pump pressure or reducing a fuel temperature. 6. A method for a fuel system including a fuel composition sensor and a fuel lift pump, comprising: monitoring fuel capacitance via the fuel composition sensor;determining a fuel vapor pressure and an amount of ethanol in the fuel based on the fuel capacitance;in a first mode, maintaining a fuel lift pump pressure at a selected pressure above the fuel vapor pressure, and adjusting a fuel lift pump voltage responsive to the fuel capacitance;if the fuel system has been operating for greater than a threshold duration and no change in capacitance has been detected, temporarily reducing fuel lift pump pressure until fuel vaporization is detected by the fuel composition sensor, and adjusting the selected pressure based on the reduced fuel lift pump pressure at which fuel vaporization was detected;in a second mode, maintaining a temperature of the sensor at a selected temperature, and adjusting the fuel lift pump pressure responsive to an indication of fuel vaporization, the indication responsive to the fuel vapor pressure which is based on the fuel capacitance; andin a third mode, increasing the fuel lift pump pressure responsive to the indication of fuel vaporization. 7. The method of claim 6, wherein the fuel composition sensor is disposed in a fuel passage downstream of the fuel lift pump and upstream of a higher pressure pump which operates at a higher pressure than the fuel lift pump. 8. The method of claim 6 further comprising, in the third mode, reducing a fuel temperature responsive to the indication of fuel vaporization. 9. The method of claim 6, wherein the fuel lift pump voltage in the first mode is adjusted independent of the fuel lift pump voltage in the second mode. 10. The method of claim 6, wherein the fuel lift pump voltage in the first mode is adjusted independent of the fuel lift pump voltage in the third mode. 11. The method of claim 6, further comprising, operating the fuel system in only one of the first, second, or third modes at one time. 12. The method of claim 6, wherein the fuel composition sensor is part of a gasoline direct injection engine system. 13. A fuel system, comprising: a fuel lift pump;a sensor positioned downstream of the fuel lift pump in a fuel passage, and configured to output a signal indicating fuel capacitance; anda control system in communication with the sensor, the control system including non-transitory instructions to, during a first mode of operation of the fuel system: monitor fuel capacitance via the sensor;responsive to detection of a change in fuel capacitance, adjust a fuel lift pump voltage to maintain a fuel lift pump pressure at a selected pressure above a fuel vaporization point;if no change in fuel capacitance has been detected, and if the fuel system has been operating for greater than a threshold duration, temporarily reduce fuel lift pump pressure until fuel vaporization is detected by the sensor, and adjust the selected pressure based on the fuel lift pump pressure at which fuel vaporization was detected; andif no change in fuel capacitance has been detected, and if the fuel system has not been operating for greater than the threshold duration, continue current operation and operate the sensor as a fuel composition sensor. 14. The fuel system of claim 13, wherein the control system further includes instructions to, in a second mode of operation, adjust the fuel lift pump voltage responsive to an indication of fuel vaporization, the indication of fuel vaporization based on the fuel capacitance, and maintain a temperature of the sensor at a selected temperature. 15. The fuel system of claim 13, wherein the control system further includes instructions to, in a third mode of operation, adjust the fuel lift pump voltage responsive to an indication of fuel vaporization, the indication of fuel vaporization based on the fuel capacitance, and increase the fuel lift pump pressure responsive to the indication of fuel vaporization. 16. The fuel system of claim 13, wherein the fuel system is part of a gasoline direct injection engine system. 17. The method of claim 1, wherein the threshold duration is smaller when the engine system is operating under a higher load compared with the threshold duration when the engine is operating under a lower load. 18. The method of claim 1, further comprising, if the system has not been operating for greater than the threshold duration, continuing current operation. 19. The method of claim 6, further comprising, during operation in the first mode, if the fuel system has not been operating for greater than the threshold duration, operating the sensor as the fuel composition sensor, wherein the threshold duration is smaller when an engine is operating under a higher load compared with the threshold duration when the engine is operating under a lower load. 20. The fuel system of claim 14, wherein the threshold duration is smaller when an engine is operating under a higher load compared with the threshold duration when the engine is operating under a lower load.
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