Patent ID: 8073636

Claim:
A method for determining the gas composition of a gas mixture in a fuel tank of a motor vehicle filled with a compressed natural gas (CNG) mixture, comprising the steps of: using a pressure sensor to measure a gas pressure and using a temperature sensor to measure a gas temperature in the fuel tank of the motor vehicle; using a processor embodied in hardware to: execute an algorithm that relates temperature with vapor pressure to calculate a current vapor pressure of a particular component of the CNG mixture in the fuel tank based on the measured temperature in the fuel tank, the vapor pressure of the particular component of the CNG mixture being defined as the pressure at which the particular component changes state from a liquid to a gas; compare the measured as pressure in the fuel tank with the determined vapor pressure for the component of the CNG mixture; and if the measured gas pressure in the fuel tank falls below the determined vapor pressure for the particular component of the CNG mixture, determining a current composition of the CNG mixture in the fuel tank.