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The key issue in gas metering of alternative fuel vehicle is to obtain low emission and accurate air-fuel ratio. A hot wire mass air flow sensor can directly monitor the air flow by using thermal transfer amount in an unit time to keep the hot wire at a certain temperature. Surveys were conducted regarding this method and it was verified that this method enables to monitor mass gas flow in applications such as Compressed Natural Gas(CNG) and propane(C3H8). The gas passage body for this sensor, which consists of a 10mm diameter bypass and a main pass has been surveyed and developed. This electrical sensing device for CNG has been completed and its performance was verified with a CNG flow test stand and a CNG engine. We have found that this thermal transfer monitoring method is not affected by a pressure change.

A new Gas Flow Sensor was derived from the current air flow sensing technology. This sensor is targeted at measuring the amount of gaseous mass flow under high pressure and with varying gas temperature. Thermodynamical properties of CH4, air, N2He and CO2 have been compiled at different pressures and temperatures. This information is required for the simulation. A theoretical model has been developed to analyze the behavior of the sensor circuit with different gases at varying pressure and temperature. The theoretical model encompasses a model of the gas flow circuit as well as a flow model with an optimized fluid dynamic equation. Fluid dynamics have also been studied to demonstrate the usage of a bypass and a mesh screen for flow regulation. A finite element analysis (FEA) is also generated to study the velocity profile and potential turbulence areas.