Hot Wire Mass Gas Flow Sensing Device

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.