In recent years,a series of studies have reported that the discrepancy between real-world and type-approval fuel consumption levels for lightduty gasoline vehicles( LDGVs) is increasing. These studies were mostly based on users' reported data or portable emission measurement system(PEMS). On-board diagnostic(OBD) is a device that is capable of monitoring real-time operating conditions of engine and exhaust control systems.Through instantaneous engine mass air flow rate data collected by the OBD decoder,the ...