An experimental investigation on OBD II techniques for fuel injection system monitoring in a common rail passenger car diesel engine

Different diagnostic techniques were experimentally tested on a common rail automotive 4 cylinder diesel engine in order to evaluate their capabilities to fulfill the California Air Resources Board (CARB) requirements concerning the monitoring of fuel injected quantity and timing. First, a comprehensive investigation on the sensitivity of pollutant emissions to fuel injection quantity and timing variations was carried out over 9 different engine operating points, representative of the FTP75 driving cycle: fuel injected quantity and injection timing were varied on a single cylinder at a time, until OBD thresholds were exceeded, while monitoring engine emissions, in-cylinder pressures and instantaneous crankshaft revolution speed. Afterwards, the different diagnostic algorithms under investigation, based both on crankshaft revolution speed sensor signal and on in-cylinder pressure sensor signal, were tested under steady state operating conditions in order to detect their fault rate detection capabilities. Finally, the more promising diagnostic algorithms, which were selected through the above mentioned process, were tested on transient conditions in order to assess their capabilities to detect both injection quantity and timing errors.