Pressure measurement in the high pressure fuel system

In order to meet the demanding legislations on diesel engines exhaust emissions, an always more accurate control over the amount of fuel injected in the cylinders is required. A comprehensive understanding of the main factors involved in the injection process, therefore, should be achieved. Such factors are the pressure in the common rail, the injection ontime and the temperature at the injector. The rail pressure, in particular, has been the focus of this project: Its accurate acquisition is crucial for the correct determination of the injection duration and, consequently, for an improved control over the amount of fuel injected. The rail pressure, however, is characterized by significant instabilities affecting the measurement. An experimental campaign has been conducted on a Scania D13 engine in order to characterize and understand the rail pressure signature during engine steady operations: The superposition of injections, pump strokes and water-hammer instabilities forms a complex pattern extensively discussed. An attempt to model the pressure fast transients has been made: While the frequency content of the phenomenon investigated is correctly interpreted, the results obtained in the time domain diverge significantly in amplitude and phase from the experimental data collected. Finally, the measurement strategy adopted today at Scania CV AB to acquire the rail pressure has been investigated and its accuracy assessed. On the basis of the knowledge achieved, a new adaptive measurement technique, capable of changing the estimation process accordingly to the engine operating condition detected, is proposed. The potentiality of an increased accuracy in controlling the amount of fuel injected is proved for engine steady operations. Further investigation regarding the method tolerance to engine transients, however, is required