A virtual injection sensor by means of time frequency analysis

A time frequency analysis has been applied to an experimental pressure signal that is measured along a high-pressure pipe that connects the rail to an injector in a fuel injection system for diesel engines. An experimental test campaign has been carried out at a high-performance hydraulic rig for Common Rail systems. The variations in the mean instantaneous frequency, which is calculated from a spectro- gram of the experimental injector inlet pressure time histories, are related to key events pertaining to the injection phase. The physical meaning of these variations in the mean instantaneous frequency is identified through a comparison with the outcomes of a numer- ical simulation using a previously developed one-dimensional model of the injection system. This tool allows the lift of the mobile valves, the instantaneous injected flow-rate and the pressure transients inside the injector to be predicted accurately. The objective of the research has been to realize a virtual sensor to detect the opening and closure instants of the mobile valves within the injector, on the basis of the pattern of the mean instantaneous frequency trace. The realized virtual sensor has been applied to the analysis of both single and multiple injection events.