Zeuch method-based injection rate analysis of a common-rail system operated with advanced injection strategies

In the present paper the results of an experimental hydraulic analysis of a common rail injection system are discussed. A complete wet system, composed of an automotive injection pump, a rail and a Bosch CRI2.16 injector, is analyzed in realistic operating conditions. The hydraulic analysis is carried out by a Zeuch method-based instrument which is used to measure the injected volume and the injection rate; both these quantities are obtained in mean terms and shot-to-shot resolved in order to investigate the system operation dispersion. The injection rate measurement is supplemented by both the rail pressure and the needle movement measurements to better analyze the injector behavior. Some different advanced injector driving strategies are analyzed, focusing on reduced dwell time operation conditions. Peculiar attention is devoted to the injection process start detection, which is of special interest in case of multiple injections. An accurate analysis of the injection rate time-history suggests that in the initial part of the process the flow is directed toward the injector nozzle (negative flow) and only after a short time the injection rate profile becomes positive, apparently indicating the start of the injection process. In order to define a proper start time detection criterion, the results of the hydraulic analysis were compared with the spray evolution analysis based on imaging carried out by an ensemble-averaged approach. This comparison suggested that the injection start can be derived by the hydraulic analysis: the outflow onset is generally synchronized with the first positive values of the injected volume, computed as the time integral of the injection rate profile.