Analysis of injected mass shot-to-shot dispersion and injection rate profile for a PFI injector in actual operating conditions

In order to improve engine emission and limit combustion instabilities, in particular for low load and idle conditions, reducing the injected fuel mass shot-to-shot dispersion is mandatory. Unfortunately, the most diffused approach for the hydraulic analysis of low-pressure injectors such as PFIs or SC R dozers is restrained to the mean injected mass measurement, since the use of conventional injection analysers is unfeasible. In the present paper, an innovative injection analyser is used to measure the injection rate and the injected mass of each single injection event, enabling a proper dispersion investigation of the studied system. The proposed instrument is an inverse application of the Zeuch’s method, which in this case is applied to a closed volume upstream the injector, with the injector being operated with the prescribed upstream-downstream pressure differential. Further, the injector can inject freely against air, thus enabling simultaneous analyses of the resulting spray such as imaging or momentum flux measurement. In the present paper, the proposed injection analyzer is used to characterize the tested PFI injector in terms of injection rate and injected mass dispersion in different operating conditions in terms of injected mass with both atmospheric and sub-atmospheric downstream pressure conditions. The simultaneous spray imaging is also used to complement the analysis of the investigated low pressure injection system in typical, throttled-like operating conditions.