Study of the influence of low needle lifts process on the internal flow and spray characteristics in Diesel injection nozzle

Abstract

In the field of Diesel injection systems of combustion engines, numerical modelling can be regarded as an essential approach to the dynamic in-depth analysis of the nozzle internal flow. Nonetheless, the low lifts process in numerical modelling that opens the needle from the closed state is usually neglected, leading to the incomplete numerical injection model which results in an incomplete analysis.

In the following study, a more complete numerical injection model was introduced to resolve the problem of the needle opening, and a detailed comparative investigation was performed pertaining to the effects of the injection process at low needle lifts on the follow-up dynamic simulation processes. For this study, a conical-orifice injector nozzle was used. CFD (Computational Fluid Dynamics) was implemented to study the behaviours of the internal nozzle flow and the corresponding spray characteristics. An external library concept was introduced to link the process of the internal nozzle injection with the formation of spray. Additionally, several comparative dynamic simulations were performed under a double-axis system.

In terms of the internal nozzle flow, the comparison of experimental result shows that the absence of low lifts process in calculation causes simulation error in the follow-up dynamic injection process. In terms of the corresponding spray behaviours, the absence of low lifts process further influences the atomization effect, to the extent of leading to more deviation in the spray angle. The conclusion is that the complete negligence of low needle lifts process in numerical injection simulation is considered not well-accepted. Besides, the processes at low lifts have been proven to be worthy of further investigation.

Keywords: Numerical Modelling, Low lifts Process, Conical Diesel Injector, Cavitation, Spray