Injection performance and cavitation analysis of an advanced 250 MPa common rail diesel injector

Abstract

The present work is to demonstrate the working process and injection performance of a new-type diesel injector, and to make a contrastive analysis of cavitation which potentially occurs near control-valves of the new and another conventional injector. The advanced injector is developed for 250MPa common rail injection systems of medium or heavy duty commercial vehicles. The originality is the development of a novel control-piston with the outward appearance of a poppet valve. The control-piston can automatically move downwards or upwards owing to pressure changes in related hydraulic chambers, and consequently appropriately activates or deactivates the function of additional inflowing control-orifices to improve system responsiveness.The injection performance demonstration was carried out by one-dimensional (1D) hydraulic mechanical simulation in combination with the experimental data input of actuators. On the other hand the cavitation evaluations, in both the conventional and new structures, were studied numerically by computational fluid dynamics (CFD) based on nonlinear cavitation model and dynamic grid method. Additionally the CFD model was validated against experimental result in terms of mass flow rate of backflow fuel in the conventional structure. The 1D simulation result shows that the new injector is capable of achieving multi-injection and ramp-shaped injection flow rate; closing-delay of injection can be reduced from 1.232 to 0.758ms, and backflow fuel quantity index can be decreased to 14.1:182.6 which means a reduction of 15.5%. As regards to the contrastive analysis of cavitation, the CFD simulation result of the new structure shows several improvements as follows: a lower velocity field (below 311.88m/s) near the control-valve, cavitation no longer occurring in the guide-hole, and a reduction of 70.22% in mass exchange rate between vapour–liquid phases near the sealing annulus of valve seat.