Studies of the effect of injector parameters on mixture formation for multi-hole nozzles in a spray-guided

This paper focuses on ways of improving the spray formation from spray-guided multi-hole gasoline direct injection injectors. Work has been done both experimentally using laser diagnostic tools as well as numerically using Computational Fluid Dynamics (CFD).Laser Induced Exciplex Fluorescence (LIEF) measurements in a constant pressure spray chamber and optical engine measurements has shown that a 6-hole nozzle with a 50 degree umbrella angle has steep air-fuel ratio gradients and too long liquid fuel penetration as well as presence of liquid fuel at the spark plug location, making it unsuitable for stratified combustion. In order to improve the injector performance, numerical calculations using the AVL FIRE CFD code have been performed. The numerical results indicate that by increasing the injector umbrella angle, the piston wall wetting can be decreased. Also, by optimizing the spray pattern through a change of the nozzle hole arrangement, the conditions for ignition and flame propagation can be improved. Furthermore, it was found experimentally by the use of PDA and Direct Imaging that an increase of the l/d ratio through a reduction of the hole diameter resulted in a decrease of the mean droplet sizes (D32). The spray angle was found to increase with decreasing l/d. It has also been shown that by choosing a suitable l/d it is possible to control the local AFR and cross-flow velocity at the spark plug