Effects of injector parameters on mixture formation for multi-hole nozzles in a spray-guided gasoline di engine
Paper i proceeding, 2005
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 and numerically using Computational Fluid Dynamics. Laser Induced Exciplex Fluorescence (LIEF) measurements in a constant pressure spray chamber and optical engine measurements have shown that injectors with 6-hole nozzles and 50-degree umbrella angles are unsuitable for stratified combustion because they produce steep air-fuel ratio gradients and create a spray with overly-deep liquid fuel penetration as well as presence of liquid fuel around the spark plug. In order to study injector performance, numerical calculations using the AVL FIRE™ CFD code were performed. The numerical results indicate that by increasing the injector umbrella angle, the extent of piston wall wetting can be decreased. Also, changing the pattern of holes in the nozzle changes the spray pattern, enabling its optimization with respect to ignition and flame propagation. Furthermore, PDA and Direct Imaging experiments showed that increasing the l/d ratio by reducing the hole diameter resulted in a decrease in the mean droplet sizes (D32). The spray angle was found to increase with decreasing l/d ratios. It has also been shown that by choosing a suitable l/d ratio it is possible to control the local AFR and cross-flow velocity at the spark plug. Copyright © 2005 SAE International.