Effects of the Ambient Conditions on the Spray Structure and Evaporation of the ECN Spray G

The use of Gasoline Direct Injection (GDI) continuously increases due to the growing demand of efficiency and power output for i.c. engines. The optimization of the fuel injection process is essential to prepare an air-fuel mixture capable to promote efficient combustion, reduced fuel consumption and pollutant emissions. Good spray atomization facilitates fuel evaporation in i.c. engines thus contributing to the fuel economy and lowering the emissions. One of the key features of a multi-hole injector is to provide an optimal spray pattern in the combustion chamber and a good mixture homogenization considering the engine-specific characteristics such fuel mass-flow rate, cylinder geometry, injector position, and charge motion. This work aims to investigate the injection processes of an eight-hole direct-injection gasoline injector from the Engine Combustion Network (ECN) effort on gasoline sprays (Spray G, serial #19). The main objective is to evaluate both liquid and vapor phase envelope to extend the dataset for the Spray G covering a broader operating range. The tests were conducted fluxing iso-octane in a heated constant-volume pressurized vessel. A hybrid optical setup, Z-type schlieren and Mie scattering, using a high-speed C-Mos camera as detector, allowed the acquisition of both the vapor and the liquid phases. A customized image-processing procedure, developed in C# environment, was used for the outline of both the fuel phases. Different morphologies of the fuel spray were studied as function of the injection pressure, the ambient temperature, and the backpressure in the vessel, through the measurement of the spray penetrations, areas, and cone angles. Results indicate that global spray parameters such as liquid and vapor penetration as well as spray angle are largely affected by charge gas conditions (mainly density). The influences of ambient and injection conditions were of particular interest providing fundamental physics insight regarding fuel penetration and vaporization.