A new technique for determination of geometry characteristics, mass flow rate and discharge coefficient of a direct gas injection nozzle

In the direct gas injection engine, the mixture formation and the combustion rate are affected by the geometry of injector holes (the diameter, angles, K-factor) and discharge the coefficient of the exit nozzle. This paper presents a new method to determine the diameter and the nozzle exit angle, based on silicone molding of the injector exit nozzle, using image processing techniques. The actual fuel mass flow rate was measured through experiments, which were done with a designed experimental set-up. Tests have been done in an optical constant volume chamber, where the ambient gas was pressurized air, limited between 5 to 15 bar and the injection gas was compressed natural gas (CNG) at two different pressures, 30 and 40 bar. Discharge coefficients have been calculated for different ambient and injection pressures, considering values of actual and ideal mass flow rates. Results verified the present approach for determining the diameter and the nozzle exit angle. Moreover, results showed that there was a direct relationship between the actual mass flow rate and the discharge coefficient with ambient and the injection pressure.