Diesel fuel and Diesel fuel with Water Emulsions Spray and Combustion Characterization

Abstract

The legislative demand to simultaneously reduce nitrogen oxide(s) emissions and particulate matter emissions from compression ignition engines is proving difficult to achieve in the real world. One promising strategy is the use of Diesel fuel emulsified with water. There is little work concerning the e↵ect of emulsification on fuel injection sprays. This work details an experimental campaign to characterize non-vaporizing sprays of Diesel fuel and Diesel emulsions, with 10% and 20% water by mass. Characterization of the fuel sprays has been done using: high speed photography, applying focused shadowgraphy and a di↵used back-lighting technique and; hydraulically using a force transducer placed 0.5mm from the injector nozzle to measure spray momentum flux. All measurements have been made in an optically accessible high pressure chamber filled with nitrogen, resulting in an ambient gas density of 22.6 kg/m3 and 34.5 kg/m3, with injection pressures of 500, 700 and 1000bar used. The images collected have been used to determine the spray cone angle, the tip penetration and the tip velocity. The signal from the force transducer has been used to determine spray momentum flux, instantaneous mass flow rate, dimensionless nozzle coefficients and injection velocity. The injection pressure had no discernible influence on the spray cone angle for the Diesel fuel sprays but did for the emulsified fuels. Increasing the ambient density resulted in an increase in the spray cone angle for Diesel fuel, this was not always the case for the emulsified fuel sprays. The spray tip emerged from the nozzle and accelerated for a very short period after the start of injection until a maximum velocity was reached. The momentum flux for each fuel was almost the same for corresponding conditions. Increasing the chamber gas density reduced the measured spray momentum. The total mass of fuel injected for Diesel fuel was larger than for the emulsions for the equivalent conditions and duration, although emulsions had a larger density and viscosity. The emulsions had a higher injection velocity. The nozzle discharge coefficient for Diesel was higher than for the emulsions. The velocities measured hydraulically are much higher than the maximum tip velocities measured optically. The study has been completed by some preliminary combustion studies of the fuels in an optically accessible combustion chamber. The emulsion tested exhibited much lower natural flame luminosity, used to determine the spatially integrated natural luminosity of the flame which may be useful as a soot indicator. There was no evidence that the microexplosion phenomenon was present in these tests.