| The objective of this thesis is to improve the understanding of different mechanisms that are encountered during fuel injection. Recently, alcohols have made their way into the market and are often blended, in different proportions, to gasoline. Therefore, it becomes crucially important to understand how fuels' physical properties influence sprays in terms of penetration. The second objective is to elaborate an analytical model using empirical correlations that can accurately reproduce the spray penetration curves. Furthermore, the construction of these correlations will help identify which variables are predominant. To acquire the necessary data, an experimental setup was elaborated together with high speed imaging techniques. This study's variables are the injection pressure, the ambient pressure, the ambient temperature, the injection duration and the physical properties of the fuels. The fuels used in this research were gasoline, iso-octane, ethanol and butanol as well as two blends in equal volume; one of ethanol and iso-octane and the other, of butanol and iso-octane. The analysis, using an imaging processing program, has yielded certain observations. Firstly, it was noted that alcohols penetrate less than gasoline and iso-octane, independently of ambient conditions. Secondly, injection pressure increases initial spray velocity but ultimately causes the spray to atomise more finely which reduces penetration. Thirdly, ambient pressure has a significant impact on spray penetration because an increase in ambient density causes the aerodynamic forces to increase systematically resulting in a shallower penetration. Fourthly, an increase in ambient temperature triggers complex evaporation mechanisms. The enthalpy of vaporization is an indicator of a fuel's sensitivity to an increase in ambient temperature. For example, ethanol, because of its high value of vaporizing enthalpy, is considerably less affected by an increase of temperature than butanol. Finally, injection duration tests have no impact on penetration curves besides increased penetration due to longer momentum flux input. These tests have helped develop correlations to be implemented in an empirical model. The advantage of this model is that it takes into account the relative weight of fuel physical properties. It was established that, amongst the three properties that were considered, fuel density is the most important throughout the injection. Then, during the early stage of the injection, the boiling temperature and the enthalpy of vaporization have similar relative weight, whereas towards the end of the injection, the boiling temperature becomes more important than the enthalpy of vaporization.;Keywords : spray characterization, gasoline, alcohol, empirical correlations... |
