Investigation of Fuel Atomization and Evaporation of a DISI Injector Spray Under Homogeneous Charge Conditions

Understanding the causal loop from injection to combustion in modern direct injection engines is essential to improve combustion and reduce emissions. In this work, the section from injection to fuel-evaporation in this causal loop was investigated using different optical measurement techniques, with a focus on drop size measurements using Phase Doppler Anemometry (PDA). One spray jet of a modern DISI multi-hole injector was investigated using gasoline RON 95 fuel and two single component alkane fuels (n-hexane / n-decane). In a first step the macroscopic spray formation and propagation of this spray jet were studied using a 2D-Mie-scattering technique in an optical injection chamber at homogenous charge DISI conditions. Furthermore, the droplet size distribution and mean diameter were determined spatially and temporally resolved for an ambient pressure of 0.3MPa and different ambient temperature (323K / 423K / 523K) conditions in the optical chamber using Phase Doppler Anemometry. For an ambient temperature of 323K, the influence of the Reynolds number on the atomization process was studied under non-evaporating conditions showing an almost linear decrease in mean diameter versus logarithmic Reynolds number. This work demonstrates that knowledge of the drop size distribution at different positions in a gasoline spray under modern charged conditions is not enough to determine an evaporation ratio, i.e. evaporated mass vs. penetration depth. However, it was possible to determine the influence of the ambient temperature on the drop size and drop size distribution at a fixed measurement position and to estimate an evaporated mass as a function of the ambient gas temperature.