Investigations of the fuel injection processes in a spark ignition direct injection engine have been performed for two different fuels. The goal of this research was to determine the differences between isooctane, which is often used as an alternative to gasoline for optical engine investigations, and a special, non-fluorescing, full boiling range multicomponent fuel. The apparent vaporization characteristics of isooctane and the multicomponent fuel were examined in homogeneous operating mode with direct injection during the intake stroke. To this end, simultaneous Mie scattering and planar laser induced fluorescence imaging experiments were performed in a transparent research engine. Both fuels were mixed with 3-Pentanone as a fluorescence tracer.
A frequency-quadrupled Nd:YAG laser was used as both the fluorescent excitation source and the light scattering source. To help counter possible attenuation effects, the laser beam was split into two laser light sheets that were directed into the combustion chamber from opposing sides. Two CCD cameras, which were positioned perpendicular to the laser light sheet, simultaneously detected the LIF and Mie scattering signals at various crank angles for individual engine cycles. This enabled the detection of both the liquid and the gas phases of the injection events.
An injection pressure variation was performed to examine the influence of fuel pressure on apparent vaporization behavior. Simultaneous Mie scattering and LIF imaging was performed for injection pressures of 200, 150 and 100 bar. Differences in the vaporization characteristics of each fuel are described in the context of the averaged Mie scattering and LIF images.