The performance of SI engines is substantially influenced by the degree of fuel atomization that occurs within the mixture preparation system. With a measuring device, based on laser Sight diffraction, it is possible to determine droplet size spectra with high temporal and spatial resolution, even if the droplets are moving with high velocity.
However, with such a measuring device, the influence of density gradients within the measuring volume, as that created by fuel vapor or temperature differences, can be critical and must be taken into consideration to provide satisfactory results.
The degree of atomization depends on the engine operating conditions, namely engine speed and load. At part load conditions, single-point systems such as carburetor or single-point injection, produce an outstanding quality of atomization due to the high velocities at the throttle plate, whilst multi-point injection systems show worse atomization behavior due to the low air density and air velocity within the manifold. Substantially changed conditions occur at full load, where multi-point injection systems prove to have the best quality of atomization.