Future requirements for lower automotive emissions have lead to the development of
new internal combustion (IC) engine technologies. Gasoline Direct Injection (GDI), for
example, is one of these promising new IC engine concepts. It offers the opportunity of
increased efficiency through unthrottled operation. However, the realisation of this
concept is critically dependent on the in-cylinder mixture formation, especially in the
late injection/lean operation mode. Ideally, this would require a precise stratification of
the in-cylinder fuel-air mixture in 3 distinct zones: an ignitable pocket located at the
spark plug, surrounded by a stoichiometric mixture of fuel and air, encompassed by air.
To enable this stratification, the GDI concept utilises advanced injector technology.
Phase Doppler Anemometry (PDA), Planar Laser-Induced Fluorescence (PLIF) and the
combination of PLIF and Mie scattering in the Laser-Sheet Dropsizing (LSD)
technique, have been applied to sprays in the past to obtain dropsize information and
study the mixture formation process. These new GDI sprays are denser, their droplet
sizes are smaller and they evaporate faster, and as such, place us at the limit of the
validity of these measurements techniques.
The diagnostics were applied to a GDI spray in a pressure vessel for realistic in-cylinder
conditions, ranging from supercooled to superheated environments. Tracer evaporation
issues in the PLIF technique were resolved by using a dual tracer system. The study
showed that the LSD technique provided good quantitative data in low evaporation
regimes. In highly evaporating regimes, the technique still gave reliable dropsize data
for the early stages of the injection, but was limited afterwards by vapour-phase
contribution to the fluorescence signal. Variations between PDA data and LSD results
also suggested a deviation of the Mie scattering signal from the assumed d2 dependence.
This was further investigated and was found to be true for small droplets (d/?. <0.2). This
source of error might be improved by using a different observation angle. High density
seriously compromises the accuracy of PDA, whilst its effect through multiple
scattering is of second order for the LSD technique. In low evaporating regimes, LSD has the overall advantage of being a 2-D measurement
technique, and will yield data with a maximum error of 30% in dense parts of the spray
where PDA data is totally unreliable. If the spray evaporates quickly, PLIF by itself is
an appropriate tool for following the air-fuel mixture, because short droplet lifetimes
limit the 2-phase flow behaviour of the spray.
Particle Image Velocimetry (PIV), the LSD technique and equivalence ratio LIF
measurements were applied to a BMW single cylinder optical GDI engine. The early
injection operation showed no particular issues. However, the results obtained in the late
injection highlighted the poor mixing and inappropriate stratification
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