The requirement of reducing worldwide CO₂ emissions and engine
pollutants are demanding an increased use of bio-fuels. Ethanol
with its established production technology can contribute to this
goal. However, due to its resistive auto-ignition behavior the use
of ethanol-based fuels is limited to the spark-ignited gasoline
combustion process. For application to the compression-ignited
diesel combustion process advanced ignition systems are required.
In general, ethanol offers a significant potential to improve the
soot emission behavior of the diesel engine due to its oxygen
content and its enhanced evaporation behavior.
In this contribution the ignition behavior of ethanol and
mixtures with high ethanol content is investigated in combination
with advanced ignition systems with ceramic glow-plugs under diesel
engine relevant thermodynamic conditions in a high pressure and
temperature vessel. The investigation focuses on optimizing the
injection conditions, especially injection pressure and rate.
Optical measurements are performed by high speed imaging of the
fuel injection and ignition, and evaluated in terms of ignition and
flame propagation. The high speed imaging technology furthermore
enables to gain information on the statistical behavior of the
ignition process and thus provides a direct assessment of the
repeatability of the ignition and combustion process.
The results of the ignition investigation aim at improving the
understanding of the glow-plug-induced ignition process in order to
provide a reliable ignition strategy for the diesel engine
operation with fuel with high ethanol content. The results show
that the favorable spray targeting relative to the glow-plug
depends on the glow-plug design. Furthermore a moderate injection
pressure improves the ignition reliability of the ethanol fuels.
The latter leads to the hypothesis that reduced injection-induced
shear rates improve the ignition behavior by diminishing
shear-induced quenching in the ignition zone in the direct vicinity
of the hot glow-plug surface.