Diesel engines face difficult challenges with respect to
engine-out emissions, efficiency and power density as the legal
requirements concerning emissions and fuel consumption are
constantly increasing. In general, for a diesel engine to achieve
low raw emissions a well-mixed fuel-air mixture, burning at low
combustion temperatures, is necessary. Highly premixed diesel
combustion is a feasible way to reduce the smoke emissions to very
low levels compared to conventional diesel combustion. In order to
reach both, very low NOX and soot emissions, high rates of cooled
EGR are necessary. With high rates of cooled EGR the NOX
formation can be suppressed almost completely.
This paper investigates to what extent the trade-off between
emissions, fuel consumption and power of a diesel engine can be
resolved by highly premixed and low temperature diesel combustion
using injection nozzles with reduced injection hole diameters and
high pressure fuel injection. However, a reduced hydraulic flow
rate usually leads to a penalty in fuel consumption and power
output at full load operation. Hence this paper also presents the
influence of hydraulic nozzle flow on indicated power output,
emissions and fuel consumption at the rated power point of the
engine.
Five nozzles with different hydraulic flow rates between 200 and
430 cm₃ in 30 s at 100 bar are investigated. The influence of the
nozzles on emission, fuel consumption, rate of heat release, and
noise are analyzed on a single-cylinder research diesel engine. In
addition a combination of different analysis methods is used in
order to investigate the influence of hydraulic nozzle flow on
mixture formation, combustion and emission in more detail. The
influence of injection hole diameter on hydraulic parameters of the
injector like injection rate, quantity and duration has been
investigated as well as the influence on spray propagation of the
liquid and gaseous phase of each nozzle. In addition, a
CFD-simulation shows the influence of different injection hole
sizes on fuel distribution, mixture formation and combustion inside
the combustion chamber during full load operation.