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.