Future Diesel engine legislation Tier 5 / Stage V and Euro 6d demand further improvements to reduce CO2 while keeping the already low NOx emissions levels while in the US further NOx emissions reduction has to be achieved. In this trade-off, system costs and complexity of the after-treatment are defining the constraint in which the common rail fuel injection system layout has to be defined. The increase of rail pressure was in the past the major step to control the soot emissions in view of high engine-out raw NOx emissions. With the on-going development of NOx-aftertreatment by Selective Catalytic Reduction (SCR) of urea-injection, conversion efficiencies of up to 97% allow to reduce the EGR usage and rail pressure usage. In that context, the steepness of injection rate, the nozzle flow rate and the injection pressure are remaining parameters to control the NOx emissions. A shallow injection rate in combination with larger nozzle flow rates is beneficial to reduce the NOx emissions thanks to less premixing of fuel with air. To study this effect, the latest solenoid injector with improved magnetic actuation is utilized and the influence of the steepness of injection rate is studied on a 6 cylinder HD Diesel engine on 3 representative part- load points of the WLTC cycle. Depending on the engine-out NOx emissions requirements, two scenarios are resulting. In case of a strong NOx aftertreatment, the shallow injection rate steepness is beneficial for the fuel consumption. In case of less NOx aftertreatment, high EGR rates are required and soot emissions can be controlled through the steepness of injection rate.