Reduction of Diesel Engine Emissions Performance – Further Steps Towards a Fast and Flexible Fuel Injection

Abstract

Diesel engines remain the main powertrain concept in view of efficiency and robustness. On the one hand the emissions towards the future EU CO2 limit of 95 g/km by 2021 further demands the reduction of the fuel consumption. On the other hand the new WLTP test cycle and RDE emissions tests demand to reduce the engine-out raw emissions. So far, the main development path of the fuel injection system is focusing on increasing the rail pressure. The increase of the no. of injection events is another approach that aims for phasing the combustion in the working process of the Diesel engine efficiently. This approach is limited by the needle opening speed and capability of closed-coupled injection events. Such features were so far restricted to Piezo injectors. Recently the solenoid injector was enhanced to close this gap and it was firstly tested on an hydraulic test bench and a 4 cyl. passenger car Diesel engine. The hydraulic and engine performance is compared against the solenoid injector G4S and the Piezo injector G4P. With increasing the injection rate steepness and reducing the hydraulic intervals, a triple pilot injection strategy is applied to control the ignition delay and rate of combustion. The steep injection rate reduces the soot emissions without compromising the combustion noise. On the other hand the short interval and fast needle actuation reduces the injection and combustion duration. Thanks to this improved hydraulic performance the BSFC could be improved by 1.7% and soot emissions reduced by 36% at engine part load conditions (2000 rpm, BMEP=6 bar).