Developing GDI engines for minimum particle emissions in RDE test conditions

How to identify situations in need of improvement and how to find correct actions to reduce PN emissions in real drive conditions?The engine development procedures include selection of best injectors at the very early stage of hardware definition, and, along the way of combustion system development, the adjustment of injection parameters to the boundary conditions given by stationary and transient engine operation modes until the final vehicle certification in today’s WLTP or future RDE test modes.The overall task: fuel injection for each combustion cycle must result in premixed combustion of a homogenous, stoichiometric charge. On this background the paper describes Selection of injectors for given combustion chamber geometry and in-cylinder flow: test procedures and selection criteria include sub-zero cold start, catalyst heating and part load / high load operation at low and moderate engine speed. Calibration of injection parameters in dynamic drive situations Identification and improvement of PN emission issues in WLTP / RDE test cycles Evaluation of injector coking issues Test methods include the cycle by cycle analysis of spray and flame signals, either recorded with high speed cameras or with fiber optic flame sensors together with cylinder pressure analysis in order to visually see diffusion flame (soot) areas or to identify them by means of their flame radiation signature. These cycle and deg CA resolved combustion signals are related to engine out particle emissions.We present a methodology to effectively use such in-cylinder diagnostics to finally meet target PN emissions levels in a vehicle’s certification test.