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EU6c Particle Number on a Full Size SUV - Engine Out or GPF?
Abstract:
This paper describes the findings of a design, simulation and test study into how to reduce particulate number (Pn) emissions in order to meet EU6c legislative limits. The objective of the study was to evaluate the Pn potential of a modern 6-cylinder engine with respect to hardware and calibration when fitted to a full size SUV. Having understood this capability, to redesign the combustion system and optimise the calibration in order to meet an engineering target value of 3×1011 Pn #/km using the NEDC drive cycle. The design and simulation tasks were conducted by JLR with support from AVL. The calibration and all of the vehicle testing was conducted by AVL, in Graz.
Extensive design and CFD work was conducted to refine the inlet port, piston crown and injector spray pattern in order to reduce surface wetting and improve air to fuel mixing homogeneity. The design and CFD steps are detailed along with the results compared to target. The redesigned high tumble combustion system enabled the engine to meet challenging combustion stability targets at low Pn-levels.
The ECU software was optimised in order to allow for calibration strategies leading to minimised wall interaction of injected fuel.
The Pn optimisation by calibration measures with the improved combustion system followed a specific development process.
Physical testing and calibration optimisation was conducted on a state of the art chassis dynamometer with rapid cooling capability and full combustion and emissions measurement capability.
In addition, optical combustion diagnostic equipment was used to determine sources of soot formation within the combustion chamber during dynamic testing on a cycle resolved basis. Within this testing environment a Pn - optimised injection strategy with special focus on dynamic, cold and high load operation was developed. This strategy allowed reducing surface impingement as a source of diffusion combustion, under all operating conditions, to an absolute minimum.
The results of the project showed that the engineering target could be achieved with a margin of robustness. The performance of the hardware and calibration was also assessed over the WLTP, FTP 75 and a real world driving cycle (AVL RDE cycle). This showed that the excellent Pn optimisation of this engine did not result in any significant detrimental effects on gaseous emissions and actually delivered a small improvement in fuel consumption. The paper concludes with a summary of considerations outside the original scope of the project which would be important for further Pn reduction.