Studies of Particle Formation and Emission of Passenger Car Gasoline Engines with Direct Fuel Injection

Authors

Prof. Dr. sc.techn. Thomas Koch, Dr.-Ing. Markus Bertsch, Denis Notheis, MSc., Dr.-Ing. Amin Velji,
Karlsruher Institute of Technology, Institut für Kolbenmaschinen, Karlsruhe

Summary

This research project was initiated to investigate the causes of particle formation in GDI engines. In the first part of the project, investigations in a rapid compression machine and a single cylinder research engine with the usage of optical diagnostics, thermodynamic analysis and exhaust gas analysis revealed several root causes for particle number (PN) emissions. Several influencing parameters were varied and the influence on PN emissions was demonstrated. Special attention was given to the particle formation at low engine load and catalyst heating operation. For the follow-up
project, the focus was shifted to higher engine load at low engine speeds with resulting low in-cylinder charge motion and a high amount of fuel injected, causing difficulties in the mixture formation process.

In the first part of this report, an overview on the composition of particle emissions and the formation of soot, as the most important fraction of particles, is given. The test bench setup of the single cylinder research engine is described in combination with the measurement devices used in the second chapter. The following
investigations in the single cylinder research engine focus on the implementation of additional charge motion, either by changed valve timings, early intake closing by reduced intake valve lift or the use of inlays in the intake port to generate a large scale charge motion. The last part of the results section describes the impact of the changed hydraulic flow and increased injection pressure on the particle formation process at various engine loads and in-cylinder charge motion levels. The analysis of the particle formation process for the various parameters investigated shows the
influence of each factor singularly and therefore strategies to operate GDI engines at high engine load with low particle number emissions.

Optical measurements in a pressure chamber with two injectors with same spray targeting but different hydraulic flow were compared under different boundary conditions (pressure and temperature in the chamber and different injection pressure). The influence of high-pressure exhaust gas recirculation (EGR) on the
particle formation and variations of the relative air-fuel ratio were investigated in a single-cylinder.

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