Effects of Fuel Composition, Additives and Injection Parameters on Particulate Formation of Gasoline DI Engines

Authors

Dr.-Ing. W. Wiese, Dipl.-Ing. C. Laidig, Dr.-Ing. E. Schünemann, Robert Bosch GmbH, Schwieberdingen; F. Balthasar MBA MEng, J. Chahal PhD MSc, Shell Research Limited, London

Year

2018

Print Info

Fortschritt-Berichte VDI, Series 12, No 807

Summary

Bosch and Shell conducted a joint study to understand the effects of fuel composition, fuel borne additives, injection pressure and injection strategy to reduce the particulate emissions of gasoline DI engines.
In the first phase of the study, engine investigations were performed to understand how different fuel compositions, injection pressure, and injection strategies impact particulate number (PN) emissions. Fuels containing a high proportion of heavy aromatics (C9+) compared to EU market average were found to be more critical for injector PN drift (deposits on injector tip) and consequently leading to higher PN emissions during endurance runs. Additionally, measures to mitigate PN emissions were investigated, and it was found that fuels containing deposit control additives (DCA) reduced injector PN drift and PN emissions significantly.
In the second phase of the study, a vehicle with the same engine was tested on a chassis dynamometer to understand the correlation between the engine test-bench and vehicle based drive cycle results. The Worldwide harmonized Light vehicles Test Cycle (WLTC) and a specific Real Driving Emissions (RDE) test cycle exhibited the same PN emission trends for the fuels containing heavy aromatics during the drive cycles as in the endurance runs. Furthermore, the engine based advanced injection strategy results correlated with the vehicle cold start emissions, clearly linking fuel volatility characteristics with PN emissions due to combustion chamber wall films.
Key findings of the study are the impact of certain fuels on PN emission and that fuels with DCA and/or higher injection pressures can mitigate the PN emissions due to injector PN drift. Additionally, an optimized injection timing can mitigate PN emissions due to wall wetting from low volatility fuels.