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Investigation of a New Injection Strategy for Simultaneous Soot and NOx Reduction in a Diesel Engine with Direct Injection
ISSN: 1946-3952, e-ISSN: 1946-3960
Published June 23, 2008 by SAE International in United States
Citation: Merkel, S., Eckert, P., Wagner, U., Velji, A. et al., "Investigation of a New Injection Strategy for Simultaneous Soot and NOx Reduction in a Diesel Engine with Direct Injection," SAE Int. J. Fuels Lubr. 1(1):1433-1442, 2009, https://doi.org/10.4271/2008-01-1790.
An important source for soot formation during the combustion of diesel engines with direct injection is the interaction of liquid fuel or a very rich air/fuel-mixture with the flame. This effect appears especially in modern direct injection engines where the injection is often split in a pre- and a main injection due to noise reasons. After the ignition of the pre-injected fuel a part of the main injection can interact with the flame still in liquid phase as the fuel is injected straight towards the already burning cylinder areas. This leads to high amounts of soot.
The injection strategy for this experimental study overcomes this problem by separating the injections spatially and therefore on the one hand reduces the soot formation during the early stages of the combustion and on the other hand increases the soot oxidation later during the combustion. In particular an injection configuration is used which gives the degree of freedom to modify the injection in the described manner. Therefore the cylinder head of a heavy duty single cylinder research engine is equipped with a second common-rail injector. This second injector is used for the pilot injection which is injected centrally in the combustion chamber while the main injection is done in a conventional manner using a seven-hole injector.
In the first step the mixture formation of the spatial separated pre- and main injection is simulated with the 3D-CFD code KIVA-3V to get a first impression on the mixture formation. Then the effects of the new injection strategy on the combustion process itself are investigated with the single cylinder engine in comparison to a conventional engine operation using cylinder pressure indication and exhaust gas analysis as well as the Two-Color-Method for observing the soot production and soot oxidation in the combustion chamber during the combustion process. This allows an assessment of the operating behaviour of the engine in comparison to the operation with a conventional injection pattern and the achievable emission reduction potential.