Numerical investigation of the effect of swirl flow in-homogeneity and stability on diesel engine combustion and emissions

Abstract

The present study is aimed at numerically investigating the effect of in-cylinder charge motion on mixture preparation, combustion and emission formation in a high-speed direct-injection diesel engine. Previous investigations have shown that different valve-lift strategies nominally lead to similar in-cylinder filling and global swirl levels. However, significant differences in engine-out emissions, especially soot emission, give rise to the assumption that the flow structure and local differences of the swirl motion distribution have a noticeable effect on emission behaviour. In this work, different swirl generation strategies applying different intake valve actuation schemes are numerically investigated by applying transient in-cylinder computational fluid dynamic simulations using both the Reynolds-averaged Navier-Stokes model and the multi-cycle large-eddy simulation approach. Two operating points within the operating range of current diesel passenger cars during federal test procedure 75 and new European driving cycles are simulated. The injection and combustion simulations of different valve strategies show that an in-homogeneity in the in-cylinder flow structure leads to a significant increase in soot emissions, and agree with the observed trends of corresponding experimental investigations.

Investigation of Boundary Condition and Field Distribution Effects on the Cycle-to-Cycle Variability of a Turbocharged GDI Engine Using LES

“…Nevertheless, LES applications to actual engine cases of practical interest are still limited, mainly because of the relevant computational costs [16][17][18][19][20][21][22][23]. In fact, despite the fact that most contributions deal with either simplified engine geometries [24][25][26][27] or idealized engine operations [28][29][30][31], very interesting and promising results are found in this paper, confirming the potentiality of the application of LES for the characterization of single cycle-resolved events typical of actual engine operations.…”

The effects of late intake valve closing and different cam profiles on the in-cylinder flow field and the combustion characteristics of a compression ignition engine

“…This also demonstrates that the smoke emissions were reduced by the enhanced swirl ratio for the asymmetric cam profile. However, it should be noted that an increase in the smoke emissions can occur when the inhomogeneity of the swirl behaviour exists despite the increased global swirl ratio, which was reported by Rezaei et al 30 The presence of an eccentric soot cloud which did not oxidize during late combustion was the main cause of the increased smoke emissions. This type of phenomenon was not observed in the current study; however, an increased swirl intensity may not always contribute to a reduction in the smoke emissions when the flow is inhomogeneous.…”