Journal
INTERNATIONAL JOURNAL OF ENGINE RESEARCH
Volume 23, Issue 10, Pages 1658-1677Publisher
SAGE PUBLICATIONS LTD
DOI: 10.1177/14680874211031370
Keywords
Low-temperature combustion; large-eddy simulations; partial fuel stratification; computational fluid dynamics; homogeneous charge compression ignition; gasoline surrogate; reduced chemical kinetic mechanism; skeletal kinetic mechanism
Funding
- [1531492]
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This study uses CFD modeling to simulate three different conditions of partial fuel stratification, with results showing that SKM3 is the most suitable mechanism for modeling research-grade gasoline with partial fuel stratification. The autoignition event progresses from richer to leaner regions, with leaner regions contributing more toward heat release due to the larger number of cells in leaner equivalence ratio ranges.
Partial fuel stratification (PFS) is a low temperature combustion strategy that can alleviate high heat release rates of traditional low temperature combustion strategies by introducing compositional stratification in the combustion chamber using a split fuel injection strategy. In this study, a three-dimensional computational fluid dynamics (CFD) model with large eddy simulations and reduced detailed chemistry was used to model partial fuel stratification at three different stratified conditions. The double direct injection strategy injects 80% of the total fuel mass at -300 CAD aTDC and the remaining 20% of the fuel mass is injected at three different timings of -160, -50, -35 CAD to create low, medium, and high levels of compositional stratification, respectively. The PFS simulations were validated using experiments performed at Sandia National Laboratories on a single-cylinder research engine that operates on RD5-87, a research-grade E10 gasoline. The objective of this study is to compare the performance of three different reduced chemical kinetic mechanisms, namely SKM1, SKM2, and SKM3, at the three compositional stratification levels and identify the most suitable mechanism to reproduce the experimental data. Zero-dimensional chemical kinetic simulations were also performed to further understand differences in performance of the three reduced chemical kinetic mechanisms to explain variations in CFD derived heat release profiles. The modeling results indicate that SKM3 is the most suitable mechanism for partial fuel stratification modeling of research-grade gasoline. The results also show that the autoignition event progresses from the richer to the leaner compositional regions in the combustion chamber. Notably, the leaner regions that have less mass per unit volume, can contribute disproportionately more toward heat release as there are more cells at leaner equivalence ratio ranges. Overall, this study illuminates the underlying compositional stratification phenomena that control the heat release process in PFS combustion.
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