Effects of fuel trapping in piston crevice on unburned hydrocarbon emissions in early-injection compression ignition engines
Im, Hong G.
KAUST DepartmentClean Combustion Research Center
Computational Reacting Flow Laboratory (CRFL)
Mechanical Engineering Program
Physical Science and Engineering (PSE) Division
Online Publication Date2021-05-24
Print Publication Date2021-09
Embargo End Date2023-05-24
Permanent link to this recordhttp://hdl.handle.net/10754/669257
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AbstractEarly injection strategy is employed in many advanced combustion concepts of modern compression-ignition engines to promote the fuel-air premixing, but it could result in fuel spray impingement on the cylinder wall and potential fuel trapping in the crevice regions. The impact of the fuel trapping on the formation and distribution of unburned hydrocarbon (UHC) in the advanced compression-ignition concepts is not well understood. In this study, the planar laser-induced fluorescence (PLIF) technique was applied in a single-cylinder optical engine to visualize the fuel distribution before combustion and the formaldehyde formation during combustion. A three-dimensional computational model was established to explore the detailed mechanism of UHC formation in the piston crevice. Three cases with injection timings of 20°, 40° (SOI-40), and 100° (SOI-100) were compared. The PLIF and simulation results indicate that, under early injection conditions, the squish region and piston crevice trap a considerable amount of fuel, resulting in increased UHC emission and reduced engine work, and the main combustion zone resides in the squish region. The simulation shows that the amount of UHC formation from the trapped fuel is highly dependent on the local equivalence ratio distribution formed by different injection timings. The local equivalence ratio within the piston crevice region for the SOI-40 case exceeds 2 before combustion; the charge sequentially undergoes both low- and high-temperature heat release (LTHR and HTHR) processes and produces less UHC in the crevice region. However, the SOI-100 case produces an overall leaner mixture with a local equivalence ratio lower than 1 before combustion; the charge undergoes LTHR without noticeable HTHR and becomes UHC near the cylinder wall. The injector dribbling results in more UHC formation in the central part of the cylinder under very early injection timing, and thus an accurate injector dribbling model is required to better reproduce the UHC emissions.
CitationTang, Q., Liu, X., Raman, V., Shi, H., Chang, J., Im, H. G., & Johansson, B. (2021). Effects of fuel trapping in piston crevice on unburned hydrocarbon emissions in early-injection compression ignition engines. Combustion and Flame, 231, 111496. doi:10.1016/j.combustflame.2021.111496
SponsorsWe acknowledge funding from KAUST and Saudi Aramco under the FUELCOM program.
JournalCombustion and Flame