Piston crevice hydrocarbon oxidation during expansion process in an SI engine |
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Authors: | Sejun?Kim Email author" target="_blank">Kyoungdoug?MinEmail author |
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Affiliation: | (1) School of Mechanical and Aerospace Engineering 301-1254, Seoul National University, San 56-1, Shillim-dong, Kwanak-gu, 151-742 Seoul, Korea |
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Abstract: | Combustion chamber crevices in SI engines are identified as the largest contributors to the engine-out hydrocarbon emissions.
The largest crevice is the piston ring-pack crevice. A numerical simulation method was developed, which would allow to predict
and understand the oxidation process of piston crevice hydrocarbons. A computational mesh with a moving grid to represent
the piston motion was built and a 4-step oxidation model involving seven species was used. The sixteen coefficients in the
rate expressions of 4-step oxidation model are optimized based on the results from a study on the detailed chemical kinetic
mechanism of oxidation in the engine combustion chamber. Propane was used as the fuel in order to eliminate oil layer absorption
and the liquid fuel effect. Initial conditions of the burned gas temperature and in-cylinder pressure were obtained from the
2-zone cycle simulation model. And the simulation was carried out from the end of combustion to the exhaust valve opening
for various engine speeds, loads, equivalence ratios and crevice volumes. The total hydrocarbon (THC) oxidation in the crevice
during the expansion stroke was 54.9% at 1500 rpm and 0.4 bar (warmed-up condition). The oxidation rate increased at high
loads, high swirl ratios, and near stoichiometric conditions. As the crevice volume increased, the amount of unburned HC left
at EVO (Exhaust Valve Opening) increased slightly. |
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Keywords: | Unburned Hydrocarbon Piston Crevice Oxidation Model SI Engine |
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