Numerical Exploration on HCCI Combustion Characteristics under NVO Strategy

Abstract

Homogeneous charge compression ignition (HCCI) offers high efficiency and ultra-low NOx and SOOT emissions which raises world-wide attention. A 3-dimensional CFD HCCI model has been established using STAR-CD code for combustion characteristics studies under negative valve overlap (NVO) strategy via an early closure of exhaust valve. The combustion characteristics of HCCI were investigated. Simulation results were in good agreement with the available experimental data. Studies on in-cylinder temperature and OH radical concentration showed almost the same spatial distribution when auto-ignition occurred, OH radical had higher concentration in the field of higher temperature. The φ-T maps showed extraordinarily low NO emissions and no soot emissions under HCCI combustion. It was found that OH concentration rapidly increased after the start of the combustion at 356°CA and NO emissions were formed when the temperature was high enough at 358°CA. Most of CO emissions were converted to CO2 through the main combustion.