Study on Gasoline HCCI Engine
CAI engine is well known to be advantageous over conventional SI engines because it facilitates higher engine efficiency and lower emission (NOx and smoke). However, its limited operation range, large cyclic variation, and difficulty in heat release control are still unresolved obstacles. Previous studies showed that a high load range of the CAI engine is limited mainly by the combustion noise caused by a stiff pressure rise (knock), and that a low load range is also limited by the combustion instability caused by the high dilution of residual gas. A reduced chemical kinetic mechanism for a gasoline surrogate was validated in this study for a CAI combustion. This gasoline surrogate was modeled as a blend of isooctane, n-heptane, and toluene. This reduced mechanism consists of 49 species and 67 reactions and it includes main reaction paths of iso-octane, n-heptane, and toluene. A RCM was used for the validation of this reduced mechanism and matched with the modeling of the RCM using STAR-CD. The results of the experiment and the simulation showed good agreement. For the analysis of CAI combustion, a multi-zone method was developed and incorporated into the computational fluid dynamics code, STAR-CD. This coupled multi-zone model can calculate 3 dimensional computational fluid dynamics and multi-zoned chemical reaction simultaneously in one time step. In other words, every computational cell interacts with the adjacent cells during the chemical reaction process. In this study, to improve combustion stability, we tested the in-cylinder fuel stratification by applying nonsymmetrical fuel injection to the intake port. Experiments were performed on a PFI single cylinder research engine equipped with dual CVVT and low lift (2 mm) cam shaft with NVO strategy. The in-house RGF prediction model was used to predict the cycle by cycle differences of in-cylinder trapped mass, RGF and bulk temperature. Non-uniformity of in-cylinder fuel concentration reduces the frequency at which the knock occurred by about 20 ％. Due to this reduction of the number of knock cycle, NIMEP is increased about 5 ％, COVIMEP improved about 1 ％, Rmax, which represents the combustion noise, reduced about 20 ％ and NOx reduced about 15 ％. These phenomena were studied by using multi-zone simulation also. There was a difference in the auto-ignition characteristic between the homogeneous and nonuniformity cases.
Seungmok Choi Kyoungdoug Min Kyeonghyeon Lee
School of Mechanical & Aerospace Engineering, Seoul National University Interdisciplinary Program in Automotive Engineering, Seoul National University
国际会议
天津
英文
1-16
2009-08-19（万方平台首次上网日期，不代表论文的发表时间）