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난류분무제트연소에서의 화염구조와 조건평균 통계에 대한 수치적 연구
서재엽(Jaeyeob Seo),허강열(Kang Y. Huh) 한국연소학회 2012 한국연소학회지 Vol.17 No.3
3D DNS is performed for n-heptane spray turbulent jet combustion. Diesel-like conditions are considered including single and multiple injections. Conditional statistics are obtained for multiple Lagrangian flame groups of sequentially evaporating fuel. Each fuel group represents the conditional statistics of an independent Lagrangian flame group. Sequentially evaporating fuel goes through different histories and residence times over the ignition delay period. Multiple flame groups are required for accurate description of combustion of a spray jet that goes through a long injection duration or multiple injections.
개선된 CMC 모델을 이용한 pHCCI 디젤 엔진의 연소 해석
서재엽(Jaeyeob Seo),허강열(Kang. Y. Huh) 한국자동차공학회 2009 한국자동차공학회 부문종합 학술대회 Vol.2009 No.4
This work presents simulation of pHCCI mode diesel combustion by an improved conditional moment closure (CMC) model. The improved CMC model involves flammability limit, multiple flame structures and additional evaporation source terms in the equation for the mixture fraction variance. The evapoation source terms affect local beta function PDFs and conditional scalar dissipation rates (CSDR). An independent transport equation is solved for the fuel vapor of each flame group sequentially injected and evaporated in the cylinder. The conventional CMC model cannot properly consider pHCCI combustion with split injections which may result in a significant amount of lean mixtures. The flammability limits do not allow lean pre-mixtures below the specified limit to participate in combustion. Measured and calculated pressure traces are presented and compared for the test cases with various fuel mass and ratios between two injections. Further research is required for the wall film effect, as fuel injected at an earlier timing goes through significant collision with the wall.
조건 평균 연소 모델과 상세화학 반응에 기초한 디젤 사이클 시뮬레이션 해석
권재성(Jaesung Kwon),서재엽(Jaeyeob Seo),허강열(Kang Y. Huh) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
A cycle simulation code is developed to model turbulent spray combustion in a direct injection diesel engine. The code is based on the multi-zone fuel spray model by Hiroyasu et al. (1983)1) and combined with the CMC (Conditional Moment Closure) combustion model employing a skeletal chemical mechanism. The spray model accounts for fuel-air mixing assuming no interaction between adjacent zones and combustion with a single flame structure introduced as fuel is injected into the cylinder. A parametric study is performed for injection timing and EGR level with the calculation results compared with pressure traces and NOx from measurements and KIVA results. Results show reasonable agreement with measured data for all six test cases. Further improvement will be made for multiple injection engines with multiple flame structures in the CMC model.