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HCCI에 적용하기 위한 EGR이 PRF70/공기 혼합기의 점화지연에 미치는 영향
백동훈(D. H. Baik),이수룡(S. R. Lee) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
The effects of EGR on ignition delay of PRF70/air mixture was numerically investigated with detailed chemical reaction mechanism. The Chemkin-III was utilized to evaluate the delay time of autoignition for isobaric conditions and simulate the HCCI engine conditions. For water vapour adding, the dilution and thermal effects cause the ignition delay to increase, while the chemical effect makes the ignition delay shortened. The ignition delay by the chemical effect is reduced by the increase of fuel oxidation rate. In the case of CO₂ addition, the higher value of specific heat of CO₂ makes thermal effect more important. The addition of CO₂ does not affect the quantity of radicals like H, O, and OH, which results in the reduction of chemical effect. In HCCI engine, adding EGR gas makes pressure rise rates decreased. As a result, the load range can be prolonged and even in higher load PRR remains acceptable. The dilution and thermal effects are more important than the chemical effect.
사각채널에서 사다리꼴 와류발생기에 의한 열전달 및 유동특성에 대한 수치해석
박태환(T.H. Park),이수룡(S.R. Lee) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
Three dimensional numerical analysis is performed on heat transfer and flow characteristics of a channel with trapezoidal vortex generator. We investigate the effects of vortex generators with two different inclined angles to flow direction which are forward and backward vortex generators (FVG and BVG). The thermal hydraulic performance such as Nusselt number and friction factor, are compared quantitatively. The result shows that vortex generator enhance the heat transfer by developing boundary layers and secondary flow in the downstream. The core of vortex behind FVG is closer to the lower wall than that behind BVG. which cause that thermal boundary layer thickness of lower wall for FVG is thinner. Therefore, The increase of Nusselt number of FVG is higher than that of BVG. However, the friction factor of channel with FVG is larger than that with BVG.
지명석,이수룡 서울産業大學校 1997 논문집 Vol.46 No.1
Combustion characteristics of natural gas premixed flames is studied experimently and numerically by adopting a counterflow as a flamelet model in turbulent flames. Parametric dependences of extinction strain rates are studied numerically with detailed kinetic mechanism to show, for example, that the addition of ethane to a methane diffusion flame makes the flame more resistent to strain rates. Extinction strain rate increases exponentially with premixture temperature and decreases linearly with the addition of EGR. The effect of pressure on the extinction strain rate is that the extinction strain rate increases up to 10atm and then decreases, which is explained by competition of chain brainching H + O₂+ M = HO₂+ M. Detailed mechanism having seventy-four step is systematically reduced to a nine-step and a five-step mechanism while five-step thermal NOx chemistry is reduced to two-step. Comparison between the results of the detailed and the reduced mechanisms demonstrates that the reduced mechanism sucessfully describes the essential features of natural gas premixed flamed including extinction strain rate and NOx production.