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DNSs of the Ignition of a Lean n-Heptane/Air Mixture under SCCI Conditions : Chemical Aspects
Gwang Hyeon Yu(유광현),Minh Bau Luong,Chun Sang Yoo(유춘상) 한국연소학회 2015 KOSCOSYMPOSIUM논문집 Vol.2015 No.5
The chemical aspects of thermally- and/or compositionally-stratified n-heptane/air mixture under HCCI conditions are examined to obtain the insight of the ignition process in HCCI combustion. Chemical explosive mode analysis (CEMA) is adopted to understand the spatial ignition characteristics of the lean n-heptane/air mixture by identifying controlling species and elementary reactions at different locations and times.
DNSs of the Ignition of a Lean PRF/Air Mixture under RCCI/SCCI Conditions
Minh Bau Luong,Kwang Hyeon Yu(유광현),Chun Sang Yoo(유광현) 한국연소학회 2014 KOSCOSYMPOSIUM논문집 Vol.2014 No.11
A comparative DNS study of the ignition characteristics of dual-fueled reactivity controlled compression ignition (RCCI) and stratification charge compression ignition (SCCI) is investigated using a 116-species reduced primary reference fuel (PRF) mechanism. In the RCCI combustion, two PRF fuels (n-heptane and iso-octane) with opposite autoignition characteristics are separatedly supplied and in-cylinder blended such that spatial variations in fuel reactivity, fuel concentration and temperature are achieved. In the SCCI combustion, however, just a single fuel (PRF50) is used such that only fuel concentration and temperature inhomoginieties are obtained. Because three factors, rather than only two as in SCCI combustion, govern the overall RCCI combustion, combustion timing and combustion duration or heat release rate of RCCI combustion are flexibly and effectively controlled. It is found that the overall RCCI combustion occurs much earlier and its combustion duration is longer compared to SCC combustionI. Moreover, the negative temperature coefficient (NTC) has a positive effect on enhancing RCCI combustion by inducing a shorter combustion timing and a longer combustion duration as a result of the occurrence of a predominant low-speed deflagration-combustion mode.
Minh Bau Luong,Kwang Hyeon Yu(유광현),Chun Sang Yoo(유춘상) 한국연소학회 2014 KOSCOSYMPOSIUM논문집 Vol.2014 No.5
The effect of the negative temperature coefficient (NTC) on the ignition of a stratified lean n-heptane/air mixture of temperature and equivalence ratio was investigated using 2-D direct numerical simulations (DNSs) with a 58-species reduced mechanism. It was found that for T? in the NTC regime, fuel stratification is more effective than thermal stratification in controlling the ignition delay and mitigating the heat release rate (HRR). One of the key finding in this study is that for the intermediate T?, the overall combustion becomes more advanced and mean heat release rate (HRR) is temporally more distributed with increasing Ø′ regardless of the negatively-correlated T-Ø relations. It is primarily because the deflagrative mode prevails at the reaction fronts for large Ø′ and hence the combustion occurs subsequently, rendering mean HRR more distributed over time.
A DNS Study of Ignition of a Lean PRF/Air Mixture under RCCI/SCCI Conditions
Minh Bau Luong,Gwang Hyeon Yu(유광현),Chun Sang Yoo(유춘상) 한국연소학회 2015 KOSCOSYMPOSIUM논문집 Vol.2015 No.5
A comparative DNS study of the ignition characteristics of dual-fueled reactivity controlled compression ignition (RCCI) and stratification charge compression ignition (SCCI) is investigated using a 116-species reduced primary reference fuel(PRF) mechanism. It is found that the overall RCCI combustion is greatly enhanced and flexibly controlled, thereby significantly reducing the peak HRR. The negative temperature coefficient has a synergistic effect on advancing the overall combustion and smoothing RCCI/SCCI combustion by inducing more low-speed deflagrations. Compared to SCCI, the overall combustion of RCCI is more advanced in time regardless of T0. However, it is also found that the effects of reactivity and/or equivalence ratio stratifications on reducing the peak are nearly eliminated with T0 in the high temperature regime for both RCCI/SCCI due to the dominant spontaneous ignition mode.
A DNS Study of RCCI Combustion
Minh Bau Luong,Gwang Hyeon Yu(유광현),Chun Sang Yoo(유춘상) 한국연소학회 2015 KOSCOSYMPOSIUM논문집 Vol.2015 No.12
The chemical aspects of primary reference fuel (PRF)/air mixture under RCCI conditions are investigated to provide fundamental insights into the ignition characteristics of RCCI combustion. Chemical explosive mode analysis (CEMA) is adopted to understand the ignition process of the lean PRF/air mixture by identifying controlling species and elementary reactions at different locations and times.