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6121737 
Journal Article 
Ignition characteristics of dual-fuel methane-n-hexane-oxygen-diluent mixtures in a rapid compression machine and a shock tube 
He, Y; Wang, Y; Gregoire, C; Niedzielska, U; Mevel, R; Shepherd, JE 
2019 
1 
Fuel
ISSN: 0016-2361
EISSN: 1873-7153 
Elsevier Ltd 
249 
379-391 
English 
WOS:000465255500037 
Ignition delay times of methane-n-hexane-oxygen-dulent mixtures were studied experimentally and numerically in a wide temperature range (640–2335 K) using both a rapid compression machine (RCM) and a shock tube (ST). The RCM results demonstrated a two-stage ignition and negative temperature coefficient (NTC) behavior. Increasing n-hexane concentration, pressure and equivalence ratio shortened the ignition delay time. For the ST experiments, the addition of 10% n-hexane (relative to methane) can reduce the ignition delay time dramatically. However, no further reduction effect can be achieved with increasing addition of n-hexane from 10% to 20%. In addition, increasing equivalence ratio reduces the effect of n-hexane addition on ignition delay time. Three detailed chemical mechanisms, CaltechMech, GalwayMech and LLNLMech, were evaluated based on a quantitative error analysis. LLNLMech and CaltechMech demonstrated the best performance in the RCM and ST temperature ranges, respectively. Chemical kinetic analyses showed that the addition of n-hexane to methane provides some chemical pathways not available for methane oxidation which result in the production of active radicals and eventually accelerate the ignition of the methane-oxygen mixtures. The crucial intermediate species for the ignition process are H2O2 and H under RCM and ST conditions, respectively. © 2019 Elsevier Ltd 
Dual-fuel ignition; Methane-n-hexane mixtures; Rapid compression machine; Shock tube; Chemical kinetics modeling