Ignition characteristics of dual-fuel methane-n-hexane-oxygen-diluent mixtures in a rapid compression machine and a shock tube
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 H_2O_2 and H under RCM and ST conditions, respectively.
© 2019 Elsevier. Received 8 January 2019, Revised 18 March 2019, Accepted 19 March 2019, Available online 29 March 2019. Financial support from the Center for Combustion Energy, and 1000 Young Talents program are highly appreciated. CG is grateful to the Conseil Régional du Centre for sponsoring a student fellowship during her stay at Caltech. UN is grateful to Polish-U.S. Fulbright Commission for sponsoring her stay at Caltech as a Visiting Special Student.
Accepted Version - Dual_Fuel_Preprint.pdf
Supplemental Material - 1-s2.0-S001623611930479X-mmc1.docx
Supplemental Material - 1-s2.0-S001623611930479X-mmc2.pdf
Supplemental Material - 1-s2.0-S001623611930479X-mmc3.pdf
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