Numerical study on tri-fuel combustion: Ignition properties of hydrogen-enriched methane-diesel and methanol-diesel mixtures

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Abstract

Simultaneous and interactive combustion of three fuels with differing reactivities is investigated by numerical simulations. In the present study, conventional dual-fuel (DF) ignition phenomena, relevant to DF compression ignition (CI) engines, are extended and explored in tri-fuel (TF) context. In the present TF setup, a low reactivity fuel (LRF), methane or methanol, is perfectly mixed with hydrogen and air to form the primary fuel blend at the lean equivalence ratio of 0.5. Further, such primary fuel blends are ignited by a high-reactivity fuel (HRF), here n-dodecane under conditions similar to HRF spray assisted ignition. Here, ignition is relevant to the HRF containing parts of the tri-fuel mixtures, while flame propagation is assumed to occur in the premixed LRF/[Formula presented] containing end gas regions. The role of hydrogen as TF mixture reactivity modulator is explored. Mixing is characterized by n-dodecane mixture fraction ξ, and molar ratio [Formula presented]. When x < 0.6, minor changes are observed for the first- and second-stage ignition delay time (IDT) of tri-fuel compared to dual-fuel blends (x = 0). For methane, when x > 0.6, first- and second-stage IDT increase by factor 1.4–2. For methanol, a respective decrease by factor 1.2–2 is reported. Such contrasting trends for the two LRFs are explained by reaction sensitivity analysis, indicating the importance of OH radical production/consumption in the ignition process. Observations on LRF/[Formula presented] end gas laminar flame speed ([Formula presented]) indicate that [Formula presented] increases with x due to the highly diffusive features of [Formula presented]. For methane, [Formula presented] increase with x is more significant than for methanol.

Details

Original languageEnglish
Number of pages17
JournalInternational Journal of Hydrogen Energy
Publication statusE-pub ahead of print - 3 Jan 2020
MoE publication typeA1 Journal article-refereed

    Research areas

  • Diesel, Dual-fuel ignition, Hydrogen, Methane, Methanol, Tri-fuel ignition

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