New ignition delay time measurements of natural gas mixtures enriched with small amounts of n­­-hexane and n-heptane were performed in a rapid compression machine to interpret the sensitization effect of heavier hydrocarbons on auto-ignition at gas-turbine relevant conditions. The experimental data of natural gas mixtures containing alkanes from methane to n-heptane were carried out over a wide range of temperatures (840–1050 K), pressures (20–30 bar), and equivalence ratios (φ = 0.5 and 1.5). The experiments were complimented with numerical simulations using a detailed kinetic model developed to investigate the effect of n-hexane and n-heptane additions. Model predictions show that the addition of even small amounts (1–2%) of n-hexane and n-heptane could lead to increase in reactivity by \~40–60 ms at T~C~ = 700 K. The IDT of these mixtures decrease rapidly with increase in concentration up to 7.5% but becomes almost independent of the C~6~/C~7~ concentration beyond 10%. This sensitization effect of C~6~ and C~7~ is also found to be more pronounced in the temperature range 700–900 K compared to that at higher temperatures (> 900 K). The reason is attributed to the dependence of IDT primarily on H~2~O~2~(+M) ↔ 2ȮH at higher temperatures while the fuel dependent reactions such as H-atom abstraction, RȮ~2~ dissociation or O~2~+ QOOH reactions are less important (unlike 700–900 K).


Ignition Studies of C1\u2013C7 Natural Gas Blends at Gas-Turbine Relevant Conditions

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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