Abstract
New ignition delay time measurements (IDT) 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 (f = 0.5 and 1.5). The experiments were complemented 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 can lead to an increase in reactivity by ~40-60 ms at a temperature of 700 K. The IDTs of these mixtures decrease rapidly with an increase in the concentration of up to 7.5% but becomes almost independent of the C6/C7 concentration >10%. This sensitization effect of C6 and C7 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 H2O2(+M)??H+?H (+M) at higher temperatures while the fuel-dependent reactions such as H-atom abstraction, RO2 dissociation, or Q OOH+O2 reactions are less important compared to the temperature range 700-900 K, where they are very important.
Optical Response Associated with the Orientation and Structure of Liquid Crystals with Respect to Phosphatidylcholine Concentration