Shock tube and kinetic study on ignition characteristics of methane/n-hexadecane mixtures

Ignition characteristics of n-hexadecane/methane mixture under low-pressure high-temperature (P: 2.0 bar, 5.0 bar &T: 1269–1887K) and high-pressure low-temperature (P: 40–140 bar &T: 700–1200 K) conditions were studied by aerosol shock tube and CHEMKIN with LLNL C16 mechanism. The results indicated that at low-pressure high-temperature conditions, increasing initial pressure and decreasing equivalence ratio could reduce ignition delay times (IDT) by 39% and 52% respectively. N-hexadecane’s addition and n-hexadecane’s replacement also shortened IDT by 88% and 96% separately. Raising n-hexadecane’s replacement further reduced IDT. The reduction degree of IDT dramatically decreased when n-hexadecane’s content was high. N-hexadecane was fully consumed earlier than methane. Radicals that formed from n-hexadecane’s decomposition induced H-abstraction of n-hexadecane, which advanced methane’s slow oxidation. H was the crucial radical in n-hexadecane’s H-abstraction reactions. At ultra-high-pressure low-temperature condition, adding n-hexadecane and increasing n-hexadecane content dramatically reduced IDT. With n-hexadecane’s H-abstraction dominating ignition process, n-hexadecane’s decomposition was significantly inhibited at low-temperature condition. OH was the key radical in n-hexadecane’s H-abstraction reactions. The obviously suppressed n-hexadecane’s decomposition was responsible for the same end time point of complete consumption of two fuels. These results are helpful for providing control methods for natural-gas preignition and abnormal combustion triggered by lubricating oil in dual-fuel marine engine.