A shock tube study of n-heptane, iso-octane, n-dodecane and iso-octane/n-dodecane blends oxidation at elevated pressures and intermediate temperatures

Ignition delay times (IDT) of n-heptane, iso-octane, n-dodecane, and iso-octane/n-dodecane blends, in stoichiometric mixtures with air, were measured behind reflected shock waves in a heated, high-pressure shock tube. Measurements were taken at temperatures of 665-1250 K, pressures of 28-70 atm, and equivalence ratios near unity. Pressure time-history recorded from sidewall piezo-electric transducers, fuel-concentration time-history obtained from fixed-wavelength laser absorption at 3.39 mu m, and OH* (306 nm) emission time-history recorded by a Si detector, were used to determine IDT. The staged ignition phenomenon in the low temperature regime was also examined with attention on the 1st stage fuel decomposition fraction. IDT measurements were also made using the constrained-reactive-volume strategy, which has the capability to eliminate non-ideal effects such as remote ignition, and were compared with measurements using a conventional filling technique. The current measurements provide a wide range (28-70 atm) of ignition delay times for key surrogate fuels under practical engine conditions, and hence provide validation targets for refinement of chemical kinetic models.