Shock tube study of ignition delay times in methaneoxygennitrogenargon mixtures

Abstract

Ignition delay times have been measured in homogeneous CH 4O 2 and CH 4O 2N 2 mixtures dilute in argon, in order to investigate the influence of molecular nitrogen. The mixtures were heated behind reflected waves in a conventional shock tube to temperatures between 1640 and 2150 °K at pressures from 1 to 6 atm. Equivalence ratios of 1.0 and 2.0 were investigated and the methane concentration ranged from 1 × 10 −7 to 9 × 10 −7 mole/cc. Ignition was identified from photometric observations of OH (3064 Å), H 2O (2.7 μ) and CO 2(4.3 μ) emission. For both the CH 4O 2 and CH 4O 2N 2 mixtures, the measured ignition delays ( τ i ) were correlated by the empirical expression τ i=4.4 x 10 —15 exp (52300/RT)[CH 4] 0.33[O 2]—1.03 , in mole, cal, cm and sec units. We conclude that molecular nitrogen has little or no influence upon the ignition delay times of methaneoxygen mixtures. This conclusion is supported by several earlier investigations of methane ignition but conflicts with the recent study by Zallen and Wittig [16].