Methane Ignition in a Shock Tube with High Levels of CO2 Dilution: Consideration of the Reflected-Shock Bifurcation

Abstract

Experiments were performed in a shock-tube facility to examine experimentally the kinetic effect, if any, of excess amounts of CO2 as part of natural-gas-based fuel–oxidizer mixtures. An important aspect of these experiments was to also observe the role excess amounts of CO2 play in causing nonidealities, particularly shock bifurcation, in shock-tube experiments using real (nondilute) fuel–air mixtures. Mixtures were composed of methane fuel at an equivalence ratio of 0.5 to represent a typical natural gas in a modified “air” mixture designed to study the effect of large levels of CO2 dilution. These oxidizer compositions maintained constant levels of O2 while exchanging N2 for CO2 in stages to give oxidizer mixture concentrations ranging from (0.21O2 + 0.79N2) to (0.21O2 + 0.79CO2). Low-pressure and high-pressure (near 1 and 10 atm, respectively) experiments were conducted over an approximate temperature range of 1450 to 1900 K. Results showed that the observed effect of CO2 relating to reflected-shock b...