A Numerical Study of Transient Ignition in a Counter ow Nonpremixed Methane-Air Flame using Adaptive Time Integration

This paper presents a computational algorithm to predict highly-transient ame behavior in counter ow situations. The rst objective of the paper is to extend the transient counter ow problem to incorporate some gasdynamic compressibility e ects, yet retain the desirable similarity structure. By relaxing assumptions in earlier formulations, the computational algorithms can deliver high accuracy even in periods of extremely rapid transients, like combustion ignition. The algorithms are demonstrated on two combustion-ignition problems for methane-air, counter ow, nonpremixed ames. The rst concerns the ignition transient in a steady strain eld. The second concerns the e ects of a high-frequency oscillatory strain eld on the ignition process. The results reveal that, when the mean strain rate is near the steady ignition limit, the ignition process is highly sensitive to the details of the strain-rate uctuations. Submitted to Combustion Science and Technology (1999).