Publications

A direct numerical simulation of cool-flame affected autoignition in diesel engine-relevant conditions

Krisman, Alexander K.; Hawkes, Evatt R.; Talei, Mohsen; Bhagatwala, Ankit; Chen, Jacqueline H.

A two-dimensional direct numerical simulation of the ignition at diesel engine-relevant conditions was performed at 40 atm and at 900 K ambient temperature using dimethyl ether (DME) as the fuel with a 30 species reduced chemical mechanism. At these conditions similar to diesel fuel DME exhibited two-stage ignition. The low-temperature chemistry analysis revealed a "spotty" first-stage autoignition in lean regions which transitions to a diffusively supported cool-flame and then propagates up the local mixture fraction gradient towards richer regions. The cool-flame speed was much faster than can be attributed to spatial gradients in first-stage ignition delay time in homogeneous reactors and it caused a shortening of the second-stage ignition delay times compared to a homogeneous reactor wherein the shortening became more pronounced at richer mixtures. Multiple high-temperature ignition kernels were noted over a range of rich mixtures that are much richer than the homogeneous most reactive mixture and most kernels formed much earlier than suggested by the homogeneous ignition delay time of the corresponding local mixture.