Front propagation speeds from fully resolved unsteady one dimensional simulations with dimethyl-ether (DME)/methane (CH4)/air mixtures under engine relevant conditions are presented using complex kinetics and transport. Different time-scales of monochromatic inhomogeneities in DME concentration with varying DME/CH4 blending ratios are simulated to unravel the fundamental aspects of auto-ignition and flame propagation under the influence of reactivity stratification. To understand the influence of different stratification time-scales on the flame-ignition interaction, two sets of conditions are simulated such that low temperature chemistry is present in only one of them. For a given amplitude of stratification, it is found that the instantaneous propagation speed is significantly affected by the level of CH4 concentration in the binary fuel blend. Specifically, for cases with low temperature chemistry, at relatively smaller time-scales, the overall fluctuation in the instantaneous propagation speed is found to subside as the level of CH4 concentration in the mixture is increased. However, for both sets of conditions, at comparatively larger time-scales, a rapid change in the instantaneous propagation speed is observed with an increase in the level of CH4 concentration in the mixture. The intrinsic effects of stratification time-scales on the low temperature chemistry and the high temperature chemistry are further examined to assess the flame-ignition interaction. A displacement speed analysis is also carried out to elucidate the underlying combustion modes that are responsible for such a variation in flame response.
|Original language||English (US)|
|Number of pages||15|
|Journal||Combustion and Flame|
|State||Published - Oct 24 2019|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This work was sponsored by competitive research funding from King Abdullah University of Science and Technology. This research used resources of the Oak Ridge Leadership Computing Facility at ORNL, which is supported by the Office of Science of the U.S. Department of Energy under contract DE-AC05-00OR22725. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (https://www.energy.gov/downloads/doe-public-access-plan).