Mixing dynamics and scalar dissipation rate in split-injection gaseous jets

Abstract

Split fuel injection is studied by Direct Numerical Simulations (DNS) to characterize the entrainment and scalar dissipation in turbulent gaseous jets. The mixing physics identified in this study are important for the understanding of split-injection compression-ignition engine operation, in which mixing rates and fuel residence time control the rate of heat release and pollutant formation. Three injection scenarios are compared: a starting jet, a stopping jet, and a restarting the fuel jet. It is observed that the entrainment is suppressed or enhanced when the jet accelerates or decelerates respectively, in agreement with previous studies. The results show that the one-dimensional entrainment model by Musculus (Journal of Fluid Mechanics 638 (2009) 117-140) provides a good qualitative description for the entrainment in the stopping jet. It is found that the suppression and enhancement due respectively to a starting and a stopping jet can be superimposed to give an estimate for the entrainment in the restarted jet simulation. Scalar dissipation rate is found to increase or decrease by one order of magnitude as the jet accelerates or decelerates respectively. The wake of the stopping jet reduces the scalar dissipation rate in the following restarting jet, implying that the dissipation rate from the stopping jet and the starting jet are not additive, and highlighting the different dynamics of the large and small scale mixing processes described by entrainment and scalar dissipation respectively

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ORCID for E.S. Richardson: orcid.org/0000-0002-7631-0377

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