Localised forced ignition (i.e. spark or laser) of turbulent stratified mixtures has been numerically analysed using three-dimensional Direct Numerical Simulations (DNS) for different level of turbulent intensities. The initial values of turbulent fluctuations and integral length scale of turbulence are modified to reflect different turbulent combustion regimes. The ignition is accounted by a source term in the energy transport equation which deposits energy over a specific time interval. It has been found that combustion takes place primarily in premixed mode of combustion following successful ignition. The percentage of heat release due to a premixed mode of combustion increases with increasing turbulent intensity due to higher rate of mixing. The effects of mixture inhomogeneity for a given turbulent intensity has favorable outcomes on sustaining combustion following successful ignition, however it has been found that an increase in turbulent intensity has adverse effects on the burned gas mass. Moreover the mixture inhomogeneity effect shows non-monotonic trends on burnt gas mass. The present DNS result shows that an increase in turbulent intensity leads to increase in Minimum Ignition Energy (MIE) (consistent with previous experimental findings). However, for a given realization of initial mixture distribution (휙), it has been found that stratified mixture to be more favorable over homogeneous mixture for a present turbulent flow condition for achieving a higher burning rate.
|The International Journal of Automotive Technology
|Accepted/In press - 2021