Effects of pre-injection on ignition, combustion and emissions of spray under engine-like conditions

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Large-eddy simulation (LES) of multiple-injection spray combustion under engine-like conditions is performed using a coupled model of a Eulerian stochastic field transported probability density function (ESF T-PDF) and a flamelet generated manifold (FGM). This coupled model allows the use of the T-PDF methods in modelling the interaction of turbulence and combustion at affordable computational costs for engine applications. Simulation results are compared with the available experimental data for engine spray flames with multiple-injection and at a high level of exhaust gas recirculation (EGR). It is shown that the T-PDF/FGM LES model is capable of reproducing not only global combustion characteristics, such as the pressure rise and ignition delay time but also replicating the evolution of liftoff length and the spray flame structure. The effects of pre-injection strategy are then investigated, by systematically varying the pre-injection duration and the dwell time between two injections, while keeping the total injected fuel mass constant. The LES results reveal different mechanisms by which a pre-injection can change the ignition delay time, the combustion mode and the emissions in spray flames, depending on the injection timing. It is shown that even an extremely short non-igniting pre-injection can substantially change the ignition and emissions characteristics of the main-injection. It is investigated that how the combustion mode of a single-injection can be modified by splitting it to preand main-injections. The current study also demonstrates that decreasing of the dwell time, within the range that is examined here, at a given preinjection, will potentially increase the soot oxidation rates while it does not significantly change the rate of soot formation.
Original languageEnglish
Article number112082
Number of pages13
JournalCombustion and Flame
Early online date2 Apr 2022
Publication statusE-pub ahead of print - 2 Apr 2022


  • Engine Combustion Network
  • Spray-A
  • Transported probability density function
  • eulerian stochastic field
  • flamlet generated manifold
  • pre-injection


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