Browse Publications Technical Papers 2019-01-2209
2019-12-19

Study of Ignition Processes of a Lean Burn Engine using Large-Eddy Simulation 2019-01-2209

Ultra-lean burn conditions (λ>1.8) is seen as a way for improving efficiency and reducing emissions of spark-ignition engines. In comparison to conventional operation with stoichiometric mixture, this itself raises fundamental issues in terms of combustion physics, among which the significant reduction of the laminar flame speed, increase of the laminar flame thickness as well as an increased sensitivity to local fuel/air equivalence ratio variations are all essential to be accounted for. In particular, the effect of modified laminar flame characteristics on flame stretch during the early flame development in a spark ignited engine is of importance.
In the present work the cycle-to-cycle combustion variations of ultra-lean burn operation is modeled, by utilizing capability of Large-Eddy Simulation (LES). Then results are analyzed after a careful validation of the aerodynamics and spray/flow interactions that have initially been predicted. This aims to simulate direct injection gasoline engine operating in ultra-lean conditions with indicated efficiency of 46%.
First, LES predictions of the cold flow are compared to High Speed Particle Image Velocimetry. Second, the injector model is compared against experimental spray measurements. Third, cyclic variability of burn rates from LES results are compared with experimental data. The simulation yielded results highlighted the importance of having accurate modelling of both flame stretch and laminar flame speed in order to capture the early phase of combustion. Therefore finally, the ignition delay, 50% burning point and the burn duration all match well with experimental data.

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