Large Eddy Simulation of Dimethyl Ether (DME) Reacting Spray Flame in Compression Ignition (CI) Engine-Relevant Conditions

摘要

As an alternative fuel for compression ignition engines, Dimethyl Ether (DME) is simulated with both standard k-ε RANS and dynamic structure LES models to understand its behavior in a turbulent spray-flame under engine-relevant condition. A low temperature combustion (LTC) condition with ambient temperature of 900 K, 18% oxygen concentration, and density of 14.8 kg/m~3 is chosen with a 750 bar liquid injection pressure. Non-reacting spray was first validated using RANS and LES models to ensure good mixing predictions. Under combusting conditions, three reduced kinetic mechanisms of DME were compared using RANS simulations for their capability of predicting ignition delay and flame stabilization (lift-off length). The better mechanism was chosen for LES combustion-spray simulation with five realizations. LES results showed multiple ignition locations closer to the injector nozzle prior to a stabilized diffusion-flame, consistent with the experimental observation. Compared to RANS, LES was able to capture the temporal evolution of lift-off with better accuracy due to prediction of combustion initiation in the mixing layers upstream of the flame stabilization zone. Furthermore, formation profile of formaldehyde species predicted with LES model was well matched with experimental PLIF images.