二甲醚/空气湍流分层燃烧的直接数值模拟与机理研究

Direct Numerical Simulation and Mechanism Study of Dimethyl Ether/Air Turbulent Stratified Combustion

针对内燃机条件下分层燃烧的情况,采用直接数值模拟方法,研究了温度分层对二甲醚(dimethyl ether,DME)/空气预混气湍流分层燃烧过程的影响机制.结果表明:与零维反应器内的均质自着火过程相比,湍流分层燃烧延长了整体燃烧过程的持续时间,平均释热率峰值明显降低;输运预算分析揭示了着火锋面的传播存在自燃波与爆燃波两种着火模式,随着温度分层程度的增大,爆燃模式逐渐增强,进而导致高温着火提前;化学爆炸模式分析明晰了燃料着火的演变过程,并且利用相关准则数准确揭示了控制低温与高温着火过程的关键变量与基元反应.研究结果对于DME均质压燃式内燃机的设计以及燃烧过程调控具有借鉴意义.

Aiming at the temperature stratification in internal combustion engine,the influence mechanism of temperature stratification on the turbulent combustion process of dimethyl ether(DME)/air premixed mixture was studied by using direct numerical simulation method.The results show that compared with the homogeneous autoignition process in the zero dimensional reactor,the turbulent stratified combustion prolongs the duration of the overall combustion process,and the peak value of the average heat release rate decreases significantly.Transport budget analysis reveals that there exist two ignition modes,namely spontaneous combustion wave and deflagration wave in the propagation of the ignition front.With the increase of temperature stratification,the deflagration mode gradually increases,which leads to the advance of high temperature ignition.Chemical explosion mode analysis is used to explore the evolution process of fuel ignition and accurately identifies the key variables and elementary reactions controlling the ignition process at low and high temperatures by using relevant criteria.The results can provide reference for the design and combustion process control of DME homogeneous compression ignition engine.