混合气分布特性对汽油压燃影响的数值模拟

Numerical Simulation of Effects of Mixture Distribution Characteristics on Gasoline Compression Ignition

利用三维计算流体力学软件CONVERGE,通过数值模拟的方法,对比研究了缸内单次喷射、缸内多次喷射、气道加缸内喷射的混合气分布及不同混合气分布特性对汽油压燃的影响.结果表明:随气道预混比例的增加,着火时刻的当量比离散度先降低后升高,放热率峰值先升高后降低,最大压力升高率先增大后下降.随预喷时刻的推迟,指示热效率先增大后降低,最大压力升高率的变化较小.在爆发压力(18 MPa)和最大压力升高率(1.5 MPa/°CA)的限制下,相比于缸内单次喷射,气道加直喷策略和缸内两次喷射策略的指示热效率分别从45.6%增加到48.3%、48.2%;碳烟排放分别从0.041 g/(kW·h)减小到0.016 g/(kW·h)、0.015 g/(kW·h).

Computational fluid dynamics software CONVERGE is used to compare the mixed gas distributions under the single-injection strategy,multi-injection strategy and combined strategy of port-injection and direct- injection through numerical simulations. In addition,the effects of different mixture distribution characteristics on gasoline compression ignition are studied. With the increase in premixed ratio,the dispersion of equivalence ratio at the moment of ignition initially decreases and then increases,whereas both the peak heat release rate and the maximum pressure rise rate increase first and then decrease. With the delay of pre-injection timing,the indicated thermal efficiency increases first and then decreases,and the change in the maximum pressure rise rate is relatively small.Under the limits of maximum in-cylinder pressure of 18 MPa and maximum pressure rise rate of 1.5 MPa/°CA,in comparison with the single-injection strategy,the indicated thermal efficiencies of port- injection combined with direct injection and double injection strategies increase from 45.6% to 48.3% and 48.2%, respectively,and soot emissions are reduced from 0.041 g/(kW h) to 0.016 g/(kW h) and 0.015 g/(kW h), respectively.