氨/柴油燃烧模型构建及低速机性能优化

Simulation on Chemical Kinetic Mechanism and Performance Optimization of Ammonia-Diesel Dual Fuel Low-Speed Engine

基于化学反应动力学及三维计算流体动力学(CFD)耦合开展了低压氨/柴油双燃料低速机的燃烧和排放仿真研究.构建了氨/柴油双燃料机理,其滞燃期、层流火焰速度及重要组分浓度的计算结果与试验结果吻合良好;在CONVERGE中建立了低速船机的三维CFD模型,确定了G方程模型中NH3燃料层流火焰速度的经验参数,研究了压缩比和当量比对氨/柴油双燃料低速机性能的影响.结果表明:适当提高压缩比可以改善氨着火燃烧的稳定性,压缩比为14.5可获得较高效率并将最大爆发压力控制在合理范围;氨燃料当量比在0.410附近性能达到最优,当量比更高使着火过于提前、燃烧温度大幅提高,导致热效率下降和NO_(x)排放明显升高,而当量比更低时指示热效率降低.在当量比为0.410、压缩比为14.5时氨/柴油双燃料低速机获得了效率及排放相互折衷下的最优值.

A simulation was carried out based on the coupling of chemical kinetics and computational fluid dynamics(CFD)to investigate the characteristics of combustion and emissions of ammonia-diesel dual fuel low-speed engine.The mechanism of ammonia-diesel dual fuel was proposed and it could predict well with experiment results including ignition delays,laminar flame speeds and important species concentrations.Then,in CONVERGE,a three-dimensional CFD model of a low-speed marine engine was established,and empirical parameters of the ammonia laminar flame speed in the G-equation model were determined.Finally,the influence of compression ratio and equivalence ratio on the ammonia-diesel dual fuel combustion process was studied.The results show that the stability of ammonia ignition combustion can be improved by appropriately increasing the compression ratio.When the compression ratio is 14.5,higher efficiency can be obtained and peak combustion pressure can be controlled within a reasonable range.When the equivalence ratio is around 0.410,the performance is optimal.A higher equivalence ratio will cause the ignition to advance too early and the combustion temperature will increase significantly,resulting in a decrease in thermal efficiency and a significant increase in NO_(x),while a lower equivalence ratio will result in a decrease in the indicated thermal efficiency.The comprehensive results show that when the equivalence ratio is 0.410 and the compression ratio is 14.5,the optimal values under the coordination of efficiency and emission can be obtained.