船用柴油机燃烧室结构分析

为探索不同燃烧室结构对大缸径船用柴油机燃烧和排放的影响，基于原机燃烧室，新设计了6种不同形状的燃烧室，采用AVL Fire软件建立燃烧室仿真模型，并结合涡流数和均匀系数来对缸内流动、混合和燃烧过程进行数值模拟分析。结果表明：燃烧室直径和凹坑深度等参数会对缸内流动产生很大影响，凹坑深度较大的缩口燃烧室能产生较强的涡流从而改善燃烧，而浅坑的开口燃烧室的缸内燃烧状况较差。同时发现，只有在缸内涡流和湍动能都较大的情况下才能使燃烧更充分。从发动机性能和排放结果来看，缩口燃烧室G1的功率输出增加4.6%，排放与原机基本持平；直口燃烧室G4在略低于原机的功率输出下，NOx排放降低43.3%；开口燃烧室的做功能力较差。

Numerical Simulations of Piston Bowl Geometry on Marine Diesel Engines

In order to investigate the effects of piston bowl geometry on the performances and emissions for large-bore marine diesel engines, six novel combustion chambers were designed based on the combustion chamber of the prototype, and combustion chamber simulation modeling was established by using AVL five code to simulate the in-cylinder flows, air-fuel mixing and combustion processes with the flow dynamics metrics such as swirl number and uniformity index. Results show that chamber diameter and bowl depth have a great influence on in-cylinder flows. The deeper depth of the re-entrant bowl may result in enhancement of swirl motions and improve the combustions, while a deficient combustion occurs at the lower depth open chamber. Further, high turbulent kinetic energy with a large swirl is important to improve the quality of combustions. It is also found that power output of re-entrant chamber G1 is increased by 4.6% and emission is almost the same as the prototype's. NOx emission of straight chamber G4 is decreased by 43.3% at a slightly lower power output than that of the prototype. And open chamber is found to have lower engine-out power.