氨-柴油双燃料船用低速机温室气体排放特性分析

Analysis of the Greenhouse Gas Emissions Characteristics of an Ammonia-Diesel Dual Fuel Low-Speed Marine Engine

针对一台低压喷射二冲程船用发动机进行三维全尺寸模拟,研究了引燃策略和掺混氢气对氨-柴油双燃料低速机燃烧及排放特性的影响.结果表明:提高引燃油能量占比(1.5%)、增加预燃室数量(3个/缸)可有效强化预燃室射流引燃能力,改善氨燃烧性能,实现高效引燃与快速燃烧;提高主燃室内氢气掺混比,可增加缸内OH等活性自由基,提升氨燃烧的强度,通过稀燃工况下掺氢反应活性调控改善了NO_(x)及N_(2)O排放;综合比较,相同的循环总能量输入工况下,在指示热效率水平相当、NO_(x)满足TierⅢ排放法规的前提下,采用氨燃料时当量CO_(2)排放(19.0 g/(kW·h))相对于天然气(393.0 g/(kW·h))降低约95.0%,在氨燃料中掺混10%(能量分数)氢、过量空气系数φa为3.4,当量CO_(2)排放(4.7 g/(kW·h))相对于天然气降低约98.8%,实现近零碳排放.

Full-scale simulations were performed on a two-stroke ammonia-diesel dual fuel marine engine,in which ammonia is injected into the cylinder with low pressure,with particular interest on the effect of ignition strategies and hydrogen blending on the combustion and emission characteristics.The results show that,an increased proportion of pilot fuel energy(1.5%)and an increased number of pre-chambers(3 pre-chambers per cylinder)can effectively enhance the jet ignition ability,thus achieving efficient ignition and rapid combustion.Increasing the blending ratio of hydrogen in the main combustion chamber can increase the in-cylinder active free radicals such as OH,enhance the intensity of ammonia combustion,and reduce NO_(x)and N_(2)O emissions under lean-burn conditions.Overall,compared to the CO_(2)emissions when using natural gas(393.0 g/(kW·h))under the conditions of same total energy per cycle,equivalent indicated thermal efficiency and same TierⅢemission regulation,the equivalent CO_(2)emissions when using ammonia(19.0 g/(kW·h))can be reduced by about 95.0%.When blending 10%(energy fraction)hydrogen into ammonia atφa=3.4,the equivalent CO_(2)emissions(4.7g/(kW·h))can be reduced by about 98.8%compared to natural gas,realizing near-zero carbon emissions.