扫气压力对船用天然气/柴油双燃料发动机燃烧排放的影响

为研究扫气压力对缸内直喷船用双燃料发动机燃烧排放特性的影响规律,在通过试验数据对模型验证的基础上,采用有限容积法进行燃烧过程方程组的离散,同时采用半隐式法进行多变量耦合数值求解,分别就船用天然气/柴油双燃料发动机不同扫气压力对发动机缸内压力、缸内温度、缸内湍流和排放产物的影响进行了数值计算。结果表明:扫气压力的提高可导致缸内最大爆压增大,缸内最高温度与缸内湍流动能峰值降低;同时NO和CH~4排放量均随扫气压力的提高呈下降趋势;扫气压力每提高0.25 bar,缸内最大爆压平均升高5%,而缸内最高温度平均降低2.5%,缸内湍流动能峰值平均降低6.9%,NO排放量减少7.8%,CH~4排放量减少10.9%,扫气压力对CH~4排放的影响比对NO排放的影响更明显。研究表明,船用天然气/柴油双燃料发动机在运行过程中,应在发动机热负荷允许的范围内,尽可能采用高的扫气压力,以降低未燃CH~4和NO的排放,从而提升发动机的动力性和经济性。

Effects of scavenging pressure on combustion and emission characteristics of marine natural gas/diesel dual fuel engines

Dual fuel engine has become an important development trend of marine engines. In order to further un-derstand the influence of scavenging pressure on combustion characteristics of marine natural gas/diesel dual fuel engine,on the basis of experimental verification,the finite volume method was adopted to discrete the equations of the combustion process,and the semi-implicit method was adopted to solve the multivariable coupling numerical a-nalysis. The effect of different scavenging pressure on combustive pressure, temperature, turbulence intensity in a cylinder,and emission of the engine were investigated. The results showed that the increase in the scavenging pres-sure increased the peak cylinder pressure,but decreased the peak temperature and peak cylinder turbulent kinetic energy. NO and CH4emission was decreased with the increase in the scavenging pressure in the meantime. It was found that,with increase in scavenging pressure every 0.25 bar, the peak cylinder pressure respectively rose by 5%,while peak temperature,peak cylinder turbulent kinetic energy,NO emissions and CH4emissions was reduced by 2.5%,6.9%,7.8% and 10.9%,respectively. The effect of scavenging pressure on CH4emission was more pro-nounced than that on NO emission. Therefore, the marine natural gas/diesel dual fuel engine should be use high scavenging pressure as far as possible,within the allowable range of engine heat load in the work condition,to re-duce unburned CH4and NO emissions,for enhancing the power and economy of an engine.