对船用低速柴油机NO_x修正系数的研究

Research on NO_x Correction Factor for Low Speed Marine Diesel Engines

通过对 MARPOL 公约附则 V I中 NOx 修正系数的研究表明 ,扫气空气温度属于可控制的进气参数 ,不需要出现在 NOx 修正系数公式中。作者研究认为进气温度、进气湿度和大气压力是三个重要影响因素 ,而将扫气空气温度与最高燃烧压力作为运行参数在 ISO状况下对 NOx 值进行修正则更为合理 ,并推导出了新的 NOx

Experience showes that the NO x correction factor range of 0.827to 1.055 (for constant scavenging air temperature) in the Annex VI of MARPOL convention is too wide for low speed marine diesel engines. The scavenging air temperature is dependent on the cooler system, coolant flow and coolant temperature, and is to some extent an adjustable feature similar to the maximum cylinder pressure, thereforeis not considered an ambient condition. The ambient pressure should be included as an ambient condition, since if influences the inlet condition to the compressor and the outlet condition of the turbine temperature, thereby influences scavenging air pressure and air amount. The research results show that the correction formula for tow stroke low speed marine diesel engines should be different from those for four stroke diesel engines. One of the major differences between the operation of the engines is the maximum cylinder pressure design criteria. For 2 stroke engines, the maximum cylinder pressure is to be kept at the specified value during operation. An increase in ambient temperature will result in a lower scavenging air pressure and reduce the compression pressure. For the 4 stroke engines the maximum cylinder pressure will decrease as a consequence of the lower compression pressure and similar injection timing. In order to fulfill the maximum cylinder pressure design criteria, the 2 stroke engine needs advanced injection timing. The NO x emission will be different for the two cases. The ambient temperature, the ambient humidity and the atmospheric pressure are three affecting factors in the ambient correction formula. And a new NO x correction factor formula for two stroke engines was brought forward by calculation. The scavenging air temperature and maximum cylinder pressure are adjustable features which have to be separately corrected.