Study On NO_x Displacement Of Marine Diesel Engine With EGR

If the ship diesel can not meet the standard of Tier Ⅲ, it will loss the competitive-nse in the matket. The exhaust gas recirculation technology is one of the most effective methods to reduce the nitrogen oxides. In this paper, one model basing on low-speed two-stroke main engine was made. After calibration with the data of standtest, a EGR system was added to the model. The running status of diesel under different EGR rates can be imitated. The aim of simulation is to find a appropriate EGR system which can be added to the low-speed two-stroke main engine.All the simulations are done with the simulation software GT-Power. The model founded in this software is one dimensional model. The combustion model is based on oil drop evaporation, porposed by Hrioyasu etc. In this model, NOx and soot are calculated separate, considering the effection of temperture and fuel air ratio. The gas flow in the model is calculated by the theory of one-dimensional flow. The veracity of the model is increased by calibration with the data of standtest. The selected running conditions are 100% load、108RPM,75% load、98.1RPM,50% load、85.7RPM,25% load、68RPM. The prupose of simulation is to find a EGR rate under which the displacement of NOx is drastically reduced, and at the same time there is a little effection on the dynamic property and ecomony property.It can be seen from the calculation result that the displacement of NOx fall qucikly with the EGR rate accreting. And the displacement of NOx can reduce more zhan 70% under all the running conditions. But the EGR rate can not be too big, because that when it is bigger than someone, there will be poor combustion in the cylinder. According to the analysis of calculation, the best EGR rates under the four running condition are 18.9%、18.9%、19.3%、14.1%, when the displacement of NOx meeting the Tier Ⅲ. But the cost is that BSFC rising 3.56%, displacement of soot being 7.75 g/KW·h. Besides, the simulation with LNG as fuel is also done. Comparing the result, it can be find that the cost to meet Tier III is that Brake Power reducing 1.69%, BSFC rising 1.81%. It is less than the simulation with diesel oil as fuel.From the calculation result, it is proved that the EGR technology can be used to reduce the displacement of NOx for the Tier III.