Computational Study On Emission Control Strategy For Marine Medium And High Speed High Power Diesel Engine

Nowadays,the emissions of NOx from marine diesel engiens have become the main pollutants in ports.To limit the emissions,striker emission regulations have been put into force by the IMO(international matitime organization).With limited space for ships to install addinatioal equipments and limit to carry chemical reagents,internal measures such as EGR and fuel injection strategy are useful to meet the emission regulations.Based on a certain type of marine diesel engine in active service,the author established the simulation model of the diesel engine using the GT-power simulation software,and verified the accuracy of the model compared with the test data.And a high pressure EGR system was set based on this model.The results show that NOx emissions were different under different loads,which caused the different EGR rates for IMO Tire II limit.In 75% and 100% condition,the running point of compressor was closed to the surge line,at the same time,the NO emissions could not meet the IMO Tire II requirements.So cylinder-bypass was taken in the high pressure EGR system to get a higher EGR rate in 100% working condition,and to make the running point away from the surge line and running in high effective areas.And more,the EGR rates rose up than before,with more NOx reduction.Meanwhile,the NOx emissions could meet the IMO Tier II requirements.Using the measures mentioned above in this paper,the reductions of power in different working conditions were less than 3.8%,and the BSFC increased no more than 3.8%,which can satisfy the working requirements.In order to study the effects of EGR on combustion process and NOx generation,a three dimensional model was established by using the FIRE simulation software.Related parameters were changed by using EGR in 100% working condition,and these parameters were analysised to show the effects on the NOx generation.Changing the fuel injection time was another effective measure to reduce NOx emissions.In this paper,the author analysised the effects of pilot injection and post-injection by using the FIRE simulation software.The results show that the smaller the pilot injection mass and larger primary pilot injection interval were helpful to reduce NOx emissions,a proper post spray mass and post spray interval could show a good relationship on NOx and soot tread-offs.EGR combined with post-injection can significantly improve trade-offs relationship between NOx and soot.However it is essential to use the advanced electronic control fuel injection system to achieve pilot injection and post injection.In order to reduce the difficulty and complexity of the reform,the author analysised the effects of late injection and EGR combined with late injection on engine performance and NOx emissions without the change of the original fuel system.The results show that NOx emissions can be reduced by using late injection.NOx emissions can be further reduced by using EGR combined with late injection.What's more,these techniques can help marine diesel engines meet the stricter IMO Tier III requirements.