Research On Performance And Emission Characteristics On Marine EGR Diesel Engine

Marine diesel engines,especially two-stroke diesel engines fueled with high-sulfur fuel,are one of the main sources of marine atmospheric pollutions.The pollutants emitted by them cause great harm to the environment and humans.The pollutants emitted by them cause great harm to the environment and humans.Therefore,countries and organizations around the world have formulated corresponding regulations and divided the control areas to limit the emission of pollutants from marine diesel engines.The use of EGR technology can effectively reduce NOx emissions.At present,the core of this technology is to solve the two key problems of the removal of SO₂ and PM under high sulfur fuel conditions and the matching of the operation of the host and the EGR system.Based on this,this article carried out the following work:（1）A low-pressure EGR system for marine diesel engines with an EGR scrubber was established,and the effects of EGR on performance and emissions were studied.Studies have shown that when fuels with different sulfur contents were used,the introduction of EGR could reduce NOx emissions,and meet the requirements of IMO Tier Ⅲ emission regulations at large EGR rates.EGR combined washing technology could effectively reduce SO₂ and achieve near-zero emissions,decreased the trade-off relationship in certain degrees.At the same time,the scrubber also had a certain effect on NOx removal,reducing the EGR rates when reaching IMO Tier Ⅲ.（2）The PM produced under the action of EGR was analyzed based on quantity,quality and composition.Studies have shown that when fuels with different sulphur contents were used,the particle size distribution curve had a multimodal distribution,and with increasing load,the peak value gradually increased,the total number concentration increased,and the average particle size increased.The increase of EGR rates could promote the increase of particulate matter concentration,but did not change the peak particle size range.The sensitivity of particulate matter concentration under high sulfur fuel conditions to EGR rate was higher than that of LSDF.At the same time,with the increase of fuel sulfur contents,load,and EGR rate,the particulate matter specific emissions increased gradually.The influence of different sulfur content fuels,loads,and EGR rates on the particulate matter components was analyzed.The results showed that the increase of EGR rates led to the increase of the carbon components（OC+EC）in the particulate matter.The increase of sulfur contents in diesel fuel resulted in the increase of carbon components where OC was the main source,the sensitivity of OC to the EGR rates was stronger than EC.The effect of EGR rates and fuel sulfur contents on water-soluble ions was mainly manifested in the change ofSO₄^2-andNO₃^-.The matal elements in inorganic elements are Na、Mg、Ca、Fe and Zn,and the non-metallic elements are mainly S.When high sulphur diesel fuel was used,S content increased obvirously.The effect of EGR scrubber on the removal of particulate matter was obvious.The removal efficiency was more than 98%and the distribution peak of the particle size of the particulate matter mainly presented a unimodal distribution.In addition,the peak particle size range was in the range of 200-400 nm and the particulate matter was mainly concentrated in the accumulation state while the average particle size distribution was in the range of 400-500 nm.Moreover,the specific mass emission of the particulate matter was 22.136 mg/k Wh,which met China’s first and second-stage emission regulations and the U.S.EPA Tier 4 emission regulations.Furthermore,the absorption of OC in the particulate carbon components of EGR scrubber,SO₄^2-in the water-soluble ion,and S in the inorganic element were obvious.（3）A high-pressure EGR system simulation model of low-speed marine diesel engine with cylinder bypass（CB）and exhaust gas bypass（EGB）was established,and the changes of diesel engine performance and NOx emissions under different EGR operating modes（NONEGR mode,ECOEGR mode,and ECAEGR mode）were studied.And through high-pressure EGR combined with different technical measures,the possibility of near-zero emissions was discussed.The variation of combustion and emission performance of the diesel engine under different EGR operation modes was studied.Besides,the possibility of near-zero discharge was discussed through the combination of high-pressure EGR with different technical measures.The results showed that the deterioration of the fuel consumption was improved in some loads with the reduction of NOx when the diesel engine was operating in the ECOEGR mode.When the diesel engine was operating in the ECAEGR mode,NOx emissions could meet IMO Tier Ⅲ regulations.However,this caused the BSFC to increase and the engine power to decrease.Moreover,the possibility of near-zero discharge of NOx was discussed through the combination of high-pressure EGR with low-pressure EGR and the combination of high-pressure EGR with injection delay.The results showed that combining the high-pressure and the low-pressure EGR could further reduce NOx emissions to 1.69 g/k Wh while the power and fuel consumption were not greatly changed.（4）A multi-objective genetic optimization algorithm simulation model based on different EGR operating modes was established,and EGR operating mode matching optimization was carried out to obtain the optimal valve opening and fan speed of each load.The above two methods provide data references for solving the trade-off relationship between NOx and BSFC.The effect of the exhaust gas components on NOx emissions were analyzed through the simulation of a single-cylinder simulation model.It was concluded that H₂O had a catalytic effect on the reduction of NOx,which deepened the knowledge of recirculated exhaust gas components on dilution combustion at large EGR rate.By analyzing the combined removal of SO₂ and PM pollutants when the marine EGR diesel engine is fueled with high sulfur fuel and matching optimization of different operating modes in marine EGR diesel engines,the results obtained can support the optimal design of the washing system and performance matching for marine diesel engines,especially marine two-stroke diesel engines.