Study And Application On The Key Technology Of Medium And High Speed Marine DMCC Engine Meeting China Ⅱ Emission Legislation For Marine Diesel Engine

In recent years,with the increasing severity of global warming,air pollution and depletion of petroleum resources,energy conservation and pollution reduction have become an important direction of the development in the future ship field.The research and application of green,efficient and clean alternative fuel oil have become a hot issue in the shipping industry.Methanol,as a commercially and technically feasible alternative fuel for ships,is regarded as the future fuel for the shipping industry due to its excellent environmental protection characteristics,low carbon dioxide emissions,wide production sources and huge production capacity.At present,methanol fuel has been successfully used in low speed marine engines in the world,but it has not been used in medium and high speed marine engines.Among the technical routes of Marine methanol engine,diesel methanol combined combustion(DMCC)is a feasible technical scheme.In this technology,methanol is injected from the intake manifold to form a quasi homogeneous mixture with the intake air,and then burned with the injected diesel in the cylinder.Preliminary research shows that when the technology is applied to power plants such as heavy-duty diesel engines and construction machinery,it can simultaneously reduce engine NOx and PM emissions,reduce fuel consumption and improve thermal efficiency.It is one of the most promising and feasible schemes for the application of methanol fuel in compression ignition diesel engines.However,it is still doubtful whether the medium and highspeed marine engine can meet the national II emission requirements of marine engine after applying DMCC technology.It is still unknown how the power,economy and reliability of marine diesel equipped with methanol injected in intake air(MIIA)are.This work revolves around the Z6170 high speed diesel engine that meets the China Ⅰemission legislation for marine diesel engine.Without changing the fuel system of the original engine,the MIIA is installed at the intake manifold,and the diesel oxidation catalyst(DOC)is installed in the exhaust system of the engine to form a marine engine operating in DMCC mode.On the premise of not losing power and improving fuel economy,the research is carried out to meet the strict China Ⅱ emission legislation for marine diesel engine.The research starts with the installation of methanol injection and control system,and works on the engine running in DMCC mode which is transformed from Z6170 high speed marine engine.After a large number of bench and matching tests,the emission level of the transformed medium and high speed marine DMCC engine has reached the requirements of national II standard for marine power,and the structure and layout have passed CCS certification.The main work completed in the whole engine R&D process is as follows:(1)The influence of cooling water temperature on engine performance is studied in detail.Cooling water temperature has a great influence on the economy of Marine DMCC engine,and the maximum methanol replacement rate that can be realized at different cooling water temperatures is significantly different.Increasing cooling water temperature within the allowable range of engine thermal load and mechanical load can improve methanol replacement ratio and optimize the replacement ratio.The highest methanol replacement ratio is 72% and the optimal replacement ratio is 1.75.However,it will be accompanied by a significant increase in NO emissions.(2)The influence of fuel injection time on engine emission is systematically studied.Delayed diesel injection time is still an effective means to reduce NO and NOx emissions of Marine DMCC engine.With the delay of injection timing,NO and NOx decreased significantly,but smoke emission increased slowly and CO also increased significantly.HC changed little.There is an u-shaped relationship between diesel fuel consumption,methanol replacement ratio and fuel injection time.(3)The effect of valve overlap time on high HC emission of DMCC engine is expounded.By changing the camshaft with small valve overlap Angle,methanol escape can be effectively reduced and Marine DMCC engine HC emission can also be reduced.But at the same time,engine thermal load will exceed the design limit and NO and NOx will be greatly increased.(4)The relationship between multi parameters of DMCC engine is optimized and determined.By changing the methanol replacement rate,cooling water temperature,diesel injection timing and other variables,the inherent contradiction between engine emission characteristics and economy and the relationship of balance between different emissions can be optimized.The calibration of medium and high speed marine DMCC engine is completed,and a specially developed efficient DOC system is installed.In addition,the goal of fully automatic operation and good reliability of the inlet alcohol injection system is realized,so as to ensure that it will not cause large fluctuations in engine speed during instantaneous opening and emergency stop under various loads.(5)A special and efficient DOC system meeting China Ⅱ emission legislation for marine diesel engine is developed.The data show that after installing the specially developed high-efficiency doc system,the exhaust pollutants of Marine DMCC engine can be significantly reduced to a level below the emission limits of national II requirements of marine engine under the premise of maintaining the same power performance.The NOx+HC emission is 5.04 g/k W·h,which is far lower than the emission level of 5.894 g/k W·h of the original engine and is lower than the limit of5.8 g/k W·h.The CO emission is 0.07 g/k W·h,which is far lower than the 1.43g/k W·h of the original engine and is 0.014 times of the limit of 5 g/k W·h.The PM emission is 0.096 g/k W·h,which is lower than the limit of 0.12 g/k W·h and is 49.7%lower than that of the original engine of 0.191 g/k W·h.(6)Medium and high speed marine DMCC engine can achieve high MSP and its economy is better than that of the original engine.The average MSP of engine under five operation conditions is 42.32%,and the MMSP is 72%.While achieving high MSP,the engine can achieve the mass replacement ratio of 1.7-1.9,and the BTE is 4.7%percentage points higher than that of the original engine.