Study On The Application Of Diesel Methanol Compound Combustion In Marine Diesel Engine

In recent years,with the increasing severity of air pollution and depletion of petroleum resources,the development of clean and renewable alternative fuels for marine engines has become one effective method to solve the problem of pollutant emissions from marine engines and alleviate energy crisis.Due to the wide range of sources,high oxygen content and fast burning speed,methanol is considered as one of the most promising alternative fuels.Diesel/methanol compound combustion(DMCC)technology is one of the most successful ways to apply methanol to diesel engines.A large number of tests on vehicle diesel engine show that DMCC technology can effectively reduce NOx and PM emissions,at the same time increase thermal efficiency and decrease fuel consumption.However,the research about DMCC technology on marine diesel engines has not been reported in China.The working characteristics of marine diesel engine are quite different from that of vehicle engine,although the working principle of them are similar.Therefore,in order to explore the characteristics of marine engine running with diesel methanol dual fuel,the following works were carried out in this study.Firstly,the feasibility study of DMCC technology was explored on a mechanical pump-type supercharged intercooled marine diesel engine.Then,the characteristics of combustion,emission and fuel consumption were studied on a supercharged intercooled marine diesel engine equipped with high-pressure common rail system.Finally,the application practice of DMCC technology was carried out on a fishing boat.Through the above tests and data analysis,the conclusions are as follows:1)The application of DMCC technology in marine diesel engines does not change the power performance of the engine.The intake air and exhaust gas temperatures of the engine all decrease as the methanol substitution proportion increase.The methanol substitution proportion is limited by engine misfire at medium and low loads,and it is subject to excessive peak pressure at full load.2)DMCC technology can improve the engine performance,based on a highpressure common rail marine diesel engine.With original diesel calibration spectrum(MAP)unchanged,the application of DMCC technology can notably advance the combustion phase,increase the combustion ratio in constant volume,improve the thermal efficiency,and decrease fuel consumption.Although the reduction of NOx and PM emissions is not obvious under the four operating conditions in propulsion characteristics,NOx and PM emissions have a remarkable drop from the perspective of all operating conditions.Although HC and CO emissions increase significantly,they can be substantially eliminated by using an oxidation catalytic converter(DOC).In dual fuel mode with DOC,the engine can meet National I emission requirements.3)Pilot injection has a great impact on combustion,gas emission and fuel consumption characteristics of high-pressure common rail DMCC marine engine.After adopting pilot-injection strategy,the peaks of heat release rate and pressure rise rate in dual fuel mode are greatly reduced,the ignition timing advanced,and the combustion stability improved,leading to the increased methanol substitution proportion.At the same time,the brake specific fuel consumption and NOx emissions decreased notably.Although PM emission increased slightly,they are still lower than that in pure diesel mode without pre-spray.4)The application of DMCC technology on real ship engine can greatly improve its performance without any adverse effects on its start-stop system and power performance.The exhaust smoke is greatly reduced,and the engine thermal efficiency is improved.Replacing 1.0 kg diesel just need 1.1kg methanol,which is much lower than theoretical replacement ratio 2.16.The fuel economy improved 18.7% in dual fuel mode.