Numerical Simulation Of The Combustion Process And NO_x Emission Of Homogeneous Charge Compression Ignition Marine Diesel Engines

As the fast developing of shipping industry,the number of global operational ships increases continuously.At the same time,environment pollution problem caused by harmful emissions especially the NO_X from marine diesel engine is more serious. Annexâ…¥to MARPOL73/78 for the prevention of air pollution from ships has became effective on May 19,2005.Also MARPOL73/78 is worked out by the International Maritime Organization(IMO) in 1973 and 1978.In order to fit the stricter emission regulations,it must be to find a new combustion mode which is more efficiency and more clean.Homogeneous charge compression ignition(HCCI) has become the key subject,as the hybrid of conventional spark ignition engine and compression ignition engine,it has the potential of very low emissions of oxides of nitrogen(NO_X),as well as high thermal efficiency.Firstly,a new n-heptane HCCI combustion model is established in this paper based on the traditional single-zone combustion model.The model is close to the real combustion process with the characteristic of the n-heptane's detailed chemical kinetic and the formation mechanism of NO_X.Then the software package CHEMKIN is used to simulate n-heptane HCCI combustion in marine diesel engine,The simulation results of combustion process show that the n-heptane HCCI combustion process presents three burning phases.They are low-temperature reaction,middle-temperature reaction zone and high-temperature reaction zone.On this basis,the influences of compression ratio valence ratio,intake temperature,pressure,excess air radio and engine speed on combustion process of the HCCI are further discussed.While at the same time,this paper puts comparatively deep research on the three forming factors of NO_X:cylinder temperature,oxygen concentration and the retention time of oxygen and nitrogen at high temperatures.Afterward,this thesis discusses the influences of compression ratio valence ratio,intake temperature,pressure,excess air radio and engine speed on formation process and emission of NO_X,and tries to analyse the effect of the three forming factors of NO_X when these operating parameters are changed.Finally,this thesis calculates the NO_X emissions of the n-heptane HCCI engine in the same working conditions compared with the test NO_X emissions data of used marine diesel engine and proves that the HCCI combustion mode has an excellent characteristic of low NO_X emission in theory.