Research On High Efficiency Combustion And Low Emission Of Marine Engine Fueled With Biodiesel

From the first industrial revolution in 18^th century,the rapid developments of science and technology have brought earth-shaking changes to human society.At the same time,the dependence of human society on fossil fuels has been further increased with the progress of social civilization.However,due to the depletion of fossil fuel resources,the energy issues will become a major problem for human survival and development.Because fossil fuel is a kind of non-renewable resources,it is closely related to human transportation,military,industrial,life and so on.In order to alleviate the world’s energy problems,lots of scholars and experts from all over the world are trying to explore suitable alternative energy sources.However,it makes biodiesel present in people’s vision,and biodiesel fuel gets the favor of many scholars,due to the advantages of abundant feed stock,simple production process,low cost and empolyed directly in diesel engine without any modification,etc.In recent years,there are many studies on biodiesel and various additives at home and abroad,but there are many kinds of additives,and scholars’understanding of biodiesel still has some limitations.According to the research status of biodiesel at home and abroad,the experimental investigations were carried mainly by the diesel engine fueled with the different proportion blend fuel of biodiesel and diesel.In the field of diesel engine,there are few studies on the effect of biodiesel on cold start performance of diesel engine,and there are few studies on injection,atomization and combustion performance of biodiesel with different fuel additives.In addition,domestic and foreign researches have not systematically analyzed the effects of diesel engine input parameters on the output parameters.Therefore,this topic is based on the research projects of the National Natural Science Foundation of China“Synergistic optimization of regeneration by microwave heating and thermo-electro-chemical-mechanical coupling for rotating particulate filter of Pd/graphene catalytic”（No.51676066）and the National Science Foundation of China“Research on hydrocarbon capture mechanism and thermal-flow-mechanics coupling optimization for the zeolite molecular sieve hydrocarbon tarp of gasoline engine in the cold start”.From the above as a breakthrough,the corresponding numerical simulation and experimental research are carried out.The main research work and innovations of this paper are as follows:（1）Firstly,an improved thermodynamic model of cold start is developed in the present study,and the thermodynamic model is verified by experiments.The effects of gas leakage rate,heat loss and cylinder clearance volume on the cold start pe rformance of diesel engine are considered in the process of calculation.Furthermore,the entropy production response surface as a function of parameters is compared and investigated under different cold-start conditions.The findings in this work will be useful for the improvements of the diesel engine performance under the cold starting condition.The result shows that the ignition temperature predicted by the improved thermodynamic model is closer to the experimental value when the adiabatic index of compressed gas（k=cp/cv）is equal to 1.34.The model can accurately calculate the compression temperature and pressure predicted by the thermodynamic parameters of diesel engine.Similarly,the entropy and exergy theory can effectively evaluate the thermal system of diesel engine.（2）Secondly,a two-stage MLP artificial neural network（ANN）model is established to study the relative contribution of the input parameters（injection pressure,EGR,fuel injection mass,injection timing,fuel injection persistence angle,compression ratio,intake pressure,intake temperature）of diesel engine on the output parameters（output torque,fuel consumption,Soot and NOx）of diesel engine at different speeds and equivalent ratios.The results show that high intake pressure and low exhaust pressure can promote the complete combustion of fuel,improve the combustion of diesel engine and increase the output torque of diesel engine.Cyclic fuel injection mass is one of the main factors affecting the power and emission characteristics of diesel engine under the whole working conditions.The effects of EGR and injection timing on NOx emission are the most obvious.Increasing EGR or decreasing injection timing will significantly increase NO x emission.In addition,increasing compression ratio and intake pressure are conducive to the complete combustion of fuel and reducing soot emission.But increasing EGR will increase soot emission.The increase of compression ratio and intake pressure of diesel engine is beneficial to increasing the torque of diesel engine.At high speed,the fuel injection rate of diesel engine has the greatest influence on the torque,followed by compression ratio and intake pressure.At low equivalent ratio,the influence of intake pressure is not obvious.Simally,the fuel injection quantity of diesel engine plays a very important role,and the influence of intake pressure on fuel consumption is not obvious at low load.（3）Thirdly,pure diesel and four typical biodiesel are used to investigate the effects of fatty acid methyl esters proportion on combustion and emission characteristics of a diesel engine in terms of heat release rate,cylinder pressure,brake specific fuel consumption（BSFC）,indicated power,CO,HC and NOx emissions.The results show that the ignition delay of diesel engine is effected by the both of chemical and physical delays,and the kinematic viscosity of biodiesel is an important factor.The ignition delay is delayed with the increase of C18:1,C18:0 and C16:0.Higher kinematic viscosity is not conducive to improving fuel-air mixing,fuel evaporation and combustion efficiency.Meanwhile,the higher the saturation,the shorter the chemical ignition delay time.Compared with diesel,biodiesel has the poor performance characteristic of diesel engine due to its low calorific value and high viscosity.Biodiesel increases the CO and HC emissions at low loads,but significantly reduces the CO and HC emissions at medium and high loads.At medium and high loads,biodiesel improves diesel engine combustion in cylinder,but the NOx emission of diesel engine increases significantly.（4）Then,the corresponding three-dimensional CFD model is performed by AVL-Fire coupled CHEMKIN II code,and an improved chemical kinetics mechanism containing 475 reactions and 134 species is developed to simulate the fuel spray process and combustion process since it contained methyl linolenate,methyl linoleate,methyl oleate,methyl stearate,methyl palmitate,a majority component in most biodiesel,thus improved the accuracy of simulation.The results obtained show that the water addition in fuel plays an important role in fuel spray process and fuel com-bustion process.The fuel-air mixing is improved due to the micro-explosion.More specifically,the findings reveal that low-level water addition in biodiesel fuel can reduce NOx,CO and CO2 emissions.The optimal water addition level in terms of diesel engine emission and performance parameters is found at 4 wt%among WBE fuels.In particular,the NOx,CO and CO2 emissions are reduced at maximum speed of 1000rpm.Thus,the relationship between water addition rate and combustion and emission characteristics is not straightforward,the balance between water addition and fuel is very important.（5）Lastly,the combined application of water additive and metal-based additive is investigated in the biodiesel-diesel blend fuel.Varied mixtures of biodiesel-diesel（B5）,water（i.e.2%,4%and 6%wt.）and cerium oxide（CeO 2）nanoparticles（90 ppm）components are compared with pure diesel in terms of heat release rate,cylinder pressure,BSFC,indicated power,CO,HC and NOx emissions.The results show that the water additive in the biodiesel-diesel fuel is beneficial to improving the mixing of air and fuel due to the micro-explosion.Proper water additive is beneficial to improving performance and decreasing the CO,PM,NOx and HC emissions.As well as the metal-based additives in the blend fuels can further improve the overall combustion quality and decrease the emissions.More specifically,the metal-based additive is beneficial to improving the brake power and brake thermal efficiency and decreasing the brake specific fuel consumption and emissions due to the improved combustion caused by the catalytic activity during the combustion process.