| With the increasingly severe energy situation and the increasingly prominent environmental pollution problems,various regulations for marine diesel engines are becoming more and more strict,which has led to the development of marine diesel engines in the direction of high efficiency and low pollution,reducing the emissions of marine diesel engines while ensuring the diesel engines.Power and economy are very important.Since electronically controlled high pressure common rail,Miller cycle,exhaust gas recirculation(EGR)and water-injection combustion technologies have great potential and obvious advantages in reducing diesel NOX emissions,and they all have low-temperature combustion characteristics,this paper chooses this Four technologies and their combination are studied.Finding an effective method to reduce the NOx and Soot emissions of the diesel engine provides a valuable reference for energy saving and emission reduction of marine diesel engines.The main research contents are as follows:(1)Establish a 620 single-cylinder multi-functional test platform with electronically controlled high pressure common rail,Miller cycle,exhaust gas recirculation(EGR),and variable intake and exhaust pressure.Designing a single-cylinder diesel engine with electronically controlled high pressure common rail,Miller cycle,exhaust gas recirculation(EGR),variable intake and exhaust pressure system,setting up a single cylinder performance test bench,and a single cylinder engine fuel system,sliding Oil system,cooling water system and components of various systems such as EGR and Miller are designed,manufactured and selected.(2)Design and process the intake camshafts of different Miller degrees,carry out the Miller cycle test,study the propeller characteristics and load characteristics of the marine diesel engine,and the combustion and emission characteristics of the Miller system marine diesel engine with the variable rail pressure and the fuel injection advance angle.The results show that the Miller cycle can effectively reduce the NOx emission concentration of diesel engines,improve the emission performance of diesel engines,and reduce the fuel consumption rate.The best Miller degree in the promotion of characteristic conditions is derived from emission economy as the main evaluation index.With the increase of rail pressure and injection advance angle,the maximum combustion pressure increases,the fuel consumption rate decreases,the exhaust gas temperature increases,the NOx emission concentration increases,and the Soot content decreases.(3)The three-dimensional combustion chamber model and one-dimensional model of the diesel engine were established by AVL-FIRE and GT-POWER simulation software respectively.The accuracy of the simulation model was verified by comparison with experimental data.Based on this,the Miller cycle simulation study was carried out to analyze its influence on diesel combustion characteristics and NOx emissions.Through simulation calculation,when the diesel engine adopts the Miller cycle,with the increase of Miller degree,the maximum combustion pressure in the cylinder decreases,the highest average temperature decreases,the retardation period increases,the CA50 delays,and the combustion continues with the air-fuel ratio unchanged.The period is shortened,the combustion heat release rate is affected significantly,the fuel consumption rate is reduced,the economy is improved,the NOx concentration and distribution space are reduced,the emission is improved significantly,the overall economy and emissions are determined,and the best diesel engine is determined.Miller is M60.Based on the simulation of Miller system diesel engine,the effects of intake pressure,injection advance angle and intake air temperature on its performance were studied.(4)Using the simulation platform established,the simulation study of EGR combined with Miller cycle is carried out.With the increase of exhaust gas introduction(EGR rate),the power and economy of the diesel engine are reduced,and the maximum temperature in the cylinder is The maximum burst pressure drops,the NOx emissions decrease,the Soot content increases,the combustion start point is delayed,the retardation period is extended,the combustion duration is extended,and the combustion center of gravity is shifted.The EGR rate has a 75%load on the performance of the diesel engine.The EGR rate is 0.2.The diesel exhaust gas recirculation(EGR)test is carried out on the built single-cylinder test rig.The test data is compared with the simulation results.Analysis,the two trends are the same,the test verified the accuracy of the simulation.On this basis,the influence of Miller cycle combined with EGR technology on diesel engine performance is studied.The results show that when Miller degree is constant,the increase of EGR rate will reduce the in-cylinder pressure and the cylinder temperature.At the same time,the effect of EGR technology on the reduction of NOx production in the cylinder is increased by the combination of the Miller cycle technology.In this paper,the diesel engine performance is further optimized by changing the compression ratio and the fuel injection advance angle.The compression ratio and the fuel injection advance angle are determined by analyzing the effects of the combination of the two on the diesel engine cylinder temperature,pressure and NOx generation.(5)The simulation study of water-mixing combustion was carried out,and the influence of the rated conditions of water-incorporated emulsified oil and inlet water spray technology on the combustion situation,dynamic performance,economic performance and emission performance of the cylinder was calculated and analyzed by grey theory and combined weight method.The optimal water mixing ratio of the two combustion modes was compared.The application range of the two water-mixing combustion modes was compared and analyzed,and the working state and applicability under the variable working conditions were analyzed by selecting the method of preparing the emulsified oil.When the diesel engine is burned with emulsified oil,the highest burst pressure,average temperature and tailing temperature decrease in the cylinder as the water content increases,the emission decreases,and the optimal water mixing ratio is 10%through gray decision theory analysis.The power is 5.68%lower than the original machine,the fuel consumption rate is reduced by 6.54%,the NOX emission is reduced by 36.06%,and the Soot emission is reduced by 5.99%.When the diesel engine uses water injection from the inlet,the optimal spray flow rate is 0.5kg/h.At this time,the power is 6.13%higher than the original machine,the specific fuel consumption rate is reduced by 5.79%,the NOx emission is reduced by 45.75%,and the Soot emission is reduced.33.34%. |
PDF Full Text Request