Simulation And Experimental Research On The Emissions Of A Four-cylinder Turbocharged And Intercooled Diesel Engine

Nowadays, diesel engine has been widely used because of its good performance of power, economy, thermal efficiency, etc. However, with the increasing global attention on environment protection, the emission regulations are becoming stringent.The main emissions from diesel engine are NOX and particulate PM, as already known, PM is one of the main causes of haze, which possess serious challenges to the development of the diesel engine. Therefore how to reduce the main pollutants of diesel engine has became an important problem that every country is trying to solve.The researches on the emission control of diesel engines have great significance to the development of independent research and development and the competitiveness of domestic diesel engine.In this paper, the formation mechanism and corresponding harms of emission of diesel engine are analyzed. At the same time, various emission control technologies of diesel engine around the world are reviewed.A four cylinders turbocharged diesel engine from a domestic supplier was used in this research. The emission control of the diesel engine was studied through simulation and test for further optimization and improvements in this paper.In simulation calculation part, three dimensional calculation model and numerical calculation method of combustion process are discussed, the turbulence model, spray model, ignition and combustion model, emission model are analyzed and selected.According to the actual parameters of the diesel engine, setting related parameters and boundary conditions. Computational software was used to simulate the gas flow and combustion process in the diesel engine and also the effects of injection timing,nozzle diameter and nozzle protrusion on the combustion process were analyzed. The fuel evaporation rate, fuel/air equivalence ratio distribution, average temperature,average pressure and heat release rate were also studied, and a prediction of emissions was made. The results show that, when the injection timing is decreased, the ignition delay period become shorter, the fuel evaporation rate is lower, the mixed gas distribution range in ignition timing become smaller, the maximum combustion temperature and the maximum combustion pressure are decreased. With the decreasing of injector diameter, mixtures in cylinder become more uniform, the rich mixture areas are reduced, combustion become more complete, the heat release rate curve shifts forward, and the whole combustion process is advanced. At the same time,the maximum combustion temperature and maximum combustion pressure in thecylinder are increased.The test bench was established to carry out the emission test according to the relevant requirements of the emission test. The effect of compression ratio, injection timing, sac, hole diameter, open pressure and nozzle protrusion of injector on the emission characteristics of diesel engine was analyzed based on the comparative tests on a four cylinder turbocharged inter-cooling diesel engine at different conditions.The experimental results show that, the NOX emission is increased with the increasing of compression ratio,meanwhile,soot emission also changes with the decreasing of compression ratio.The highest soot emission occurs at compression ratio of 16.7.soot emission is reduced when compression ratio is increased to 17.2, when compression ratio continues to rise to 17.7,the soot emission do not continue to fall but rise, there is little change in diesel fuel consumption under these three different compression ratio. At any conditions, NOX emission increases with the increasing of injection timing, soot emission and specific fuel consumption are reduced with the increasing of injection timing. The soot emission is reduced, and the NOX emission is increased with the VCO nozzle,there is little change in diesel fuel consumption under three different compression ratio. Soot emission and diesel fuel consumption are reduced, and NOX emission is increased with decreasing of hole diameter except under 2850r/min and high load conditions. With the increasing of nozzle protrusion,NOX emission increases gradually as well as soot emission and specific fuel consumption decrease gradually. With the increasing of open pressure, soot emission reduces, and NOX emission increases, especially at low speed and low load conditions.Finally, compression ratio 17.2, 7×0.155 mm VCO injector, 25 MPa open pressure,3.67 mm nozzle protrusion are selected.