| The rapid development of the automotive industry has brought great convenience to people's lives,but also caused serious environmental pollution,energy saving and emission reduction is an urgent task facing the automotive industry today.For heavy-duty diesel engines,due to stricter emission regulations and fuel consumption regulations,the traditional single-stage turbocharger has been unable to meet the engine's demand for intake air,and the turbocharging system has developed toward higher pressure.The 2TC system can realize high pressure,flexible pressure ratio and wide flow range,which is an effective means for high pressure ratio of heavy-duty diesel engines.After the engine adopts a 2TC system,the intake air amount and the air-fuel ratio are greatly increased,which effectively improves the combustion condition of the engine and creates conditions for the introduction of a large proportion of EGR.The electronically controlled fuel injection system can independently control the fuel injection timing,fuel injection pressure and other injection parameters to achieve the ideal fuel injection law,and plays an important role in further optimizing the combustion and emission performance of the 2TC engine.In this paper,a heavy-duty 2TC diesel engine for a vehicle was used as a prototype,and a one-dimensional simulation model was established using GT-power software.Firstly,I studied the influence of the opening degree of the turbine bypass valve on the pressure ratio distribution of 2TC,the total pressure ratio and the efficiency of the turbocharger.The results show that: With the increase of the opening of the turbine bypass valve under different operating conditions,the pressure ratio of the high pressure stage decreases,the pressure ratio of the low pressure stage increases,and the total pressure ratio decreases.And there is a suitable bypass valve opening,so that the high and low pressure compressors are all in high efficiency area.Secondly,for the problem that the introduction of EGR is difficult after the 2TC system is adopted,this study selected the B75 working condition as the design condition,I designed the the EGR system based on the Venturi tube.In order to achieve a higher EGR rate,a lower fuel consumption rate,and at the same time to meet the principle of sufficient air intake,The ESE-diesel model of AVL-Fire was used to establish a three-dimensional simulation model,and used the GT-power one-dimensional simulation result as the initial condition of the three-dimensional simulation.The influence of intake and injection parameters on the formation of engine mixture,combustion process,fuel economy,and the generation history of discharged pollutants were calculated using the single-factor method.The results show:(1)In the intake pressure adjustment range of the 2TC system(1.8-2.7 bar),as the intake pressure increases,the air-fuel ratio increases,the engine fuel consumption rate and soot emissions decrease,but due to increased oxygen content makes NO increase more than emissions.(2)Under the condition of high pressurization of intake air,lowering the intake air temperature can further increase the intake air amount,and can simultaneously improve the fuel economy,NO,and soot emissions of the 2TCengine.(3)With the increase of EGR rate,the combustion duration is prolonged,NO emissions are significantly reduced,but the fuel consumption rate and soot emissions increase.At the same time,coMPared with the conventional turbocharging,increasing the intake pressure can make the engine maintain good dynamic,economical and emission performance in a wider EGR rate range.(4)Increasing the injection pressure can improve the increase of soot emissions when the 2TC diesel engine is introduced with high EGR,but it will slightly increase the NO emission.At the same time,the effect of injection pressure on the fuel consumption rate,indicated torque,and soot emissions under different intake pressures was coMPared.The results show that increasing the intake pressure to a certain extent can reduce the engine's demand for high injection pressure.(5)With the advancement of the main injection timing,the cylinder pressure peak of the two-stage supercharged engine is significantly increased.Fuel injection can improve soot emissions in advance,but it will increase NO emissions,and there is an optimal main injection timing of 10°CA BTDC,making the fuel consumption rate the lowest.(6)When the proportion of post-injection fuel is in the range of 0% to 12%,post-injection can simultaneously reduce the NO and soot emissions of the secondary supercharged engine.The amount of post-spray continues to increase,soot and fuel economy have deteriorated significantly.Finally,I used the AVL-Fire simulation analysis platform,the NO,soot specific emission and effective fuel consumption rate were used as response indicators,and multi-factor coupled orthogonal test design methods were used to determine the progress of the 2TC diesel engine.The results show that in the factors and levels selected in this study,the main injection timing is the most important influencing factor for the fuel consumption rate;for NO emissions,EGR is the most important influencing factor;for soot emissions,the injection pressure is the main influencing factors.Using the multi-index comprehensive balance method to determine the best combination of intake and fuel injection parameters: EGR rate 30%,intake pressure 2.4bar,intake air temperature 350 K,injection pressure 140 MPa,main injection timing 10° CA BTDC,post spray 2mg.Co MPared with the boundary conditions adopted by the original machine,the combination of intake and injection parameters optimized by the two-stage booster system and fuel injection strategy resulted in a 5.3% reduction in fuel consumption rate,a 54.6% reduction in NO,and a 78% reduction in soot. |
PDF Full Text Request