Research On Matching Design And Performance Of High-power Diesel Engine Urea Injection System

Engine exhaust emissions are one of the important factors causing environmental pollution,and emission regulations promulgated by various countries are becoming increasingly strict.SCR technology is the most efficient method for removing nitrogen and oxygen in diesel exhaust after-treatment.By spraying urea solution into the exhaust pipe,the ammonia generated by the decomposition reacts with NOx under the catalyst.The nitrogen and oxygen content in the exhaust gas reaches the emission regulations.Currently,the SCR system of small-power diesel engines is mainly on the market.In the face of the upgrade of emission regulations,this paper designs a gas-assisted urea injection system for high-power 400kW-1200kW marine diesel engines,so that the diesel engine emission reaches Tire III level.Simulate a certain type of spray gun,study the internal flow field of the spray gun with a pressure of 1.0 bar,1.5 bar,2.0 bar and a urea injection volume of 4.5 L/h,12 L/h,22.5 L/h,and derive the relevant parameters to simulate the external flow.The simulation found that the higher the gas-assisted pressure,the smaller the spray SMD,which is conducive to urea decomposition.The designed urea injection system was tested off-line,including urea pump metering accuracy,spray characteristics,and gas consumption.In order to verify the feasibility of the multi-pump parallel urea injection system,the injection measurement accuracy of single pump and multi-pump parallel mode under different gas path pressures and different injection quantities was tested.The metering accuracy is low when the low injection amount is under the gas assist pressure,and the injection amount tends to decrease as the injection back pressure increases.The metering accuracy of the single pump and the three pump in parallel is similar,indicating that the interaction of the pump during operation and the increase in the back pressure caused by the increased injection volume are not sufficient to cause a significant change in the metering accuracy.The three-dimensional particle dynamic analyzer of Tianjin University Laboratory was used to measure the spray characteristics and spray particle uniformity.The higher the gas-assisted pressure,the smaller the droplet SMD is,which is within 50?m,and tends to increase along the spray direction;the spray particle size uniformity is good under different cross-sections,and the 90%droplet SMD is less than 60?m.The spray cone angle is basically unchanged under different boundary conditions,and the gas consumption of the injection system is calculated.The calculation result requires that the gas path component of the injection system needs to reach a gas flow rate of 120 L/min under a pressure of 2.5bar.Using Matalab/Simulink to build a urea injection system control strategy for DeNOx,using a marine engine parameter of 880 kW as the basis of the control strategy,calculating the exhaust gas flow rate and NOx mass through CAN receiving engine speed,torque,exhaust temperature,NOx concentration and other information.Install the SCR of the matched design urea injection system on the engine test rig for E₃ emission verification.The original engine exhaust value is reduced from9.63g/kW·h to 1.42g/kW·h,which meets the requirements of the Tire III emission regulations.The NOx emission value of the segment engine reached 2.26 g/kW·h.