Numerical Simulation Of Diesel Engine Combustion In Cylinder And Study Of Valve Timing

At present,compared with the traditional test,numerical simulation method has obvious advantages.It not only saves a lot of cost in terms of test equipment,region and labor,but also saves time and efficiency.It can realize the transformation of test conditions through parametric management.In order to study the relationship between the gas distribution process,the stored gas volume in the intake process and the power loss in the exhaust process of a diesel engine under the condition of good combustion performance,and to obtain the optimal valve distribution phase,the simulation of the working process and the timing matching of the diesel engine were carried out by using the computational fluid dynamics method.The working process of diesel engine is studied under three different speeds(1500r/min,2000r/min and 2500r/min),and its working cycle is simulated by CFD method.In the process of simulation,Solid Works is used to draw the cylinder block model of diesel engine;In the process of discretization,the mixed use of moving grid and fixed grid is adopted to reduce the amount of calculation while ensuring the accuracy of calculation;The three conservation laws,turbulent flow,ignition,combustion,droplet breakup and atomization are discussed in detail.Diesel ignition model,EUB eddy current breakup model and droplet dispersion(DDM)spray model are chosen as research means.Through the visualization of the calculation results,the temperature cloud diagram,particle velocity vector diagram and turbulent kinetic energy distribution diagram of the cylinder and combustion chamber were obtained.The flow field layout,vortex and tumble flow,oil-gas mixing and combustion heat release process in the cylinder were studied to verify the rationality of the simulation results.The effects of different speeds on the temperature,pressure,turbulent kinetic energy and heat release rate were analyzed.Under the condition of ensuring the reasonable intake combustion layout of diesel engine,the research on valve distribution process is carried out under three different speeds and the principle of optimal intake phase and optimal exhaust phase by setting 10 °CA、20 ° CA、25 ° CA and 30 ° CA four kinds of CA inlet advance angles were used to analyze their effects on the air storage and scavenging volume in the inspiratory phase;Set15 ° CA、20 ° CA、25 ° CA and 30 °CA four kinds of exhaust advance angles of CA are used to analyze their influence on exhaust power loss.The results show that the peak value of air volume in cylinder decreases with the increase of inlet advance angle under different working conditions;At low speed,the scavenging volume is very large.Reducing the intake advance angle will reduce the air volume in the cylinder.At this time,the backflow phenomenon at the end of intake will be aggravated.Increasing the intake advance angle by VVT technology will further increase the scavenging volume;Under high load condition,the internal gas storage can be increased by 1.8% under low speed operation and 3.9% under high speed operation.The exhaust loss is affected by engine speed.The power loss is larger at high speed and smaller at low speed;The exhaust advance angle is increased by 10 ° To 20 ° CA can minimize the exhaust power loss;After VVT technology optimization,the increase of exhaust advance angle will reduce the valve overlap angle,which will reduce the optimization effect of intake advance angle,reduce the scavenging volume,increase the working heat load,and improve the heat dissipation requirements.