Simulation Research On Cylinder-to-Cylinder Distribution Of EGR For Diesel Engine

Nowadays, people have shown solicitude for diesel engine with more and more serious environmental pressure and energy crisis. Due to its high compression ratio, lower rate of fuel consumption and greater power, diesel engine has the potential for significant improvement in fuel economy, power and durability performance, and has an increasingly wide range of applications in high-power loading vehicles, large and medium-size buses and special vehicles. At the same time, the world's production of diesel saloon car was increasing year by year.EGR technology, namely, Exhaust Gas Recirculation technology. It is an exhaust purification device in allusion to harmful gas (NOx). Part of exhaust gas is lie back the intake system by the device and then mixes with fresh air to increase the heat capacity of mixture, reduce the maximum combustion temperature, thereby inhibit generation of NOx. EGR technology has been widely used as a mature technology in the gasoline vehicles. Started from the 70's, EGR technology in foreign was employed as one mature enabler in the diesel engine. A large number of studies have shown that it is also the same with diesel engines.Although diesel engine with EGR system has multiple advantages, it also faces some issues to be resolved.For multi-cylinder engine with EGR system, sometimes the problem of cylinder-to-cylinder EGR maldistribution was very serious. This maldistribution could possibly result in a situation where there is excessive NOx emissions from cylinders getting too little EGR, along with excessive smoke emissions from those cylinders that get too much EGR. Improved cylinder-to-cylinder distribution of EGR in a diesel engine has been identified as one enabler to help reach more stringent emission standards.Specifically, the work presented in this paper examines the cylinder-to-cylinder EGR maldistribution of early design model and its late production four-cylinder diesel engine to compare the cylinder EGR distribution determined in the early design with that from late production. Besides, one of the modified manifolds, based on better alternative between early design and late production, provided a useful improvement over the original design that meets Euro IV emission standards. CFD simulation and analysis were required to fully understand the magnitude and cause of the EGR maldistribution. The use of analysis tools has become increasingly useful in solving such complex flow problem. A combination of UG and CATIA software is required to finish early aided design of intake manifolds. Pouring of sillicagel for its production intake manifolds of diesel engine in order to get the 3D surface cloud data. Deal with the 3D surface cloud data with Gemagic. Export the surface model of them in STL format, mesh generation with AVL FIRE and calculation with FLUENT. At the same time, the boundary datas on the boundaries of a 3D-CFD grid under certain conditions are received by 1D-CFD programm(GT-POWER).In this paper, the cylinder-to-cylinder maldistribution of EGR in early design model and its production intake manifolds was respectively mapped over a range of work-condition's for which there was EGR flow for the diesel engine with 147Nm, EGR ratio of 4.22% at 2366 rev/min, 92 Nm, EGR ratio of 7.62% at 1519 rev/min and 72 Nm, EGR ratio of 13.61% at 2366 rev/min. The most revealing presentation of the 3D-CFD result was an animation of the EGR movement within the intake plenum during the intake events. The EGR motion was visualized using surface concentration contours. From the pictures they were clear that to a large extent the EGR flow in the intake manifold could be describes as a periodic slug flow with slugs of EGR being drawn out of the EGR passage and pulled to each manifold during their respective induction event.For model I, in the same speed, the mass flow rate in the inlet was unchanged. With EGR ratio's increasing, the mass flow rate in EGR-entrance was increscent. Manifolds No. 2, 3 & 4 during their respective induction indicates higher EGR concentrations, but manifold No.1 has a little change. With speed reducing and EGR ratio increasing, EGR and air are not well mixed within the manifold No.1 & 3 throughout the cycle. However, the EGR concentrations within the manifold No.2 & 4 are closer to EGR ratio than manifold No.1 & 3 in the work condition. Especially in the manifold No.4, cylinder maldistribution decreases from 77.53% to 6.07% as work condition has changed.For model II, in the same speed, the mass flow rate in the inlet was also unchanged. With EGR ratio's increasing, the mass flow rate in EGR-entrance was increscent. Manifolds No. 4 indicates higher EGR concentrations, but manifold No.1, 2 & 3 have a little change during their respective induction. With speed reducing and EGR ratio increasing, the EGR concentrations within the manifold No.4 was greater than the first condition, but manifold No.1 has a little change.Although the model I and model II manifolda improved EGR maldistribution and resulted in lower PM-NOx emissions, there all appeared to be room for improvement. As can be seen in Table 3-1, 3-2 & 3-3, model I was a better choice as the original model.Using the CAD data for the new manifold designs, the first revision, modifed program A, showed potential for a little improvement in EGR distribution. In the design, the angle between the axises of the plenum and EGR line. It was attractive because it involved only minor changes to the intake system and EGR line. The second revision, modified program B, has the location of the EGR outlet level with the surface of the air inlet. Merely advancing the outlet closer to the inlet of intake tube was suggested as a means to enhance mixing and distribution of EGR.The 3D-CFD simulation tool, FLUENT, compute the flow field based on three-dimensional Reynolds-averaged Navier-Stokes equations, giving a spatially resolved, realistic image of the processes inside an intake manifold of the diesel engine. Concluded that the changes of the location of EGR-outlet and angle between two axises all can make an improvement for cylinder-to-cylinder distribution of EGR, especially the second revision. Due to time constraints, related work has yet to be refined in this paper.