Simulation Research For Effects Of Rail Pressure And EGR On Diesel Engine Performance

The internal combustion engine has been experienced a long-term development with improving optimizations on the structure and combustion technologies since its appearance a hundred years ago. Conveniences have been brought to human life, and the emissions of cars are being tightened all over the world as a result of severe problems came with ICE cars, especially of consumption and environment pollutions.With the stricter of emission control regulations and the pursuing of higher thermal efficiency, large numbers of investigation are carrying out on diesel engine structure factors, fuel injection law, the shape of combustion chamber, Exhaust Gas Recirculation and so on. To reduce emissions in diesel engine cylinder, only seeing about the general parameter to research the performance of diesel engine is not enough. Combustion, air flow in cylinder and mix of fuel and air must be investigated thoroughly. In-depth study on the effect of relative factors on the combustion process is imperative under current situation.For finding out a measure that simultaneously reducing the soot and NOx, in this dissertation I use STAR-CD which is a CFD software establishing a numerical simulation platform based upon high-pressure common rail diesel engine CA6DL2-35E3, researching how rail pressure and EGR rate influence the performance of it from microscopic and macroscopic angle. The main work and conclusions are summarized:1. Simulation platform is set upEstablished the model of simulation using STAR-CD software. According to CA6DL2-35E3 diesel geometric parameters to draw geometric figure through Pro/E code, then part of combustion bowl was input to Pro-am to divide static meshes, and the other was input to ES-ICE to divide moving mesh, moreover they was combined to the calculated meshes.Set up initial and boundary conditions, then choose fit models and arithmetic in Pro-star, caculated it in STAR, go along post processing, at last complete the validation process. Validation results suggest all models and arithmetic are right. They are fit for combustion numerical simulation analysis. 2. The combustion process of prototype engine was simulated and investigated Analyzed operation simulation of prototype engine operation at speed of 1650r/min and load of 50% and single injection MAP, two sectional figures of micro-field are obtained which displayed the transformation course of in-cylinder flow, spray, and combustion; to catch the focus spray area and get oil drop movement on swirl orientation through the cone spray section formed from eight spray center lines. A longitudinal section cut by a couple spray center lines indicated the movement along with the combustion chamber. The method attempts to show more information with fewer figures.NO start to produce a great lot at earlier period of combustion, once appear, they will not reduce almost. We should control the temperature of combustion; We should attach importance to soot produce at earlier period, so we need to raise mix speed and the level of uniformity of fuel and air. We also need attach importance to soot being oxidated later period, so we should enhance the mix of fuel and air, and maintain the oxidation temperature.3. Both rail pressure and EGR simulationAt 1650r/min, 50% load, single injection, the influence of rail pressure (including 100MPa, 120MPa, 140MPa) to high-pressure common rail diesel engine performance were simulated. Through the change injection rule, namely increasing the injection speed, reducing injection duration to realize simulation for raising rail pressure; And at every rail pressure, I did simulation by changing EGR rate (including 0%,5%,10%,20%,30%). Enhance rail pressure through changing nozzle diameter finding whether it is similar to Plan One or not. The conclusions are following:i. Rail pressure increases, heat release rate arises, combustion center of gravity comes ahead, indicated thermal efficiency augments, but pressure arise rate augments.ii. The microscopic statistical result showed: The rail presses enhances, the fuel infuse to the flow field perturbation is bigger, SMD obviously reduces, it explained that the atomization quality improves,fuel evaporation rate increase more quickly, the quantity of premixed aggrandizes, through the related statistics of equivalence ratio also prove this point.iii. The rail pressure increases, in the combustion the preliminary temperature is higher, the NO production quantity are more; Enhancing the rail pressure make it possible to strengthen the fuel and air mixing, the turbulent motion becomes even more fierce, it causes the mixture be even more thin and uniform, so soot reduces. Use the procedure statisticing cell volume of intersection with equivalence ratio and the high temperature area, Its change tendency tally NO and soot production quantity, the production time accurately.iv. For achieving the goal of raising the economical value and redusing the soot, enhancing the rail pressure is an important technological measure. But only enhancing the rail pressure NOx production will excessively high, and combustion crudely will appear.v. The conclusion for enhancing the rail pressure through changing nozzle diameter simulation is similar to Plan One.vi. In view of diesel engine's emissions aspect, the EGR technology with enhancing rail pressure is supplementary. With enhanceing the rail pressure and the EGR technology may compromise solves NO and soot emissions question.4. Multi-Injection simulationAt 1650r/min, 50% load, Multi-injection, the influence of EGR to high-pressure common rail diesel engine performance were simulated. The conclusions are following:i. Regarding different EGR rate, the injection parameters should be optimized. The post injection interval has little effect to indicated thermal efficiency. The overall evaluation soot emissions and the indicated thermal efficiency, 5.5°CA post injection interval is more ideal.ii. The injection start angle is ahead of time suitably, it is advantageous to the inflation work; the cylinder pressure elevates obviously; the heat release center of gravity moves ahead, the indicated thermal efficiency obviously increases.iii. With changing multi-injection parameters and the EGR technology may compromise solves NO and soot emissions question.