The Influence Of The Performance And Emission On The HD Diesel Engine With VGT And EGR System

Under the pressure of oil crisis and increasingly strict emission regulations, the direction of diesel engine development is supposed to be higher heat efficiency, greater power density and lower emission. Thanks to the positive effects of decreasing the pollution and noise, and boosting the power density, Turbocharging has been one of the most basic features among modern diesel engines. But there are still problems remained in the matching between turbocharger and engine, such as torque deficiency at low speed, bad economy performance in part loads, dynamical slow response and etc. The variable geometry turbine (VGT) is an ideal solution to such problems so that it attracts great attention worldwide. EGR system equipped with VGT not only holds VGT with definite performances, it also can work out the converse pressure problem effectively between inlet manifold and outlet manifold, expand the EGR scope with low pump loss and low additional cost. Therefore, as one of the most important technologies of Euro-Ⅳstandard emission, the EGR/VGT matching technology, which can decrease the NOx emission in effect, and ultimately keep the engine with excellent power and economy performance, is hopefully being applied to the future diesel engine products to satisfy the increasingly strict emission regulations.This research which utilizes the CA6DL2-35E3 common-rail diesel engine with the turbocharger and intercool system as the sample subject, has designed the experiment control system and cooler parameters in engine cooling system to meet the experiment needs. By virtue of adjusting VVP45.40-25 temperature control proportion valve supplied by Siemens Company, temperature fluctuation is realized within 3°C, which can be considered as invariable temperature control.HOLSET400V VGT control system is designed, including calibrating the VGT speed by XSM Speed Measure Apparatus; measuring 5 pressure (inc. inlet manifold pressure, VGT control pressure, etc.) according to time-sharing method by BP800 pressure transducer; making rod displacement indirectly reflect the size of turbine section, setting up the linearity relation between rod displacement and VGT control pressure to obtain the information of turbine section.This research also determines to adopt external high-pressure-loop EGR as ERG method; the hand-controlled EGR valve equipment supplied by Mitsubishi Company can be used for 2 EGR valve controlling.According to the results of matching experiment between VGT and engine under Euro-ESC13 test cycle, the influence of the VGT section on the engine performance is analyzed and summarized. Under B speed for example within 600 kPa VGT control pressure, the maximum decreasing amplitude of specific CO emission is up to 82.2%; the maximum increasing amplitude of specific HC and NOx emission respectively are 36.2% and 36.6%; one characteristic is pointed out that be transformation curve with VGT control pressure exists a peak value, which means the best economy performance. And by virtue of the variation of engine performance parameters under the same load efficiency, the influence of VGT control on the engine performance with different speed is summarized too: with the VGT control pressure increasing under the same load efficiency, the be increasing amplitude exists a peak with the different speed, especially the higher the speed is, the smaller the VGT control pressure is while the inflexion appears; the decreasing amplitude of specific CO emission goes up more evidently under lower speed operation condition; and the increasing amplitude of specific NOx and HC emission raises directly under higher speed except parts of operation conditions.Furthermore, combining realized VGT control pressure scope with the result of single-object engine performance optimization, a conclusion is made that this VGT system has a potential to optimize the be and HC emission, but the VGT section can not be adjusted widely all over the operation conditions.According to the results of matching experiment between VGT and EGR on diesel engine under Euro-ESC13 test cycle, the influence of the VGT section and EGR valve section on the engine performance is analyzed and summarized, and the possibility of optimizing the be, HC and NOx emission with EGR&VGT matching is discussed, and the best EGR efficiency about 25% is obtained, because of the VGT condition limits, EGR efficiency also can be reached about 15% under some loads. In addition, comparing with the results of the matching experiment with low pressure EGR valve on this sample engine, VGT and EGR matching strategy has less influence on the other engine parameters while decreasing the NOx emission. And single-object optimization results indicate VGT and EGR matching strategy has a great potential to synthetically optimize the be, HC and NOx emission, but this VGT system is not so suitable to the sample engine that restricting this potential to be realized because of narrow turbine section and only adjusting under parts of operation conditions.