Study On EGR For A Turbocharged And Intercooled Heavy-duty Diesel Engine

With the development of automobile technologies and the enlarge- ment of infrastructure, the heavy duty trucks and engineering machine becomes more and more popular. As heart of these vehicles the heavy duty diesel engine will take an important role and be prosper in the future several years. Unfortunately, with the dramatic increasing of the engine amount it becomes the main pollution source in the urban and harmful to people's health. In order to protect ours healt and improve the quality of living environmental, the stricter and stricter emission legislations have been constituted. In order to meet the demand of emission regulations, more and more novel technologies have been developed and applied in .manufacture. Because the PM and NOx emissions are the main pollutants in diesel engines, the research focus concentrates to reducing NOx an PM emission control.The First Auto Works Wuxi diesel corporation have recently produced CA6DL series diesel engines, which adopt high pressure common rail injection system, turbo charge together with inter-cooled technique. This engine has met EuropeⅢemission legislation and been potential to meet EuropeⅣlegislation. The effects of EGR rates gained by external EGR system on the emission behavior and the other performance of CA6DL have been studied and detailed discussed in this dissertation. The EGR rates control MAP has been optimized based on the objective of meeting the NOx emission limitation in Europe IV legislation. The main contains and conclusions are as following.Low-pressure route EGR system designing. The exhaust gas recirculates from high pressure turbine import manifold to low pressure compressor import manifold to over come the obstacle of negative pressure drop inherited in conventional high-pressure route EGR system. Aconventional ball-valve coupled with a electronic controlled reciprocating has been adopted to change the EGR rate within 2 percent resolution. An EGR inter-cooler has been adopted to stabilize the temperature of recirculated exhaust gas varying within the range from 120℃to 160℃.Effects of EGR rates on the performance research .According to the European 13-mode test cycle 1330 r/min, 1650 r/min and 1965 r/min engine speeds are selected to research. The fuel supply increases from 0 percent to 100 percent by the step of 25 percent in order to gain different power output operations. Then, the fuel supply and engine speed are fixed and change the EGR rates so as to reveal the effects of EGR rates on the performance.Test results indicate that with the increase of EGR rate the NOx emission monotonous decreases and the smoke opacity monotonous increases, while the brake fuel specification will meet the minimal value under certain EGR rate. This means that the NOx emission can be controlled to meet Europe IV legislation by adopting the optimized control MAP based on certain principle. Generally, the EGR rates control principle can be described as following. Because the unsteady combustion process lower EGR rates are required under low load operations. Because of higher NOx emission the highest EGR rates are demanded under medium load operations. High EGR rate will decrease torque output under high load operations. So, lowest EGR rates are expected.EGR rate control MAP calibration. Based on the adequate testing results gained from 6 different speed mutipled 8 loads per-speed operations testing and taken the principle mentioned above in to consideration the minimal be and minimal NOx emission EGR control MAP have been established. Conclusions can be drawn as following by analyzing the single objective based MAP.1. The EGR technique can obviously lower diesel engine NOx emissions. The EGR rate was controlled below 12% in the whole work conditions. Acquiring an ESC13 work condition emissions is:The NOx emissions is 3.095 g/kW.h, the CO emissions is 0.795 g/kW.h, the HC is 0.146 g/kW.h, and the exhaust emissions reached to the request of laws in EuropeⅣcompletely.2. After excellent, torque value have a little descend, but not largely; the oil supply is 219.9 g/kW.h, the same as original .3. The smoke opacity degree value control at lower 10% .3. The smoke opacity degree value was controlled in 10% .According to excellent principle, 13 work conditions experiment was carried on , result indicates: under the EGR doesn't influence economy, the exhaust emissions come to EuropeⅣemission standard completely.EGR rate control MAP optimizing. The flow and heat transfer of recirculated exhaust gas have been calculated out based on simplified model. The heat transfer and flow are great under C75 and C100 operations, but the NOx emission under the two operations is not so vast and is not necessary for much EGR rate. Therefore, in order to release the pressure to the cooling system of diesel engine resulted by EGR system the EGR control MAP should be optimized. The engine performance and heat transfer of EGR system have been researched after the EGR rate of C75 and C100 decreased respectively from 11.9 and 7.9 percent to 5 and 4 percent. Results are shown as following.1. The above two work conditions'EGR rates were decresed later , torque value has a certain increase than correction before. The oil consumption is 219.7 g/kW.h.1. The torque restores a little and the BSFC decreases from 219.9 g/kW.h to 219.7 g/kW.h compared with the former control MAP.2. The BS NOx emission is 3.446 g/kW.h, which is still lower than the limitation of EuropeⅣlegislation. The BS CO, BS HC and smoke opacity are kept the same to the former MAP.3. The quantity of EGR system transferring to cooling system decreases dramatically. The heat transferred to cooling system of C75 and C100 operation respectively decreases from 48.34 kW and 34.81kW to25.2 kW and 18.7 kW.4. Therefore, in order to gain an optimized control MAP the heat transfer quantity from EGR system to cooling system must be taken into consideration.