【作者】 朱昌吉；

【导师】 刘忠长；

【作者基本信息】 吉林大学 ， 动力机械及工程， 2005， 博士

【摘要】 在YC4112ZLQ 柴油机上设计了转阀式EGR系统。在EGR的实现方式上,采用由涡轮机前到中冷器后的高压回路方案,设计了基于80C196KC 单片机控制的软硬件。在全工况范围内对YC4112ZLQ 柴油机进行了EGR 的试验研究。得出了EGR 对该柴油机排放性能和经济性能的影响规律。制取了全工况的最佳EGR率脉谱,进行了最佳EGR率下的13 工况排放测试,结果表明:13 工况NOx降低18.3%,HC 增加2.6%, CO 增加5.8%,微粒排放没有变化, 13 工况加权比油耗增加了1.4%。本研究提出了测量EGR 率的新方法“热线温度法”,进行了测试电路的设计及标定,对瞬态EGR率的测量方法进行了研究。建立了瞬态数据采集系统,在此基础上对有EGR时柴油机柴油机瞬态工况特性、缸内燃烧过程进行了研究。对恒转速变转矩的瞬态工况研究表明:瞬态EGR 率存在响应超调现象,由于瞬态EGR 率超调使燃烧过程拖后,是消光烟度、CO 排放急剧增加的一个重要因素。通过对电控EGR系统柴油机的过渡工况排放特性研究,为过渡工况EGR率的优化提供了基础数据,提出了瞬态工况EGR 的控制策略。更多还原

【Abstract】 Higher compression ratio, lean mixture combustion, lower fuel consumption and higher thermal efficiency make the direct injection diesel engine preferred to commercial vehicle. Nowadays, heavy-medium duty commercial vehicles have been basically dieselized in developed countries. With the development of automobile industry, automobile tenure increases deeply. With people’s increased caring about automobile exhaust pollution problem, automobile exhaust regulations are stricter than before in America, Japan, and Europe and so on. Automobile exhaust regulations also have been issued in China, emphatically on NOx and particulate limits to diesel engines. During the last ten years, automobile diesel engine exhaust control technology developed rapidly, such as turbocharging and intercooling, high pressure injection, exhaust gas recirculation, electronically fuel injection, lower lube consumption, and after-treatment and so on. Automobile exhaust regulation can be met by combination of several different exhaust control technologies during different periods. There are two ways to decrease NOx emissions, one is to restrain its production, and the other is to control its emission by after-treatment. Production rate of NOx in the combustion chamber of diesel engine is mainly affected by combustion temperature and oxygen concentration. In other words, to control NOx production some strategies must be adopted to decrease combustion temperature and oxygen concentration. Decreasing combustion temperature can be realized by retarded suspend fuel injection, cooling air intake and so on. Furthermore, controlling fuel injection rate, multi-injection, lower swirl ratio and so on can decrease NOx emission, too. Technologies listed above have been adopted to meet Europe Ⅱexhaust regulation, and they have little potential to meet Europe Ⅲexhaust regulation, and only adopting above-mentioned EGR technology NOx emission can be decreased. EGR technology is an efficiency way to decease NOx. EGR technology is by recirculating a certain quantity of exhaust gas to air intake system, which leads to add some inert gases in the air intake increase. The inert gases do not take part in combustion, and can absorb more heat for its higher specific heat, content which lead to decrease combustion temperature. At the same time, because of the importing of exhaust gases, oxygen concentration in the in-cylinder charge decreases and restraines the production of NOx. YC4112ZLQ turbocharged intercooled diesel engine was employed as a test engine. A high pressure circulate project between the upstream of turbocharger to the downstream of intercooler was designed to realize EGR. Air intake throttle EGR system designed in this study was controlled by step motor; exhaust throttle rotating valve EGR system designed in this study was controlled by pneumatic cylinders. Software and hardware based on 80C196KC SCM were designed, which were controlled by accelerator position and engine rotation. During the engine running process, ECU checks loading signal and rotation signal of the engine continuously, and consulting step motor and working cylinder map and gets corresponding control parameters, and drivies executor through circuit to ensure pre-cabibrated EGR rate. 1 Investigation of EGR characteristics under steady operating conditions The effect of different EGR rates on engine emissions and performance were investigated under whole steady operating conditions. The results show that: 1 With the increasing of EGR rate, NOx emissions decrease under all static operating conditions, especially more obviously under the increasing of load conditions. EGR leads smoke emission rise, and the increasing extents under large load conditions are bigger than that under lower load conditions. EGR leads CO emissions rise, and the increasing extents rise with the increasing of load and EGR rate. EGR has little effect on HC emissions relatively. 2 NOx emissions rise deeply with the increasing of EGR temperature, so hot EGR go against control its emissions. 3 Under low load operating conditions, EGR have a little effect on engine power performance, but with the increasing of load EGR have more bad effect on engine power performance. Under low load operating conditions, EGR don’t have obviously effect on fuel consumption, and with the increasing of load brake specific fuel consumption have a little rise under high EGR rate conditions. The reason of those is EGR decrease air/fuel ratio under large operating conditions, which lead to combustion doesn’t complete. 4 EGR rates may realize maximum 45% by rotating valve EGR system, and which provide new way to realize HCCI combustion mode with large EGR rate. 5 With the increasing of EGR rate in the rotating valve EGR system under large EGR rate conditions, the pressure of after cooled, before turbo charger and exhaust pressure of the fourth cylinder rise, which has obvious different with air-intake throttle EGR system. The EGR uniformity ability of the rotatingvalve EGR system is worse than that of air-intake throttle EGR system under low load operating conditions. Based on static test data, EGR rates under all operating conditions were optimized. The principle of optimization is keeping particulate emissions don’t have big change to decrease NOx emissions. Under low load area, EGR rates have little effect on CO, HC emissions, so the particulate and NOx as the effect factor to EGR rate. Under low load operating conditions, for the high air/fuel ratio, the large EGR rate has a little effect on particulate emissions, so large EGR rate should be adopted. Under large load operating conditions, with the increasing of EGR rate particulate emissions rise, and rapid increasing inflexion exist, so EGR rate selected should be less than the inflexion. Considering the change of atmosphere temperature and pressure, a relevant little EGR rate should be selected. Considering exhaust gases temperature was lower under idle operating conditions, to avoid producing condensation water, which will erode diesel engine, so EGR shouldn’t be adopted. Considering of air/fuel ratio is lower under full load conditions, EGR shouldn’t be adopted. Under speed less than 1300r/min operating conditions, NOx emissions don’t the main problem, so EGR shouldn’t be adopted. Based on EGR rates optimization principle, EGR rates under all operating conditions were optimized, and the best EGR rates map was obtained. With the optimized EGR map, ETC R49 test results show that: 1 NOx emissions decrease 19.9%; HC emissions increase 12.2%; CO emissions increase 6.8%; particulate emissions has no change and add authority brake specific fuel consumption decrease. 2 With the same optimized EGR map and increasing advance angle of fuel supply, NOx emissions rise deeply; HC emissions decrease; CO emissions rise and add authority brake specific fuel consumption decrease. With the increasing of advance angle of fuel supply, particulate emissions have no change, but NOx emissions rise deeply, so to control NOx emissions advance angle of fuel supply shouldn’t be rise. With the same electronically controlled system’s map, changing advance angle of fuel supply have no effect on EGR rates. 2 Investigation of EGR characteristics under transient operating conditions Transient operating conditions are important conditions for the vehicle engine performance, in which the combustion process is dominant. In the past years, there are many investigations on EGR characteristics under static operating conditions, but little under transient operating conditions. There are many differences duringcombustion process between under transient operating conditions and under static operating conditions of turbo-charged diesel engine. Benson et al. has investigated systemically on those from 1970. For the difference of tested engine and operating conditions, some main factors such as combustion efficiency and engine running factors had been changed. EGR makes some conclusions got before don’t fit modern engines anymore, so it is important to investigation from the beginning. In order to investigate engine performance with EGR under transient operating conditions, transient testing system was built on the common eddy current dynamometer test-bed. Transient testing system has simultaneously measured engine performances parameters such as combustion process, torque, fuel consumption, and inlet air flow rate and smoke opacity. In order to investigate EGR characteristics under transient operating conditions, EGR rate must be simultaneously measured. The tested results show that there exists delay when measuring the EGR rate under transient operating conditions. Hot wire measuring temperature method was used to measure EGR rate in this investigation. Testing circulate was designed and demarcated in this investigation. The tested results show that hot wire measuring temperature method can save 2.80 second relative to CO2 track method, and have the same respond time with air intake, so which can meet test require. EGR responding characters, emission performance, combustion process and so on were investigated on the rotating valve EGR system under transient operating with EGR conditions. Engine running parameter measurements under transient operating with EGR conditions showed that: 1 EGR rate exist response-overshoot phenomenon under constant speed increasing torque transient operating conditions. EGR rate response exceeding is one of main factors, which leads to increase smoke opacity significantly under heavy-and-middle-load operating conditions. There exits difference between EGR rate control strategy under transient operating conditions and static operating conditions, so EGR should be cancel under transient operating conditions. Air-intake exits response-exceeding phenomenon under constant speed increasing torque transient operating conditions, which is another main factor leading to smoke opacity increasing deeply under large and middle load operating conditions. 2 Air-intake, pressure after intercooler and EGR rate responding performance is better under constant torque increasing speed transient operating conditions. But fuel supply exits response-exceeding phenomenon, so smoke opacity increased under high speed area. Under transient operating with EGR conditions, exhaust gases emission showed that:1 The peaks of CO, HC emissions increase with the increasing of torque increasing rate under constant torque increasing speed operating conditions. NOx emissions had no obvious peak with the increasing of torque increasing rate, but increasing of NOx emissions had a delay relative to the increasing of torque increasing rate. 2 The peaks of CO, HC emissions increase with the increasing of speed increasing rate under constant-speed-increasing-torque operating conditions. NOx emissions had no obvious change with the increasing of speed increasing rate, and just decreasing with the time. Under transient operating with EGR conditions, combustion process showed that: 1 Because of the EGR rate overshoot, combustion process delayed, the crank angle relative to the maximum pressure rise rate delayed and the maximum combustion pressure decreased with the increasing of torque rise rate under constant-speed-increasing-torque operating conditions. 2 The crank angle relative to the maximum combustion pressure increased and the crank angle relative to the maximum pressure rise rate increased under high speed rise rate and constant-torque-increasing-speed operating conditions. Under transient operating with EGR conditions, EGR jump process showed that: 1 Air intake respond relative to EGR rate had no obviously delay during the EGR jump process, but the respond of torque, pressure after intercooler and pressure before turbocharger were slower relative to EGR rate. 2 The changing rate of exhaust gases emissions was slow during the EGR jump process. The changing rate of exhaust gases emissions was quicker during decreasing EGR rate process than increasing EGR rate process. 3 The maximum combustion pressure decreased slowly, and the respond time closed to torque and pressure after intercooler during jump process. The crank angle of the maximum combustion pressure advanced, and combustion process delayed during jump process. For the delay of the turbocharger, combustion pressure was increasing gradually during decreasing EGR rate process. The crank angle of the maximum pressure rise rate quickly reached the primary position without EGR. Cylinder pressure had a obviously effect on combustion start point, and the combustion start point will advance with the increasing of cylinder pressure. 4 The responsed time of air-intake throttle EGR system is longer than that of rotating valve EGR system. The rotating speed of step motor is slower, which restricts the respond time of air-intake throttle EGR system. 3 The main innovation points of this study:1 Rotating valve EGR system was designed, and which realized controlled EGR rate on all engine operating conditions. According to EGR rate, one or two rotating valve was fixed on engine, which resolved the difficulty of higher EGR rate on turbocharged and intercooled engine. By using cylinder drived EGR valve, the response time was improved, which can switch on/off EGR valve in one or two circle. Rotating valve is a feasible control method to investigate transient operationg condtions. 2 Hot wire measuring temperature method was designed to measure EGR rate in this study, which is a new method to investigate transient operating conditions. 3 EGR rate exist response-exceeding phenomenon under constant speed increasing torque transient operating conditions. EGR rate response-exceeding is one of main factors, which lead to smoke opacity increasing deeply under large and middle load operating conditions. The results show that combustion process exist delay phenomenon. 4 By investigating the effect of different EGR rate on transient combustion process, basical data were getted and a new EGR rate control strategy was designed.更多还原