| After the development for more than a century, the internal combustion engine has been the most efficient and reliable power machine for vehicles. Powered vehicles enhance the human mobility and improve the life quality, but the pollutants exhausted from the vehicle engines constitute major portion of air pollution in urban areas, do serious harm to the health of urban people. With going deep into study of the internal combustion engine exhaust emissions, it is known that the exhaust emissions and operation noise at transient operating conditions of automotive diesel engines are more serious than those at steady operating conditions. Therefore, reducing the transient emissions from the vehicle engines is important to ameliorate the air pollution and improve the living condition of urban habitants. In fact, in the developed countries and regions, several transient test cycles for the engine and vehicle emission approval have been promulgated and implemented, for example, by Environment protection Agency, USA, and EU. It is obvious that the emission behaviour of automotive diesel engines under the transient operating conditions has been an important research topic.In this thesis a measure and control system at transient conditions of diesel engine was integrated on the basis of a conventional eddy current dynamometer type CW260, taking a MCS51 single chip processor as the controller and a step motor and an accelerator as the actuator. By means of the developed system it is possible to realize repeatedly the single variable transient operation of the diesel engine, such as constant speed and increasing torque (CSIT) condition and constant torque and increasing speed (CTIS) condition. After refitting of the dynameter, the smoke opacimeter, the air flowmeter, and the fuel flowmeter, the Yanhua PCL-818 A/D data acquisition board was used with its data acquisition strategy software to acquire data from these refitted measure apparatuses, including the engine torque, air flow, fuel consumption, and exhaust opacity, and to store these parameters into the computer. The data acquisition frequency is 20 Hz and can satisfy the requirements of transient test cycles. The developed system provides a technical platform for transient performance research of diesel engines. Because the transient operation conditions with increasing fuel supply are more problematic than those with decreasing fuel supply, the research was focused on CSIT and CTIS conditions.The supercharging has been the effective means to enhance the power performance, reduce fuel consumption and improve the exhaust emission behaviour of the automotive diesel engine. But the turbocharged diesel engine usually has disadvantages such as inadequate torque under low speed, bad engine acceleration and smoking and accelerating conditions. In order to overcome these disadvantages, some measures have been adopted, such as variable nozzle geometry turbine charging system.In the thesis the effects of variable nozzle turbine turbocharger (VNT) on the steady and transient performances of an automotive diesel engine CA6DE1-21K were investigated experimentally in detail by means of a type GT35V VNT turbocharger, and their improvements were suggested. The results can be summarised as follows:At the low speed and high load conditions decreasing nozzle opening of VNT leads to improve the fuel economy of the engine, but when control rod displacement is more than 9mm at the low speed and medium to low load conditions, the fuel economy goes inversely. The effect of nozzle opening on fuel economy is little at other conditions.At the low speed and high load conditions, decreasing the nozzle opening of VNT decreases the brake specific emission of CO. At the low speed and medium load conditions, if control rod displacement is less than 9mm, it has little effect on the specific CO emission, and if control rod displacement is more than 9mm,its increase leads to rapid increase of the specific CO emission. At other operating conditions, the nozzle opening of VNT has no evident ef... |
PDF Full Text Request