| With the increase of diesel engines in the world, the pollution of particulate emissions from diesel engines, which are harmful to the atmosphere environment and human health, is getting more and more serious. Therefore, it has a great practical significance to study the formation mechanism of the modern diesel particulates and then work out the control techniques for them. In this paper, a total cylinder sampling system was developed on the model CY6102 DI diesel engine with some advanced functions, such as simulating intercooling, exhaust gas recirculation (EGR), high pressure common rail (CR) and so on. The physicochemical characteristics of in-cylinder particulates were investigated using this sampling system, and three-dimensional numerical simulation was adopted to shed light on the soot formation histories. The main contents of the dissertation are as follows:1. The total cylinder dumpling equipment was developed, which mainly contained dumping mechanism, valves deactivator and sampling dilution system. During the development, the emphases were given on the design of cutter assembly, dumping port in the engine head and rebuilding of rocker arm shaft.2. Based on the PC resources of hardware and software, the electronic control unit (ECU) was designed using the interruption technology. The closed loop control of common rail pressure was accomplished by fuzzy control strategy. This control system could not only assure the injection duration and the timing of fuel injection, sample dumping, valve closed and dilution to be controlled accurately, but also make injection pressure controlled intelligently. And the control for all the parameters was flexible and reliable.3. The number and size distributions of in-cylinder particulate were investigated by the Electrical Low Pressure Impactor (ELPI) detection method. The experimental results indicated that the particulate number concentration showed unimodal distribution with the crank angle (°CA), and the peak point lied at about 14~18°CA ATDC. The particulate was oxidized by above 70% in the late combustion phase. During the combustion process, the particulate number size distribution was lognormal analogously in form with the particulate diameter, and the maximum value was lied at about 100~200nm aerodynamics diameter.4. The investigation on the morphology, microstructure and size distribution of primary carbon particle in-cylinder particulates were conducted on a field emission gun transmission electron microscopy (FEG TEM), and the results were analyzed by the image technology. The main study results obtained are as followed: The in-cylinder particulates present two morphologies: One is representative particulate which formed through agglomeration of small sphere-like primary carbon particles during combustion process. The other is amorphous particulate which contained abundant metal elements mainly originating from lubricant and nonmetal element, and these particulate had absolute structure and existed cross the whole combustion process. The representative particles were aggregated in the form of fractal-like geometry. The fractal dimension was in a range of 1.2~1.74, and it declined at the early diffusive combustion period.The primary particles translated to graphite gradually and formed crystallitic onion-shell carbon finally during the combustion process of diesel engine. The crystal plane spacing composed of graphite crystallites was decreased from 0.39nm to 0.36nm, and the crystal layer number was increased with the burning process.It was also found that the size distribution of primary particles was Gauss distribution and the maximum value was lied at about 15~30nm particle diameter. The average diameter was measured in a range of 19.7~29.7nm, and the peak value present at 12~15°CA ATDC.5. The soluble organic fraction (SOF) was extracted from the particulates, and its mass in particulates was measured. Meanwhile, the polycyclic aromatic hydrocarbons (PAHs) in SOF were analyzed by gas chromatography-mass spectrometry (GC-MS). The analytical results showed that the SOF mass changed much with the crank angle. In particular, at the initial combustion stage, the proportion could be over 80%, and it decreased in the combustion process, the minimum value was about 20%. The distribution curve of the total PAH mass with the sampling crank angle was in accord with that of the dry soot mass concentration. It was also found that whichever of fuel injection pressure or the engine speed increased could result in the loss of PAH mass.6. A numerical simulation model was established by Star-CD software, and comparison was carried out between the simulation calculation and the data obtained from the total cylinder sampling experiments. The result showed that the simulation calculation of soot formation histories was consistent with the experiment data. |
PDF Full Text Request