| Direct injection technology can improve transient response and fuel economy. Compared with the particle amount of conventional port injection gasoline engine, that of direct injection gasoline engine has increased. With the increasingly strict emission regulations, the regulations of gasoline engine exhaust emission has changed several times, and the mass and number of particulate is gradually limited. Therefore, the control technology of GDI engine for particulate has become the focus. So it’s of importance for improving the GDI engine emission that what the factors for particle generation are and how they changed the particles with variation of the time and space.Therefore, this article, with the help of the project of "Optical Research on Particulate Matter Generation Process Under GDI Engine Transient Conditions", set up a visual constant volume combustion platform to simulate in-cylinder environment at injection timing. By this platform, the transient particle generation process can be studied. In this paper, the main conclusions are as follows:1. Visualization platform was built and optical measurement methods were designed: this article completed the constant volume combustion visualization platform design. It can simulate in-cylinder high temperature and high pressure environment by the use of acetylene combustion. The platform contained a constant volume combustion cylinder, fuel supply system, intake and exhaust systems, optical measurement systems. To achieve accurate measurement for particle generation process, the article built optical measure system of forward illumination light extinction based on light extinction method; At the same time, transient combustion process can be monitored by natural flame luminosity.2. In-cylinder particle transient generation process at typical condition was studied and the main factors for particle generation was determined. The test showed that during combustion process, there was a high consistency between natural flame luminosity and instantaneous particle generation mass in terms of space or time. The particle focused on two areas. One is the flame front, where the drastic fuel pyrolysis reaction happens. The other is the central region where the flame front went through. The particles at this area experienced a relatively long process of oxidation. Excess air ratio and ambient temperature can affect the fuel pyrolysis reaction and particulate oxidation process, so they are the main factors for particle generation.3. The study of the different excess air ratio impact on particle generation process was conducted and a clear influence of different excess air ratio for particles with time and space distribution was known. When excess air ratio decreased, particle mass increased for every moment, mainly in the flame front and the cylinder center, and particle mass peak appears earlier. This is because the excess air ratio changes the pyrolysis reaction and particulate oxidation rate, changing transient particulate generation mass. And the study have shown that the wall film makes instantaneous generation particle concentrations near cylinder wall increase. Therefore rational and effective air movement near the cylinder wall can reduce occurrence of wall film. It is a method to reduce instantaneous particle generation mass.4. The effects of different ambient temperature on the generation process and combustion process was conducted : This article used two excess air ratio 0.8 and 1.0 as the basic conditions, and the initial ambient temperature was set at 458 K, 493 K, 528 K. When the standard mixture(λ=1.0), with the ambient temperature up, the instantaneous particle generation mass decreased, especially flame front and the center of the cylinder and particle generation duration was shortened. When the rich mixture(λ=0.8), the ambient temperature has little effect on particle generation, and particle concentration and spatial distribution are mostly the same, but with the ambient temperature up, the duration of particle generation was shorter. |
PDF Full Text Request