Exhaust Emissions & Formation Of Volatile Organic Compounds During Cold-Start Periods From A Gasoline Passenger Car

Volatile organic compounds (VOCs) as one kind of the main hazardous exhaust pollutants from gasoline passenger cars have a great hazard to the atmospheric environment and human health, and most of them emitted in cold-start phase. In this thesis, based on the former investigations, a novel sampling system was developed to quickly collect VOCs in the exhaust emissions, including polycyclic aromatic hydrocarbons (PAHs), carbonyl compounds(CBCs), nano-particulate and so on. With this system developed, the specific emphasis was lay upon the emission characteristics of VOCs during each stage of cold-start phase. Meanwhile, the formation mechanism of hydrocarbons (HC) in cold-start condition was simulated using KIVA-3V software. The main work and conclusions to the study are summarized as follows:1. Based on the conventional automobile exhaust testing bed, a novel exhaust emissions sampling system was developed. The system can not only fulfill the collection of regulated exhaust emissions according to Stage III Standard, but also actualize to sample the VOCs at each applied operation mode expeditiously and consecutively. The collecting pattern of VOCs facilitates the contrast and analysis of the samples. In addition, the collecting programs were designed in accordance with the chemical characteristics of components in the gasoline engine exhaust emissions.2. New pretreatment and analytical methods were established to detect the hazardous components in the VOCs from a gasoline passenger car. By means of the methods, the recovery rate of PAHs exceeds 90 % with the relative standard deviation (RSD) less than 15 %, the average recovery of CBCs ranges from 96.07 % to 99.99 % with the RSD in the range of 0.193 % - 0.409 %. The results prove that the accuracy of analytical methods is high enough to detect the trace substances in the engine exhaust emissions.3. The VOCs have a so high content in the exhaust emissions from the gasoline passenger car during the cold-start period as to reach 10000ppm. According to the EPA TO-14/TO-15 methods, aromatic hydrocarbons are the major sort in the VOCs, and account for approximately 50 %. Toluene, xylene and trimethylbenzene are the most predominant components in aromatic hydrocarbons. PAHs are also found in the exhaust emissions, and the 2-ring or 3-ring aromatics such as naphthalene, acenaphthene, phenanthrene and fluorene are the PAHs quantified in higher concentration and share about 98 % of PAHs. A large number of nano-particulates were detected in the engine exhaust emissions by electrical low-pressure impactor (ELPI), and the number concentration of particulates with the aerodynamics diameter less than 1μm can reach 4.35x107 (1/cm3) in cold-start phase.4. In order to study the generation and evolution of hydrocarbons in the cold-start condition, a new framework mechanism of isooctane oxidation reaction and a new mesh independent collision (MIC) spray drop collision model were constructed and added to the overall dynamic reaction of KIVA-3V. The effect of several parameters, such as ignition advance angle, inlet temperature, ignition energy, on HC generation in cold-start phase of the gasoline engine were studied. The simulation results show that the reasonable decrease in ignition advance angle during cold-start period can increase after-burning, and then raise the cylinder's temperature quickly, reducing cold-start HC emissions. Also, enhancing the intake air temperature and ignition energy are the feasible approach to reducing the cold-start HC emissions.