| Summary: | 碩士 === 國立臺北科技大學 === 車輛工程系所 === 97 === Automotive emission regulations are becoming more and more stringent. The NOx standards still pose a formidable challenge. As we known, lean combustion is one of the best ways to reduce fuel consumption at part engine load. However, it produces higher NOx emissions. The reasons are high combustion temperature and excess of oxygen in cylinder. Both water-gasoline fuel emulsions and exhaust gas recirculation (EGR) are used to absorb the heat in cylinder and reduce the combustion temperature. This paper introduces the process of intake port modification to develop a lean burn system. It also studies about applicable technique –water-gasoline emulsions - used in this engine for reducing the NOx. To reach the lean combustion, the original intake port of a four-stroke spark-ignition (SI) engine was modified to generate tumble by using various flow control baffles. The in-cylinder air motion generated by each configuration was characterized using swirl and tumble flow bench to choose the optimum one. The first test is trying to reach the lean-limit of both original engine and modified one using pure gasoline. After that, this lean burn engine was tested with three different water concentrations of water-gasoline emulsions – 5%, 10% and 15% respectively. Test conditions are based on vehicle running at 90 km/h on the high way. The engine torque, fuel consumption, exhaust emissions, and combustion characteristics of all tests were investigated. Water-gasoline emulsion has a positive effect on NOx reduction with a suitable water concentration at 5% by mass. The NOx emission has been decreased 35.0% approximately in comparison with lean-burn engine using pure gasoline. However, HC emission is increased 13.5% as a backward of the using of water-gasoline emulsion.
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