Development Of In-Cylinder Fast-Acting Gas Sampling System For A Diesel Engine

With the increase of automobiles in our country, the pollution of exhaust emissions from the vehicle engines has done serious harm to the atmosphere environment and human health. Therefore, it has a great practical significance to study the formation mechanism and control techniques of the engine exhaust emissions. In order to investigate the generation and evolution of the diesel engine emissions, an in-cylinder fast-acting sampling system has been developed which can obtained small gas samples from the desired position in the combustion chamber of an operating engine at any desired crank angle. Focusing on the design and development of this system, the main contents of the dissertation are as follows:1. Based on the PC resources of hardware and software, the electronic control unit(ECU) using the interruption technology was developed. The high control precision could be obtained, for the timing card and A/D card were programmed under DOS. By means of real time processing and control signal logic synthesis, the sampling parameters could be controlled easily. N-channel enhancement-mode MOSFET with fast intrinsic diode was used to control the valve.2. A needle-type sampling valve (inward-opening), which could reduce the disturbance to the combustion process, has been designed and developed. The valve parts in contact with combustion gases were made from the refractory steel 4Cr9Si2 that was well resistance to corrosion and could meet the desire of long service life of the valve. Good precision was achieved through carefully lapping of contact surfaces of the needle mating parts and the connect-rod mating parts. The sample in the valve could be rapidly diluted with N2 so as to"quench"chemical reactions in the sampling system.The maximum needle lift was 0.5mm and the sampling duration was about 1ms. The sample volume under the combustion conditions was only relative to the temperature in the chamber, and the volume of per sampling cycle was about 0.59 cm3, 0.65 cm3, 0.7cm3 at 1500K, 1800K and 2100K, respectively.3. The sampling diesel engine test bench was built up and the fast-acting sampling system was debugged in the test bench. When sampling duration was 1ms, the sampling system could operate successfully under the operating engine conditions. The gas leakage from the valve was measured during the engine operation when the valve was shut. The experimental results showed that the gas leakage rate stayed at acceptable low level. So the in-cylinder fast-acting sampling system was reasonable and suitable for the investigation on formation mechanism of emission pollutants from diesel engine.