| Single-cylinder diesel engines account for a large percentage of the small power non-road diesel engines in China and large quantities of production,usage and export of single-cylinder diesel engines have become an unique feature of Chinese internal combustion industry.As the emission standard of non-road diesel engine in China is gradually strict,the research and the optimization of the low emission mechanism as well as the technology of single-cylinder diesel engine has great academic significance and engineering application value.To take S1100,a horizontal water-cooled single-cylinder direct injection diesel engine,as a sample,the research of emission control technology of diesel engine has been done based on the interior and external purification by the method of experiment and simulation.At the point of interior purification,the relationships between air-fuel mixture and “quantity”,“time” and “space” were analyzed,which are related to the combustion.To match the quantity of fuel and air,the structure of the intake and exhaust port structure was optimized to increase the flow coefficient and fresh charge,which can increase the value of excess air ratio so as to improve combustion and to decrease the specific fuel consumption.The excess air ratio of the optimized engine increased from1.36 to 1.68,which increased by 24.4% compared with the ratio of the original engine.The NO_x emissions decreased from 712×10-6 to 594.3×10-6 and the smoke emission decreased from 3.1 BSU to 2.2 BSU respectively,which show that the quantity of fuel and air is crucial to the performance of the engine.The combustion start timing which changes with crank angle(“time”)was adjusted by changing fuel supply advanced angle to control the NO_x emission.Under the rated working condition,the fuel supply advanced angle was initially set to 10 °CA and the NO_x emission was about 450×10-6.The structure of combustion chamber was improved and the compression clearance was controlled to reduce the invalid combustion zone and optimize the flow rate of injector.Moreover,the spatial distribution of fuel spray increases the efficient use of “space” and promotes the uniformity of air-fuel mixture,therefore,faster burning was obtained,the performance of diesel engine was improved while the emission was decreased.The mechanism of the engine’s decreasing emission was studied by measuring and analyzing the in-cylinder pressure of optimized and original S1100 diesel engine before and after.The initial value of the emissions was lower than the China III emission limits,but PM degradation margin was relatively small.The degradation margin of all emissions was increased and the engine can meets the discharge requirements within its effective life span through the installation of a muffler with DOC and the reduction of CO,HC and PM emissions in the process of external purification.The test results of optimized and original engine show that the specific fuel consumption were 250.2 g/(kW·h)and 272.2 g/(kW·h)respectively,decreasing by 8.1%,the smoke emission were 1.6 BSU and 3.1 BSU respectively,reducing by 1.5 BSU.The emission results based on stationary eight-mode test cycle showed that the specific emissions of CO,HC+NO_x and PM were 0.38,5.63 and 0.41 g/(kW·h),which decreased by 94.2%,40.2% and 43.1% respectively compared with the original engine.The S1100 can meet the China III emission standard for non-road diesel engines.The technical routine in this article can provide reference for the same type diesel engine meeting the requirements of China III emission standard. |
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