| The china Ⅲ emission limits of non-road diesel engine is very strict for the small power non-road diesel engine,where the main type of small power diesel engine is the single cylinder diesel engine.But at present,there are few researches about the low-emissions of single cylinder water-cooled direct injection diesel engine at home and abroad.Therefore,in order for low-emission,the research on optimization of combustion process of such type diesel engine has important engineering value and academic significance.The 1115 water-cooled direct injection diesel engine was the research prototype in this paper,which is the dominant models of china’s single cylinder diesel engines.Based on analysis of available low-emission technologies for the single cylinder diesel engine,change rules of emissions with the modes of the emission test cycle and requirements of the china Ⅲ emission limits of non-road diesel engine,the rated power,internal purification scheme and target values of emissions in the first test were determined.By studying the relationship between the structure and parameters of combustion chamber and fuel injection pressure.The combustion chamber structure of 1115 diesel engine was determined by the tested fuel injection pressure and improved by the simulation method.The influence of the fuel injection system and combustion process on emissions was studied by combining experiment and numerical simulation.The quantitative relationship of fuel supply advanced angle and NOx emission was studied and the fuel supply advanced angle where NOx emission was less than the first test target value(5.2 g/(kW·h))was found.The effects on combustion and emissions was researched by increasing the injector opening pressure and nozzle flow to getting circumferential homogeneous mixture of fuel and gas in the combustion chamber.By reducing the compression clearance to increase the compression ratio and effective combustion volume,and matching reasonably nozzle protrusion,axial homogeneous mixture of fuel and gas in the combustion chamber was achieved,the combustion rate was improved,the combustion process was optimized and the Soot emission was reduced.Optimization plans for the low-emission diesel engine were confirmed by experiment.The test results of 1115 diesel engine optimized by simulation showed that the performances were greatly improved.The values of CO,HC+NOx andPM emissions in the first test were 2.45 g/(kW·h),5.57 g/(kW·h)and 0.49 g/(kW·h),which compared with the original,decreased by 32.3%,30.5% and 25.8% respectively.The emissions of first test results of optimized engine were lower than the china Ⅲ emission limits of non-road diesel engine,and there was certain deterioration margin,which provided a guarantee for the discharge of the 3000 hour effective using period mentioned in the non-road china Ⅲ emission legislation.The researched method and technical scheme for improving the combustion and emission of the water-cooled single cylinder diesel engine could provide technical route and theoretical support for the similar type of diesel engines to meet the non-road china Ⅲ emission legislation.Based on the optimized diesel engine,the influences of key parameters in production process of the diesel engine on emissions was analyzed by simulation.The calculation results showed that,compared with previous requirements,the variance ranges of the key parameters should be narrowed to ensure the consistency of the emission performance in practical production.The fuel supply advance angle,compression clearance and injector protrusion were controlled within±0.5 °CA,±0.08 mm,±0.1 mm,NOx emission increased less than 9.8% compared with the optimized scheme,and the percentage of soot emission gain was less than 8.4%.The research can be used to guide the control of important parameters of diesel engines and the tolerance of the components in practical production. |
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