Study Of Working Process And Emission On Small Air-cooled Direct Injection Diesel Engine Based On China ? Emission Standard

Small air-cooled direct injection diesel engine occupies a larger proportion in production and application of single cylinder engine in China,and people gradually pay attention to the emission control of small air-cooled direct injection diesel engine with the strictness of emission standard and the strengthen of people's environment protection consciousness.Therefore,it is of great engineering significance and practical value to carry out the working process and emission research of the small air-cooled direct injection diesel engine which meets the china ? emission standard of non-road diesel engine.Based on 186 F that is a typical air-cooled direct injection single cylinder diesel engine as the prototype,the original performance test results: the fuel consumption at rated condition was 272.2g/(kW·h),and smoke at the maximum torque mode was 3.1BSU;according to the steady-state 8-mode emission test cycle,the CO and HC+NOX emissions exceed 26.2% and 3.5% of the china ? emission standard respectively,based on the calculation of sharing rate,the total sharing rates of CO and HC emissions in the third and the fourth mode were 43.4% and 40.7%;timing of combustion lagged according to the collection and calculation of the in-cylinder pressures,the steady flow test results of intake and exhaust ports showed that the poor flow coefficient of exhaust port mismatched with the flow coefficient of intake port.In order to solve the problems of the poor flow coefficient of exhaust port and high CO and HC emissions at small and medium load,the following works of the original engine systems were carried out.Combining the steady flow test and plaster models to optimize the structure of the exhaust port,the flow coefficient of the optimized exhaust port was 0.68 in the largest valve lift and increased by 13.1% compared with the original.Applying Solidworks software to build the three-dimension model of the injection fuel line,the placement of the fuel line and the installation angle of injector were optimized based on the static geometry,the optimized differences of fuel line height and length were reduced by 1.31 mm and 0.63 mm.The fuel consumption was reduced from 272.7 to 269.5g/(kW·h)and the excess air coefficient was increased from 1.70 to 1.74 under rated condition,meanwhile the emissions of CO,HC+NOX and PM were reduced by 9.4%,0.3% and 3.7% respectively based on the steady-state 8-mode emission test cycle.The combustion chamber was optimized by using AVL-Fire simulation and experimentation,the volume of combustion chamber reduced to 16.7cm~3 and 16.3cm~3 from 18 cm~3.The combustion simulation and the analysis of the indicator diagram results: with the optimized combustion chamber,the distribution of equivalent air fuel ratio was more perfect,combustion rate of diffusion combustion phase increased,and afterburning phenomenon weakened,because of the increase of fuel vaporization rate and improvement of the air motion in cylinder.The fuel consumption,the excess air coefficient and the thermal efficiency under the same working condition were better.In the meantime,the improvement of the combustion made the emissions a larger decline except the NOX.The final program was the second combustion chamber according to the comprehensive performances of the engine,the emissions of CO,HC+NOX and PM were 4.88,7.18 and 0.46g/(kW·h),however,the higher NOX was 6.17g/(kW·h)and needed to be reduced further.The fuel supply advanced angle was optimized in order to reduce the emission of NOX,and 14°CA BTDC was selected.The new EGR construction with different EGR ratios(the diameter of connection channels were 5 and 6mm)was designed and tested at the same time,finally 5 mm connection channel was selected as the best solution.The final prototype optimization program was determined through optimizing and matching the exhaust port,the fuel line,the combustion chamber,the fuel supply advanced angle and the external EGR.After optimization,the fuel consumption under rated condition was 264.1g/(kW·h)and reduced by 4.3%,the emissions of CO,HC+NOX and PM were 4.97,6.47 and 0.45g/(kW·h)and reduced by 28.4%,16.6% and 23.7% respectively compared to the original,the emissions have met the china ? emission standard of non-road diesel engine.The result of the research can provide technical reference for the small air-cooled direct injection diesel engine to meet the china ? emission standard of non-road diesel engine.