A Study On The Emission Control Of A Four Cylinder High Pressure Common Rail Naturally Aspirated Diesel Engine Of Non-Road Mobile Machinery

Compared with on-road diesel engines,the emission control technology of non-road diesel engines are relatively less developed,their pollutant problems are becoming increasingly prominent.With the promulgation of the III and IV stage emission regulations for diesel engines of non-road mobile machinery in China,controlling the emission level of non-road diesel engines is becoming urgent.Therefore,it is of great significance to carry out research on the fourth stage emission for non-road diesel engines.A non-road four cylinder high pressure common rail naturally aspirated diesel engine was used as the research object.In order to meet the emission standard,the comprehensive performance of the diesel engine was optimized through simulation conducted with AVL BOOST and also bench testing.During the simulation,AVL BOOST software was used to set up the working model of the test prototype.After setting up the relevant parameters and boundary conditions,the model simulation was performed under the external characteristic conditions.To ensure that the model was acceptably accurate,compared analysis between simulation and experiment were conducted.The results obtained from this analysis showed a good agreement between simulation and experiment.On this basis,the nozzle hole diameters and the main injection timings of the injector were simulated and analyzed.And afterwards,preliminary predictions of engine performance were made.The results showed that,with the increase of the nozzle hole diameter,the maximum combustion temperature and the maximum cylinder pressure were decreased,but fuel consumption was increased.When fuel injection timing was postponed,the maximum combustion temperature in the cylinder was decreased,the exhaust temperature was increased and fuel consumption was increased.During the bench testing(experiment),the injection parameters of the test prototype injector and the high-pressure common rail system were optimized.The different nozzle hole diameters and the different nozzle protrusion of the injector were tested under the external characteristic conditions.The common rail pressure,the main injection timing,the pilot injection quantity and the interval angle between pilot and main injection,were tested under eight working conditions.By analyzing the influence of each parameter on the emissions and fuel consumption of the prototype,it was observed that,increasing the nozzle hole diameter from 0.142 mm to 0.160 mm,the NO_X emission was improved,but the smoke emission and fuel consumption were deteriorated.When the nozzle hole diameter was 0.142 mm,the emission and fuel consumption of the prototype were compromised.When the nozzle protrusion was 3.0 mm,smoke emission was the best,fuel consumption was also relatively low.With the increase of rail pressure,the NO_X emission was increased,the smoke emission and fuel consumption were improved.Early fuel injection led to a significant increase in NO_X emission.Too large or too small quantities of fuel pilot injection led to an increase in NO_X emission,fuel consumption was increased with the increase of the pilot injection quantity.With the increase of the interval angle between pilot and main injection,the NO_X emission was decreased,the fuel consumption was increased.By analyzing the emissions and fuel consumption of the engine,the optimal rail pressure,the main injection timing,the pilot injection quantity and the interval angle between pilot and main injection were determined for each working condition.The steady-state and transient cycle emission tests of the prototype were carried out on a test bench.The steady-state results obtained were 0.26 g/(kW·h)for PM,6.14 g/(kW·h)for NO_X+HC and 1.67 g/(k W·h)for CO.The results of transient weighted emission obtained were0.23 g/(kW·h)for PM,6.86 g/(kW·h)for NO_X+HC and 2.39 g/(kW·h)for CO.The test results were within the limits of national emission standardⅣ.The differences between the cold start and warm start emissions characteristics were analyzed together with emissions characteristics of gaseous pollutants on the basis of the transient cycle.