Improvement Of Emission Behavior Of A China State Ⅳ Diesel Engine With Optimization Of Combustion Chamber Structure

With the full implementation of the China Ⅳ emissions standard,the research and development of diesel engine to meet the more stringent emissions standards is imminent. In this paper, prediction of combustion and emissions with single sample point and optimization of combustion chamber structure to improve the emission behavior with diverse sample points was combined for research.A mechanism contains 64 speciesand 154-step reactions of C14H28 surrogate diesel, coupled with 9 steps NOx model and 23-step reaction Soot model were used to simulate the process of combustion and emissions generate of the engine. By comparing the calculated and experimental data at ESC steady state cycle, the model was checked assessment. In-depth compare of three NOx mechanism, the effects of changes of concentration and regional distribution of associated species on NOx generate process was analyzed based on a single sample point. The results showed that, O concentration and O concentration/UHC concentration is an important factor affecting NO production. NO2 can not be ignored in the study of diesel NOx emissions, NO2 account for over 10% of NOx at full load At low-load high EGR rate condition, NO2 accounted for a higher proportion.NO was generated mainly in the high-temperature oxygen-rich region, while NO2 was mainly generated in the lower temperature peripheral region of NO. HO2 was one factor effecting NO2 production,and it promoted NO2 generation.N2O emissions increased and accounted for a larger proportion of NOx at low-load high EGR rate condition.N2O is mainly generated in high temperature and high HO2 region.Optimization study of the combustion chamber was carried out with approximate model instead of a complex three-dimensional numerical model based on diverse points of multi-objective work. Optimal Latin Hypercube DOE method was used to get diverse sampling point within the range of the depth of the diameter necking, necking position the depth of combustion chamber pit,in order to obtain the ability to predict the entire design domain. AMGA multi-objective optimization algorithm was used to optimize the combustion chamber based on the established Kriging approximation model with setting the Soot and NOx Emissions Optimization targets reasonably based on engineering practice.And then selected a solution from the group of Pareto solutions to be the final solution which can reduce the emissions of NOx and Soot at every working conditions in larger extent.And a three-dimensional numerical simulation of a single sample point was carried out based on the final solution.The compare of optimal results with the simulation result of original machine showed that:Soot and NOx emissions were reduced in varying degrees, NOx weighted emission was reduced by 6.6%, Soot weighted emissionwas decreased by 19.8%.The trade-off of Soot and NOx emissions of diesel engine was improved after optimized, and the emissions performance of diesel engine was improved.In this paper,three kinds of NOx mechanism were used to predict the emissions of engine with single sample point and the combustion chamber structure was multi-objective optimized with diverse sample points, which support important guiding significance to enhance the emissions performance of China state IV diesel engine.