| Combustion and emission problems of turbo-charged diesel engine under transientoperations have become inevitable focuses with increasingly stringent emission regulations.In order to alleviate the pressure of experiment research under transient operations, such ashigh cost, high experiment difficulty and time consuming, a whole process simulationplatform of turbo-charged diesel engine under transient operations was established accordingto the high pressure common rail turbo-charged inter-cooled diesel engine which type isCA6DL2-35E3. It based on a large amount of experimental data and coupling technologiesof Matlab/Simulink, GT-Power, STAR-CD and artificial neural network. With theexperiment and simulation method verified and replenished each other, the transientperformances of turbo-charged diesel engine were optimized. Through experiments, thefeasibility and availability of the control strategies were demonstrated. Main contents andconclusions are summarized as follows:1. A measurement and control platform of diesel engine under transient operations wasbuilt up. The measurement and control object of the platform is a high pressure common railturbo-charged inter-cooled diesel engine of CA6DL2-35E3. Together with other transientmeasurement and control equipment, this platform can realize millisecond timescale A/Dacquisition, sampling control, EGR control transient control and calibration systemadjustment. It satisfies the measurement and control requirements of turbo-charged dieselengine under typical transient conditions.2. Based on the coupling technology of Matlab/Simulink and GT-Power, a transientoperations simulation platform of turbo-charged diesel engine was established. Through thecomparison between results of simulation and experiment, the accuracy of the simulationplatform was verified. On this basis, in order to optimize transient response of the air-fuelratio,three different injection control strategies were simulated to verify the feasibility ofsimulation optimization. Compared with the original "linear" injection control strategy, theinjection quantity rate of "sunken" injection control strategy is lower at beginning and higherat later. Although the air-fuel ratio show linear down trend during the whole injectionprocess, the imbalance of fuel and air ratio was increased due to large proportion injection atthe later period, which caused emissions deterioration and transient response time elongation.This goes against the transient control. The injection quantity rate of "cast" injection controlstrategy is higher at beginning and lower at later. Although in the first half of the transientprocess, air-fuel ratio falls down quickly, it was not below the target steady-state value. Thisinjection control strategy can shorten transient response time relatively and is better at theaspect of air-fuel ratio stability and controllability. Through the comparison of simulation and experiment control strategies, the feasibility of transient optimal control based on thetransient operations simulation platform of the turbo-charged diesel engine was proved.3. Based on the requirement of EGR rate step switched between traditional combustionmode and novel combustion mode such as HCCI, transient response influence factors ofEGR step change were researched, and the double targets control strategy of EGR stepchange response and torque fluctuation was proposed.On the conditions of the same target EGR valve opening degree, the transient responseof EGR mass flow, torque and other parameters were better while EGR valve opening ratefaster. On the conditions of the same EGR valve opening degree and the same EGR valveopening rate,"comprehensive" control strategy has the advantage of better EGR transientresponse and lower torque fluctuation among the four EGR valve opening characteristiccontrol strategies. The others were "cast","linear" and "sunken" control strategies.On the basis of qualitative analysis, various―comprehensive‖control strategy curveswere quantitative analyzed by Design of Experiment (DOE). Thus, the double objectiveoptimization control strategy of EGR step change transient response and torque fluctuationwas confirmed finally: During the first quarter of EGR valve opening time, EGR valveshould be opened to three-quarters opening degree rapidly. In the middle half of EGR valveopening time, EGR valve opening degree remains the same. During the last quarter of EGRvalve opening time, EGR valve finish the last quarter of opening valve trip. According to therequirements of different operations, the piecewise function to different EGR rate of thiscontrol strategy was presented.Coupled with STAR-CD software, a complete parameters transient simulation platformof turbo-charged diesel engine was built. Based on this platform, the influences of EGR stepchange optimization control strategy of turbo-charged diesel engine transient performancewas analyzed.Compared with the original "linear" control strategy, EGR response time canbe shortened by25%~40%. Compared with "cast" control strategy, the torque fluctuationscan be reduced by10%~18%. In the NOx emissions aspect, it can reduce6%emissionswhile improve19%response time than―linear‖control strategy. In the soot emissions aspect,it can reduce11%emission and delayed17%generating time than "cast" control strategy.4. Based on the limitation of transient emission simulation using coupled computationalfluid dynamics (CFD) code, the artificial neural network technology is applied to simulatetransient emission.On the basis of analyzing characteristics of Europe Transient test Cycle (ETC), thetypical ETC operation modeling method is put forward. In the transient emission neuralnetwork modeling process, torque transient rate and air-fuel ratio transient rate was linearcompounded as the input layer parameters of transient emission neural network model.Therefore the whole process simulation platform of diesel engine under transient operationswas constructed based on the multiple software coupling technologies of Matlab/Simulink, GT-Power, neural network technology.The accuracy and generalization ability of the simulation platform were verifiedthrough the simulation of different EGR rates under diesel test cycle operations and variableload operations in different transient rate, the difference of steady state emission simulationresult is below3%, and the difference of transient emission simulation is below4%. Thetrend of generalization simulation of transient emission is similar, and peak value differenceis within8%.The platform can be applied to ETC typical operations simulation that focus on controlstrategy developing.5. Based on the trade-off of NOx and PM emission especially for transient operations,an EGR valve control method was put forward, which adjust the EGR valve opening degreein adjacent level. On one hand, smoke is constrained under the given limitation, on the otherhand, NOx emission is considered.Based on the emissions analysis of different transient process and different stages in atransient process, the distinguish method of high and low torque transient rate was concludedby considering control strategy applicability. Finally, the comprehensive optimizationcontrol strategy of transient NOx and smoke emission on turbo-charged diesel engine wascompleted and the modeling difficulties of fast soot calculation and soot estimation wereeffectively solved. Taking dimensionless23%as smoke control target, the comprehensiveoptimization effect of control strategy was quantitative analyzed. On one hand, comparedwith EGR valve in the first level which means the EGR valve was closed, smoke value undercontrol strategy increased by9.5%, however it is still9%lower than the limitation. It meetsthe requirement of control strategy. Compared with EGR valve in the fifth level, which is themaximum level of EGR valve opening degree, it pruned the smoke peak obviously. On theother hand, compared with EGR valve in the first level, NOx emissions was decreased by44%.At the premise of keeping the same effect of the control strategy, based on the originaldiesel transient measurement and control platform, an EGR loop with controllable fourbranches was extended. Through the verification test of the transient emissioncomprehensive optimization control strategy on turbo-charged diesel engine, the feasibilityand simulation effectiveness of the control strategy were verified.
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