Study Of Heating Control Strategy For DPF Active Regeneration Based On Exhaust Thermal Management

DPF(Diesel Particulate Filter)can reduce the particulate emissions from diesel engines effectively.However,the long-term use of DPF will cause a large amount of particulate accumulation,the exhaust back pressure increase and the engine performance deterioration.So periodic regeneration of DPF is required.The control of DPF regeneration temperature is related to the safe and effective regeneration of DPF,which is one of the key issues in the research.In this paper,a four-cylinder diesel engine used for light-duty vehicle was the research prototype.The combination of theoretical research,simulation analysis and experiment were used in the research.The influences of exhaust thermal management including intake throttle,fuel injection strategy and coupling DOC on exhaust thermal state and other performances were studied.The heating control strategy for DPF active regeneration based on exhaust thermal management under the whole working conditions of prototype was given and verified under steady-state working conditions on the engine test bench.The main research contents and conclusions are as follows.A one-dimensional model of the prototype was built based on the simulation software GT-Power and the accuracy of the model was verified by experimental results using the engine test bench.The typical working conditions of light and medium loads with low exhaust temperature were selected to study the change rules of exhaust thermal state,economy and emission performance of diesel engine under different intake throttle and fuel injection strategy.The simulation results under different intake throttle opening showed that the original exhaust temperature was increased with reducing the opening of intake throttle,but excessive intake throttle would deteriorate the economy performance,NOx and soot emissions of diesel engine.Therefore,the intake throttle control strategy should be reasonably selected according to the heating demand under different working conditions and the deterioration of engine performances.The simulation results of fuel injection strategy showed that original exhaust temperature was increased by delaying the main injection,but the later main injection timing would deteriorate the economy performance and soot emission.The exhaust temperature were increased effectively and NOx emission was decreased by reasonable match parameters between the close post injection quantity and timing,but the economy performance and soot emission were deteriorated.The original exhaust temperature was increased slightly,economy and emission performance were deteriorated seriously as the rail pressure decreased,so reducing rail pressure was not suitable to increase the exhaust temperature.The influence of the late post injection coupling DOC on the heating characteristics of DOC and other performances of diesel engine were studied by the means of experiment.The results showed that increasing late post injection quantity had little effect on the exhaust temperature at the entrance of DOC,but the heating rate inside DOC was significantly increased and the more late post injection quantity the faster and higher heating rate.BSFC(Brake Specific Fuel Consumption)and oil dilution were deteriorated,the catalytic conversion efficiency of HC and CO were improved but HC emission increased with increasing late post injection quantity.According to the exhaust temperature distribution under the whole working conditions of the prototype,the heating control strategy for DPF active regeneration based on exhaust thermal management was obtained.At light load conditions,the intake throttle valve opening was set 30°~40°,the timing of main injection and close post injection delayed,a large amount of fuel quantity of close and late post injection was adopted.At medium load conditions,the close and late post fuel injection quantity reduced,the intake throttle valve opening was set 40°~60°.At heavy load conditions,the intake throttle valve opening was set 60°~80° and late post injection with a small amount of fuel quantity was adopted,and the fuel injection quantity of late post injection and the intake throttle were gradually reduced to zero in the process of approaching the full load conditions.The steady-state test results showed that the temperature at the entrance of DPF was increased to 450℃~650℃ under most working conditions with using the heating control strategy based on exhaust thermal management.The temperature at the entrance of DPF increased obviously under light and medium load conditions and can meet the heating requirements under 80% working conditions.The research works have achieved the expected goals.