Study Of DPF Active Regeneration Based On Exhaust Thermal Management For Light-duty Diesel Vehicle

Diesel engines have been widely used due to their advantages such as good power,economy and reliability,but the subsequent pollutant emissions are increasingly serious.Among them,the particulate emissions seriously pollute the environment and endanger human health,so the technology of particulate aftertreatment has been a hot spot for research.DPF(Diesel Particulate Filter)has been proved to be the most effective after-treatment equipment to control diesel particulate emission,and the regeneration control is the core of the DPF.In view of the status of after-treatment technology for light-duty diesel vehicles,the exhaust thermal management including intake throttle,fuel injection strategy and coupling DOC were studied in detail on the control strategy of DPF active regeneration and trigger of regeneration timing through the experimental research and theoretical analysis.In this paper,four-cylinder high-pressure common rail diesel engine used for light-duty vehicle was the research prototype.The control strategy of exhaust thermal management for DPF regeneration was studied under the typical working conditions covering low,medium and high loads.The intake throttle experiment results showed that the increasing of exhaust temperature while BSFC,CO,NO_X and smoke emissions would be deteriorated with reducing the opening of intake throttle valve.When the intake throttle valve opening was 20%,the exhaust temperature increased by up to 62.7%at the low speed and light load while increased slightly at high speed and heavy load.The intake throttling strategy was that the small throttle valve opening was needed at the low speed and light load and the throttle valve was open up until 100%with the increasing the speed and load.The fuel injection strategy experiment results showed that the exhaust temperature was increased limitedly but smoke and CO emissions was deteriorated by postponing the main injection timing or reducing common rail fuel pressure.The exhaust temperature could be increased up to 21.1%,smoke and NO_X emissions were improved effectively with the reasonable match between the post-injection quantity and timing.Therefore,the post-injection strategy that the larger quantity and retarded timing was needed with the lower speed and lighter load was effective to improve the exhaust temperature.The steady-state testing results showed that the inlet temperature of DPF was increased effectively but needed to be further increased when the working conditions were below the middle speed and load.The control strategy of LPI(Late Post Injection)coupling DOC was studied in order to further increasing the inlet temperature of DPF.The results showed that the exhaust temperature could be significantly increased up to 69.5%by LPI coupling DOC under the part load.The heating rate of DOC was accelerated,but HC emissions and BSFC were increased and oil dilution was obvious with the larger LPI fuel quantity.So the improved fuel injection strategy was that the extra larger LPI fuel quantity was needed at the low speed&light load,the LPI fuel quantity was reduced until to zero with the increasing of the speed and load.The test bench results showed that inlet temperature of DPF can be increased up to 550~650?which could meet the temperature need for DPF regeneration with the exhaust thermal management under widely working conditions of the engine.In the paper,the exhaust resistance monitoring carbon load was defined to trigger the DPF regeneration timing.The test results showed that the exhaust resistance had a approximate linear relationship with the actual carbon load,so the exhaust resistance could represent the actual carbon load and trigger the DPF regeneration timing.Finally,the logic diagram of the DPF active regeneration control strategy combined the exhaust thermal management was given and was verified under the NEDC test cycle.The results showed that the inlet temperature of DPF could be increased rapidly and stably to meet the temperature requirement for DPF regeneration.The research works have achieved the desired purpose.