Experimental Study On Diesel DPF Regeneration Heat Management Strategy

In order to make the diesel engine reach the national V and higher emission levels,the traditional internal cleaning technology has been difficult to meet the requirements,and must be combined with the exhaust gas aftertreatment technology to reduce the pollutant emissions.Temperature is an important factor influencing the conversion efficiency of DOC and the regeneration efficiency of DPF.In this paper,a high-pressure common-rail diesel engine,active control strategy of exhaust heat management and experimental study of DOC + DPF system characteristics are carried out.(1)The influence of different exhaust heat management measures on DOC inlet temperature and DPF inlet temperature was studied.The results showed that: intake throttle is effective for improving DOC inlet temperature;EGR valve opening is changed;main injection timing is delayed Lowering the injection pressure is less effective for increasing the DOC inlet temperature.Near-injection not only improves the DOC inlet temperature,but also contributes to the oxidation of soot.The far-injection has a significant effect on raising the inlet temperature of the DPF,and the discharge is large in a short time,so it is necessary to reasonably control the far-injection amount.(2)Conducting the system characteristic test of DOC + DPF Firstly,we tested the conversion efficiency of DOC under actual operating conditions.The results show that:.Airspeed and exhaust temperature are the main factors affecting the conversion efficiency of DOC.With the increase of exhaust temperature,the conversion efficiency of CO and THC increases.With the increase of airspeed,the conversion efficiency of CO and THC decreases.The influence of temperature on the conversion efficiency of NO is greater.The conversion efficiency of NO shows a parabolic trend with temperature increase,peaking around 350°C.However,different components of CO,THC,and NO in the exhaust gas will affect each other's conversion efficiency and then conduct a DPF equilibrium temperature test.The results show that the emission of soot and NOx under different conditions and the exhaust temperature will lead to the same The DPF has multiple equilibrium point temperatures,and most of the equilibrium point temperature is concentrated in the range of 300-400°C.The effect of exhaust back pressure on the combustion and emission characteristics of the engine is studied.The results show that the exhaust pressure increases with the DPF pressure drop.As the back pressure increases,the cylinder pressure decreases gradually,the combustion end time of the pre-injection fuel is postponed,the peak value of the heat release rate decreases,the peak value of the heat release rate of the main injection fuel slightly increases,the combustion duration increases,and the average temperature in the cylinder Ascending gradually As for emissions,soot significantly increases,CO emissions increase,but NOx decreases.(3)The effect of thermal management strategy on engine combustion and emission characteristics was studied.A single post-injection strategy test was conducted first.The results showed that the average temperature in the cylinder in the late expansion gradually decreased with the delay of the timing of the near post injection.The delay period increased,soot and NOx decreased.However,when the timing of further postponement was further delayed,soot increased and CO and THC emissions deteriorated;then two post-injection tactics experiments were conducted.The results showed that: with the post-spray interval The trend of changes in cylinder pressure,temperature,instantaneous heat release rate and cumulative heat release remained basically the same,and the fuel at the far post injection was hardly involved in combustion.Compared with a single post-injection,two post-injection strategies can not only significantly increase the exhaust temperature,but also reduce NOx and soot emissions at the same time;but the CO and THC deteriorate seriously.Finally,active regeneration tests of different target temperatures were conducted.The results show that compared with before the trigger regeneration,the combustion phase in the regeneration state is significantly delayed,the exothermic process is lagging;the heat release rate is slow,and the peak heat release rate is low;the cylinder pressure curve changes from double peak to single peak state,and the peak pressure Relatively increased;the temperature inside the cylinder decreases,and the cumulative heat release increases.The higher the regeneration target temperature,the higher the peak pressure and the greater the heat release,but the average peak temperature in the cylinder decreases.During the regeneration period,CO and THC emissions at the entrance to the DOC increased sharply within a short period of time.However,the relatively high emission of CO and nitrogen oxides at the outlet of the DPF caused secondary pollution due to the following: First,the fuel mixture that was not fully oxidized.Will be directly with the exhaust gas to the atmosphere;Second,particulate matter in the DPF is not completely burned to generate CO.(4)An exhaust heat management strategy was proposed,and the DOC + DPF regeneration control test results showed that under the regenerative heat management mode,the inlet temperature of the DPF reached the target temperature,and the DPF began to oxidize particulate matter and reduce the particulate matter deposited in the DPF;The higher the regeneration target temperature is,the faster the regeneration rate is,and the thermal management strategy of the stage regeneration is proposed,that is,the exhaust gas flow rate is high,and when the carbon load is small,a higher regeneration target temperature is adopted;the exhaust gas flow is low and the carbon load is low.When larger,select a lower regeneration target temperature.