Control Strategies For Temperature Of Diesel Particulater Filter During Regeneration Process

With the application of diesel engine becoming more and more wider, theemission of particulate matter (PM) has been a great problem that should be solvedquickly. PM does not only pollute the environment, but also have adverse effect onhuman health. Diesel Particulate Filter (DPF) is the most effective after-treatmentequipment which can remove the particulate matters from the exhaust，its filterefficiency can be higher than90%and it has got more and more attentions recently.The main working of DPF is the filtration and the regeneration. With the enginerunning, the filter continuously filter particulate matters from the exhaust, once theexhaust back pressure has gradually increased to a certain limit, the regeneration starts.The normal regeneration process is a controlled, steady-state process, but in the actualvehicle use, there will be some "uncontrolled" regeneration process occurs inevitably,one of the most dangerous cases is the "Drop to Idle (DTI)" regeneration, in which theengine drops to idle as soon as the regeneration starts. With the temperature of filterincreasing rapidly, the filter works under great thermal shock and thermal stress, andusually results in damage to the filter and the catalyst. Therefore, the temperature ofthe filter during the process of DTI regeneration must be controlled, in order to extendthe using life of filter.In this paper, the control strategies for the temperature of the filter during DTIregeneration are studied on the engine bench, and the filter is made by CoringCorporation. The main content and results are listed below:The characteristics of the temperature fields both in the Steady-state controlledregeneration and DTI regeneration are studied by the engine bench experiment as thesoot loading is7g/L. During the Steady-state controlled regeneration process, the peaktemperature and the temperature gradients of the filter is710℃and156℃/cmrespectively. The temperature of filter is distributed uniformly, and the margin andspeed of the filter’s temperature rise is60℃and2.5℃/s respectively. During the DTIregeneration process the peak temperature and the temperature gradients of the filteris870℃and170℃/cm respectively. The uniformity of the temperature distribution has declined, and the margin and speed of the filter’s temperature rise is390℃and6.75℃/s respectively, which is6~7times to the Steady-state controlled regenerationprocess. All of the indicators are within the safe limit which is defined by themanufacturer, and the soot loading of7g/L is defined as the safe limit for theregeneration of the filter. By the further analysis of test results, three key factorsincluding the soot loading rate of filter, the O2concentration in exhaust, and the massflow of exhaust are obtained, which can influence the temperature of filter duringregeneration process directly. The control strategies for the temperature of the filterduring DTI regeneration are proposed.The control strategies for the temperature of the filter during DTI regenerationwhich is based on the O2concentration and mass flow respectively are studied. Atfirst, the strategy to control the exhaust O2concentration during the process of DTIregeneration were studied by the bench test, the methods including increasing theEGR rate, intake throttling and increasing the idle speed, can make the O2concentration reach to the lowest value of6%. When this method is applied in theDTI regeneration process as the soot loading is7g/L, the peak temperature is reducedfrom870℃to740℃, which can verify the effect of the temperature reduction in thiscontrol strategy, and as the soot loading is9g/L, the peak temperature and maximumtemperature gradient can maintained at950℃and245℃/cm respectively, which arestill within the safe limit of the material, and this result can also verify that the safelimit for the regeneration of the filter could be increased by reducing the O2concentration in the exhaust to a specific value. At last, the relationships between thetemperatures rise of filter, the temperature rise of exhaust, and the mass flow ofexhaust are studied by theoretical analysis and experimental verification. Therelationship between the maximum temperature rise of the filter and exhaust is got,which can verity that the temperature of filter during DTI regeneration could becontrolled by increasing the mass flow of exhaust, which can be achieved byincreasing the idle speed merely.