Active Regeneration Characteristics in Diesel Particulate Filters (DPFs) EMPA

Format:

Conference/Event

Author/Creator:

Dimopoulos Eggenschwiler, Dimopoulos Eggenschwiler, author.

Contributor:

Liati, Anthi

Schreiber, Daniel

Conference Name:

10th International Conference on Engines & Vehicles (2011-09-11 : Naples, Italy)

Language:

English

Physical Description:

1 online resource

Place of Publication:

Warrendale, PA SAE International 2011

Summary:

Particulate matter (PM) captured in diesel particulate filters(DPF) consists of: (a) soot, the product of incomplete combustionof the fuel and (b) ash, produced by combustion of lubricating oilplus minor amounts of metal components in the fuel. Among thevarious types of DPFs, most efficient are the so-called wall flowfilters, where the exhaust gas is forced to pass through porouswalls of adjacent channels, which are plugged alternately at theiropposite ends. Accumulation of PM in DPFs leads to increasingpressure drop across the filter. Since increased PM load in thefilter and thus increased pressure drop across the filterdeteriorates the engine performance, the filter load of the DPF hasto be periodically removed during a process referred to asregeneration. During the regeneration process, soot PM captured inthe DPF is expected to be oxidized. The temperature needed foroxidation of PM is usually exceeding circa 550°C. Since dieselexhaust temperatures seldom reach these levels, oxidation of sootis promoted by the so-called passive regeneration by means ofdifferent technologies: (1) the continuous regenerating trap (CRT)technology, which takes advantage of the NO₂ produced by oxidationof engine-out NO over a Pt catalyst preceding the DPF; (2)incorporation of a catalyst precursor in the fuel, so that PM andcatalyst are built together and facilitate PM combustion in thepresence of oxygen at lower temperatures. Both of these techniquesare, however, only partly successful. Higher degrees of sootoxidation are achieved during the so-called active regeneration,whereby higher exhaust temperatures are enforced.In this study we have measured and computed the soot oxidationrates during active and passive regeneration in a small heavy-dutytruck. By means of the measured species mass flow balances over thediesel oxidation catalysts (DOC) and the DPF we are able to computethe soot burning rates and to compare them with the weight decreaseof the DPF. In addition, we have examined in detail the emissioncharacteristics of the entire aftertreatment system during definedactive regenerations. Particulate emissions have been measured byparticle number counting. Moreover, soot was measuredoptoacoustically.The emissions during active regenerations deviate substantiallyfrom those in normal operation. Tailpipe CO and unburnthydrocarbons, soot mass and particulate matter are significantlyhigher. Only NOx is rather unaffected. The overallemission profile is not severely influenced given the rareoccurrence of active regenerations.Based on the species balances over the DPF, the soot oxidationrate and the oxidized soot mass during active regeneration werecomputed. The obtained remaining soot mass in the filter was ingood agreement with the weight of the filter. Based on the sootoxidation rate and the temperature measurement characteristic,kinetic parameters for soot oxidation have been computed. Theactivation energies have been in reasonable agreement withcomparable values reported in the literature lying between 80 and170 kJ/kmol in the different regeneration phases. The computedpre-exponential factors are also in agreement with reported values,their high variations though renders interpretation more difficult.Targeted optimization in analytics and measurement techniques areexpected to improve the accuracy of the kinetic parameters

Notes:

Vendor supplied data

Publisher Number:

2011-24-0185

Access Restriction:

Restricted for use by site license