Thorsten Boger

Regeneration Strategies for an Enhanced Thermal Management of Oxide Diesel Particulate Filters

Diesel particulate filters are expected to be used on most passenger car applications designed to meet coming European emission standards, EU5 and EU6. Similar expectations hold for systems designed to meet US Tier 2 Bin 5 standards. Among the various products oxide filter materials, such as cordierite and aluminum titanate, are gaining growing interest due to their unique properties. Besides the intrinsic robustness of the filter products a well designed operating strategy is required for the successful use of filters. The operating strategy is comprised of two elements: the soot estimation and the regeneration strategy. In this paper the second element is discussed in detail by means of theoretical considerations as well as dedicated engine bench experiments. The impact the key operating variables, soot load, exhaust mass flow, oxygen content and temperature, have on the conditions inside the filter are discussed. Their practical relevance and the ability to use them for control purposes is analyzed. Guidelines are presented that should be considered when applying oxide diesel particulate filters. The differences between oxides and materials with higher thermal conductivity are discussed with respect to the relationship between regeneration conditions and the achievable regeneration efficiency. Experimental data show benefits for oxide materials vs. SiC, expected to come from their low conductivity. For the regeneration strategy a simple approach is proposed and illustrated by means of examples. The benefits of a staged regeneration approach are discussed, using two temperature levels during the regeneration.

A monolith loop reactor as an attractive alternative to slurry reactors

A new reactor concept to replace slurry bed catalysts with monolithic catalysts is described. Different configurations are presented, all requiring minimal hardware modifications for revamp. One key feature of the new concept is that no troublesome filtration step is required, while maintaining the benefits of high catalyst effectiveness and selectivity. Furthermore, higher catalyst loads per reactor volume can be achieved with the monolith. Cold flow experiments are used to demonstrate the feasibility of the concept and to determine some empirical parameters for a simple hydrodynamic model. Characteristic performance data for the monolith reactor, such as mass transfer, heat transfer, and reactive performance, as well as their dependence on the type of monolith used are discussed on the basis of model calculations.

A Next Generation Cordierite Diesel Particle Filter with Significantly Reduced Pressure Drop

Diesel particle filters (DPF) have become a standard after treatment component for all current and future on-road diesel engines used in the US. In Europe the introduction of EUVI is expected to also result in the broad implementation of DPF’s. The anticipated general trend in engine technology towards higher engine out NOx/PM ratios results in a somewhat changing set of boundary conditions for the DPF predominantly enabling passive regeneration of the DPF. This enables the design of a novel filter concept optimized for low pressure drop, low thermal mass for optimized regeneration and fast heat-up of a downstream SCR system, therefore reducing CO 2 implications for the DPF operation. In this paper we will discuss results from a next generation cordierite DPF designed to address these future needs. The new materials are based on a thinwall design with optimized material and microstructure, resulting in an almost linear pressure drop response with soot loading in the bare and catalyzed state. A significant reduction in soot loaded pressure drop for uncoated and coated filters is demonstrated of the new filter design vs. current EPA 2010 filter technologies. The optimized microstructure also enables high filtration efficiency for mass and number. Results from a wide range of regeneration experiments will be used to discuss the thermal operating window of the new material and the thermal response during normal operation and active regeneration. A uniform temperature distribution and the fast thermal response of the low mass filter minimize implications on fuel consumption.

Oxidation of Soot (Printex® U) in Particulate Filters Operated on Gasoline Engines

Gasoline particulate filters are one potential technology path to address the EU6 particulate number regulation for gasoline-powered vehicles. While the passive and active soot regeneration with diesel particulate filters is well understood, almost no data exist under gasoline engine conditions where there is essentially no NO2 and O2 available for soot oxidation under normal stoichiometric λ = 1 operation. The aim of this paper is to provide information and data to address these gasoline engine-specific conditions. The operation and conditions for a particulate filter in a gasoline direct injection engine environment are discussed utilizing results obtained in a broad range of laboratory and vehicle experiments. Since the accumulation of sufficient soot mass quantities proofed to be challenging on a vehicle, the present study is using Printex® U as surrogate soot, representing the least reactive fraction of particulate matter originating from the combustion. Conditions which enable the oxidation of soot under normal driving operation are identified. Conditions enabling passive soot oxidation in a gasoline engine exhaust system are proposed as well as potential worst case conditions.

On Road Durability and Field Experience Obtained with an Aluminum Titanate Diesel Particulate Filter

A novel diesel particulate filter for passenger car applications was introduced by Corning, based on a stabilized aluminum titanate composition. As part of the development and material evaluation Corning has performed extensive on-road testing of the new material. The testing included several vehicles, filters, system layouts and driving profiles. The filters were tested from 100,000 km to 240,000km. All test vehicles were equipped with instrumentation and data acquisition hardware, enabling the detailed recording of the relevant parameters such as temperature profiles inside the filter, the pressure drop as well as engine data. Throughout the field evaluations the filters were regularly checked for emissions over the NEDC on a chassis dynamometer according to the current European test protocol. In all cases excellent emission performance has been observed over the duration of the tests. The pressure drop performance has generally been good. After the on-road testing all filters have been analyzed following a detailed protocol. No negative material changes or changes in the thermo-mechanical properties have been observed. Some information about the accumulation of ash has been obtained through CT scans. Details of the tests and the results obtained are discussed in this manuscript.

Untersuchung der Eigenschaften neuer Dieselpartikelfilter

Eine neue Generation von Dieselpartikelfiltern basierend auf einer Aluminiumtitanat-Keramik ist von Corning entwickelt worden. Die neuen DuraTrap-AT-Filter verfugen uber eine extrem hohe Bestandigkeit gegenuber thermischen Spannungen, kombiniert mit einer hohen volumetrischen Warmespeicherfahigkeit. In dem vorliegenden Beitrag werden experimentelle Ergebnisse diskutiert, die mit dem neuen Material in Laborversuchen, am Motorprufstand und in Fahrzeugtests ermittelt wurden.

Integration of SCR Functionality into Diesel Particulate Filters

Most modern diesel engine aftertreatment systems comprise functions to oxidize hydrocarbons and CO, reduce particulate emissions (mass and number), and reduce NOx enabling compliance with ever tightening regulations. A typical system layout based on SCR as a means to reduce NOx is shown in Fig. 20.1a.

Evaluation of new diesel particulate filters based on stabilized aluminium titanate

A new generation of wall-flow diesel particulate filters based on an aluminium titanate composition has recently been developed by Corning, and marketed as the Corning Dura-Trap AT filter. The new material combines extremely high resistance to thermal stresses with a high bulk heat capacity. In this article, the test results obtained with this new material in laboratory tests, engine bench experiments and on-road vehicle durability runs are presented and discussed.