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.