Comparative Diesel Particulate Trap Performance Assessment: Impact of Catalyst Loading and Feed Gas Characteristics in a Modern CI Engine

摘要

Projected future emissions standards for locomotive, marine category 1 and 2, and stationary diesel engines all show a trend toward achieving compliance with current U.S. Tier 1-4 mobile non-road emissions and fuel quality standards. The inability of engine manufacturers to meet the proposed limits through in-cylinder optimization alone has led to an increased focus on emission aftertreatment technology, and it is widely anticipated that diesel particulate traps will be needed to achieve compliance with the projected particulate emission limits. The benefits of diesel particulate traps and many of the difficulties associated with trap regeneration and long-term durability are well known. However, the specific factors affecting trap performance and service life are still not well understood. The type of diesel particulate trap and the composition and nature of the exhaust entering the trap, both gaseous and particulate components, are two of the most important parameters affecting short-term trap operation and long-term durability. In this study a 2002, six-cylinder, 5.9l Cummins ISB 300 diesel engine, outfitted with fully-instrumented cordierite diesel particulate traps, was subjected to a series of steady-state engine operating conditions. The performance, loading, and regeneration characteristics of two catalyzed diesel particulate traps, each with varying levels of precious metal loading, as well as two un-catalyzed traps were evaluated. Changes in gaseous and particulate emissions across the particulate filters during low-temperature loading cycles and high temperature regeneration were measured. Further, the influence of the geometric distribution of the trapped soot on pressure drop was also investigated and quantified. In order to gain insight into the observed differences in trap performance, the diesel fuels, engine oil, and particulate samples were subjected to a detailed chemical and thermal analysis. Variations in particulate composition, SOF, SOL, SO_4, and total ash content, for samples collected before and after the traps were analyzed. Furthermore, differences in particulate phase sulfate and gaseous SO_2 levels measured before and after the clean and loaded traps provided further insight into the processes occurring within the traps and interactions between the various exhaust constituents and catalyst. Based on the differences in trap type, catalyst loading, and feed gas and particulate characteristics, explanations for the observed differences in trap performance were developed.