Cause and Effect of Reversible Deactivation of Diesel Oxidation Catalysts
Bibliographic record
Abstract
To meet TierII/LEVII emissions standards, light duty diesel (LDD) vehicles require high conversion efficiencies from the Aftertreatment Systems (ATS) for the removal of both Hydrocarbon (HC) and Nitrogen Oxide (NOx) species. The most populous configuration for LDD ATS have the Selective Catalytic Reduction (SCR) catalyst positioned on the vehicle behind the close coupled Diesel Oxidation Catalyst (DOC) and Catalyzed Diesel Particulate Filter (CDPF). This SCR position may require active heating measures which rely on the DOC/CDPF to provide heat through the combustion of HC and CO in the exhaust. Although DOCs are always impacted by their aging conditions, some aging conditions are shown to be both reversible and irreversible. Under continuous, high speed and high mileage conditions such as experienced in a modified Standard Road Cycle (SRC) or as it is better known, the High Speed Cycle (HSC), it is shown that the DOC's activity can deteriorate initially but significantly recover over repeated FTP-75 test cycles on fully aged catalysts. The stable, lean and hot environment experienced during these durability cycles, create a temporary condition on the PGM sites that can be reversed when the system is exposed to cooler, transient environment in the presence of additional reductant. This mechanism is similar to that experienced with lean NOx traps (LNT) under NOx regeneration conditions.1,2 Mechanisms of shifting PGM oxidation states have been observed in PdO containing methane oxidation when exposed to various thermal conditions3, 4, 5, 6. This phenomenon is successfully recreated under controlled laboratory settings utilizing both oven and engine aging methods. Furthermore, the performance of the aged catalyst was evaluated to highlight the re-activation of the catalyst for HC/CO and NO oxidation. The advantage of using the HSC cycle is self-evident. The cycle's high speed allows the required 120k miles to be reached at a significantly shorter period of time, realizing substantial savings in time and program development costs. The harsher thermal environment of the cycle creates a worst case aging scenario that is discussed in this paper.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".