An Experimental Study on NOx Emissions of a Heavy-Duty Diesel Engine during Cold Start and Idling
Bibliographic record
Abstract
In North America, heavy-duty diesel engines for on-road use have to meet strict regulations for their emissions of nitric oxide and nitrogen dioxide (cumulatively referred to as ‘NOx’) besides other criteria pollutants. Over the next decade, regulations for NOx emissions are expected to becoming more stringent in North America. One of the major technical barriers for achieving in-use NOx emissions commensurate with the levels determined from in-laboratory test procedures required by regulations is controlling NOx emissions during cold start and engine idling. Since the exhaust gas temperature can be low during these conditions, the effectiveness of the exhaust after-treatment (EAT) system may be reduced. Under colder climate conditions like in Canada, the impact may be even more significant. In the experimental study of this paper, certain engine operation parameters such as the fuel injection timing, fuel injection frequency per cycle, engine speed, and exhaust gas recirculation (EGR) ratio are evaluated for their impact on NOx emissions during idling conditions. The study is conducted on a single-cylinder, four stroke, heavy-duty research engine equipped with an intake charge cooling system and an EAT system with independent control of diesel exhaust fluid injection. In order to partially simulate a cold operational environment for the engine and highlight the associated challenges for NOx control, tests are conducted at an intake charge temperature of 10 degrees Celsius below the Federal Test Protocol mandated cold start temperature, and auxiliary cooling is used for the engine oil and coolant to maintain the temperature of these fluids to below 50 degrees Celsius. Results indicate that in-use NOx emissions can be more than an order of magnitude higher than levels determined by the present in-laboratory test procedures required by regulations immediately after cold start and during engine idling. Using a combination of medium levels of EGR, elevated idling speed and injection timing control, the gas temperature in the exhaust manifold can be ramped up to higher than 200 °C in a short duration while simultaneously reducing engine-out NOx emissions. The use of a fuel post-injection during the expansion stroke can further reduce NOx emissions at the expense of thermal efficiency.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
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".